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  • touch事件的分发机制

    作者:谢昆

    一段伪代码反应整个touch事件的分发

    public boolean dispatchTouchEvent(MotionEvent event) { 
        boolean consume = false;
        if (onInteceptTouchEvent(event)) { 
            consume = onTouchEvent(event); 
        } else { 
            consume = child.dispatchTouchEvent(event); 
        } 
        return consume;
    }
    

    View的事件分发

    image

    public boolean dispatchTouchEvent(MotionEvent event) {  
        if (mOnTouchListener != null && (mViewFlags & ENABLED_MASK) == ENABLED &&  
                mOnTouchListener.onTouch(this, event)) {  
            return true;  
        }  
        return onTouchEvent(event);  
    }  
    
    1. 第一个参数是我们设置的onTouchListener
    2. 第二个参数(mViewFlags & ENABLED_MASK) == ENABLED是判断当前点击的控件是否是enable的,按钮默认都是enable的,因此这个条件恒定为true
    3. 第三个参数就是mOnTouchListener.onTouch(this, event)方法的返回值

    onTouchEvent(MotionEvent event)的源码:

    public boolean onTouchEvent(MotionEvent event) {  
        final int viewFlags = mViewFlags;  
        if ((viewFlags & ENABLED_MASK) == DISABLED) {  
            // 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));  
        }  
        if (mTouchDelegate != null) {  
            if (mTouchDelegate.onTouchEvent(event)) {  
                return true;  
            }  
        }  
        if (((viewFlags & CLICKABLE) == CLICKABLE ||  
                (viewFlags & LONG_CLICKABLE) == LONG_CLICKABLE)) {  
            switch (event.getAction()) {  
                case MotionEvent.ACTION_UP:  
                    boolean prepressed = (mPrivateFlags & PREPRESSED) != 0;  
                    if ((mPrivateFlags & 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 (!mHasPerformedLongPress) {  
                            // 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) {  
                            mPrivateFlags |= PRESSED;  
                            refreshDrawableState();  
                            postDelayed(mUnsetPressedState,  
                                    ViewConfiguration.getPressedStateDuration());  
                        } else if (!post(mUnsetPressedState)) {  
                            // If the post failed, unpress right now  
                            mUnsetPressedState.run();  
                        }  
                        removeTapCallback();  
                    }  
                    break;  
                case MotionEvent.ACTION_DOWN:  
                    if (mPendingCheckForTap == null) {  
                        mPendingCheckForTap = new CheckForTap();  
                    }  
                    mPrivateFlags |= PREPRESSED;  
                    mHasPerformedLongPress = false;  
                    postDelayed(mPendingCheckForTap, ViewConfiguration.getTapTimeout());  
                    break;  
                case MotionEvent.ACTION_CANCEL:  
                    mPrivateFlags &= ~PRESSED;  
                    refreshDrawableState();  
                    removeTapCallback();  
                    break;  
                case MotionEvent.ACTION_MOVE:  
                    final int x = (int) event.getX();  
                    final int y = (int) event.getY();  
                    // Be lenient about moving outside of buttons  
                    int slop = mTouchSlop;  
                    if ((x < 0 - slop) || (x >= getWidth() + slop) ||  
                            (y < 0 - slop) || (y >= getHeight() + slop)) {  
                        // Outside button  
                        removeTapCallback();  
                        if ((mPrivateFlags & PRESSED) != 0) {  
                            // Remove any future long press/tap checks  
                            removeLongPressCallback();  
                            // Need to switch from pressed to not pressed  
                            mPrivateFlags &= ~PRESSED;  
                            refreshDrawableState();  
                        }  
                    }  
                    break;  
            }  
            return true;  
        }  
        return false;  
    }
    

    首先在第14行我们可以看出,如果该控件是可以点击的就会进入到第16行的switch判断中去,而如果当前的事件是抬起手指,则会进入到MotionEvent.ACTION_UP这个case当中。在经过种种判断之后,会执行到第38行的performClick()方法

    performClick()的源码:

    public boolean performClick() {  
        sendAccessibilityEvent(AccessibilityEvent.TYPE_VIEW_CLICKED);  
        if (mOnClickListener != null) {  
            playSoundEffect(SoundEffectConstants.CLICK);  
            mOnClickListener.onClick(this);  
            return true;  
        }  
        return false;  
    }  
    

    setOnClickListener(OnClickListener l)的源码:

    public void setOnClickListener(OnClickListener l) {  
        if (!isClickable()) {  
            setClickable(true);  
        }  
        mOnClickListener = l;  
    }
    

    ViewGroup的事件分发

    image

    public boolean dispatchTouchEvent(MotionEvent ev) {  
        final int action = ev.getAction();  
        final float xf = ev.getX();  
        final float yf = ev.getY();  
        final float scrolledXFloat = xf + mScrollX;  
        final float scrolledYFloat = yf + mScrollY;  
        final Rect frame = mTempRect;  
        boolean disallowIntercept = (mGroupFlags & FLAG_DISALLOW_INTERCEPT) != 0;  
        if (action == MotionEvent.ACTION_DOWN) {  
            if (mMotionTarget != null) {  
                mMotionTarget = null;  
            }  
            if (disallowIntercept || !onInterceptTouchEvent(ev)) {  
                ev.setAction(MotionEvent.ACTION_DOWN);  
                final int scrolledXInt = (int) scrolledXFloat;  
                final int scrolledYInt = (int) scrolledYFloat;  
                final View[] children = mChildren;  
                final int count = mChildrenCount;  
                for (int i = count - 1; i >= 0; i--) {  
                    final View child = children[i];  
                    if ((child.mViewFlags & VISIBILITY_MASK) == VISIBLE  
                            || child.getAnimation() != null) {  
                        child.getHitRect(frame);  
                        if (frame.contains(scrolledXInt, scrolledYInt)) {  
                            final float xc = scrolledXFloat - child.mLeft;  
                            final float yc = scrolledYFloat - child.mTop;  
                            ev.setLocation(xc, yc);  
                            child.mPrivateFlags &= ~CANCEL_NEXT_UP_EVENT;  
                            if (child.dispatchTouchEvent(ev))  {  
                                mMotionTarget = child;  
                                return true;  
                            }  
                        }  
                    }  
                }  
            }  
        }  
        boolean isUpOrCancel = (action == MotionEvent.ACTION_UP) ||  
                (action == MotionEvent.ACTION_CANCEL);  
        if (isUpOrCancel) {  
            mGroupFlags &= ~FLAG_DISALLOW_INTERCEPT;  
        }  
        final View target = mMotionTarget;  
        if (target == null) {  
            ev.setLocation(xf, yf);  
            if ((mPrivateFlags & CANCEL_NEXT_UP_EVENT) != 0) {  
                ev.setAction(MotionEvent.ACTION_CANCEL);  
                mPrivateFlags &= ~CANCEL_NEXT_UP_EVENT;  
            }  
            return super.dispatchTouchEvent(ev);  
        }  
        if (!disallowIntercept && onInterceptTouchEvent(ev)) {  
            final float xc = scrolledXFloat - (float) target.mLeft;  
            final float yc = scrolledYFloat - (float) target.mTop;  
            mPrivateFlags &= ~CANCEL_NEXT_UP_EVENT;  
            ev.setAction(MotionEvent.ACTION_CANCEL);  
            ev.setLocation(xc, yc);  
            if (!target.dispatchTouchEvent(ev)) {  
            }  
            mMotionTarget = null;  
            return true;  
        }  
        if (isUpOrCancel) {  
            mMotionTarget = null;  
        }  
        final float xc = scrolledXFloat - (float) target.mLeft;  
        final float yc = scrolledYFloat - (float) target.mTop;  
        ev.setLocation(xc, yc);  
        if ((target.mPrivateFlags & CANCEL_NEXT_UP_EVENT) != 0) {  
            ev.setAction(MotionEvent.ACTION_CANCEL);  
            target.mPrivateFlags &= ~CANCEL_NEXT_UP_EVENT;  
            mMotionTarget = null;  
        }  
        return target.dispatchTouchEvent(ev);  
    }
    

    在第13行可以看到一个条件判断,如果disallowIntercept和!onInterceptTouchEvent(ev)两者有一个为true,就会进入到这个条件判断中。接着如果进入条件语句就回去遍历查找点击的是哪一个子view,进而调用子view的dispatchTouchEvent(ev)方法将事件传递下去。

    那如果遍历没有找到目标的子view,则会继续往下面走,会在第50行调用super.dispatchTouchEvent(ev),这里就是View中的dispatchTouchEvent(ev),这样就执行完整个的流程。

    image

    activity对事件的分发过程

    activity的dispatchTouchEvent(MotionEvent ev)方法:

    public boolean dispatchTouchEvent(MotionEvent ev) {
        if (ev.getAction() == MotionEvent.ACTION_DOWN) {
            onUserInteraction();
        }
        if (getWindow().superDispatchTouchEvent(ev)) {
            return true;
        }
        return onTouchEvent(ev);
    }
    

    主要就通过window来分发事件,如果没有view消费掉事件,就调用activity的onTouchEvent(ev)

    Window是一个抽象类,他的实现类就是PhoneWindow,PhoneWindow中的superDispatchTouchEvent(ev)的方法:

    public boolean superDispatchTouchEvent(MotionEvent ev){
        return mDecor.superDispatchTouchEvent(ev);
    }
    
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  • 原文地址:https://www.cnblogs.com/Free-Thinker/p/7809936.html
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