Android View的事件分流源码，安卓app启动速度优化

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• 默认情况下事件分发会按照由Activity到ViewGroup再到View的顺序进行分发

• 事件的传递流程是从PhoneWindow->DecorView(mDecor是getWindow().getDecorView()返回的View，通过setContentView设置的View是该View的子View)，再传递到Activity的View树。

[](

)1.View的事件分发的重要的方法：diapatchTouchEvent和touchEvent,onClick

================================================================================================================

|---View

|   |---boolean dispatchTouchEvent(MotionEvent event)

|   |--- boolean onTouchEvent(MotionEvent event)

[](

)1.1 dispatchTouchEvent: 如果事件由视图处理，则为true，否则为false。

===========================================================================================================

public boolean dispatchTouchEvent(MotionEvent event) {

        // If the event should be handled by accessibility focus first.

        if (event.isTargetAccessibilityFocus()) {

            // We don't have focus or no virtual descendant has it, do not handle the event.

            if (!isAccessibilityFocusedViewOrHost()) {

                return false;

            }

            // We have focus and got the event, then use normal event dispatch.

            event.setTargetAccessibilityFocus(false);

        }



        boolean result = false;



        if (mInputEventConsistencyVerifier != null) {

            mInputEventConsistencyVerifier.onTouchEvent(event, 0);

        }



        final int actionMasked = event.getActionMasked();

        if (actionMasked == MotionEvent.ACTION_DOWN) {

            // Defensive cleanup for new gesture

            stopNestedScroll();

        }



        if (onFilterTouchEventForSecurity(event)) {

            if ((mViewFlags & ENABLED_MASK) == ENABLED && handleScrollBarDragging(event)) {

                result = true;

            }

            // 重点 判断listenerInfo 中是否有事件listenter 并且mOnTouchListener.onTouc 返回true 

            ListenerInfo li = mListenerInfo;

            if (li != null && li.mOnTouchListener != null

                    && (mViewFlags & ENABLED_MASK) == ENABLED

                    && li.mOnTouchListener.onTouch(this, event)) {

                result = true;

            }

						// 第二个重点，如果上述判断为false,并且 onTouchEventr返回为true,消耗事件

            if (!result && onTouchEvent(event)) {

                result = true;

            }

        }



        if (!result && mInputEventConsistencyVerifier != null) {

            mInputEventConsistencyVerifier.onUnhandledEvent(event, 0);

        }



        // Clean up after nested scrolls if this is the end of a gesture;

        // also cancel it if we tried an ACTION_DOWN but we didn't want the rest

        // of the gesture.

        if (actionMasked == MotionEvent.ACTION_UP ||

                actionMasked == MotionEvent.ACTION_CANCEL ||

                (actionMasked == MotionEvent.ACTION_DOWN && !result)) {

            stopNestedScroll();

        }



        return result;

    }

1. dispatchTouchEvent中final int actionMasked = event.getActionMasked();

2. ListenerInfo :将view所有的listener信息封装到一个对象中。

3. 在该方法中有两个判断：

 ListenerInfo li = mListenerInfo;

            if (li != null && li.mOnTouchListener != null

                    && (mViewFlags & ENABLED_MASK) == ENABLED

                    && li.mOnTouchListener.onTouch(this, event)) {

                result = true;

            }



            if (!result && onTouchEvent(event)) {

                result = true;

            }

复制代码

如果onTouchEvent或者是onTouchListenner是true的话，会消费此事件，同时，在这里也走了onTouchEvent

• boolean onTouchEvent

• MotionEvent.ACTION_UP:调用了PerformClick()

[](

)三个问题：

==============================================================

[](

)1. 在activity中调用了

==========================================================================

 mTouchView.setOnTouchListener(new View.OnTouchListener() {

            @Override

            public boolean onTouch(View v, MotionEvent event) {

                Log.e("TAG", "onTouch: " + event.getAction());

                return false;

            }

        });

        mTouchView.setOnClickListener(new View.OnClickListener() {

            @Override

            public void onClick(View v) {

                Log.e("TAG", "onClick: " );

            }

        });



     /***********TabLayout************/   

    @Override

    public boolean onTouchEvent(MotionEvent event) {

        Log.e("TAG", "onTouchEvent: "+event.getAction());

        return super.onTouchEvent(event);

    }

复制代码

执行顺序：

[](

)2. 如果是Tablyout中直接return ture呢？

========================================================================================

不执行onClick,因为onClick在View.OntouchEvent中的ACTION_UP中，若直接return true 就不会走super中的方法。

[](

)3. 如果是dispatchEvent return true呢？

===========================================================================================

什么都不执行

[](

)分发流程

=============================================================

super.dispatchEvent->ListenerInfo->super.onTouchEvent(event)->ACTION_UP->performListener().

复制代码

[](

)2. ViewGroup的事件分发：

============================================================================

首先是actionDown:

 if (actionMasked == MotionEvent.ACTION_DOWN

                    || mFirstTouchTarget != null) { //

                final boolean disallowIntercept = (mGroupFlags & FLAG_DISALLOW_INTERCEPT) != 0;

                if (!disallowIntercept) {

                    intercepted = onInterceptTouchEvent(ev);

                    ev.setAction(action); // restore action in case it was changed

                } else {

                    intercepted = false;

                }

            }
 

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