android处理处理触屏事件的流程

第一次认真写博客，各位大哥大姐，弟弟妹妹请指教。(如有需要讨论的地方，尽可以评论)

首先附上美国大牛Dave Smith的PPT--Mastering Android Touch System的相关部分，以及自己的翻译（翻译的不好请尽情指出）

• Each user touch event is wrapped up as a MotionEvent(每一个触摸事件被封装成一个MotionEvent类)

• Describes user's current action（描述用户的当前动作的有以下常量）

-ACTION_DOWN

– ACTION_UP

– ACTION_MOVE

–ACTION_POINTER_DOWN（当第一根之后的手指按下用此常量表示）

– ACTION_POINTER_UP(当第一根之后的常量按下用此常量表示)

– ACTION_CANCEL（此处不太清楚，哪位大神知道可告诉我）

• Event metadata included(每一个触摸事件包括触摸的信息有触摸坐标，触摸的手指数，触摸的事件)

– Touch location

– Number of pointers (fingers)

– Event time

• A “gesture” is defined as beginning with ACTION_DOWN and endingwith ACTION_UP.（一个手势以ACTION_DOWN开始，以ACTION_UP结束

（鉴于大家英语应该不错我就不逐句翻译了）

Events start at the Activiry with dispatchTouchEvent()

• Events flow top down through views（事件自顶向下通过视图）

– Parents (ViewGroups) dispatch events to their children

– Can intercept events at any time(父视图可在任何时候拦截传向其子视图的事件)

• Events flow down the chain (and back up) until consumed

– Views must declare interest by consuming ACTION_DOWN（视图必须对ACTION_DOWN感兴趣，即当action为ACTION_DOWN时在onTouchEvent中返回true,才能对之后的事件进行处理）

– Further events not delivered for efficiency

• Any unconsumed events end at the Activity with onTouchEvent()

• Optional External OnTouchListener can intercept touches on any View/ViewGroup（使用视图或视图容器的setOnTouchListener（）拦截任何触摸事件，此方法优先于onTouchEvent）

对于以下两点总的说一下流程

触屏事件首先传到Activity的dispatchTouchEvent中再将其传给Activity的根布局文件（为一个ViewGroup的子类）的dispatchTouchEvent，

然后再传递给根布局文件onInterceptionTouchEvent(),

如果返回true，则将事件拦截，传递给当前ViewGroup的onTouchEvent

若返回false,ViewGroup在dispatchTouchEvent中将事件的坐标转化为相对于子View的坐标再传递给子View的dispatchTouchEvent()

若子View为最小视图单元（即不为ViewpGroup的子类），子View直接将事件传递给onTouchLister()或onTouchEvent。

若onTouchLister()或onTouchEvent返回true则表示消费了事件，

若返回false则传递给上一级视图的onTouchEvnet。

Activity.dispatchTouchEvent()

– Always first to be called

– Sends event to root view attached to Window

– onTouchEvent()

• Called if no view，s consume the event

• Always last to be called

• View.dispatchTouchEvent()

– Sends event to listener first, if exists

• View.OnTouchListener.onTouch()

– If not consumed, processes the touch itself

• View.onTouchEvent()this.setOnTouchListener

ViewGroup.dispatchTouchEvent()

– onInterceptTouchEvent()

• Check if it should supersede children

• Passes ACTION_CANCEL to active child

• Return true once consumes all subsequent events

– For each child view, in reverse order they were added

• If touch is relevant (inside view), child.dispatchTouchEvent()

• If not handled by previous, dispatch to next view

– If no children handle event, listener gets a chance

• OnTouchListener.onTouch()

– If no listener, or not handled

• onTouchEvent()

• Intercepted events jump over child step

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