Which method is used to request audio focus in Android?

Introducing Audio Focus

Audio focus refers to the system that manages audio playback between apps in Android. It allows apps to coordinate their audio streams so only one app plays audio at a time. When an app requests audio focus, it signals to the system that it intends to output audio. The system will then duck, mute, or pause any other app that is already playing audio.

Audio focus is needed in Android so multiple media apps don’t play over each other creating a bad user experience. It provides a mechanism for coordinated shared use of the audio output hardware. Typical use cases include media players starting/pausing playback, notification sounds interrupting music, and voice call audio muting other streams.

Without audio focus, multiple apps would output audio simultaneously. This results in a jarring experience for users trying to listen to music or podcasts. Proper use of audio focus results in smooth transitions between audio streams and a seamless audio experience.

AudioManager Class

The AudioManager class provides access to the audio operations and configuration on an Android device. It is the primary API to request audio focus and manage audio resources. To access it in your code, you need to call the getSystemService() method:

AudioManager audioManager = (AudioManager) getSystemService(Context.AUDIO_SERVICE);

Some key methods provided by the AudioManager class include:

• requestAudioFocus() – Requests audio focus so that the app can output audio sound.
• abandonAudioFocus() – Abandons audio focus after use.
• setStreamVolume() – Sets the volume index for a particular stream type.
• adjustStreamVolume() – Adjusts the volume for a particular stream type.
• setMode() – Sets the audio mode such as MODE_NORMAL, MODE_RINGTONE etc.
• setSpeakerphoneOn() – Turns on speakerphone or not.

So the AudioManager allows centralized control of audio across various sources on the device. Using it properly helps avoid conflicts between multiple audio streams.

Requesting Audio Focus

To request audio focus, apps call the requestAudioFocus() method on the AudioManager class. This method takes in three parameters:

• An OnAudioFocusChangeListener – This listener will get callbacks whenever audio focus is gained or lost.
• The audio stream type – For example STREAM_MUSIC for media playback streams.
• An int focus gain request – This specifies the type of focus request like AUDIOFOCUS_GAIN or AUDIOFOCUS_GAIN_TRANSIENT.

For example, to request focus for music playback:

AudioManager am = (AudioManager)getSystemService(Context.AUDIO_SERVICE);

am.requestAudioFocus(afChangeListener, AudioManager.STREAM_MUSIC, AudioManager.AUDIOFOCUS_GAIN); 

The OnAudioFocusChangeListener passed will get callbacks like onAudioFocusChange() whenever focus is gained or lost so the app can pause/resume playback accordingly. See reference for details.

Managing Audio Focus

The key to properly handling audio focus is having a strategy for responding to focus changes in your app. When your app gains focus, it should resume playback or raise its audio volume. When your app loses focus, it should pause playback or lower its volume. The requestAudioFocus() method allows passing an OnAudioFocusChangeListener to be notified of focus updates.

For example, when regaining focus, the listener’s onAudioFocusChange() method would be called with the AUDIOFOCUS_GAIN argument. The app could resume playback in response. When losing focus, onAudioFocusChange() would be called with AUDIOFOCUS_LOSS and the app could pause playback. There are also transient loss states like AUDIOFOCUS_LOSS_TRANSIENT that may warrant briefly lowering volume vs completely stopping playback.

By properly handling audio focus changes, apps can seamlessly cooperate with other media apps on the device. Music players can pause when a notification plays, then resume automatically. Video players can lower volume during navigation prompts. Implementing a robust audio focus strategy improves the overall media experience for users.

Audio Focus Request Types

There are a few different audio focus request types that apps can use when requesting audio focus in Android:

GAIN – This request type indicates your app would like to gain audio focus for a long amount of time. Examples could be a music streaming app or podcast app. Using this focus type signals to the system that your app expects to hold audio focus for minutes or more.

GAIN_TRANSIENT – This request type indicates your app would like to gain audio focus for a short amount of time. Examples could be for playing a sound effect, alert, or voice command prompt. The system will return audio focus back to the previous app after a short time when using this type.

GAIN_TRANSIENT_MAY_DUCK – This request type is similar to GAIN_TRANSIENT, but also indicates to the system that your app is ok with the previous app ducking its audio while your transient audio plays. This avoids complete silence from the other app and allows both to play audio at the same time.

Choosing the appropriate focus request type allows the system to best arbitrate and manage audio across different apps based on their usage and needs. Using the right focus type helps avoid conflicts between apps trying to play audio at the same time.

More details can be found at: Android AudioFocusRequest Docs

Handling Focus Changes

To handle changes in audio focus, you need to implement the onAudioFocusChange() callback in your AudioManager.OnAudioFocusChangeListener. This method gets called whenever there is a change in audio focus for your app. You can check the focusChange parameter to determine what kind of change occurred:

• AUDIOFOCUS_GAIN – Your app gained audio focus
• AUDIOFOCUS_LOSS – Your app lost audio focus temporarily
• AUDIOFOCUS_LOSS_TRANSIENT – Your app lost audio focus temporarily due to another app requesting focus
• AUDIOFOCUS_LOSS_TRANSIENT_CAN_DUCK – Your app lost audio focus but can continue playing at lower volume

Based on the focus change value, you can adjust your app’s audio playback accordingly. For example, when losing focus you may want to pause playback. And when gaining focus back, you can resume playback.

Here is an example onAudioFocusChange() implementation from the Stack Overflow post:

@Override
public void onAudioFocusChange(int focusChange) {
  switch (focusChange) {
    case AudioManager.AUDIOFOCUS_GAIN:
      // resume playback
      break;

    case AudioManager.AUDIOFOCUS_LOSS:
      // Lost focus for an unbounded amount of time: stop playback and release media player
      break;

    case AudioManager.AUDIOFOCUS_LOSS_TRANSIENT:
      // Lost focus for a short time, but we have to stop
      // playback. We don't release the media player because playback
      // is likely to resume
      break;

    case AudioManager.AUDIOFOCUS_LOSS_TRANSIENT_CAN_DUCK:
      // Lost focus for a short time, but it's ok to keep playing
      // at an attenuated level
      break;
  }
}  

Properly implementing onAudioFocusChange() allows your app to seamlessly handle audio focus changes and provide a good user experience.

Example App

To demonstrate how to request and manage audio focus in an Android app, let’s walk through a simple music player example. We will use the AudioFocusController library to simplify the focus management code.

First, when the music player activity starts, we need to request audio focus. We can do this by calling the AudioFocusController.requestAudioFocus() method. We will pass in the audio focus request type, which in our case is AudioManager.AUDIOFOCUS_GAIN since we want to gain exclusive audio playback control.

Next, our activity needs to register a broadcast receiver to listen for audio focus changes. The AudioFocusController handles dispatching these focus change events. In our receiver, we can update the music playback based on whether focus was gained or lost. For example, we would pause playback if we lost focus.

When our activity is stopped or done playing audio, we need to abandon focus by calling AudioFocusController.abandonAudioFocus(). This notifies the system that we are done with audio playback so focus can be granted to another app.

By properly requesting, handling, and abandoning audio focus, our music player can cooperate with other media apps on the device. The AudioFocusController library handles the messy focus management code so we can focus on the app logic.

Best Practices

Properly handling audio focus is critical for creating a good user experience in Android apps. Here are some tips for implementing audio focus correctly:

Request audio focus when your app needs to play audio using AudioManager.requestAudioFocus(). Be sure to specify the appropriate focus gain request type based on your audio playback needs.

Always check the return value of requestAudioFocus() to see if focus was granted before starting playback. Be prepared to handle AUDIOFOCUS_REQUEST_FAILED.

Implement an AudioManager.OnAudioFocusChangeListener to handle focus changes gracefully. Reduce playback volume when losing focus and resume normal playback when gaining focus again.

Abandon audio focus once playback is finished by calling AudioManager.abandonAudioFocus(). This allows other apps to gain focus and play audio.

Avoid streaming/playing audio constantly in the background without user interaction. This deprives other apps of audio focus.

Never start playback or assume you have audio focus without explicitly requesting it first. Attempting to “steal” focus from other apps leads to a bad user experience.

Following proper audio focus best practices helps ensure multiple media apps can coexist harmoniously on Android devices and provide a quality experience for users.

Audio Focus for Media Players

Media player apps have specific guidance when requesting audio focus in Android. As noted in the Android documentation, media players should request a temporary audio focus using AudioManager.AUDIOFOCUS_GAIN_TRANSIENT. This allows other apps to temporarily take over audio output, such as for notifications or navigation prompts.

Requesting permanent audio focus with AUDIOFOCUS_GAIN is not recommended for media players, as this will prevent other apps from playing audio. Temporary focus allows seamlessly ducking your media playback as needed.

Upon losing focus, media players should pause playback. When focus returns, playback can resume from the same position. This provides a smooth user experience without abrupt stops and starts.

See the Request audio focus section of the Android developer documentation for code samples and additional best practices.

Conclusion

In summary, requesting audio focus in Android is done through the AudioManager class and its requestAudioFocus() method. There are different audio focus request types like AUDIOFOCUS_GAIN that indicate the priority level. When focus changes, the app will receive callbacks like onAudioFocusChange() to handle it properly, such as pausing playback. Following best practices like handling all audio focus changes gracefully creates a good user experience. The audio focus system allows media playback apps to coordinate with each other so audio doesn’t get disrupted. Overall, requesting audio focus with the AudioManager is essential for creating well-behaved audio apps in Android.