理解Android View的事件传递机制

在android事件传递一般包括三个对象: Activity,ViewGroup,View，事件分发顺序为:Activity->ViewGroup->View，事件分发过程由

onTouchEvent()

onInterceptTouchEvent()

dispatchTouchEvent()

这三个方法协助完成, 其中View没有onInterceptTouchEvent()方法

下面用一个简单的例子进行说明:

testButton, testLayout为自定义控件

class MainActivity : AppCompatActivity(), View.OnTouchListener {

　override fun onCreate(savedInstanceState: Bundle?) {
    super.onCreate(savedInstanceState)
    setContentView(R.layout.activity_main)
    //view没有onInterceptTouchEvent
    //onTouch事件优于onClick
    btnTest.setOnTouchListener(this)
    btnTest.setOnClickListener {
        Toast.makeText(this@MainActivity,"te", Toast.LENGTH_LONG).show()
    }
}

override fun onTouch(v: View?, event: MotionEvent?): Boolean {
    when (v){
        mainLayout->{
            when (event?.action){
                MotionEvent.ACTION_DOWN->{
                    Log.d("touch event","mainLayout ACTION_DOWN")
                }
                MotionEvent.ACTION_UP->{
                    Log.d("touch event","mainLayout ACTION_UP")
                }
            }
        }
        btnTest->{
            when (event?.action){
                MotionEvent.ACTION_DOWN->{
                    Log.d("touch event","btnTest ACTION_DOWN")
                }
                MotionEvent.ACTION_UP->{
                    Log.d("touch event","btnTest ACTION_UP")
                }
            }
        }
    }
    return true
}

//activity的dispatchTouchEvent
override fun dispatchTouchEvent(ev: MotionEvent?): Boolean {
    //事件分派
    when (ev?.action){
        MotionEvent.ACTION_DOWN->{
            Log.d("touch event","activity dispatchTouchEvent ACTION_DOWN")
            //在ACTION_DOWN return true,子view收不到后面的事件
            //return true
        }
        MotionEvent.ACTION_UP->{
            Log.d("touch event","activity dispatchTouchEvent ACTION_UP")
            //ACTION_UP return true,子view收不到ACTION_UP
            //return true
        }
    }
    return super.dispatchTouchEvent(ev)
}

override fun onTouchEvent(event: MotionEvent?): Boolean {
    return super.onTouchEvent(event)
}

}

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class TestButton:Button {       constructor(mContext: Context) : super(mContext) {         val context = mContext     }     constructor(mContext: Context, mAttributeSet: AttributeSet) : super(mContext, mAttributeSet) {         val context = mContext     }       override fun onTouchEvent(event: MotionEvent?): Boolean {         //return super.onTouchEvent(event)         when (event?.action){             MotionEvent.ACTION_DOWN->{                 Log.d("touch event","btnTest ACTION_DOWN")                 return true             }             MotionEvent.ACTION_UP->{                 Log.d("touch event","btnTest ACTION_UP")             }         }         //如果返回true,不会把onTouch事件传递回activity,就是说activity的onTouchEvent不会被调用           return true     }       override fun dispatchTouchEvent(event: MotionEvent?): Boolean {         return super.dispatchTouchEvent(event)     }   }

　　

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class TestLayout : ConstraintLayout{       constructor(mContext: Context) : super(mContext) {         val context = mContext     }     constructor(mContext: Context, mAttributeSet: AttributeSet) : super(mContext, mAttributeSet) {         val context = mContext     }       override fun onTouchEvent(event: MotionEvent?): Boolean {         //return super.onTouchEvent(event)         Log.d("touch event","view group")         return true     }       override fun onInterceptTouchEvent(ev: MotionEvent?): Boolean {         //return super.onInterceptTouchEvent(ev)         //true:中断事件         //中断后, TestLayout的子view btnTest的onTouch，onClick都不会执行         return true     }       override fun dispatchTouchEvent(ev: MotionEvent?): Boolean {         //事件分派         when (ev?.action){             MotionEvent.ACTION_DOWN->{                 Log.d("touch event","view group dispatchTouchEvent ACTION_DOWN")                 //在ACTION_DOWN return true,子view收不到后面的事件                 //return true             }             MotionEvent.ACTION_UP->{                 Log.d("touch event","view group dispatchTouchEvent ACTION_UP")                 //ACTION_UP return true,子view收不到ACTION_UP                 //return true             }         }         return super.dispatchTouchEvent(ev)     } }

 

我们通过log查看到，每次touch btnTest或mainLayout，都会先打印Activity里的dispatchTouchEvent里的ACTION_DOWN，是传递的起点

a. 如果Activity的dispatchTouchEvent里的ACTION_DOWN return true，子view就收不到事件传递了；

b. TestLayout的onInterceptTouchEvent，如果return true，表示中断传递给子view的事件，TestButton的onTouch，onClick都不会执行，会走TestLayout的onTouchEvent；就是说如果ViewGroup的onInterceptTouchEvent return true，就会走自已的onTouchEvent()；

c. 如果TestLayout的onTouchEvent return true，就是消费掉事件,不会把onTouch事件传递回activity,就是说activity的onTouchEvent不会被调用

d. 同理TestButton的onTouchEvent return true，也不会把onTouch事件传递回activity,就是说activity的onTouchEvent不会被调用

 

如果view,viewgroup都没有对事件进行消费，会以activity的onTouchEvent作为终点；

如果viewgroup中断事件并对事件进行消费，会以viewgroup onTouchEvent作为终点；

如果viewgroup没有中断事件，但view(如button)对事件进行消费，会以button ACTION_UP作为终点；

如果viewgroup没有中断事件，view也没有对事件进行消费，会以activity的onTouchEvent作为终点；

另一理解点