自定义View-21.ViewGroup的事件分发的源码解析
1.ViewGroup的事件分发
在上篇文章的基础上加上这个类.
public class ViewGroupView extends LinearLayout {
private static final String TAG = "ZsjTAG";
public ViewGroupView(Context context) {
super(context);
}
public ViewGroupView(Context context, @Nullable AttributeSet attrs) {
super(context, attrs);
}
public ViewGroupView(Context context, @Nullable AttributeSet attrs, int defStyleAttr) {
super(context, attrs, defStyleAttr);
}
@Override
public boolean dispatchTouchEvent(MotionEvent ev) {
Log.e(TAG, "ViewGroup dispatchTouchEvent "+ev.getAction());
return super.dispatchTouchEvent(ev);
}
@Override
public boolean onInterceptTouchEvent(MotionEvent ev) {
Log.e(TAG, "ViewGroup onInterceptTouchEvent "+ev.getAction());
return super.onInterceptTouchEvent(ev);
}
@Override
public boolean onTouchEvent(MotionEvent event) {
Log.e(TAG, "ViewGroup onTouchEvent "+event.getAction());
return super.onTouchEvent(event);
}
}
效果如下:
1.1 正常情况下
第一次DOWN ViewGroup.dispatchTouchEvent -> ViewGroup.onInterceptTouchEvent -> View.dispatchTouchEvent -> View.onTouch -> View.onTouchEvent
第二次MOVE ViewGroup.dispatchTouchEvent -> ViewGroup onInterceptTouchEvent -> View.dispatchTouchEvent -> View.onTouch -> View.onTouchEvent
第三次UP ViewGroup.dispatchTouchEvent -> ViewGroup onInterceptTouchEvent -> View.onTouch -> View.onTouchEvent -> View.onclick
1.2 onClick 没有
ViewGroup.dispatchTouchEvent -> ViewGroup.onInterceptTouchEvent -> View.dispatchTouchEvent -> View.onTouch -> View onTouchEvent -> ViewGroup.onTouchEvent
1.3 在 View 的 onTouchEvent() 方法里面返回true 的情况下
第一次DOWN ViewGroup.dispatchTouchEvent -> ViewGroup.onInterceptTouchEvent -> View.dispatchTouchEvent -> View.onTouch -> View.onTouchEvent
第二次MOVE ViewGroup.dispatchTouchEvent -> ViewGroup.onInterceptTouchEvent -> View.dispatchTouchEvent -> View.onTouch -> View.onTouchEvent
第三次UP ViewGroup.dispatchTouchEvent -> ViewGroup.onInterceptTouchEvent -> View.onTouch -> View.onTouchEvent
1.4 在 ViewGroup 的 onInterceptTouchEvent() 方法里面返回 true 的情况下
ViewGroup.dispatchTouchEvent -> ViewGroup.onInterceptTouchEvent -> ViewGroup.onTouchEvent
ViewGroup的事件分发的源码分析
@Override
public boolean dispatchTouchEvent(MotionEvent ev) {
boolean handled = false;
final int action = ev.getAction();
final int actionMasked = action & MotionEvent.ACTION_MASK;
if (actionMasked == MotionEvent.ACTION_DOWN) {
//清除TouchTargets,按下的时候把 mFirstTouchTarget = null
cancelAndClearTouchTargets(ev);
}
// Check for interception.
final boolean intercepted;
if (actionMasked == MotionEvent.ACTION_DOWN
|| mFirstTouchTarget != null) {
//默认返回false
final boolean disallowIntercept = (mGroupFlags & FLAG_DISALLOW_INTERCEPT) != 0;
if (!disallowIntercept) {
//onInterceptTouchEvent方法默认返回false.
intercepted = onInterceptTouchEvent(ev);
ev.setAction(action); // restore action in case it was changed
} else {
intercepted = false;
}
} else {
// There are no touch targets and this action is not an initial down
// so this view group continues to intercept touches.
intercepted = true;
}
if (!canceled && !intercepted) {//默认是TRUE,if能够执行
if (newTouchTarget == null && childrenCount != 0) {//down的时候可以执行
final View[] children = mChildren;
for (int i = childrenCount - 1; i >= 0; i--) {
//反序for循环,获取子View
if (dispatchTransformedTouchEvent(ev, false, child, idBitsToAssign)) {
//如果子View 返回 true.就会进来,主要是给mFirstTouchTarget赋值.
newTouchTarget = addTouchTarget(child, idBitsToAssign);
}
}
}
}
if (mFirstTouchTarget == null) {
handled = dispatchTransformedTouchEvent(ev, canceled, null,
TouchTarget.ALL_POINTER_IDS);
} else {
}
return handled;
}
private boolean dispatchTransformedTouchEvent(MotionEvent event, boolean cancel,
View child, int desiredPointerIdBits) {
final boolean handled;
final int oldAction = event.getAction();
if (cancel || oldAction == MotionEvent.ACTION_CANCEL) {
event.setAction(MotionEvent.ACTION_CANCEL);
//参数传值为null
if (child == null) {
handled = super.dispatchTouchEvent(event);
} else {
handled = child.dispatchTouchEvent(event);
}
event.setAction(oldAction);
return handled;
}
private TouchTarget addTouchTarget(@NonNull View child, int pointerIdBits) {
final TouchTarget target = TouchTarget.obtain(child, pointerIdBits);
target.next = mFirstTouchTarget;
//给mFirstTouchTarget 赋值
mFirstTouchTarget = target;
return target;
}
private boolean dispatchTransformedTouchEvent(MotionEvent event, boolean cancel,
View child, int desiredPointerIdBits) {
final boolean handled;
final int oldAction = event.getAction();
if (cancel || oldAction == MotionEvent.ACTION_CANCEL) {
event.setAction(MotionEvent.ACTION_CANCEL);
if (child == null) {
//child 为空,会调 自己的 super view.dispatchTouchEvent
handled = super.dispatchTouchEvent(event);
} else {
//child 不是空,会调用child的dispatchTouchEvent方法 //上节课分析的内容
handled = child.dispatchTouchEvent(event);
}
event.setAction(oldAction);
return handled;
}
public boolean onInterceptTouchEvent(MotionEvent ev) {
if (ev.isFromSource(InputDevice.SOURCE_MOUSE)
&& ev.getAction() == MotionEvent.ACTION_DOWN
&& ev.isButtonPressed(MotionEvent.BUTTON_PRIMARY)
&& isOnScrollbarThumb(ev.getX(), ev.getY())) {
return true;
}
return false;
}
private void cancelAndClearTouchTargets(MotionEvent event) {
if (mFirstTouchTarget != null) {
//清除TouchTargets
clearTouchTargets();
}
}
/**
* Clears all touch targets.
* 这个方法主要的是把 mFirstTouchTarget = null
*/
private void clearTouchTargets() {
TouchTarget target = mFirstTouchTarget;
if (target != null) {
do {
TouchTarget next = target.next;
target.recycle();
target = next;
} while (target != null);
mFirstTouchTarget = null;
}
}
2.1 onClick 没有 理解为没有消费事件
相当于dispatchTransformedTouchEvent 方法 返回false,mFirstTouchTarget没有赋值.
if (mFirstTouchTarget == null) {
handled = dispatchTransformedTouchEvent(ev, canceled, null,
TouchTarget.ALL_POINTER_IDS);
}
调用dispatchTransformedTouchEvent,看上面代码可以看到调用父类的super.dispatchTouchEvent(event)方法.
2.2 在 View 的 onTouchEvent() 方法里面返回true 的情况下
相当于dispatchTransformedTouchEvent 方法 返回true.所以转成情况打印一致.
2.3 在 ViewGroup 的 onInterceptTouchEvent() 方法里面返回 true 的情况下
这个方法就进不去.所以不会调用子View的dispatchTouchEvent方法.
if (!canceled && !intercepted) {
}
总结:
如果 子View 没有一个地方返回 true,只会进来一次.只会响应 DOWN事件,代表不需要消费该事件.如果你想响应 MOVE,UP必须找个地方返回True.
对于ViewGroup来说.如果你想拦截 子View 的onTouch事件,可以复写 onInterceptTouchEvent方法返回true即可.返回的是true 会执行该ViewGroup的onTouchEvent 方法,如果子 View没有消费 Touch事件也会调用该ViewGroup的onTouchEvent 方法.
