一、兩處呼叫playSoundEffect：

其一：繼承ViewGroup類的子類內部View切換；例如ViewPager

frameworks/support/v4/java/android/support/v4/view/ViewPager.java

public boolean dispatchKeyEvent(KeyEvent event) {
  // Let the focused view and/or our descendants get the key first
  return super.dispatchKeyEvent(event) || executeKeyEvent(event);
}

public boolean executeKeyEvent(KeyEvent event) {
  handled = arrowScroll(FOCUS_LEFT);
}
public boolean arrowScroll(int direction) {
  if (handled) {
    playSoundEffect(SoundEffectConstants.getContantForFocusDirection(direction));
  }
}
 

其二：ViewRootImpl完成兩個ViewGroup的切換

frameworks/base/core/java/android/view/ViewRootImpl.java

private int processKeyEvent(QueuedInputEvent q) {
  if (mView.dispatchKeyEvent(event)) {
    Log.d(TAG,"mView.dispatchKeyEvent()== true,return finished");
    return FINISH_HANDLED;
  }
  if (v.requestFocus(direction, mTempRect)) {
    Log.d("ViewRootImpl","TK--------->>>>>requestFcous>>playSoundEffect");//add by 
 
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    playSoundEffect(SoundEffectConstants.getContantForFocusDirection(direction));
    return FINISH_HANDLED;
  }
}