Android开发总结笔记 View的事件分发机制 3-９

来源：互联网发布：手机网络有问号编辑：程序博客网时间：2024/05/27 00:41

参考 http://blog.csdn.net/yanbober/article/details/45887547

关于View事件分发机制，一般就是从两个方法开始。

setOnClickListener 　回调onClick方法
setOnTouchListener 回调onTouch方法，其中有ACTION_DOWN，ACTION_UP，ACTION_MOVE方法

如果一个组件同时注册了两个事件，onTouch是先于onClick执行的

 mIvEditBarEdit.setOnTouchListener(new View.OnTouchListener() {
            @Override
            public boolean onTouch(View v, MotionEvent event) {
                return false;
            }
        });

但是，有个关键点，onTouch方法中有一个布尔类型的返回值，如果把这个返回值改成true

onClick方法就不会执行了，因为返回了true，所以事件被onTouch方法消费了，从而导致事件不再向下传递

从源码里面找理由(API 22)

首先要知道的一点是，只有触碰了任何一个控件，就一定会调用该控件的dispatchTouchEvent方法

而这个方法在View类中

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;
    }

前面都是一些标记的设置和手势的传递，看２０行

onFilterTouchEventForSecurity(event)判断组件有没有被遮住

ListenerInfo是View的静态内部类，用来定义各种XXXListener方法

重点是２３行

li!=null
li.mTouchListener!=null 只要调用了setonTouchListener方法，这个值就不为空
(mViewFlags & ENABLED_MASK) == ENABLED 只要View是可点击的，就为真
li.mOnTouchListener.onTouch(this, event) 而这个值，是最关键的，是onTouch方法的返回值

如果这四个条件都成立，接下来if (!result && onTouchEvent(event))就不会执行，最终dispatchTouchEvent就会返回true

如果有一个条件不成立的话，if (!result && onTouchEvent(event))就会执行，onTouchEvent(event))返回false则dispatchTouchEvent返回false

那么这样的话，点击事件就一定在onTouchEvent(event)方法中

 public boolean onTouchEvent(MotionEvent event) {
        final float x = event.getX();
        final float y = event.getY();
        final int viewFlags = mViewFlags;
        final int action = event.getAction();
        if ((viewFlags & ENABLED_MASK) == DISABLED) {
            if (action == MotionEvent.ACTION_UP && (mPrivateFlags & PFLAG_PRESSED) != 0) {
                setPressed(false);
            }
            // A disabled view that is clickable still consumes the touch
            // events, it just doesn't respond to them.
            return (((viewFlags & CLICKABLE) == CLICKABLE
                    || (viewFlags & LONG_CLICKABLE) == LONG_CLICKABLE)
                    || (viewFlags & CONTEXT_CLICKABLE) == CONTEXT_CLICKABLE);
        }
        if (mTouchDelegate != null) {
            if (mTouchDelegate.onTouchEvent(event)) {
                return true;
            }
        }
        if (((viewFlags & CLICKABLE) == CLICKABLE ||
                (viewFlags & LONG_CLICKABLE) == LONG_CLICKABLE) ||
                (viewFlags & CONTEXT_CLICKABLE) == CONTEXT_CLICKABLE) {
            switch (action) {
                case MotionEvent.ACTION_UP:
                    boolean prepressed = (mPrivateFlags & PFLAG_PREPRESSED) != 0;
                    if ((mPrivateFlags & PFLAG_PRESSED) != 0 || prepressed) {
                        // take focus if we don't have it already and we should in
                        // touch mode.
                        boolean focusTaken = false;
                        if (isFocusable() && isFocusableInTouchMode() && !isFocused()) {
                            focusTaken = requestFocus();
                        }
                        if (prepressed) {
                            // The button is being released before we actually
                            // showed it as pressed.  Make it show the pressed
                            // state now (before scheduling the click) to ensure
                            // the user sees it.
                            setPressed(true, x, y);
                       }
                        if (!mHasPerformedLongPress && !mIgnoreNextUpEvent) {
                            // This is a tap, so remove the longpress check
                            removeLongPressCallback();
                            // Only perform take click actions if we were in the pressed state
                            if (!focusTaken) {
                                // Use a Runnable and post this rather than calling
                                // performClick directly. This lets other visual state
                                // of the view update before click actions start.
                                if (mPerformClick == null) {
                                    mPerformClick = new PerformClick();
                                }
                                if (!post(mPerformClick)) {
                                    performClick();
                                }
                            }
                        }
                        if (mUnsetPressedState == null) {
                            mUnsetPressedState = new UnsetPressedState();
                        }
                        if (prepressed) {
                            postDelayed(mUnsetPressedState,
                                    ViewConfiguration.getPressedStateDuration());
                        } else if (!post(mUnsetPressedState)) {
                            // If the post failed, unpress right now
                            mUnsetPressedState.run();
                        }
                        removeTapCallback();
                    }
                    mIgnoreNextUpEvent = false;
                    break;
                case MotionEvent.ACTION_DOWN:
                    mHasPerformedLongPress = false;
                    if (performButtonActionOnTouchDown(event)) {
                        break;
                    }
                    // Walk up the hierarchy to determine if we're inside a scrolling container.
                    boolean isInScrollingContainer = isInScrollingContainer();
                    // For views inside a scrolling container, delay the pressed feedback for
                    // a short period in case this is a scroll.
                    if (isInScrollingContainer) {
                        mPrivateFlags |= PFLAG_PREPRESSED;
                        if (mPendingCheckForTap == null) {
                            mPendingCheckForTap = new CheckForTap();
                        }
                        mPendingCheckForTap.x = event.getX();
                        mPendingCheckForTap.y = event.getY();
                        postDelayed(mPendingCheckForTap, ViewConfiguration.getTapTimeout());
                    } else {
                        // Not inside a scrolling container, so show the feedback right away
                        setPressed(true, x, y);
                        checkForLongClick(0);
                    }
                    break;
                case MotionEvent.ACTION_CANCEL:
                    setPressed(false);
                    removeTapCallback();
                    removeLongPressCallback();
                    mInContextButtonPress = false;
                    mHasPerformedLongPress = false;
                    mIgnoreNextUpEvent = false;
                    break;
                case MotionEvent.ACTION_MOVE:
                    drawableHotspotChanged(x, y);
                    // Be lenient about moving outside of buttons
                    if (!pointInView(x, y, mTouchSlop)) {
                        // Outside button
                        removeTapCallback();
                        if ((mPrivateFlags & PFLAG_PRESSED) != 0) {
                            // Remove any future long press/tap checks
                            removeLongPressCallback();
                            setPressed(false);
                        }
                    }
                    break;
            }
            return true;
        }
        return false;
    }

从这段源码的第2４行看起，如果当前组件可以点击，就会进入到swich，然后就在case ACTION_UP中经过一系列的判断后调用了performClick方法

关于touch事件的一系列ACTION_UP，ACTION_DOWN和ACTION_MOVE方法

在上面的onTouchEvent方法中可以看到，只要组件可以点击，走到 2４行的里面的判断，不管ACTION是什么，最终都会返回１３４行的true

所以，如果想要拦截ACTION事件，把组件设为不可点击即可

那样的话，onTouchEvent方法就不会进入２４行的判断而直接返回１３７的false，只有ACTION_DOWN得到执行

所以，只有前一个action返回true,才会触发下一个action

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