如今開始做音乐播放器的模块。遇到了几个问题
当播放音乐的过程中，去调节音量或者情景模式中的铃声设置，结果会有两种声音同一时候响起。
引起此问题的解决办法是音乐焦点问题没弄清
现分析一下音乐焦点的几个属性：源代码在frameworks/base/media/java/andorid/media/AudioManager.java中
public static final int AUDIOFOCUS_NONE = 0;
指示申请得到的Audio Focus不知道会持续多久，通常是长期占有。获得了Audio Focus；
public static final int AUDIOFOCUS_GAIN = 1;
指示要申请的AudioFocus是临时性的，会非常快用完释放的；
public static final int AUDIOFOCUS_GAIN_TRANSIENT = 2;
不但说要申请的AudioFocus是临时性的。还指示当前正在使用AudioFocus的能够继续播放，仅仅是要“duck”一下（减少音量）。
public static final int AUDIOFOCUS_GAIN_TRANSIENT_MAY_DUCK = 3;
public static final int AUDIOFOCUS_GAIN_TRANSIENT_EXCLUSIVE = 4;
AudioManager.OnAudioFocusChangeListener是申请成功之后监听AudioFocus使用情况的Listener，兴许假设有别的程序要竞争AudioFocus，都是通过这个Listener的onAudioFocusChange()方法来通知这个Audio Focus的使用者的。
失去了Audio Focus，并将会持续非常长的时间
public static final int AUDIOFOCUS_LOSS = -1 * AUDIOFOCUS_GAIN;
临时失去Audio Focus，并会非常快再次获得。必须停止Audio的播放。可是由于可能会非常快再次获得AudioFocus。这里能够不释放Media资源；
public static final int AUDIOFOCUS_LOSS_TRANSIENT = -1 * AUDIOFOCUS_GAIN_TRANSIENT;
临时失去AudioFocus，可是能够继续播放，只是要在减少音量。
public static final int AUDIOFOCUS_LOSS_TRANSIENT_CAN_DUCK =
-1 * AUDIOFOCUS_GAIN_TRANSIENT_MAY_DUCK;
看看刚才改动的一个问题：
问题描写叙述：播放音乐时闹钟到来，把闹钟放在后台时进入文件管理器播放音频。闹钟仍然在响应，闹钟和音乐同一时候响起；
问题分析：在闹钟铃声响起时，没有去做音频焦点的处理
解决方式：在packages/apps/deskclock/src/com/android/deskclock/alarms/AlarmKlaxon.java文件里加上焦点处理
改动后的源代码：package com.android.deskclock.alarms;
import android.content.Context;
import android.content.res.AssetFileDescriptor;
import android.media.AudioManager;
import android.media.MediaPlayer;
import android.media.MediaPlayer.OnErrorListener;
import android.media.RingtoneManager;
import android.net.Uri;
import android.os.Vibrator;
import com.android.deskclock.Log;
import com.android.deskclock.R;
import com.android.deskclock.provider.AlarmInstance;
import java.io.IOException;
/*add by leo.tan 20140717 for bugzilla 20064 start */
import android.os.Handler;
import android.media.AudioManager.OnAudioFocusChangeListener;
import android.os.Message;
/*add by leo.tan 20140717 for bugzilla 20064 end */
/**
* Manages playing ringtone and vibrating the device.
*/
public class AlarmKlaxon {
private static final long[] sVibratePattern = new long[] { 500, 500 };
// Volume suggested by media team for in-call alarms.
private static final float IN_CALL_VOLUME = 0.125f;
private static boolean sStarted = false;
private static MediaPlayer sMediaPlayer = null;
/*add by leo.tan 20140717 for bugzilla 20064 start */
private static final int FOCUSCHANGE = 3000;
private static final int FADEDOWN = 5;
private static final int FADEUP = 6;
private static final int RETRY_REQUEST_FOCUS = 7;
private static final int OVER_SHORT_VIBRATOR = 8;
private static OnAudioFocusChangeListener mAudioFocusListener = new OnAudioFocusChangeListener() {
public void onAudioFocusChange(int focusChange) {
android.util.Log.v("AlarmKlaxon", "mAudioFocusListener::focusChange-->" + focusChange);
mHandler.obtainMessage(FOCUSCHANGE, focusChange, 0).sendToTarget();
}
};
/*add by leo.tan 20140717 for bugzilla 20064 end */
public static void stop(Context context) {
Log.v("AlarmKlaxon.stop()");
if (sStarted) {
sStarted = false;
// Stop audio playing
if (sMediaPlayer != null) {
sMediaPlayer.stop();
AudioManager audioManager = (AudioManager)
context.getSystemService(Context.AUDIO_SERVICE);
audioManager.abandonAudioFocus(null);
sMediaPlayer.release();
sMediaPlayer = null;
}
/*add by leo.tan 20140717 for bugzilla 20064 start */
final AudioManager audioManager = (AudioManager) context.getSystemService(Context.AUDIO_SERVICE);
audioManager.abandonAudioFocus(mAudioFocusListener);
/*add by leo.tan 20140717 for bugzilla 20064 end */
((Vibrator)context.getSystemService(Context.VIBRATOR_SERVICE)).cancel();
}
}
public static void start(final Context context, AlarmInstance instance,
boolean inTelephoneCall) {
Log.v("AlarmKlaxon.start()");
// Make sure we are stop before starting
stop(context);
if (!AlarmInstance.NO_RINGTONE_URI.equals(instance.mRingtone)) {
Uri alarmNoise = instance.mRingtone;
// Fall back on the default alarm if the database does not have an
// alarm stored.
if (alarmNoise == null) {
alarmNoise = RingtoneManager.getDefaultUri(RingtoneManager.TYPE_ALARM);
if (Log.LOGV) {
Log.v("Using default alarm: " + alarmNoise.toString());
}
}
TODO: Reuse mMediaPlayer instead of creating a new one and/or use RingtoneManager.
sMediaPlayer = new MediaPlayer();
sMediaPlayer.setOnErrorListener(new OnErrorListener() {
@Override
public boolean onError(MediaPlayer mp, int what, int extra) {
Log.e("Error occurred while playing audio. Stopping AlarmKlaxon.");
AlarmKlaxon.stop(context);
return true;
}
});
try {
// Check if we are in a call. If we are, use the in-call alarm
// resource at a low volume to not disrupt the call.
if (inTelephoneCall) {
Log.v("Using the in-call alarm");
sMediaPlayer.setVolume(IN_CALL_VOLUME, IN_CALL_VOLUME);
setDataSourceFromResource(context, sMediaPlayer, R.raw.in_call_alarm);
} else {
sMediaPlayer.setDataSource(context, alarmNoise);
}
startAlarm(context, sMediaPlayer);
}catch (Exception ex) {
Log.v("Using the fallback ringtone");
// The alarmNoise may be on the sd card which could be busy right
// now. Use the fallback ringtone.
try {
// Must reset the media player to clear the error state.
sMediaPlayer.reset();
setDataSourceFromResource(context, sMediaPlayer, R.raw.fallbackring);
startAlarm(context, sMediaPlayer);
} catch (Exception ex2) {
// At this point we just don't play anything.
Log.e("Failed to play fallback ringtone", ex2);
}
}
}
if (instance.mVibrate && !inTelephoneCall) {
Vibrator vibrator = (Vibrator) context.getSystemService(Context.VIBRATOR_SERVICE);
vibrator.vibrate(sVibratePattern, 0);
}
sStarted = true;
}
// Do the common stuff when starting the alarm.
private static void startAlarm(Context context, MediaPlayer player) throws IOException {
AudioManager audioManager = (AudioManager) context.getSystemService(Context.AUDIO_SERVICE);
// do not play alarms if stream volume is 0 (typically because ringer mode is silent).
if (audioManager.getStreamVolume(AudioManager.STREAM_ALARM) != 0) {
player.setAudioStreamType(AudioManager.STREAM_ALARM);
player.setLooping(true);
player.prepare();
audioManager.requestAudioFocus(null,
AudioManager.STREAM_ALARM, AudioManager.AUDIOFOCUS_GAIN_TRANSIENT);
player.start();
}
/*add by leo.tan 20140717 for bugzilla 20064 start */
//在这个地方进行焦点的请求
final int requestResult = audioManager.requestAudioFocus(mAudioFocusListener,
AudioManager.STREAM_ALARM,
AudioManager.AUDIOFOCUS_GAIN_TRANSIENT);
/*add by leo.tan 20140717 for bugzilla 20064 end */
}
private static void setDataSourceFromResource(Context context, MediaPlayer player, int res)
throws IOException {
AssetFileDescriptor afd = context.getResources().openRawResourceFd(res);
if (afd != null) {
player.setDataSource(afd.getFileDescriptor(), afd.getStartOffset(), afd.getLength());
afd.close();
}
}
/*add by leo.tan 20140717 for bugzilla 20064 start */
private static void setVolume(float vol) {
if(sMediaPlayer != null){
sMediaPlayer.setVolume(vol, vol);
}
}
//用handler来对焦点进行处理
private static Handler mHandler = new Handler() {
public void handleMessage(Message msg) {
switch (msg.what) {
case FOCUSCHANGE: {
switch (msg.arg1) {
case AudioManager.AUDIOFOCUS_LOSS:
case AudioManager.AUDIOFOCUS_LOSS_TRANSIENT:
case AudioManager.AUDIOFOCUS_LOSS_TRANSIENT_CAN_DUCK:
mHandler.removeMessages(FADEUP);
mHandler.sendEmptyMessage(FADEDOWN);
break;
case AudioManager.AUDIOFOCUS_GAIN:
mHandler.removeMessages(FADEDOWN);
mHandler.sendEmptyMessage(FADEUP);
break;
}
break;
}
case FADEDOWN:
// Turn off the sound
setVolume(0.0f);
break;
case FADEUP:
// Turn on the sound
setVolume(1.0f);
break;
}
}
};
/*add by leo.tan 20140717 for bugzilla 20064 end */
}