onDraw() method. Simple graphics can be created in the layout XML file too. <?xml version="1.0" encoding="utf-8"?>In the oval.xml file we create a circle shape. We define its colour and size. The oval.xml file is located in the res/drawable directory. The directory had to be created.
<shape xmlns:android="http://schemas.android.com/apk/res/android"
android:shape="oval">
<solid
android:color="#666666"/>
<size
android:width="70dp"
android:height="70dp"/>
</shape>
<?xml version="1.0" encoding="utf-8"?>In the main.xml file, we define a simple View. The background of this view is filled with our drawable object.
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
android:orientation="vertical"
android:layout_width="fill_parent"
android:layout_height="fill_parent"
>
<View
android:layout_width="100dp"
android:layout_height="100dp"
android:layout_marginTop="5dp"
android:background="@drawable/oval"
/>
</LinearLayout>
<?xml version="1.0" encoding="utf-8"?>Resources file.
<resources>
<string name="app_name">OvalShape</string>
</resources>
package com.zetcode.ovalshape;The file just loads the defined layout.
import android.app.Activity;
import android.os.Bundle;
public class MainActivity extends Activity
{
@Override
public void onCreate(Bundle savedInstanceState)
{
super.onCreate(savedInstanceState);
setContentView(R.layout.main);
}
}
onDraw() method of the View. Since we will be drawing on an existing View, we will have a predefined Canvas with its Bitmap. We do not need to worry about them. The manifest file is not modified. In this example the main.xml file will not be needed. <?xml version="1.0" encoding="utf-8"?>Resources.
<resources>
<string name="app_name">DrawRect</string>
</resources>
package com.zetcode.drawrect;We have a custom DrawView class. The file is located in the src/com/zetcode/drawrect/ directory.
import android.content.Context;
import android.graphics.Canvas;
import android.graphics.Color;
import android.graphics.Paint;
import android.view.View;
public class DrawView extends View
{
Paint paint = new Paint();
public DrawView(Context context)
{
super(context);
paint.setColor(Color.GREEN);
}
@Override
public void onDraw(Canvas canvas)
{
canvas.drawRect(30, 30, 100, 100, paint);
}
}
public class DrawView extends ViewThe custom DrawView class inherits from the base View class.
Paint paint = new Paint();An instance of the Paint class is created. It will define a colour for drawing.
paint.setColor(Color.GREEN);We will paint in green colour.
@OverrideThe drawing is performed in the
public void onDraw(Canvas canvas)
{
canvas.drawRect(30, 30, 100, 100, paint);
}
onDraw() method. The method provides the Canvas object for us. We call the drawRect() to draw the rectangle on the View. package com.zetcode.drawrect;In the MainActivity.java source file we set the custom DrawView to be the content View of the Activity.
import android.app.Activity;
import android.graphics.Color;
import android.os.Bundle;
public class MainActivity extends Activity
{
@Override
public void onCreate(Bundle savedInstanceState)
{
super.onCreate(savedInstanceState);
DrawView drawView = new DrawView(this);
drawView.setBackgroundColor(Color.WHITE);
setContentView(drawView);
}
}
DrawView drawView = new DrawView(this);We create an instance of the
DrawView class. drawView.setBackgroundColor(Color.WHITE);We specify the background colour for the View.
setContentView(drawView);The DrawView becomes the content View of the Activity.
<?xml version="1.0" encoding="utf-8"?>In the main.xml layout file, we have a Button widget. This button will display an AlertDialog.
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
android:orientation="vertical"
android:layout_width="fill_parent"
android:layout_height="fill_parent"
>
<Button
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:layout_marginTop="10dip"
android:onClick="onClicked"
android:text="@string/btn_label" />
</LinearLayout>
<?xml version="1.0" encoding="utf-8"?>This is strings.xml file.
<resources>
<string name="app_name">DisplaySize</string>
<string name="btn_label">Show</string>
</resources>
package com.zetcode.displaysize;We use the AlertDialog to display the size of the display.
import android.app.Activity;
import android.os.Bundle;
import android.view.View;
import android.graphics.Point;
import android.app.AlertDialog;
import android.content.DialogInterface;
import android.view.WindowManager;
import android.view.Display;
public class MainActivity extends Activity
{
@Override
public void onCreate(Bundle savedInstanceState)
{
super.onCreate(savedInstanceState);
setContentView(R.layout.main);
}
public void onClicked(View view)
{
Point p = getDisplaySize();
AlertDialog ad = new AlertDialog.Builder(this).create();
ad.setTitle("Display size");
String msg = String.format("Width:%d, Height:%d", p.x, p.y);
ad.setMessage(msg);
ad.setIcon(android.R.drawable.ic_dialog_info);
ad.setButton("OK", new DialogInterface.OnClickListener() {
public void onClick(DialogInterface dialog, int which) {
dialog.cancel();
}
});
ad.show();
}
public Point getDisplaySize()
{
WindowManager wm = (WindowManager) getSystemService(WINDOW_SERVICE);
Display ds = wm.getDefaultDisplay();
Point p = new Point();
ds.getSize(p);
return p;
}
}
Point p = getDisplaySize();In the custom getDisplaySize() method, we determine the size of the display.
AlertDialog ad = new AlertDialog.Builder(this).create();An instance of the
AlertDialog is created. ad.setTitle("Display size");
String msg = String.format("Width:%d, Height:%d", p.x, p.y);
ad.setMessage(msg);
ad.setIcon(android.R.drawable.ic_dialog_info);
We set a title, message and an icon for the dialog. ad.setButton("OK", new DialogInterface.OnClickListener() {
public void onClick(DialogInterface dialog, int which) {
dialog.cancel();
}
});
We add a button to the dialog. When we click on the OK button, the dialog is closed. ad.show();The
show() method shows the dialog. WindowManager wm = (WindowManager) getSystemService(WINDOW_SERVICE);We get the default display.
Display ds = wm.getDefaultDisplay();
Point p = new Point();We find out the size of the display with the
ds.getSize(p);
getSize() method. 
<?xml version="1.0" encoding="utf-8"?>This is main.xml file. We have a Button widget and a TextView widget. The button will show the dialog window. The TextView will receive the input text from the dialog.
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
android:orientation="vertical"
android:layout_width="fill_parent"
android:layout_height="fill_parent"
>
<Button
android:id="@+id/btnId"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:layout_marginTop="10dip"
android:onClick="onClicked"
android:text="@string/btn_label" />
<TextView
android:id="@+id/tvId"
android:layout_width="fill_parent"
android:layout_height="wrap_content" />
</LinearLayout>
<?xml version="1.0" encoding="utf-8"?>This is the strings.xml resource file.
<resources>
<string name="app_name">InputDialog</string>
<string name="btn_label">Show dialog</string>
</resources>
package com.zetcode.input;Clicking on the button widget will display the AlertDialog. It has an EditText to receive the input from a user.
import android.app.Activity;
import android.os.Bundle;
import android.app.AlertDialog;
import android.view.View;
import android.widget.EditText;
import android.widget.TextView;
import android.content.DialogInterface;
public class MainActivity extends Activity
{
private TextView tv;
@Override
public void onCreate(Bundle savedInstanceState)
{
super.onCreate(savedInstanceState);
setContentView(R.layout.main);
tv = (TextView) findViewById(R.id.tvId);
}
public void onClicked(View view)
{
AlertDialog.Builder ad = new AlertDialog.Builder(this);
ad.setTitle("Input");
ad.setMessage("Enter your name");
final EditText input = new EditText(this);
ad.setView(input);
ad.setPositiveButton("Ok", new DialogInterface.OnClickListener() {
public void onClick(DialogInterface dlg, int which) {
String val = input.getText().toString();
String msg = String.format("Hello %s!", val);
tv.setText(msg);
}
});
ad.setNegativeButton("Cancel", new DialogInterface.OnClickListener() {
public void onClick(DialogInterface dlg, int which) {
dlg.cancel();
}
});
ad.show();
}
}
AlertDialog.Builder ad = new AlertDialog.Builder(this);We set a title and a message for the dialog.
ad.setTitle("Input");
ad.setMessage("Enter your name");
final EditText input = new EditText(this);We add the
ad.setView(input);
EditText widget to the dialog. ad.setPositiveButton("Ok", new DialogInterface.OnClickListener() {
public void onClick(DialogInterface dlg, int which) {
String val = input.getText().toString();
String msg = String.format("Hello %s!", val);
tv.setText(msg);
}
});
Clicking on the OK button of the dialog, we get the text from the EditText widget. The text used to format a greeting which is set to the TextView. ad.setNegativeButton("Cancel", new DialogInterface.OnClickListener() {
public void onClick(DialogInterface dlg, int which) {
dlg.cancel();
}
});
Clicking on the Cancel button will dismiss the dialog. 
<?xml version="1.0" encoding="utf-8"?>In the main.xml layout file, we have one TextView widget. It will display a welcome message.
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
android:orientation="vertical"
android:layout_width="fill_parent"
android:layout_height="fill_parent"
>
<TextView
android:layout_width="fill_parent"
android:layout_height="wrap_content"
android:text="@string/message" />
</LinearLayout>
<?xml version="1.0" encoding="utf-8"?>This is strings.xml file.
<resources>
<string name="app_name">OptionsMenu</string>
<string name="message">Demonstrating Options Menu</string>
<string name="om1">Settings</string>
<string name="om2">Tools</string>
</resources>
<?xml version="1.0" encoding="utf-8"?>This is options_menu.xml file. It defines two menu items. The file is located in the res/menu/ subdirectory.
<menu xmlns:android="http://schemas.android.com/apk/res/android">
<item android:id="@+id/settings"
android:title="@string/om1" />
<item android:id="@+id/tools"
android:title="@string/om2" />
</menu>
package com.zetcode.opmenu;To enable an options menu in an activity, we need to override the
import android.app.Activity;
import android.os.Bundle;
import android.view.Menu;
import android.view.MenuInflater;
import android.view.MenuItem;
import android.widget.Toast;
public class MainActivity extends Activity
{
@Override
public void onCreate(Bundle savedInstanceState)
{
super.onCreate(savedInstanceState);
setContentView(R.layout.main);
}
@Override
public boolean onCreateOptionsMenu(Menu menu)
{
MenuInflater inflater = getMenuInflater();
inflater.inflate(R.menu.options_menu, menu);
return true;
}
@Override
public boolean onOptionsItemSelected(MenuItem item)
{
switch (item.getItemId())
{
case R.id.settings:
Toast.makeText(MainActivity.this, "Settings menu selected.",
Toast.LENGTH_SHORT).show();
return true;
case R.id.tools:
Toast.makeText(MainActivity.this, "Tools menu selected.",
Toast.LENGTH_SHORT).show();
return true;
default:
return super.onOptionsItemSelected(item);
}
}
}
onCreateOptionsMenu()and the onOptionsItemSelected() methods. @OverrideInside the
public boolean onCreateOptionsMenu(Menu menu)
{
MenuInflater inflater = getMenuInflater();
inflater.inflate(R.menu.options_menu, menu);
return true;
}
onCreateOptionsMenu() method, we build the options menu from the options_menu.xml file. We use the MenuInflater class to do the job. @OverrideThe
public boolean onOptionsItemSelected(MenuItem item)
{
...
}
onOptionsItemSelected() method handles the click events on the menu items. case R.id.settings:In case of the selection of the Settings menu item we show a Toast window with "Settings menu selected" message.
Toast.makeText(MainActivity.this, "Settings menu selected.",
Toast.LENGTH_SHORT).show();
return true;
<?xml version="1.0" encoding="utf-8"?>This is main.xml file. It contais a ListView widget.
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
android:orientation="vertical"
android:layout_width="fill_parent"
android:layout_height="fill_parent"
>
<ListView
android:id="@+id/lvId"
android:layout_width="fill_parent"
android:layout_height="fill_parent" />
</LinearLayout>
<?xml version="1.0" encoding="utf-8"?>This is the strings.xml resource file.
<resources>
<string name="app_name">ContextMenu</string>
<string-array name="planets">
<item>Mercury</item>
<item>Venus</item>
<item>Earth</item>
<item>Mars</item>
<item>Jupiter</item>
<item>Saturn</item>
<item>Uranus</item>
<item>Neptune</item>
<item>Pluto</item>
</string-array>
</resources>
<?xml version="1.0" encoding="utf-8"?>This is the row.xml resource file. Each row of a ListView consists of a single TextView.
<TextView xmlns:android="http://schemas.android.com/apk/res/android"
android:layout_width="fill_parent"
android:layout_height="fill_parent"
android:padding="10dp"
android:textSize="20sp">
</TextView>
package com.zetcode.conmenu;In order to implement the context menu, we have to override the
import android.app.Activity;
import android.os.Bundle;
import android.widget.ArrayAdapter;
import android.widget.ListView;
import android.view.View;
import android.view.Menu;
import android.view.MenuInflater;
import android.view.MenuItem;
import android.view.ContextMenu;
import android.view.ContextMenu.ContextMenuInfo;
import android.widget.AdapterView.AdapterContextMenuInfo;
import java.util.Arrays;
import java.util.ArrayList;
public class MainActivity extends Activity
{
private ListView lv;
private ArrayAdapter<String> la;
@Override
public void onCreate(Bundle savedInstanceState)
{
super.onCreate(savedInstanceState);
setContentView(R.layout.main);
setupUI();
}
public void setupUI()
{
lv = (ListView) findViewById(R.id.lvId);
String[] planets = getResources().getStringArray(R.array.planets);
ArrayList<String> lst = new ArrayList<String>();
lst.addAll(Arrays.asList(planets));
la = new ArrayAdapter<String>(this, R.layout.row, lst);
lv.setAdapter(la);
registerForContextMenu(lv);
}
@Override
public void onCreateContextMenu(ContextMenu menu, View v,
ContextMenuInfo menuInfo)
{
super.onCreateContextMenu(menu, v, menuInfo);
MenuInflater inflater = getMenuInflater();
inflater.inflate(R.menu.context_menu, menu);
}
@Override
public boolean onContextItemSelected(MenuItem item)
{
AdapterContextMenuInfo info = (AdapterContextMenuInfo) item.getMenuInfo();
int pos = info.position;
String i = la.getItem(pos);
switch (item.getItemId())
{
case R.id.delId:
la.remove(i);
return true;
case R.id.upId:
String upln = i.toUpperCase();
la.remove(i);
la.insert(upln, pos);
return true;
case R.id.loId:
String lpln = i.toLowerCase();
la.remove(i);
la.insert(lpln, pos);
return true;
default:
return super.onContextItemSelected(item);
}
}
}
onCreateContextMenu() and the onContextItemSelected() methods. We also need to call the registerForContextMenu()method for a specific view. String[] planets = getResources().getStringArray(R.array.planets);We will be deleting items of the ListView. Therefore, we need to use an ArrayList. Otherwise the list would be read-only.
ArrayList<String> lst = new ArrayList<String>();
lst.addAll(Arrays.asList(planets));
registerForContextMenu(lv);The context menu is registered for the ListView widget.
@OverrideIn the
public void onCreateContextMenu(ContextMenu menu, View v,
ContextMenuInfo menuInfo)
{
super.onCreateContextMenu(menu, v, menuInfo);
MenuInflater inflater = getMenuInflater();
inflater.inflate(R.menu.context_menu, menu);
}
onCreateContextMenu() method we build the context menu from the context_menu.xml file. @OverrideThe
public boolean onContextItemSelected(MenuItem item)
{
...
}
onContextItemSelected() reacts to list item selection events. AdapterContextMenuInfo info = (AdapterContextMenuInfo) item.getMenuInfo();To find out more about the selected item, we use the
int pos = info.position;
String i = la.getItem(pos);
AdapterContextMenuInfo class. We get the position and the text of the selected item. case R.id.delId:If we select the Delete context menu option, we remove the item from the ArrayAdapter.
la.remove(i);
return true;
case R.id.upId:For the Uppercase option, we modify the string, remove the original one and insert a new one.
String upln = i.toUpperCase();
la.remove(i);
la.insert(upln, pos);
return true;
<?xml version="1.0" encoding="utf-8"?>This is main.xml file. We have a Button widget and a TextView widget. The button will show a PopupMenu.
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
android:orientation="vertical"
android:layout_width="fill_parent"
android:layout_height="fill_parent"
>
<Button
android:id="@+id/btnId"
android:layout_height="wrap_content"
android:layout_width="wrap_content"
android:layout_marginTop="10dip"
android:text="@string/btn_label"
android:onClick="onClick" />
<TextView
android:id="@+id/tvId"
android:layout_width="fill_parent"
android:layout_height="wrap_content"
android:layout_marginTop="10dip" />
</LinearLayout>
<?xml version="1.0" encoding="utf-8"?>This is the strings.xml resource file.
<resources>
<string name="app_name">PopupMenu</string>
<string name="btn_label">Show menu</string>
<string name="pm1">Item 1</string>
<string name="pm2">Item 2</string>
</resources>
<?xml version="1.0" encoding="utf-8"?>This is popup_menu.xml file. It defines two menu items. The file is located in the res/menu/ subdirectory.
<menu xmlns:android="http://schemas.android.com/apk/res/android">
<item android:id="@+id/settings"
android:title="@string/pm1" />
<item android:id="@+id/tools"
android:title="@string/pm2" />
</menu>
package com.zetcode.popmenu;A PopupMenu is displayed after clicking on the button widget.
import android.app.Activity;
import android.os.Bundle;
import android.view.View;
import android.view.MenuItem;
import android.widget.TextView;
import android.widget.PopupMenu;
import android.widget.PopupMenu.OnMenuItemClickListener;
public class MainActivity extends Activity
implements OnMenuItemClickListener
{
private TextView tv;
@Override
public void onCreate(Bundle savedInstanceState)
{
super.onCreate(savedInstanceState);
setContentView(R.layout.main);
tv = (TextView) findViewById(R.id.tvId);
}
public void onClick(View v)
{
showPopupMenu(v);
}
public void showPopupMenu(View v)
{
PopupMenu pm = new PopupMenu(MainActivity.this, v);
pm.getMenuInflater().inflate(R.menu.popup_menu, pm.getMenu());
pm.setOnMenuItemClickListener(this);
pm.show();
}
@Override
public boolean onMenuItemClick(MenuItem item)
{
tv.setText(item.toString() + " selected");
return true;
}
}
public void onClick(View v)This method is a callback to the button click. The relation is set in the main.xml file via an attribute. The method calls the showPopupMenu() method.
{
showPopupMenu(v);
}
public void showPopupMenu(View v)We create an instance of the
{
PopupMenu pm = new PopupMenu(MainActivity.this, v);
pm.getMenuInflater().inflate(R.menu.popup_menu, pm.getMenu());
pm.setOnMenuItemClickListener(this);
pm.show();
}
PopupMenu class. It builds the menu, sets the OnMenuItemClickListener and shows the PopupMenu. @OverrideAfter selecting a menu item the
public boolean onMenuItemClick(MenuItem item)
{
tv.setText(item.toString() + " selected");
return true;
}
onMenuItemClick() method is called. It sets the item's title to the TextView widget. <?xml version="1.0" encoding="utf-8"?>In the layout file we have a NumberPicker widget and a TextView widget. The TextView widget will display the selected value of the NumberPicker.
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
android:orientation="vertical"
android:layout_width="fill_parent"
android:layout_height="fill_parent"
>
<NumberPicker android:id="@+id/npId"
android:layout_marginTop="5dp"
android:layout_width="wrap_content"
android:layout_height="wrap_content" />
<TextView
android:id="@+id/tvId"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:layout_marginTop="5dp"
android:layout_marginLeft="5dp"
android:text="0"
android:textSize="30sp" />
</LinearLayout>
<?xml version="1.0" encoding="utf-8"?>The strings resource file.
<resources>
<string name="app_name">NumberPicker</string>
</resources>
package com.zetcode.numpick;Clicking on the plus and minus signs of the NumberPicker we select a new value. The currently selected value is displayed in the TextView widget.
import android.app.Activity;
import android.os.Bundle;
import android.widget.NumberPicker;
import android.widget.TextView;
import android.widget.NumberPicker.OnValueChangeListener;
public class MainActivity extends Activity
{
private TextView tv;
@Override
public void onCreate(Bundle savedInstanceState)
{
super.onCreate(savedInstanceState);
setContentView(R.layout.main);
setupUI();
}
public void setupUI()
{
tv = (TextView) findViewById(R.id.tvId);
NumberPicker np = (NumberPicker) findViewById(R.id.npId);
np.setOnValueChangedListener(new OnValueChangeListener()
{
public void onValueChange(NumberPicker picker, int oldVal,
int newVal)
{
tv.setText(String.valueOf(newVal));
}
});
np.setMaxValue(100);
np.setMinValue(0);
}
}
NumberPicker np = (NumberPicker) findViewById(R.id.npId);A reference to the
NumberPicker widget is retrieved from the main.xml file. np.setOnValueChangedListener(new OnValueChangeListener()A
{
public void onValueChange(NumberPicker picker, int oldVal,
int newVal)
{
tv.setText(String.valueOf(newVal));
}
});
OnValueChangeListener is added to the NumberPicker widget. It will call the onValueChange() method when the value of the NumberPicker is changed. Inside this method, we set the currently selected value to the TextView widget. np.setMaxValue(100);We set the maximum and minimum value for the NumberPicker.
np.setMinValue(0);
<?xml version="1.0" encoding="utf-8"?>In the main.xml file we have a TimePicker and TextView widgets. The selected time is displayed in the TextView.
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
android:orientation="vertical"
android:layout_width="fill_parent"
android:layout_height="fill_parent"
>
<TimePicker android:id="@+id/tpId"
android:layout_marginTop="5dp"
android:layout_width="wrap_content"
android:layout_height="wrap_content" />
<TextView
android:id="@+id/tvId"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:layout_marginTop="5dp"
android:layout_marginLeft="5dp"
android:textSize="30sp" />
</LinearLayout>
<?xml version="1.0" encoding="utf-8"?>This is the strings.xml resource file.
<resources>
<string name="app_name">TimePicker</string>
</resources>
package com.zetcode.timepicker;The TimePicker listens to the
import android.app.Activity;
import android.os.Bundle;
import android.widget.TimePicker;
import android.widget.TextView;
import android.widget.TimePicker.OnTimeChangedListener;
public class MainActivity extends Activity
{
private TextView tv;
@Override
public void onCreate(Bundle savedInstanceState)
{
super.onCreate(savedInstanceState);
setContentView(R.layout.main);
setupUI();
}
public void setupUI()
{
tv = (TextView) findViewById(R.id.tvId);
TimePicker tp = (TimePicker) findViewById(R.id.tpId);
displayCurrentTime(tp);
tp.setOnTimeChangedListener(new OnTimeChangedListener()
{
public void onTimeChanged(TimePicker view, int hourOfDay,
int minute)
{
StringBuilder tm = new StringBuilder();
tm.append(hourOfDay);
tm.append(" h ");
tm.append(minute);
tm.append(" m");
tv.setText(tm);
}
});
}
public void displayCurrentTime(TimePicker tp)
{
int h = tp.getCurrentHour();
int m = tp.getCurrentMinute();
StringBuilder tm = new StringBuilder();
tm.append(h);
tm.append(" h ");
tm.append(m);
tm.append(" m");
tv.setText(tm);
}
}
OnTimeChangedListener. When the time is changed, the new time value is set to the TextView inside the onTimeChanged() method. tp.setOnTimeChangedListener(new OnTimeChangedListener()Inside an anonymous
{
public void onTimeChanged(TimePicker view, int hourOfDay,
int minute)
{
StringBuilder tm = new StringBuilder();
tm.append(hourOfDay);
tm.append(" h ");
tm.append(minute);
tm.append(" m");
tv.setText(tm);
}
});
OnTimeChangedListener class we implement the onTimeChanged() method. With the StringBuilder we build the string to be displayed and set it to the TextView widget. public void displayCurrentTime(TimePicker tp)When the activity is first shown, we display the current time.
{
int h = tp.getCurrentHour();
int m = tp.getCurrentMinute();
StringBuilder tm = new StringBuilder();
tm.append(h);
tm.append(" h ");
tm.append(m);
tm.append(" m");
tv.setText(tm);
}
<?xml version="1.0" encoding="utf-8"?>In the main.xml file we define one ListView widget.
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
android:orientation="vertical"
android:layout_width="fill_parent"
android:layout_height="fill_parent">
<ListView
android:id="@+id/lvId"
android:layout_width="fill_parent"
android:layout_height="fill_parent" />
</LinearLayout>
<?xml version="1.0" encoding="utf-8"?>In the row.xml file we define, how a list row will look like. We will have one TextView in each row of a ListView. The sp is a unit used for setting the font size.
<TextView xmlns:android="http://schemas.android.com/apk/res/android"
android:layout_width="fill_parent"
android:layout_height="fill_parent"
android:padding="10dp"
android:textSize="20sp">
</TextView>
<?xml version="1.0" encoding="utf-8"?>The names of the planets are specified in the strings.xml file within a string array attribute.
<resources>
<string name="app_name">ListView</string>
<string-array name="planets">
<item>Mercury</item>
<item>Venus</item>
<item>Earth</item>
<item>Mars</item>
<item>Jupiter</item>
<item>Saturn</item>
<item>Uranus</item>
<item>Neptune</item>
<item>Pluto</item>
</string-array>
</resources>
package com.zetcode.listview;This is the MainActivity.java source file.
import android.app.Activity;
import android.os.Bundle;
import android.widget.ArrayAdapter;
import android.widget.ListView;
public class MainActivity extends Activity
{
private ListView lv;
private ArrayAdapter<String> la;
@Override
public void onCreate(Bundle savedInstanceState)
{
super.onCreate(savedInstanceState);
setContentView(R.layout.main);
setupUI();
}
public void setupUI()
{
lv = (ListView) findViewById(R.id.lvId);
String[] planets = getResources().getStringArray(R.array.planets);
lv.setAdapter(new ArrayAdapter<String>(this, R.layout.row, planets));
}
}
lv = (ListView) findViewById(R.id.lvId);We get the reference to the ListView widget.
String[] planets = getResources().getStringArray(R.array.planets);This code line retrieves the names of the planets from the resource file.
lv.setAdapter(new ArrayAdapter<String>(this, R.layout.row, planets));An ArrayAdapter is created and set to the ListView.
<?xml version="1.0" encoding="utf-8"?>In the row.xml file we define one TextView in each row of a ListView.
<TextView xmlns:android="http://schemas.android.com/apk/res/android"
android:layout_width="fill_parent"
android:layout_height="fill_parent"
android:padding="10dp"
android:textSize="20sp">
</TextView>
<?xml version="1.0" encoding="utf-8"?>This is the strings.xml resource file.
<resources>
<string name="app_name">ListView2</string>
</resources>
package com.zetcode.listview2;We programatically create the items of the ListView. We react to click and select events of the ListView. The planet that we select or click on will be shown in the titlebar.
import android.app.ListActivity;
import android.os.Bundle;
import android.view.View;
import android.widget.ArrayAdapter;
import android.widget.AdapterView;
import android.widget.AdapterView.OnItemClickListener;
import android.widget.AdapterView.OnItemSelectedListener;
import android.widget.ListView;
import android.widget.TextView;
public class MainActivity extends ListActivity
implements OnItemClickListener, OnItemSelectedListener
{
@Override
public void onCreate(Bundle savedInstanceState)
{
super.onCreate(savedInstanceState);
setupUI();
}
public void setupUI()
{
ArrayAdapter<String> la = new ArrayAdapter<String>(this, R.layout.row);
la.add("Mercury");
la.add("Venus");
la.add("Earth");
la.add("Mars");
la.add("Jupiter");
la.add("Saturn");
la.add("Uranus");
la.add("Neptune");
la.add("Pluto");
setListAdapter(la);
ListView lv = getListView();
lv.setOnItemClickListener(this);
lv.setOnItemSelectedListener(this);
}
public void onItemClick(AdapterView<?> parent, View view,
int position, long id)
{
String planet = ((TextView) view).getText().toString();
setTitle(planet);
}
public void onItemSelected(AdapterView<?> parent, View view,
int position, long id)
{
String planet = ((TextView) view).getText().toString();
setTitle(planet);
}
public void onNothingSelected(AdapterView<?> parent)
{
// not implemented
}
}
public class MainActivity extends ListActivityThe MainActivity extends the
implements OnItemClickListener, OnItemSelectedListener
ListActivity and implements two listeners. By implementing these two listeners, we must implement three abstract methods that are associated with these listeners. @OverrideIn the onCreate() method we do not call the setContentView() method. The ListView widget of the ListActivity will take up the whole screen.
public void onCreate(Bundle savedInstanceState)
{
super.onCreate(savedInstanceState);
setupUI();
}
ArrayAdapter<String> la = new ArrayAdapter<String>(this, R.layout.row);We create an instance of the
la.add("Mercury");
la.add("Venus");
la.add("Earth");
...
ArrayAdapter. We add names of the planets to the adapter. setListAdapter(la);Sets the adapter for the associated ListView object.
ListView lv = getListView();From the ListActivity we get the ListView widget. The two listeners are set for the ListView widget.
lv.setOnItemClickListener(this);
lv.setOnItemSelectedListener(this);
public void onItemClick(AdapterView<?> parent, View view,Implementing the
int position, long id)
{
String planet = ((TextView) view).getText().toString();
setTitle(planet);
}
OnItemClickListener, we have to define the onItemClick() method. We get the planet name from the TextView of the clicked row and set it to the titlebar. public void onItemSelected(AdapterView<?> parent, View view,After implementing the
int position, long id)
{
String planet = ((TextView) view).getText().toString();
setTitle(planet);
}
public void onNothingSelected(AdapterView<?> parent)
{
// not implemented
}
OnItemSelectedListener we have to define two abstract methods. The first method sets the currently selected planet to the titlebar. The second method is not implemented. 
<?xml version="1.0" encoding="utf-8"?>In the main.xml layout file, we have a ProgressBar and a TextView. The
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
android:orientation="vertical"
android:layout_width="fill_parent"
android:layout_height="fill_parent"
>
<ProgressBar
android:id="@+id/pbId"
android:layout_width="fill_parent"
android:layout_height="wrap_content"
style="?android:attr/progressBarStyleHorizontal"
android:layout_margin="10dp"
/>
<TextView
android:id="@+id/tvId"
android:layout_width="fill_parent"
android:layout_height="wrap_content"
android:layout_margin="10dp"
/>
</LinearLayout>
style="?android:attr/progressBarStyleHorizontal" style makes the ProgressBar horizontal. The default mode of the ProgressBar is the circular mode. <?xml version="1.0" encoding="utf-8"?>String resource file.
<resources>
<string name="app_name">ProgBar</string>
</resources>
package com.zetcode.progbar2;We create a thread to control the progress of a ProgressBar.
import android.app.Activity;
import android.os.Bundle;
import android.os.Handler;
import android.os.Message;
import android.widget.ProgressBar;
import android.widget.TextView;
import android.util.Log;
public class MainActivity extends Activity
{
ProgressBar pb;
TextView tv;
int prg = 0;
@Override
public void onCreate(Bundle savedInstanceState)
{
super.onCreate(savedInstanceState);
setContentView(R.layout.main);
pb = (ProgressBar) findViewById(R.id.pbId);
tv = (TextView) findViewById(R.id.tvId);
new Thread(myThread).start();
}
private Runnable myThread = new Runnable()
{
@Override
public void run()
{
while (prg < 100)
{
try
{
hnd.sendMessage(hnd.obtainMessage());
Thread.sleep(100);
}
catch(InterruptedException e)
{
Log.e("ERROR", "Thread was Interrupted");
}
}
runOnUiThread(new Runnable() {
public void run() {
tv.setText("Finished");
}
});
}
Handler hnd = new Handler()
{
@Override
public void handleMessage(Message msg)
{
prg++;
pb.setProgress(prg);
String perc = String.valueOf(prg).toString();
tv.setText(perc+"% completed");
}
};
};
}
new Thread(myThread).start();A new thread is started. In Android, lengthy tasks should by performed inside a thread to prevent the application from appearing unresponsive. A thread ends by returning from its main() method, or by an exception.
@OverrideThe code in a thread is placed in the
public void run()
{
while (prg < 100)
{
try
{
hnd.sendMessage(hnd.obtainMessage());
Thread.sleep(100);
}
catch(InterruptedException e)
{
Log.e("ERROR", "Thread was Interrupted");
}
}
runOnUiThread(new Runnable() {
public void run() {
tv.setText("Finished");
}
});
}
run() method. We will simulate a lengthy task by calling the Thread.sleep() method. This forces us to handle the InterruptedException. Android application runs in a single-thread model. All components of the main activity are created in the main thread. These components cannot be manipulated in other threads. To work around this, we use either the Handlerobject or call the runOnUiThread() method. runOnUiThread(new Runnable() {
public void run() {
tv.setText("Finished");
}
});
Only the original thread that created a view hierarchy can touch its views. Here we are modifying the TextView widget. Therefore we have put the code into the runOnUiThread() method, which runs the code in the main, UI thread, where the widget was created. Handler hnd = new Handler()Another way to touch widgets from another thread is to use the Handler object. It is used to enqueue an action to be performed on a different thread than its own. We update the progress bar and set a percentage of the task completed to the text view.
{
@Override
public void handleMessage(Message msg)
{
prg++;
pb.setProgress(prg);
String perc = String.valueOf(prg).toString();
tv.setText(perc+"% completed");
}
};
<?xml version="1.0" encoding="utf-8"?>In the main.xml file we have a ProgressBar and a TextView. The ProgressBar has the default style, which is the circular style. This is the same as if we have used the style="?android:attr/progressBarStyle" attribute.
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
android:orientation="vertical"
android:layout_width="fill_parent"
android:layout_height="fill_parent"
>
<ProgressBar
android:id="@+id/pbId"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
/>
<TextView
android:id="@+id/tvId"
android:layout_width="fill_parent"
android:layout_height="wrap_content"
android:text="@string/msg"
/>
</LinearLayout>
<?xml version="1.0" encoding="utf-8"?>We have two string resources in the strings.xml file.
<resources>
<string name="app_name">CirProgBar</string>
<string name="msg">Please wait...</string>
</resources>
package com.zetcode.progbar;The code is similar to the first example with a few modifications.
import android.app.Activity;
import android.os.Bundle;
import android.os.Handler;
import android.os.Message;
import android.widget.ProgressBar;
import android.widget.TextView;
import android.view.View;
import android.util.Log;
public class MainActivity extends Activity
{
ProgressBar pb;
TextView tv;
int prg = 0;
@Override
public void onCreate(Bundle savedInstanceState)
{
super.onCreate(savedInstanceState);
setContentView(R.layout.main);
pb = (ProgressBar) findViewById(R.id.pbId);
tv = (TextView) findViewById(R.id.tvId);
new Thread(myThread).start();
}
private Runnable myThread = new Runnable()
{
@Override
public void run()
{
while (prg < 100)
{
try
{
hnd.sendMessage(hnd.obtainMessage());
Thread.sleep(100);
}
catch(InterruptedException e)
{
Log.e("ERROR", "Thread was Interrupted");
}
}
runOnUiThread(new Runnable() {
public void run() {
tv.setText("Finished");
pb.setVisibility(View.GONE);
}
});
}
Handler hnd = new Handler()
{
@Override
public void handleMessage(Message msg)
{
prg++;
pb.setProgress(prg);
}
};
};
}
runOnUiThread(new Runnable() {
public void run() {
tv.setText("Finished");
pb.setVisibility(View.GONE);
}
});
After the task was completed, we hide the ProgressBar using the setVisibility() method. The circle itself is an endless animation, so after the task was finished, we need to hide the widget. 
<?xml version="1.0" encoding="utf-8"?>In the main.xml layout file, we have two widgets defined. The SeekBar widget and the TextView widget.
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
android:orientation="vertical"
android:layout_width="fill_parent"
android:layout_height="fill_parent"
>
<SeekBar
android:id="@+id/sbId"
android:layout_width="fill_parent"
android:layout_height="wrap_content"
android:layout_margin="10dp"
android:max="100"
android:progress="50"
/>
<TextView
android:id="@+id/tvId"
android:layout_width="fill_parent"
android:layout_height="wrap_content"
android:layout_marginLeft="10dp"
/>
</LinearLayout>
<?xml version="1.0" encoding="utf-8"?>This is strings.xml resource file. The init_tv_value is the initial value of the TextView widget.
<resources>
<string name="app_name">SeekBar</string>
<string name="init_tv_value">50</string>
</resources>
package com.zetcode.seekbar;The current value from the SeekBar is set to the TextView widget.
import android.app.Activity;
import android.os.Bundle;
import android.widget.TextView;
import android.widget.SeekBar;
import android.widget.SeekBar.OnSeekBarChangeListener;
public class MainActivity extends Activity implements
OnSeekBarChangeListener
{
TextView tv;
@Override
public void onCreate(Bundle savedInstanceState)
{
super.onCreate(savedInstanceState);
setContentView(R.layout.main);
SeekBar sb = (SeekBar) findViewById(R.id.sbId);
sb.setOnSeekBarChangeListener(this);
tv = (TextView) findViewById(R.id.tvId);
String val = this.getString(R.string.init_tv_value);
tv.setText(val);
}
@Override
public void onProgressChanged(SeekBar seekBar, int progress,
boolean fromUser)
{
tv.setText(String.valueOf(progress));
}
@Override
public void onStartTrackingTouch(SeekBar seekBar)
{
// not implemented
}
@Override
public void onStopTrackingTouch(SeekBar seekBar)
{
// not implemented
}
}
public class MainActivity extends Activity implementsThe MainActivity class implements the OnSeekBarChangeListener. We neet to define three abstract methods. The onProgressChanged(), the onStartTrackingTouch() and the onStopTrackingTouch() method. The last two methods are not implemented. They are related to touch gestures. We provide only empty methods.
OnSeekBarChangeListener
SeekBar sb = (SeekBar) findViewById(R.id.sbId);We get the reference to the SeekBar widget and set a listener for it.
sb.setOnSeekBarChangeListener(this);
tv = (TextView) findViewById(R.id.tvId);We get the reference to the TextView widget. We retrieve the init_tv_value from the string resources and set it to the TextView.
String val = this.getString(R.string.init_tv_value);
tv.setText(val);
@OverrideWhen we move the thumb of the SeekBar, the
public void onProgressChanged(SeekBar seekBar, int progress,
boolean fromUser)
{
tv.setText(String.valueOf(progress));
}
onProgressChanged()method is called. The progress parameter is the current value of the SeekBar. The default range is 0..100. We set the current value of the SeekBar to the TextView widget. 
Spinner class is used to create a spinner widget. <?xml version="1.0" encoding="utf-8"?>This is the manifest file for the program.
<manifest xmlns:android="http://schemas.android.com/apk/res/android"
package="com.zetcode.finish"
android:versionCode="1"
android:versionName="1.0">
<application android:label="@string/app_name" android:icon="@drawable/ic_launcher">
<activity android:name="MainActivity"
android:label="@string/app_name">
<intent-filter>
<action android:name="android.intent.action.MAIN" />
<category android:name="android.intent.category.LAUNCHER" />
</intent-filter>
</activity>
</application>
</manifest>
<?xml version="1.0" encoding="utf-8"?>In the main.xml layout file, we have a Spinner and a TextView. The android:entries="@array/dlangs" attribute defines a XML resource that provides an array of strings. The strings are written in the strings.xmlfile.
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
android:orientation="vertical"
android:layout_width="fill_parent"
android:layout_height="fill_parent"
>
<Spinner
android:id="@+id/spn"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:entries="@array/dlangs"
android:layout_marginTop="10dip"
android:prompt="@string/spn_title" />
<TextView
android:id="@+id/tvId"
android:layout_width="fill_parent"
android:layout_height="wrap_content"
android:layout_marginTop="10dip"
/>
</LinearLayout>
<?xml version="1.0" encoding="utf-8"?>In the strings.xml file we have the elements of the string array. These are displayed when we click on the Spinner widget.
<resources>
<string name="app_name">Spinner</string>
<string name="spn_title">Choose a language</string>
<string-array name="dlangs">
<item>Python</item>
<item>PHP</item>
<item>Perl</item>
<item>Tcl</item>
<item>Ruby</item>
</string-array>
</resources>
package com.zetcode.spinner;The selected item from the Spinner widget is displayed in the TextView widget.
import android.app.Activity;
import android.os.Bundle;
import android.view.View;
import android.widget.TextView;
import android.widget.Spinner;
import android.widget.AdapterView;
import android.widget.AdapterView.OnItemSelectedListener;
public class MainActivity extends Activity implements OnItemSelectedListener
{
private TextView tv;
@Override
public void onCreate(Bundle savedInstanceState)
{
super.onCreate(savedInstanceState);
setContentView(R.layout.main);
tv = (TextView) findViewById(R.id.tvId);
Spinner spn = (Spinner) findViewById(R.id.spn);
spn.setOnItemSelectedListener(this);
}
@Override
public void onItemSelected(AdapterView<?> parent, View v, int pos, long id)
{
String item = parent.getItemAtPosition(pos).toString();
tv.setText(item);
}
@Override
public void onNothingSelected(AdapterView<?> arg0)
{
tv.setText("");
}
}
public class MainActivity extends Activity implements OnItemSelectedListenerThe MainActivity class implements the
OnItemSelectedListener. The class must now implement two methods. The onItemSelected() and onNothingSelected() methods. Spinner spn = (Spinner) findViewById(R.id.spn);These two lines get the reference to the Spinner widget and set the OnItemSelectedListener for it.
spn.setOnItemSelectedListener(this);
@OverrideIn the
public void onItemSelected(AdapterView<?> parent, View v, int pos, long id)
{
String item = parent.getItemAtPosition(pos).toString();
tv.setText(item);
}
onItemSelected() method we get the currently selected Spinner item with the getItemAtPosition(). The item is transformed to a string and set to the TextView. 
ArrayAdapter in conjunction with the ArrayList. ArrayAdapter is an intermediary between the data source and the data view. In this case the data source is the ArrayList and the view is the Spinner widget. Using an adapter we are decoupling our code. <?xml version="1.0" encoding="utf-8"?>This is the manifest file.
<manifest xmlns:android="http://schemas.android.com/apk/res/android"
package="com.zetcode.toast"
android:versionCode="1"
android:versionName="1.0">
<application android:label="@string/app_name"
android:icon="@drawable/ic_launcher">
<activity android:name="MainActivity"
android:label="@string/app_name">
<intent-filter>
<action android:name="android.intent.action.MAIN" />
<category android:name="android.intent.category.LAUNCHER" />
</intent-filter>
</activity>
</application>
</manifest>
<?xml version="1.0" encoding="utf-8"?>In the main.xml file we have two widgets. The Spinner and the TextView widget. This time we do not define the array data entries for the Spinner.
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
android:orientation="vertical"
android:layout_width="fill_parent"
android:layout_height="fill_parent"
>
<Spinner
android:id="@+id/spnId"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:layout_marginTop="10dip"
android:prompt="@string/spn_title" />
<TextView
android:id="@+id/tvId"
android:layout_width="fill_parent"
android:layout_height="wrap_content"
android:layout_marginTop="10dip" />
</LinearLayout>
<?xml version="1.0" encoding="utf-8"?>This is the strings.xml resource file.
<resources>
<string name="app_name">Spinner2</string>
<string name="spn_title">Choose a language</string>
</resources>
package com.zetcode.spinner2;In the MainActivity.java source file we fill the Spinner widget with data and implement the OnItemSelectedListener for the widget.
import java.util.ArrayList;
import java.util.List;
import android.app.Activity;
import android.os.Bundle;
import android.view.View;
import android.widget.Spinner;
import android.widget.ArrayAdapter;
import android.widget.TextView;
import android.widget.AdapterView;
import android.widget.AdapterView.OnItemSelectedListener;
public class MainActivity extends Activity implements OnItemSelectedListener
{
private TextView tv;
private Spinner spn;
@Override
public void onCreate(Bundle savedInstanceState)
{
super.onCreate(savedInstanceState);
setContentView(R.layout.main);
setup();
}
public void setup()
{
tv = (TextView) findViewById(R.id.tvId);
spn = (Spinner) findViewById(R.id.spnId);
fillSpinner(spn);
spn.setOnItemSelectedListener(this);
}
public void fillSpinner(Spinner spn)
{
List<String> lst = new ArrayList<String>();
lst.add("Python");
lst.add("PHP");
lst.add("Perl");
lst.add("Tcl");
lst.add("Ruby");
ArrayAdapter<String> da = new ArrayAdapter<String>(this,
android.R.layout.simple_spinner_item, lst);
da.setDropDownViewResource(android.R.layout.simple_spinner_item);
spn.setAdapter(da);
}
@Override
public void onItemSelected(AdapterView<?> parent, View v, int pos, long id)
{
String item = parent.getItemAtPosition(pos).toString();
tv.setText(item);
}
@Override
public void onNothingSelected(AdapterView<?> arg0)
{
tv.setText("");
}
}
spn = (Spinner) findViewById(R.id.spnId);We get the reference to the
fillSpinner(spn);
Spinner widget and call the fillSpinner() method to populate it with data. List<String> lst = new ArrayList<String>();An
lst.add("Python");
lst.add("PHP");
lst.add("Perl");
lst.add("Tcl");
lst.add("Ruby");
ArrayList is created and filled with strings. ArrayAdapter<String> da = new ArrayAdapter<String>(this,The instance of the
android.R.layout.simple_spinner_item, lst);
ArrayAdapter is created. It takes the ArrayList as a parameter. da.setDropDownViewResource(android.R.layout.simple_spinner_item);This line determines the look of the dropdown menu of the Spinner widget. This one is a dropdown without radio buttons. A spinner with the
android.R.layout.simple_spinner_dropdown_item defined has radio buttons in its rows. spn.setAdapter(da);The adapter is set for the Spinner widget.
$ ls res/drawable-hdpi/Depending on a android virtual device we are using, we put the image in the corresponding subdirectory of the res directory.
ic_launcher.png zamok.jpg
<?xml version="1.0" encoding="utf-8"?>In the FrameLayout manager, we put one ImageView.
<FrameLayout xmlns:android="http://schemas.android.com/apk/res/android"
android:layout_gravity="top"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
>
<ImageView
android:layout_height="match_parent"
android:layout_width="match_parent"
android:src="@drawable/zamok" />
</FrameLayout>
<FrameLayout xmlns:android="http://schemas.android.com/apk/res/android"The
android:layout_gravity="top"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
>
FrameLayout is big enough to display the ImageViewby setting the layout width and height to wrap_content. It is pushed to the top using the layout_gravity attribute. <ImageViewThe
android:layout_height="match_parent"
android:layout_width="match_parent"
android:src="@drawable/zamok" />
ImageView displays an image. The image is located in a subdirectory of the res directory. 
<?xml version="1.0" encoding="utf-8"?>We have a horizontal
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
android:orientation="horizontal"
android:layout_width="match_parent"
android:layout_height="match_parent"
>
<Button
android:layout_height="wrap_content"
android:layout_width="wrap_content"
android:text="Button1" />
<Button
android:layout_height="wrap_content"
android:layout_width="wrap_content"
android:text="Button2" />
<Button
android:layout_height="wrap_content"
android:layout_width="wrap_content"
android:text="Button3" />
<Button
android:layout_height="wrap_content"
android:layout_width="wrap_content"
android:text="Button4" />
</LinearLayout>
LinearLayout. In this layout, we add four buttons. <LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"We create a horizontal LinearLayout manager. The width and height of the layout match the parent which means that it fills the entire screen.
android:orientation="horizontal"
android:layout_width="match_parent"
android:layout_height="match_parent"
>
<ButtonEach of the four buttons use the wrap_content property. They are then just big enough to display their content.
android:layout_height="wrap_content"
android:layout_width="wrap_content"
android:text="Button1" />
package com.zetcode.btnrow2;Four buttons are placed in a horizontal LinearLayout. We will not use the layout XML file in this sample.
import android.app.Activity;
import android.os.Bundle;
import android.widget.Button;
import android.widget.LinearLayout;
public class ButtonRow2 extends Activity
{
@Override
public void onCreate(Bundle savedInstanceState)
{
super.onCreate(savedInstanceState);
initUI();
}
public void initUI()
{
Button btn1 = new Button(this);
btn1.setText("Button");
Button btn2 = new Button(this);
btn2.setText("Button");
Button btn3 = new Button(this);
btn3.setText("Button");
Button btn4 = new Button(this);
btn4.setText("Button");
LinearLayout ll = new LinearLayout(this);
ll.setOrientation(LinearLayout.HORIZONTAL);
ll.addView(btn1);
ll.addView(btn2);
ll.addView(btn3);
ll.addView(btn4);
setContentView(ll);
}
}
Button btn1 = new Button(this);A
btn1.setText("Button");
Button widget is created. The text is set for the button with the setText() method. LinearLayout ll = new LinearLayout(this);A horizontal
ll.setOrientation(LinearLayout.HORIZONTAL);
LinearLayout is created. ll.addView(btn1);Buttons are added to the layout manager.
ll.addView(btn2);
ll.addView(btn3);
ll.addView(btn4);
setContentView(ll);The linear layout manager is set to be the content view of the activity.
<?xml version="1.0" encoding="utf-8"?>A LinearLayout manager with four buttons is placed in the FrameLayout manager.
<FrameLayout
xmlns:android="http://schemas.android.com/apk/res/android"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:layout_gravity="center"
>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
android:orientation="vertical"
android:layout_width="match_parent"
android:layout_height="match_parent"
>
<Button
android:layout_height="wrap_content"
android:layout_width="wrap_content"
android:text="Button" />
<Button
android:layout_height="wrap_content"
android:layout_width="wrap_content"
android:text="Button" />
<Button
android:layout_height="wrap_content"
android:layout_width="wrap_content"
android:text="Button" />
<Button
android:layout_height="wrap_content"
android:layout_width="wrap_content"
android:text="Button" />
</LinearLayout>
</FrameLayout>
<FrameLayoutThe FrameLayout does not occupy all the available space. It is just big enough to take all the four buttons. And therefore we can use the
xmlns:android="http://schemas.android.com/apk/res/android"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:layout_gravity="center"
>
layout_gravityattribute to center the LinearLayout and its four buttons. <LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"A vertical LinearLayout is created.
android:orientation="vertical"
android:layout_width="match_parent"
android:layout_height="match_parent"
>
<?xml version="1.0" encoding="utf-8"?>The XML code displays an EditText with two buttons.
<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
android:layout_width="fill_parent"
android:layout_height="fill_parent"
>
<EditText
android:id="@+id/etId"
android:layout_marginTop="10dp"
android:layout_width="match_parent"
android:layout_height="wrap_content" />
<Button
android:id="@+id/btn_sendId"
android:layout_below="@+id/etId"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:text="Send" />
<Button
android:id="@+id/btn_clearId"
android:layout_below="@+id/etId"
android:layout_toRightOf="@+id/btn_sendId"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:text="Clear" />
</RelativeLayout>
<EditTextThe
android:id="@+id/etId"
android:layout_marginTop="10dp"
android:layout_width="match_parent"
android:layout_height="wrap_content" />
EditText will be stretched from right to left by setting the android:layout_width to android:match_parent. The widget will be high enough to show its contents. We specify some gap between the widget and the border of the screen with android:layout_marginTopproperty. <ButtonThe Send button widget will be placed below the EditText widget. To accomplish this, we use the
android:id="@+id/btn_sendId"
android:layout_below="@+id/etId"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:text="Send" />
android:layout_below property. Note that we reference the id of the widget that we relate to. <ButtonThe Clear button is placed below the EditText widget and to the right of the Send button. We accomplish this by two properties. The
android:id="@+id/btn_clearId"
android:layout_below="@+id/etId"
android:layout_toRightOf="@+id/btn_sendId"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:text="Clear" />
android:layout_below and the android:layout_toRightOfproperty. 
<?xml version="1.0" encoding="utf-8"?>In the example we put a few buttons in a GridLayout. We show how a button can stretch over several cells.
<GridLayout xmlns:android="http://schemas.android.com/apk/res/android"
android:layout_width="match_parent"
android:layout_height="match_parent"
>
<Button
android:text="(0, 0)"
android:layout_row="0"
android:layout_column="0" />
<Button
android:layout_row="0"
android:layout_column="1"
android:layout_columnSpan="2"
android:layout_gravity="fill_horizontal" />
<Button
android:text="(0, 3)"
android:layout_row="0"
android:layout_column="3" />
<Button
android:text="(0, 4)"
android:layout_row="0"
android:layout_column="4" />
<Button
android:layout_row="1"
android:layout_column="0"
android:layout_rowSpan="3"
android:layout_columnSpan="5"
android:layout_gravity="fill" />
<Button
android:text="Center"
android:layout_row="4"
android:layout_column="0"
android:layout_columnSpan="5"
android:layout_gravity="center_horizontal" />
<Button
android:text="Right"
android:layout_row="5"
android:layout_column="0"
android:layout_columnSpan="5"
android:layout_gravity="right" />
</GridLayout>
<ButtonUsing the
android:text="(0, 0)"
android:layout_row="0"
android:layout_column="0" />
layout_row and layout_column properties, we place a button at top-left cell. The indeces start from zero. <ButtonThis button will span two columns. The
android:layout_row="0"
android:layout_column="1"
android:layout_columnSpan="2"
android:layout_gravity="fill_horizontal" />
layout_gravity property will cause the button to fill the two columns. <ButtonThis button will span three rows and five columns.
android:layout_row="1"
android:layout_column="0"
android:layout_rowSpan="3"
android:layout_columnSpan="5"
android:layout_gravity="fill" />
<ButtonA view may not occupy all the space that was allotted to it. This button is horizontally centered within five columns.
android:text="Center"
android:layout_row="4"
android:layout_column="0"
android:layout_columnSpan="5"
android:layout_gravity="center_horizontal" />
