Android事件分发机制——ViewGroup(二)
上一篇文章我们已经分析了Android事件分发机制——View(一),今天给大家带来ViewGroup事件分发的源码解析。
案例
public class MyLinearLayout extends LinearLayout { private static String TAG = MyLinearLayout.class.getSimpleName(); public MyLinearLayout(Context context) { super(context); } public MyLinearLayout(Context context, @Nullable AttributeSet attrs) { super(context, attrs); } @Override public boolean onTouchEvent(MotionEvent event) { int action = event.getAction(); switch (action) { case MotionEvent.ACTION_DOWN: Log.e(TAG, "onTouchEvent ACTION_DOWN"); break; case MotionEvent.ACTION_MOVE: Log.e(TAG, "onTouchEvent ACTION_MOVE"); break; case MotionEvent.ACTION_UP: Log.e(TAG, "onTouchEvent ACTION_UP"); break; default: break; } return super.onTouchEvent(event); } @Override public boolean dispatchTouchEvent(MotionEvent ev) { int action = ev.getAction(); switch (action) { case MotionEvent.ACTION_DOWN: Log.e(TAG, "dispatchTouchEvent ACTION_DOWN"); break; case MotionEvent.ACTION_MOVE: Log.e(TAG, "dispatchTouchEvent ACTION_MOVE"); break; case MotionEvent.ACTION_UP: Log.e(TAG, "dispatchTouchEvent ACTION_UP"); break; default: break; } return super.dispatchTouchEvent(ev); } @Override public boolean onInterceptTouchEvent(MotionEvent ev) { int action = ev.getAction(); switch (action) { case MotionEvent.ACTION_DOWN: Log.e(TAG, "onInterceptTouchEvent ACTION_DOWN"); break; case MotionEvent.ACTION_MOVE: Log.e(TAG, "onInterceptTouchEvent ACTION_MOVE"); break; case MotionEvent.ACTION_UP: Log.e(TAG, "onInterceptTouchEvent ACTION_UP"); break; default: break; } return super.onInterceptTouchEvent(ev); } @Override public void requestDisallowInterceptTouchEvent(boolean disallowIntercept) { Log.e(TAG, "disallowIntercept = " + disallowIntercept); super.requestDisallowInterceptTouchEvent(disallowIntercept); }}
<?xml version="1.0" encoding="utf-8"?><com.example.dispatchevent.MyLinearLayout xmlns:android="http://schemas.android.com/apk/res/android" xmlns:tools="http://schemas.android.com/tools" android:layout_width="match_parent" android:layout_height="match_parent" tools:context=".MainActivity"> <com.example.dispatchevent.MyButton android:id="@+id/my_button" android:layout_width="wrap_content" android:layout_height="wrap_content" android:text="click me"/>com.example.dispatchevent.MyLinearLayout>
MyLinearLayout中包含一个MyButton,MyButton在上篇博客中已经出现过,这里就不再贴代码了,看一下输出Log。
01-07 19:32:44.385 6515-6515/com.example.dispatchevent E/MyLinearLayout: dispatchTouchEvent ACTION_DOWN01-07 19:32:44.385 6515-6515/com.example.dispatchevent E/MyLinearLayout: onInterceptTouchEvent ACTION_DOWN01-07 19:32:44.386 6515-6515/com.example.dispatchevent E/MyButton: dispatchTouchEvent ACTION_DOWN01-07 19:32:44.386 6515-6515/com.example.dispatchevent E/MyButton: onTouch ACTION_DOWN01-07 19:32:44.386 6515-6515/com.example.dispatchevent E/MyButton: onTouchEvent ACTION_DOWN01-07 19:32:44.420 6515-6515/com.example.dispatchevent E/MyLinearLayout: dispatchTouchEvent ACTION_MOVE01-07 19:32:44.420 6515-6515/com.example.dispatchevent E/MyLinearLayout: onInterceptTouchEvent ACTION_MOVE01-07 19:32:44.420 6515-6515/com.example.dispatchevent E/MyButton: dispatchTouchEvent ACTION_MOVE01-07 19:32:44.421 6515-6515/com.example.dispatchevent E/MyButton: onTouch ACTION_MOVE01-07 19:32:44.421 6515-6515/com.example.dispatchevent E/MyButton: onTouchEvent ACTION_MOVE01-07 19:32:44.428 6515-6515/com.example.dispatchevent E/MyLinearLayout: dispatchTouchEvent ACTION_UP01-07 19:32:44.428 6515-6515/com.example.dispatchevent E/MyLinearLayout: onInterceptTouchEvent ACTION_UP01-07 19:32:44.428 6515-6515/com.example.dispatchevent E/MyButton: dispatchTouchEvent ACTION_UP01-07 19:32:44.429 6515-6515/com.example.dispatchevent E/MyButton: onTouch ACTION_UP01-07 19:32:44.429 6515-6515/com.example.dispatchevent E/MyButton: onTouchEvent ACTION_UP
可以看到大体的事件流程为:
MyLinearLayout的dispatchTouchEvent -> MyLinearLayout的onInterceptTouchEvent -> MyButton的dispatchTouchEvent->Mybutton的onTouch ->Mybutton的onTouchEvent
可以看出,在View上触发事件,最先捕获到事件的为View所在的ViewGroup,然后才会到View自身。
源码解析
当你点击了某个控件,首先会去调用该控件所在布局的dispatchTouchEvent方法,然后在布局的dispatchTouchEvent方法中找到被点击的相应控件,再去调用该控件的dispatchTouchEvent方法。
由于MyLayout中没有会一直向上寻找,最终发现ViewGroup.dispatchTouchEvent。
ViewGroup.dispatchTouchEvent
public boolean dispatchTouchEvent(MotionEvent ev) { final int action = ev.getAction(); final float xf = ev.getX(); final float yf = ev.getY(); final float scrolledXFloat = xf + mScrollX; final float scrolledYFloat = yf + mScrollY; final Rect frame = mTempRect; boolean disallowIntercept = (mGroupFlags & FLAG_DISALLOW_INTERCEPT) != 0; if (action == MotionEvent.ACTION_DOWN) { if (mMotionTarget != null) { mMotionTarget = null; } //(1)是否需要拦截 if (disallowIntercept || !onInterceptTouchEvent(ev)) { ev.setAction(MotionEvent.ACTION_DOWN); final int scrolledXInt = (int) scrolledXFloat; final int scrolledYInt = (int) scrolledYFloat; final View[] children = mChildren; final int count = mChildrenCount; for (int i = count - 1; i >= 0; i--) { final View child = children[i]; if ((child.mViewFlags & VISIBILITY_MASK) == VISIBLE || child.getAnimation() != null) { child.getHitRect(frame); if (frame.contains(scrolledXInt, scrolledYInt)) { final float xc = scrolledXFloat - child.mLeft; final float yc = scrolledYFloat - child.mTop; ev.setLocation(xc, yc); child.mPrivateFlags &= ~CANCEL_NEXT_UP_EVENT; //(2)调用子View.dispatchTouchEvent()方法 if (child.dispatchTouchEvent(ev)) { mMotionTarget = child; return true; } } } } } } boolean isUpOrCancel = (action == MotionEvent.ACTION_UP) || (action == MotionEvent.ACTION_CANCEL); if (isUpOrCancel) { mGroupFlags &= ~FLAG_DISALLOW_INTERCEPT; } final View target = mMotionTarget; //(3)如果子View.dispatchTouchEvent返回false,调用Group的OnTouch相关方法 if (target == null) { ev.setLocation(xf, yf); if ((mPrivateFlags & CANCEL_NEXT_UP_EVENT) != 0) { ev.setAction(MotionEvent.ACTION_CANCEL); mPrivateFlags &= ~CANCEL_NEXT_UP_EVENT; } return super.dispatchTouchEvent(ev); }//...
1、进入ACITON_DOWN操作后,首先将mMotionTarget=null,然后进行判断if(disallowIntercept || !onInterceptTouchEvent(ev))。
(1)当前不允许拦截,即disallowIntercept =true;
(2)当前允许拦截但是不拦截,即disallowIntercept =false,但是onInterceptTouchEvent(ev)返回false ;
(3)disallowIntercept 可以通过viewGroup.requestDisallowInterceptTouchEvent(boolean)进行设置,而onInterceptTouchEvent(ev)可以进行复写;
2、循环遍历子View,通过坐标定位事件的子View,执行child.dispatchTouchEvent(ev),之后的操作请参考Android事件分发机制——View(一)。
(1)调用子View的dispatchTouchEvent后是有返回值的,如果一个控件是可点击的,那么点击该控件时,dispatchTouchEvent的返回值必定是true;
(2)当返回true时,导致条件判断成立,于是ViewGroup.dispatchTouchEvent方法直接返回了true,导致后面代码无法执行,也就会把MyLayout的touch事件拦截掉;
if (child.dispatchTouchEvent(ev)) {mMotionTarget = child;return true;}
3、当我们点击的不是按钮,而是空白区域呢?此时将不会调用child.dispatchTouchEvent(ev),所以target==null,将会调用后面的super.dispatchTouchEvent(ev),由于ViewGroup的父类就是View,因此MyLayout中注册的onTouch方法也会得到执行。
现在再来看一下整个ViewGroup事件分发过程的流程图:
如何拦截事件
复写ViewGroup的onInterceptTouchEvent方法:
//grouppublic boolean onInterceptTouchEvent(MotionEvent ev) { int action = ev.getAction(); switch (action) { case MotionEvent.ACTION_DOWN: Log.e(TAG, "onInterceptTouchEvent ACTION_DOWN"); break; case MotionEvent.ACTION_MOVE: Log.e(TAG, "onInterceptTouchEvent ACTION_MOVE"); break; case MotionEvent.ACTION_UP: Log.e(TAG, "onInterceptTouchEvent ACTION_UP"); break; default: break; } return true; //return super.onInterceptTouchEvent(ev); }//子View事件全部被拦截01-07 04:28:05.588 15966-15966/com.example.dispatchevent E/MyLinearLayout: dispatchTouchEvent ACTION_DOWN01-07 04:28:05.588 15966-15966/com.example.dispatchevent E/MyLinearLayout: onInterceptTouchEvent ACTION_DOWN01-07 04:28:05.590 15966-15966/com.example.dispatchevent E/MyLinearLayout: onTouchEvent ACTION_DOWN
//grouppublic boolean onInterceptTouchEvent(MotionEvent ev) { int action = ev.getAction(); switch (action) { case MotionEvent.ACTION_DOWN: Log.e(TAG, "onInterceptTouchEvent ACTION_DOWN"); break; case MotionEvent.ACTION_MOVE: Log.e(TAG, "onInterceptTouchEvent ACTION_MOVE"); return true; //break; case MotionEvent.ACTION_UP: Log.e(TAG, "onInterceptTouchEvent ACTION_UP"); break; default: break; } return super.onInterceptTouchEvent(ev); } //子View的Move之后事件全部被拦截01-07 04:31:51.459 17533-17533/com.example.dispatchevent E/MyLinearLayout: dispatchTouchEvent ACTION_DOWN01-07 04:31:51.459 17533-17533/com.example.dispatchevent E/MyLinearLayout: onInterceptTouchEvent ACTION_DOWN01-07 04:31:51.459 17533-17533/com.example.dispatchevent E/MyButton: dispatchTouchEvent ACTION_DOWN01-07 04:31:51.461 17533-17533/com.example.dispatchevent E/MyButton: onTouch ACTION_DOWN01-07 04:31:51.461 17533-17533/com.example.dispatchevent E/MyButton: onTouchEvent ACTION_DOWN01-07 04:31:51.481 17533-17533/com.example.dispatchevent E/MyLinearLayout: dispatchTouchEvent ACTION_MOVE01-07 04:31:51.481 17533-17533/com.example.dispatchevent E/MyLinearLayout: onInterceptTouchEvent ACTION_MOVE01-07 04:31:51.497 17533-17533/com.example.dispatchevent E/MyLinearLayout: dispatchTouchEvent ACTION_UP01-07 04:31:51.498 17533-17533/com.example.dispatchevent E/MyLinearLayout: onTouchEvent ACTION_UP
默认是不拦截的,即返回false,如果你需要拦截,只要return true就行了。这样该事件就不会往子View传递了,并且如果你在DOWN retrun true ,则DOWN,MOVE,UP子View都不会捕获事件,如果你在MOVE return true,则子View在MOVE和UP都不会捕获事件。
如何不被拦截
如果ViewGroup的onInterceptTouchEvent(ev) 当ACTION_MOVE时return true ,即拦截了子View的MOVE以及UP事件,此时子View希望依然能够响应MOVE和UP时该咋办呢?
Android给我们提供了一个方法:requestDisallowInterceptTouchEvent(boolean) 用于设置是否允许拦截,我们在子View.dispatchTouchEvent中这样。
//grouppublic boolean onInterceptTouchEvent(MotionEvent ev) { int action = ev.getAction(); switch (action) { case MotionEvent.ACTION_DOWN: Log.e(TAG, "onInterceptTouchEvent ACTION_DOWN"); break; case MotionEvent.ACTION_MOVE: Log.e(TAG, "onInterceptTouchEvent ACTION_MOVE"); return true; //break; case MotionEvent.ACTION_UP: Log.e(TAG, "onInterceptTouchEvent ACTION_UP"); break; default: break; } return super.onInterceptTouchEvent(ev); } //childpublic boolean dispatchTouchEvent(MotionEvent event) { getParent().requestDisallowInterceptTouchEvent(true); int action = event.getAction(); switch (action) { case MotionEvent.ACTION_DOWN: Log.e(TAG, "dispatchTouchEvent ACTION_DOWN"); break; case MotionEvent.ACTION_MOVE: Log.e(TAG, "dispatchTouchEvent ACTION_MOVE"); break; case MotionEvent.ACTION_UP: Log.e(TAG, "dispatchTouchEvent ACTION_UP"); break; default: break; } return super.dispatchTouchEvent(event); }
getParent().requestDisallowInterceptTouchEvent(true),这样即使ViewGroup在MOVE的时候return true,子View依然可以捕获到MOVE以及UP事件。
注:但是如果ViewGroup.onInterceptTouchEvent(ev)在ACTION_DOWN里面直接return true了,那么子View是没有办法捕获事件的。
总结
- Android事件分发是先传递到ViewGroup,再由ViewGroup传递到View的;
- 当onTouch()返回true时,onTouchEvent()将不会被执行;
- 当设置了longClick并且返回true时,onClick将不被执行,当没有设置longClick或者返回false时,onClick仍将被执行;
- 在ViewGroup中可以通过onInterceptTouchEvent()对事件进行拦截,当返回true时表示事件不允许向子View传递(事件交给自己的onTouchEvent处理),返回false代表不对事件进行拦截,默认返回false;
- 子View中如果将传递的事件消费掉,ViewGroup中将无法接收到任何事件;
- 子View可通过调用getParent().requestDisallowInterceptTouchEvent(true)来阻止ViewGroup对其MOVE/UP事件进行拦截;
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