Android Input输入系统之五：KeyEvent按键调节音量加减流程

本文主要是介绍Android Input输入系统之五：KeyEvent按键调节音量加减流程，希望对大家解决编程问题提供一定的参考价值，需要的开发者们随着小编来一起学习吧！

《Android按键Input KeyEvent》
《Android Input输入系统之一：KeyEvent事件监听及事件分发流程》
《Android Input输入系统之二：KeyEvent注入事件及事件分发流程》
《Android Input输入系统之三：KeyEvent事件分发和上层应用层对事件的接收》
《Android Input输入系统之四：KeyEvent事件中的InputChannel通信》
《Android Input输入系统之五：KeyEvent按键调节音量加减流程》

在上一章节，我们讲到了将按键消息传递分发给View。

在ViewPostImeInputStage阶段，调用了processKeyEvent()，其中：

// Deliver the key to the view hierarchy.
if (mView.dispatchKeyEvent(event)) {return FINISH_HANDLED;
}

通过dispatchKeyEvent将按键消息分发给了View.

那我们就从dispatchKeyEvent()说起。

View的根类是DecorView。

最终都会调用到DecorView中的dispatchKeyEvent()。
frameworks\base\core\java\com\android\internal\policy\DecorView.java

    @Overridepublic boolean dispatchKeyEvent(KeyEvent event) {final int keyCode = event.getKeyCode();final int action = event.getAction();final boolean isDown = action == KeyEvent.ACTION_DOWN;if (isDown && (event.getRepeatCount() == 0)) {// First handle chording of panel key: if a panel key is held// but not released, try to execute a shortcut in it.if ((mWindow.mPanelChordingKey > 0) && (mWindow.mPanelChordingKey != keyCode)) {boolean handled = dispatchKeyShortcutEvent(event);if (handled) {return true;}}// If a panel is open, perform a shortcut on it without the// chorded panel keyif ((mWindow.mPreparedPanel != null) && mWindow.mPreparedPanel.isOpen) {if (mWindow.performPanelShortcut(mWindow.mPreparedPanel, keyCode, event, 0)) {return true;}}}if (!mWindow.isDestroyed()) {final Window.Callback cb = mWindow.getCallback();final boolean handled = cb != null && mFeatureId < 0 ? cb.dispatchKeyEvent(event): super.dispatchKeyEvent(event);if (handled) {return true;}}return isDown ? mWindow.onKeyDown(mFeatureId, event.getKeyCode(), event): mWindow.onKeyUp(mFeatureId, event.getKeyCode(), event);}

cb 是一个Activity或者Dialog对象。用于回调上层应用app中监听的dispatchKeyEvent();

如果经过所有应用层的View，Activity等都没有消耗掉key事件，最终会走到PhoneWindow中：

return isDown ? mWindow.onKeyDown(mFeatureId, event.getKeyCode(), event): mWindow.onKeyUp(mFeatureId, event.getKeyCode(), event);

frameworks\base\core\java\com\android\internal\policy\PhoneWindow.java

    /*** A key was pressed down and not handled by anything else in the window.** @see #onKeyUp* @see android.view.KeyEvent*/protected boolean onKeyDown(int featureId, int keyCode, KeyEvent event) {/* ***************************************************************************** HOW TO DECIDE WHERE YOUR KEY HANDLING GOES.** If your key handling must happen before the app gets a crack at the event,* it goes in PhoneWindowManager.** If your key handling should happen in all windows, and does not depend on* the state of the current application, other than that the current* application can override the behavior by handling the event itself, it* should go in PhoneFallbackEventHandler.** Only if your handling depends on the window, and the fact that it has* a DecorView, should it go here.* ****************************************************************************/final KeyEvent.DispatcherState dispatcher =mDecor != null ? mDecor.getKeyDispatcherState() : null;//Log.i(TAG, "Key down: repeat=" + event.getRepeatCount()//        + " flags=0x" + Integer.toHexString(event.getFlags()));switch (keyCode) {case KeyEvent.KEYCODE_VOLUME_UP:case KeyEvent.KEYCODE_VOLUME_DOWN:case KeyEvent.KEYCODE_VOLUME_MUTE: {// If we have a session send it the volume command, otherwise// use the suggested stream.if (mMediaController != null) {mMediaController.dispatchVolumeButtonEventAsSystemService(event);} else {getMediaSessionManager().dispatchVolumeKeyEventAsSystemService(event,mVolumeControlStreamType);}return true;}//省略一部分代码//...}//省略一部分代码//...}

因为我们只分析音量的调节，这里列出来了KeyEvent.KEYCODE_VOLUME_UP的按键消息。

下面即使我们比较熟悉的音量调节流程了。我们走一遍这个流程。

这个流程分两个：
//UI 按钮画面上进行音量调节
dispatchVolumeButtonEventAsSystemService()

//硬件按键进行调节
dispatchVolumeKeyEventAsSystemService()

我们需要关注的是按键的调节。按钮调节逻辑简单跟一下。

按钮执行音量调节

dispatchVolumeButtonEventAsSystemService
frameworks\base\media\java\android\media\session\MediaController.java

public void dispatchVolumeButtonEventAsSystemService(@NonNull KeyEvent keyEvent) {switch (keyEvent.getAction()) {case KeyEvent.ACTION_DOWN: {int direction = 0;switch (keyEvent.getKeyCode()) {case KeyEvent.KEYCODE_VOLUME_UP:direction = AudioManager.ADJUST_RAISE;break;case KeyEvent.KEYCODE_VOLUME_DOWN:direction = AudioManager.ADJUST_LOWER;break;case KeyEvent.KEYCODE_VOLUME_MUTE:direction = AudioManager.ADJUST_TOGGLE_MUTE;break;}try {mSessionBinder.adjustVolume(mContext.getPackageName(), mCbStub, true, direction,AudioManager.FLAG_SHOW_UI);} catch (RemoteException e) {Log.wtf(TAG, "Error calling adjustVolumeBy", e);}}case KeyEvent.ACTION_UP: {final int flags = AudioManager.FLAG_PLAY_SOUND | AudioManager.FLAG_VIBRATE| AudioManager.FLAG_FROM_KEY;try {mSessionBinder.adjustVolume(mContext.getPackageName(), mCbStub, true, 0, flags);} catch (RemoteException e) {Log.wtf(TAG, "Error calling adjustVolumeBy", e);}}}
}

/frameworks/base/services/core/java/com/android/server/media/MediaSessionRecord.java
通过ISessionController的AIDL方式调用到MediaSessionRecord中的adjustVolume().
通过SessionCb中的回调，调用mCb.onAdjustVolume()即MediaSession中的onAdjustVolume().

\frameworks\base\media\java\android\media\session\MediaSession.java

@Override
public void onAdjustVolume(String packageName, int pid, 

这篇关于Android Input输入系统之五：KeyEvent按键调节音量加减流程的文章就介绍到这儿，希望我们推荐的文章对编程师们有所帮助！

---