Android Recipes and Snippets

I've put together a small collection of Android recipes. For each of these recipes, this is an instance of Context (more specifically, Activity or Service) unless otherwise noted. Enjoy :)

Intents
One of the coolest things about Android is Intents. The two most common uses of Intents are starting an Activity (open an email, contact, etc.) and starting an Activity for a result (scan a barcode, take a picture to attach to an email, etc.). Intents are specified primarily using action strings and URIs. Here are some things you can do with the android.intent.action.VIEW action and startActivity().

Intent intent = new Intent(Intent.ACTION_VIEW);
// Choose a value for uri from the following.
// Search Google Maps: geo:0,0?q=query
// Show contacts: content://contacts/people
// Show a URL: http://www.google.com
intent.setData(Uri.parse(uri));
intent.setFlags(Intent.FLAG_ACTIVITY_NEW_TASK);
startActivity(intent);

Other useful action/URI pairs include:

• Intent.ACTION_DIAL, tel://8675309
• Intent.ACTION_CALL, tel://8675309

More interesting things are available when you use startActivityForResult(). For example, to scan a barcode:

Intent intent = new Intent("com.google.zxing.client.android.SCAN");
startActivityForResult(intent, 0);

Then, add onActivityResult to your activity.

@Override
public void onActivityResult(int requestCode, int resultCode, Intent data) {
  if (resultCode == Activity.RESULT_OK && requestCode == 0) {
    Bundle extras = data.getExtras();
    String result = extras.getStringExtra("SCAN_RESULT");
    // ...
  }
}

Taking a picture is done like so:

Intent intent = new Intent("android.media.action.IMAGE_CAPTURE");
startActivityForResult(intent, 0);
// ...

@Override
public void onActivityResult(int requestCode, int resultCode, Intent data) {
  if (resultCode == Activity.RESULT_OK && requestCode == 0) {
    String result = data.toURI();
    // ...
  }
}

Check out the OpenIntents registry for more information.

Wifi
The WifiManager can be used to enable and disable wifi. Where enabled is a boolean, it's as easy as:

WifiManager wifi = (WifiManager) getSystemService(Context.WIFI_SERVICE);
wifi.setWifiEnabled(enabled);

Notifications
Text notifications (called Toast) which appear briefly above all activities are also easy:

Toast.makeText(this, message, Toast.LENGTH_SHORT).show();

You can increase the time the notification is displayed by using Toast.LENGTH_LONG instead.

Alert and Input Dialogs
Sometimes it's useful to prompt the user for input. An easy way to do that without creating a new layout is to use AlertDialog.Builder.

AlertDialog.Builder alert = new AlertDialog.Builder(this);
alert.setTitle(title);
alert.setMessage(message);

// You can set an EditText view to get user input besides
// which button was pressed.
final EditText input = new EditText(this);
alert.setView(input);

alert.setPositiveButton("Ok", new DialogInterface.OnClickListener() {
public void onClick(DialogInterface dialog, int whichButton) {
  String value = input.getText();
  // Do something with value!
  }
});
alert.setNegativeButton("Cancel", new DialogInterface.OnClickListener() {
  public void onClick(DialogInterface dialog, int whichButton) {
    // Canceled.
  }
});

alert.show();

Location
Use the LocationManager to start up the GPS and listen for location updates.

LocationManager locator = (LocationManager) getSystemService(Context.LOCATION_SERVICE);
LocationListener mLocationListener = new LocationListener() {
  public void onLocationChanged(Location location) {
    if (location != null) {
      location.getAltitude();
      location.getLatitude();
      location.getLongitude();
      location.getTime();
      location.getAccuracy();
      location.getSpeed();
      location.getProvider();
    }
  }

  public void onProviderDisabled(String provider) {
    // ...
  }

  public void onProviderEnabled(String provider) {
    // ...
  }

  public void onStatusChanged(String provider, int status, Bundle extras) {
    // ...
  }
};

// You need to specify a Criteria for picking the location data source.
// The criteria can include power requirements.
Criteria criteria = new Criteria();
criteria.setAccuracy(Criteria.ACCURACY_COARSE);  // Faster, no GPS fix.
criteria.setAccuracy(Criteria.ACCURACY_FINE);  // More accurate, GPS fix.
// You can specify the time and distance between location updates.
// Both are useful for reducing power requirements.
mLocationManager.requestLocationUpdates(mLocationManager.getBestProvider(criteria, true),
    MIN_LOCATION_UPDATE_TIME, MIN_LOCATION_UPDATE_DISTANCE, mLocationListener,
    getMainLooper());

You can also get the phone's last known location using the LocationManager. This is faster than setting up a LocationListener and waiting for a fix.

// Start with fine location.
Location l = locator.getLastKnownLocation(LocationManager.GPS_PROVIDER);
if (l == null) {
  // Fall back to coarse location.
  l = locator.getLastKnownLocation(LocationManager.NETWORK_PROVIDER);
}

SMS
Sending a text is done with the SmsManager.

SmsManager m = SmsManager.getDefault();
String destination = "8675309";
String text = "Hello, Jenny!";
m.sendTextMessage(destination, null, text, null, null);

Vibrate
You can vibrate the phone for a specified duration like so:

(Vibrator) getSystemService(Context.VIBRATOR_SERVICE).vibrate(milliseconds);

Sensors
Accessing sensor data is done using the SensorManager.

SensorManager mSensorManager = (SensorManager) getSystemService(Activity.SENSOR_SERVICE);
private final SensorListener mSensorListener = new SensorListener() {
  public void onAccuracyChanged(int sensor, int accuracy) {
    // ...
  }

  public void onSensorChanged(int sensor, float[] values) {
    switch (sensor) {
      case SensorManager.SENSOR_ORIENTATION:
        float azimuth = values[0];
        float pitch = values[1];
        float roll = values[2];
        break;
      case SensorManager.SENSOR_ACCELEROMETER:
        float xforce = values[0];
        float yforce = values[1];
        float zforce = values[2];
        break;
      case SensorManager.SENSOR_MAGNETIC_FIELD:
        float xmag = values[0];
        float ymag = values[1];
        float zmag = values[2];
        break;
    }
  }
};

// Start listening to all sensors.
mSensorManager.registerListener(mSensorListener, mSensorManager.getSensors());
// ...
// Stop listening to sensors.
mSensorManager.unregisterListener(mSensorListener);

Silence Ringer
You can use the AudioManager to enable and disable silent mode.

mAudio = (AudioManager) getSystemService(Activity.AUDIO_SERVICE);
mAudio.setRingerMode(AudioManager.RINGER_MODE_SILENT);
// or...
mAudio.setRingerMode(AudioManager.RINGER_MODE_NORMAL);

Useful Links
That's it from me for now. But, here are some useful sources of more information:

• The official Android developer site. It used to be on Google Code, but it has since moved.
• The Android source code.
  
• Mike's guide to browsing the Android source tree in Eclipse.
• Sample Android applications from Google.
• And, of course, Google Code Search.