android mSafeMediaVolumeDevices

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android在插入耳机时默认是无法调整音量到最大值的。

base/media/java/android/media/AudioService.java

6526 private final int mSafeMediaVolumeDevices = AudioSystem.DEVICE_OUT_WIRED_HEADSET |
6527 AudioSystem.DEVICE_OUT_WIRED_HEADPHONE;

<span style="font-size:18px;">838     public void adjustStreamVolume(int streamType, int direction, int flags) {。。。。。872             if (mSafeMediaVolumeState == SAFE_MEDIA_VOLUME_ACTIVE && 873                     (device & mSafeMediaVolumeDevices) != 0) { 874                 step = mSafeMediaVolumeIndex;//这里把声音的最大值设置成了safe设备默认的最大。。。}</span>

当检测到safe设备调整的音量大于safe的最大值是弹出警告框

<span style="font-size:18px;">838     public void adjustStreamVolume(int streamType, int direction, int flags) { 839         if (mUseFixedVolume) { 840             return; 841         }........902         if (adjustVolume && (direction != AudioManager.ADJUST_SAME)) { 903             if ((direction == AudioManager.ADJUST_RAISE) && 904                     !checkSafeMediaVolume(streamTypeAlias, aliasIndex + step, device)) { 905                 Log.e(TAG, "adjustStreamVolume() safe volume index = "+oldIndex); 906                 mVolumePanel.postDisplaySafeVolumeWarning(flags); 907             } .....}</span>

base/core/java/android/view/VolumePanel.java

<span style="font-size:18px;">838     public void adjustStreamVolume(int streamType, int direction, int flags) {。。。。。872             if (mSafeMediaVolumeState == SAFE_MEDIA_VOLUME_ACTIVE && 873                     (device & mSafeMediaVolumeDevices) != 0) { 874                 step = mSafeMediaVolumeIndex;//这里把声音的最大值设置成了safe设备默认的最大。。。}</span>

582 public void postDisplaySafeVolumeWarning(int flags) {
583 if (hasMessages(MSG_DISPLAY_SAFE_VOLUME_WARNING)) return;
584 obtainMessage(MSG_DISPLAY_SAFE_VOLUME_WARNING, flags, 0).sendToTarget();
585 }

<span style="font-size:18px;">941     @Override 942     public void handleMessage(Message msg) { 943         switch (msg.what) { 944 。。。。。1007             case MSG_DISPLAY_SAFE_VOLUME_WARNING:1008                 onDisplaySafeVolumeWarning(msg.arg1);1009                 break;1010         }1011     }</span>

<span style="font-size:18px;">838     public void adjustStreamVolume(int streamType, int direction, int flags) {。。。。。872             if (mSafeMediaVolumeState == SAFE_MEDIA_VOLUME_ACTIVE && 873                     (device & mSafeMediaVolumeDevices) != 0) { 874                 step = mSafeMediaVolumeIndex;//这里把声音的最大值设置成了safe设备默认的最大。。。}</span>

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