android 事件分发

在android 中事件的分发 是执行

 /**     * Pass the touch screen motion event down to the target view, or this     * view if it is the target.     *     * @param event The motion event to be dispatched.     * @return True if the event was handled by the view, false otherwise.     */    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)) {            //noinspection SimplifiableIfStatement            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;            }        }        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;    }

我门在代码中实现 setOnTouchListener 在onTouch() 方法中实现 返回 true

注意代码

if (li != null && li.mOnTouchListener != null                    && (mViewFlags & ENABLED_MASK) == ENABLED                    && li.mOnTouchListener.onTouch(this, event)) {                result = true;                ｝

所以 当返回为true 的时候，当前的事件是自己处理，

1、事件入口是dispatchTouchEvent(),它会先执行注册的onTouch监听,如果一切顺利的话，接着执行onTouchEvent，在onTouchEvent里会执行onClick监听。
2、无论是dispatchTouchEvent还是onTouchEvent，如果返回true表示这个事件已经被消费、处理了，不再往下传了。在dispathTouchEvent的源码里可以看到，如果onTouchEvent返回了true，那么它也返回true。如果dispatch***在执行onTouch监听的时候，onTouch返回了true，那么它也返回true，这个事件提前被onTouch消费掉了。就不再执行onTouchEvent了，更别说onClick监听了。**
3、我们通常在onTouch监听了设置图片一旦被触摸就改变它的背景、透明度之类的，这个onTouch表示事件的时机。而在onClick监听了去具体干某些事。

  View.setOnTouchListener(new View.OnTouchListener() {                                private boolean mMoved = false;                                private float startX;                                private float startY;                                @Override                                public boolean onTouch(View v, MotionEvent event) {                                    int width = v.getMeasuredWidth();                                    int x = (int) event.getX();                                    int y = (int) event.getY();                                    int minWitdth = (int) (width * 0.75f);                                    if (x > minWitdth) {                                        return false;                                    }                                    if (MotionEvent.ACTION_DOWN == event.getAction()) {                                        mMoved = false;                                        startX = x;                                        startY = y;                                        return true;                                    }                                    if (MotionEvent.ACTION_MOVE == event.getAction()) {                                        int slop = ViewConfiguration.get(v.getContext()).getScaledTouchSlop() * 2;                                        if ((x - startX) * (x - startX) + (y - startY) * (y - startY) > slop) {                                            mMoved = true;                                        }                                        return true;                                    }                                    if (MotionEvent.ACTION_UP == event.getAction()) {                                        return true;                                    }                                    return true;                                }                            });                        }

在touchEvent 中返回fasle 是在点点击事件中是可以处理的，但是要是true 是自己消费，不再朝下传递