android - onAudioFocusChange 未调用

Question

private static int changedFocus;
private static boolean focusGranted;
private static AudioManager audioManager;

public static int getChangedFocus() {
    return changedFocus;
}

public static boolean isFocusGranted() {
    return focusGranted;
}

public static void requestFocus(final Context context) {
    if (audioManager == null) {
        audioManager = (AudioManager) context.getSystemService(Context.AUDIO_SERVICE);
    }
    switch (audioManager.requestAudioFocus(OnFocusChangeListener.getInstance(),
            AudioManager.STREAM_MUSIC, AudioManager.AUDIOFOCUS_GAIN)) {
        case AudioManager.AUDIOFOCUS_REQUEST_GRANTED:
            focusGranted = true;
            break;

        case AudioManager.AUDIOFOCUS_REQUEST_FAILED:
            focusGranted = false;
            break;
    }
}

private static final class OnFocusChangeListener implements AudioManager.OnAudioFocusChangeListener {

    private static OnFocusChangeListener instance;

    protected static OnFocusChangeListener getInstance() {
        if (instance == null) {
            instance = new OnFocusChangeListener();
        }
        return instance;
    }

    @Override
    public void onAudioFocusChange(final int focusChange) {
        changedFocus = focusChange;
        System.out.println("on focus change: " + focusChange);
        switch (focusChange) {
            case AudioManager.AUDIOFOCUS_GAIN:
                GlobalMusicPlayer.onFocusGained();
                break;

            case AudioManager.AUDIOFOCUS_LOSS:
                GlobalMusicPlayer.onFocusLoss();
                break;

            case AudioManager.AUDIOFOCUS_LOSS_TRANSIENT:
                GlobalMusicPlayer.onFocusLossTransient();
                break;

            case AudioManager.AUDIOFOCUS_LOSS_TRANSIENT_CAN_DUCK:
                GlobalMusicPlayer.onFocusLossTransientCanDuck();
                break;
        }
    }
}

我调用 requestFocus(context) 并获取 AudioManager.AUDIOFOCUS_REQUEST_GRANTED 作为返回值。

在那之后，onAudioFocusChange 不再调用，因此 changedFocus 始终为 0。

isFocusGranted() // true
getChangedFocus() // 0

设备:Nexus 10、摩托罗拉 Xoom。

Answer 1

case AudioManager.AUDIOFOCUS_GAIN in onAudioFocusChange() 更像是 AudioFocus 重新增益。它仅在丢失事件后触发。

case AudioManager.AUDIOFOCUS_REQUEST_GRANTED 是您应该添加另一个 GlobalMusicPlayer.onFocusGained() 的地方。