调节音量函数

/frameworks/base/services/core/java/com/android/server/audio/AudioService.java
private void adjustStreamVolume(int streamType, int direction, int flags,
            String callingPackage, String caller, int uid) {

这里check是否音量超过安全音量

 else if ((direction == AudioManager.ADJUST_RAISE) &&
                   /* !checkSafeMediaVolume(streamTypeAlias, aliasIndex + step, device)*/false) {
                Log.e(TAG, "adjustStreamVolume() safe volume index = " + oldIndex);
                mVolumeController.postDisplaySafeVolumeWarning(flags);
            }

音量控制UI

/** The controller for the volume UI. */
    private final VolumeController mVolumeController = new VolumeController();

VolumeController中的postDisplaySafeVolumeWarning方法

        public void postDisplaySafeVolumeWarning(int flags) {
            if (mController == null)
                return;
            try {
                mController.displaySafeVolumeWarning(flags);
            } catch (RemoteException e) {
                Log.w(TAG, "Error calling displaySafeVolumeWarning", e);
            }
        }

private IVolumeController mController;

提供给别的进程调用音量控制对话框的AIDL接口frameworks/base/media/java/android/media/IVolumeController.aidl

oneway interface IVolumeController {

    void displaySafeVolumeWarning(int flags);

    void volumeChanged(int streamType, int flags);

    void masterMuteChanged(int flags);

    void setLayoutDirection(int layoutDirection);

    void dismiss();
}

实际调用到音量对话框控制器

frameworks/base/packages/SystemUI/src/com/android/systemui/volume/VolumeDialogController.java
private final class VC extends IVolumeController.Stub {
        private final String TAG = VolumeDialogController.TAG + ".VC";
...
@Override
        public void displaySafeVolumeWarning(int flags) throws RemoteException {
            if (D.BUG) Log.d(TAG, "displaySafeVolumeWarning "
                    + Util.audioManagerFlagsToString(flags));
            if (mDestroyed) return;
            mWorker.obtainMessage(W.SHOW_SAFETY_WARNING, flags, 0).sendToTarget();
        }

这里的mworker是一个 handle thread拿到的looper

        mWorkerThread = new HandlerThread(VolumeDialogController.class.getSimpleName());
        mWorkerThread.start();
        mWorker = new W(mWorkerThread.getLooper());

looper进行obtain message，带三个参数

private final W mWorker;
...
mWorker.obtainMessage(W.SHOW_SAFETY_WARNING, flags, 0).sendToTarget();
...
case SHOW_SAFETY_WARNING: onShowSafetyWarningW(msg.arg1); break;

looper进行on show safety warning

private void onShowSafetyWarningW(int flags) {
        mCallbacks.onShowSafetyWarning(flags);
    }

回调到下面的代码

frameworks/base/packages/SystemUI/src/com/android/systemui/volume/VolumeDialog.java
...
        public void onShowSafetyWarning(int flags) {
            showSafetyWarningH(flags);
        }
...

    private void showSafetyWarningH(int flags) {
        if ((flags & (AudioManager.FLAG_SHOW_UI | AudioManager.FLAG_SHOW_UI_WARNINGS)) != 0
                || mShowing) {
            synchronized (mSafetyWarningLock) {
                if (mSafetyWarning != null) {
                    return;
                }
                mSafetyWarning = new SafetyWarningDialog(mContext, mController.getAudioManager()) {
                    @Override
                    protected void cleanUp() {
                        synchronized (mSafetyWarningLock) {
                            mSafetyWarning = null;
                        }
                        recheckH(null);
                    }
                };
                mSafetyWarning.show();
            }
            recheckH(null);
        }
        rescheduleTimeoutH();
    }
...

可以看到，这里新建了一个SafetyWarningDialog的对象，转到

private SafetyWarningDialog mSafetyWarning;
...
/frameworks/base/packages/SystemUI/src/com/android/systemui/volume/SafetyWarningDialog.java
...
    public SafetyWarningDialog(Context context, AudioManager audioManager) {
        super(context);
        mContext = context;
        mAudioManager = audioManager;

        getWindow().setType(WindowManager.LayoutParams.TYPE_SYSTEM_ERROR);
        setShowForAllUsers(true);
        setMessage(mContext.getString(com.android.internal.R.string.safe_media_volume_warning));
        setButton(DialogInterface.BUTTON_POSITIVE,
                mContext.getString(com.android.internal.R.string.yes), this);
        setButton(DialogInterface.BUTTON_NEGATIVE,
                mContext.getString(com.android.internal.R.string.no), (OnClickListener) null);
        setOnDismissListener(this);
        setIsHasButtonForVR(true);
        setShouldDismissforVR(false);
        final IntentFilter filter = new IntentFilter(Intent.ACTION_CLOSE_SYSTEM_DIALOGS);
        context.registerReceiver(mReceiver, filter);
    }

getWindow().setType,这里设置的窗口类型在windowmanager.java中都有定义，需要给什么样级别的type，修改后面type型的宏就可以了。理论上这里定义的级别就是window的token值，值越大，窗口的越在上面；调整这里的type类型就可以改变窗口的显示层级。当然，需要注意类似，指针、状态栏、导航栏是否有别的自定义级别，这个会影响对显示层级的理解。
通过以下配置文件可以直接禁用掉音量过大保护框

frameworks/base / core/res/res/values/config.xml
    <bool name="config_safe_media_volume_enabled">false</bool>