Android中onInterceptTouchEvent和dispatchTouchEvent的区别是什么?
根据android开发者指南,这两种方法都可以用来拦截触摸事件(MotionEvent),但有什么区别呢?
onInterceptTouchEvent, dispatchTouchEvent和onTouchEvent如何在视图(ViewGroup)的层次结构中一起交互?
Android中onInterceptTouchEvent和dispatchTouchEvent的区别是什么?
根据android开发者指南,这两种方法都可以用来拦截触摸事件(MotionEvent),但有什么区别呢?
onInterceptTouchEvent, dispatchTouchEvent和onTouchEvent如何在视图(ViewGroup)的层次结构中一起交互?
当前回答
public boolean dispatchTouchEvent(MotionEvent ev){
boolean consume =false;
if(onInterceptTouchEvent(ev){
consume = onTouchEvent(ev);
}else{
consume = child.dispatchTouchEvent(ev);
}
}
其他回答
简单回答:dispatchTouchEvent()将首先被调用。
简短的建议:不应该重写dispatchTouchEvent(),因为它很难控制,有时它会降低您的性能。恕我直言,我建议重写onInterceptTouchEvent()。
因为大多数答案都非常清楚地提到了活动/视图组/视图上的流触摸事件,我只添加了更多关于ViewGroup中这些方法的代码细节(忽略dispatchTouchEvent()):
onInterceptTouchEvent()将首先被调用,ACTION事件将分别被调用down -> move -> up。有2种情况:
If you return false in 3 cases (ACTION_DOWN, ACTION_MOVE, ACTION_UP), it will consider as the parent won't need this touch event, so onTouch() of the parents never calls, but onTouch() of the children will call instead; however please notice: The onInterceptTouchEvent() still continue to receive touch event, as long as its children don't call requestDisallowInterceptTouchEvent(true). If there are no children receiving that event (it can happen in 2 cases: no children at the position the users touch, or there are children but it returns false at ACTION_DOWN), the parents will send that event back to onTouch() of the parents. Vice versa, if you return true, the parent will steal this touch event immediately, and onInterceptTouchEvent() will stop immediately, instead onTouch() of the parents will be called as well as all onTouch() of children will receive the last action event - ACTION_CANCEL (thus, it means the parents stole touch event, and children cannot handle it from then on). The flow of onInterceptTouchEvent() return false is normal, but there is a little confusion with return true case, so I list it here: Return true at ACTION_DOWN, onTouch() of the parents will receive ACTION_DOWN again and following actions (ACTION_MOVE, ACTION_UP). Return true at ACTION_MOVE, onTouch() of the parents will receive next ACTION_MOVE (not the same ACTION_MOVE in onInterceptTouchEvent()) and following actions (ACTION_MOVE, ACTION_UP). Return true at ACTION_UP, onTouch() of the parents will NOT called at all since it's too late for the parents to steal touch event.
还有一件重要的事情是onTouch()中事件的ACTION_DOWN将决定视图是否希望从该事件接收更多的动作。如果视图在onTouch()中的ACTION_DOWN处返回true,这意味着视图愿意从该事件接收更多操作。否则,在onTouch()中的ACTION_DOWN处返回false将意味着视图不会从该事件接收更多的操作。
ViewGroup子类中的以下代码将阻止它的父容器接收触摸事件:
@Override
public boolean dispatchTouchEvent(MotionEvent ev) {
// Normal event dispatch to this container's children, ignore the return value
super.dispatchTouchEvent(ev);
// Always consume the event so it is not dispatched further up the chain
return true;
}
我使用自定义覆盖来防止背景视图响应触摸事件。
在拦截事件之前发出指示。
用这个简单的例子:
main = new LinearLayout(this){
@Override
public boolean onInterceptTouchEvent(MotionEvent ev) {
System.out.println("Event - onInterceptTouchEvent");
return super.onInterceptTouchEvent(ev);
//return false; //event get propagated
}
@Override
public boolean dispatchTouchEvent(MotionEvent ev) {
System.out.println("Event - dispatchTouchEvent");
return super.dispatchTouchEvent(ev);
//return false; //event DONT get propagated
}
};
main.setBackgroundColor(Color.GRAY);
main.setLayoutParams(new LinearLayout.LayoutParams(320,480));
viewA = new EditText(this);
viewA.setBackgroundColor(Color.YELLOW);
viewA.setTextColor(Color.BLACK);
viewA.setTextSize(16);
viewA.setLayoutParams(new LinearLayout.LayoutParams(320,80));
main.addView(viewA);
setContentView(main);
你可以看到日志是这样的:
I/System.out(25900): Event - dispatchTouchEvent
I/System.out(25900): Event - onInterceptTouchEvent
因此,如果你正在使用这两个处理程序,使用dispatchTouchEvent来处理第一个实例的事件,这将去onInterceptTouchEvent。
另一个区别是,如果dispatchTouchEvent返回'false',事件不会被传播到子,在这种情况下的EditText,而如果你在onInterceptTouchEvent返回false,事件仍然得到调度到EditText
public boolean dispatchTouchEvent(MotionEvent ev){
boolean consume =false;
if(onInterceptTouchEvent(ev){
consume = onTouchEvent(ev);
}else{
consume = child.dispatchTouchEvent(ev);
}
}
因为这是谷歌的第一个结果。我想在Youtube上分享Dave Smith的演讲:精通Android触摸系统,幻灯片可以在这里找到。让我对Android Touch System有了一个很深刻的了解:
Activity如何处理触摸:
Activity.dispatchTouchEvent () 总是第一个被叫到 发送事件到附加到窗口的根视图 onTouchEvent () 如果没有视图使用该事件则调用 总是最后一个被叫
视图如何处理触摸:
View.dispatchTouchEvent () 如果存在,首先向监听器发送事件 View.OnTouchListener.onTouch () 如果未被消费,则处理触摸本身 View.onTouchEvent ()
ViewGroup如何处理触摸:
ViewGroup.dispatchTouchEvent() onInterceptTouchEvent() Check if it should supersede children Passes ACTION_CANCEL to active child If it returns true once, the ViewGroup consumes all subsequent events For each child view (in reverse order they were added) If touch is relevant (inside view), child.dispatchTouchEvent() If it is not handled by a previous, dispatch to next view If no children handles the event, the listener gets a chance OnTouchListener.onTouch() If there is no listener, or its not handled onTouchEvent() Intercepted events jump over the child step
他还在github.com/devunwired/上提供了定制触摸的示例代码。
Answer: Basically the dispatchTouchEvent() is called on every View layer to determine if a View is interested in an ongoing gesture. In a ViewGroup the ViewGroup has the ability to steal the touch events in his dispatchTouchEvent()-method, before it would call dispatchTouchEvent() on the children. The ViewGroup would only stop the dispatching if the ViewGroup onInterceptTouchEvent()-method returns true. The difference is that dispatchTouchEvent()is dispatching MotionEvents and onInterceptTouchEvent tells if it should intercept (not dispatching the MotionEvent to children) or not (dispatching to children).
你可以想象ViewGroup的代码或多或少是这样做的(非常简化):
public boolean dispatchTouchEvent(MotionEvent ev) {
if(!onInterceptTouchEvent()){
for(View child : children){
if(child.dispatchTouchEvent(ev))
return true;
}
}
return super.dispatchTouchEvent(ev);
}