Android 点击事件分发

Android 点击事件分发

      • Activity中对事件的处理
      • ViewGroup是如何进行事件处理的
      • View的dispatchTouchEvent相当重要,让我们继续look
      • 总结

Activity中对事件的处理

Activity事件分发方法,返回true表示事件被消费掉了

public boolean dispatchTouchEvent(MotionEvent ev) {
        if (ev.getAction() == MotionEvent.ACTION_DOWN) {
        //不知道干嘛用的,空实现
            onUserInteraction();
        }
        if (getWindow().superDispatchTouchEvent(ev)) {
            return true;
        }
        return onTouchEvent(ev);
    }
  1. 调用window的事件分发,点击去,发现抽象方法,找到Window的实现类PhoneWindow的superDispatchTouchEvent方法
	@Override
    public boolean superDispatchTouchEvent(MotionEvent event) {
        return mDecor.superDispatchTouchEvent(event);
    }
  1. 调用了DecorView的superDispatchTouchEvent方法,在追进去就是ViewGroup的事件分发(DecorView继承的FrameLayout)
public boolean superDispatchTouchEvent(MotionEvent event) {
        return super.dispatchTouchEvent(event);
    }

ViewGroup是如何进行事件处理的

  1. 先进来的down事件,做一些重置操作
			// Handle an initial down.
            if (actionMasked == MotionEvent.ACTION_DOWN) {
                // Throw away all previous state when starting a new touch gesture.
                // The framework may have dropped the up or cancel event for the previous gesture
                // due to an app switch, ANR, or some other state change.
                cancelAndClearTouchTargets(ev);
                resetTouchState();
            }
  1. 判断是不是拦截,如果disallowIntercept = true禁止拦截, intercepted = false,否则的话会调用自身的onInterceptTouchEvent方法是不是需要拦截事件,默认返回false。
		// Check for interception.
            final boolean intercepted;
            if (actionMasked == MotionEvent.ACTION_DOWN
                    || mFirstTouchTarget != null) {
                    //当我们调用getParent().requestDisallowInterceptTouchEvent()方法时,改变的就是FLAG_DISALLOW_INTERCEPT这个值
                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;
                }
            } else {
                // There are no touch targets and this action is not an initial down
                // so this view group continues to intercept touches.
                intercepted = true;
            }
  1. 如果ViewGroup不拦截事件
if (!canceled && !intercepted) {
					...
                    final int childrenCount = mChildrenCount;
                    if (newTouchTarget == null && childrenCount != 0) {
                        final float x = ev.getX(actionIndex);
                        final float y = ev.getY(actionIndex);
                        // Find a child that can receive the event.
                        // Scan children from front to back.
                        //先把所有的子view按照Z轴,Z值越小排在集合的前面,也就是从最底层的view开始事件处理
                        final ArrayList<View> preorderedList = buildTouchDispatchChildList();
                        final boolean customOrder = preorderedList == null
                                && isChildrenDrawingOrderEnabled();
                        final View[] children = mChildren;
                        //从最底层到上层去找能够处理事件的子孩子
                        for (int i = childrenCount - 1; i >= 0; i--) {
                            final int childIndex = getAndVerifyPreorderedIndex(
                                    childrenCount, i, customOrder);
                            final View child = getAndVerifyPreorderedView(
                                    preorderedList, children, childIndex);

                            // If there is a view that has accessibility focus we want it
                            // to get the event first and if not handled we will perform a
                            // normal dispatch. We may do a double iteration but this is
                            // safer given the timeframe.
                            if (childWithAccessibilityFocus != null) {
                                if (childWithAccessibilityFocus != child) {
                                    continue;
                                }
                                childWithAccessibilityFocus = null;
                                i = childrenCount - 1;
                            }
							//如果子孩子不能接收事件,则跳过本次循环
                            if (!child.canReceivePointerEvents()
                                    || !isTransformedTouchPointInView(x, y, child, null)) {
                                ev.setTargetAccessibilityFocus(false);
                                continue;
                            }
							//得到处理事件的孩子,newTouchTarget为 null
                            newTouchTarget = getTouchTarget(child);
                            if (newTouchTarget != null) {
                                // Child is already receiving touch within its bounds.
                                // Give it the new pointer in addition to the ones it is handling.
                                newTouchTarget.pointerIdBits |= idBitsToAssign;
                                break;
                            }

                            resetCancelNextUpFlag(child);
                            //把位置分发给处理事件的子孩子
                            //dispatchTransformedTouchEvent把MotionEvent的坐标转换到子View的坐标空间,这不仅仅是x,y的偏移,还包括根据子View自身矩阵的逆矩阵对坐标进行变换(这就是使用setTranslationX,setScaleX等方法调用后,子View的点击区域还能保持和自身绘制内容一致的原因
                         if (dispatchTransformedTouchEvent(ev, false, child, idBitsToAssign)) {
                                // Child wants to receive touch within its bounds.
                                mLastTouchDownTime = ev.getDownTime();
                                if (preorderedList != null) {
                                    // childIndex points into presorted list, find original index
                                    for (int j = 0; j < childrenCount; j++) {
                                        if (children[childIndex] == mChildren[j]) {
                                            mLastTouchDownIndex = j;
                                            break;
                                        }
                                    }
                                } else {
                                    mLastTouchDownIndex = childIndex;
                                }
                                mLastTouchDownX = ev.getX();
                                mLastTouchDownY = ev.getY();
                                //newTouchTarget经过add,不为null
                                newTouchTarget = addTouchTarget(child, idBitsToAssign);
                                alreadyDispatchedToNewTouchTarget = true;
                                break;
                            }

                            // The accessibility focus didn't handle the event, so clear
                            // the flag and do a normal dispatch to all children.
                            ev.setTargetAccessibilityFocus(false);
                        }
                        if (preorderedList != null) preorderedList.clear();
                    }

                    if (newTouchTarget == null && mFirstTouchTarget != null) {
                        // Did not find a child to receive the event.
                        // Assign the pointer to the least recently added target.
                        newTouchTarget = mFirstTouchTarget;
                        while (newTouchTarget.next != null) {
                            newTouchTarget = newTouchTarget.next;
                        }
                        newTouchTarget.pointerIdBits |= idBitsToAssign;
                    }
                }
            }
  1. 接下来进入dispatchTransformedTouchEvent这个方法
  • 处理cancel事件
	...
  if (cancel || oldAction == MotionEvent.ACTION_CANCEL) {
            event.setAction(MotionEvent.ACTION_CANCEL);
            if (child == null) {
                handled = super.dispatchTouchEvent(event);
            } else {
                handled = child.dispatchTouchEvent(event);
            }
            event.setAction(oldAction);
            return handled;
        }
        ...
  • 主要的逻辑,如果dispatchTransformedTouchEvent这个方法传给他child参数为null(如果事件被拦截,父类自己处理事件,调用此方法传递的child为null),会调用父类View的dispatchTouchEvent方法。不为null,计算偏移量,调用子类的dispatchTouchEvent方法。
				if (child == null) {
                    handled = super.dispatchTouchEvent(event);
                } else {
                    final float offsetX = mScrollX - child.mLeft;
                    final float offsetY = mScrollY - child.mTop;
                    event.offsetLocation(offsetX, offsetY);

                    handled = child.dispatchTouchEvent(event);

                    event.offsetLocation(-offsetX, -offsetY);
                }

View的dispatchTouchEvent相当重要,让我们继续look

	...
		if (actionMasked == MotionEvent.ACTION_DOWN) {
            // Defensive cleanup for new gesture
            //停止嵌套滚动
            stopNestedScroll();
        }

        if (onFilterTouchEventForSecurity(event)) {
            if ((mViewFlags & ENABLED_MASK) == ENABLED && handleScrollBarDragging(event)) {
                result = true;
            }
            //noinspection SimplifiableIfStatement
            ListenerInfo li = mListenerInfo;
            //如果我们外面设置了mOnTouchListener,并重写onTouch方法返回true了,那么就不会走onTouchEvent方法了。
            if (li != null && li.mOnTouchListener != null
                    && (mViewFlags & ENABLED_MASK) == ENABLED
                    && li.mOnTouchListener.onTouch(this, event)) {
                result = true;
            }
			//如果我们没有设置mOnTouchListener,走到了onTouchEvent
            if (!result && onTouchEvent(event)) {
                result = true;
            }
        }
        ...

  1. 接下来是onTouchEvent()方法进行事件的处理,可以看到所有的事件都是在这个方法内部处理掉的。
 if (clickable || (viewFlags & TOOLTIP) == TOOLTIP) {
            switch (action) {
                case MotionEvent.ACTION_UP:
                    mPrivateFlags3 &= ~PFLAG3_FINGER_DOWN;
                    if ((viewFlags & TOOLTIP) == TOOLTIP) {
                        handleTooltipUp();
                    }
                    if (!clickable) {
                        removeTapCallback();
                        removeLongPressCallback();
                        mInContextButtonPress = false;
                        mHasPerformedLongPress = false;
                        mIgnoreNextUpEvent = false;
                        break;
                    }
                    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)) {
                                //回调点击事件
                                    performClickInternal();
                                }
                            }
                        }

                        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:
                    if (event.getSource() == InputDevice.SOURCE_TOUCHSCREEN) {
                        mPrivateFlags3 |= PFLAG3_FINGER_DOWN;
                    }
                    mHasPerformedLongPress = false;

                    if (!clickable) {
                        checkForLongClick(
                                ViewConfiguration.getLongPressTimeout(),
                                x,
                                y,
                                TOUCH_GESTURE_CLASSIFIED__CLASSIFICATION__LONG_PRESS);
                        break;
                    }

                    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(
                                ViewConfiguration.getLongPressTimeout(),
                                x,
                                y,
                                TOUCH_GESTURE_CLASSIFIED__CLASSIFICATION__LONG_PRESS);
                    }
                    break;

                case MotionEvent.ACTION_CANCEL:
                    if (clickable) {
                        setPressed(false);
                    }
                    removeTapCallback();
                    removeLongPressCallback();
                    mInContextButtonPress = false;
                    mHasPerformedLongPress = false;
                    mIgnoreNextUpEvent = false;
                    mPrivateFlags3 &= ~PFLAG3_FINGER_DOWN;
                    break;

                case MotionEvent.ACTION_MOVE:
                    if (clickable) {
                        drawableHotspotChanged(x, y);
                    }

                    final int motionClassification = event.getClassification();
                    final boolean ambiguousGesture =
                            motionClassification == MotionEvent.CLASSIFICATION_AMBIGUOUS_GESTURE;
                    int touchSlop = mTouchSlop;
                    if (ambiguousGesture && hasPendingLongPressCallback()) {
                        final float ambiguousMultiplier =
                                ViewConfiguration.getAmbiguousGestureMultiplier();
                        if (!pointInView(x, y, touchSlop)) {
                            // The default action here is to cancel long press. But instead, we
                            // just extend the timeout here, in case the classification
                            // stays ambiguous.
                            removeLongPressCallback();
                            long delay = (long) (ViewConfiguration.getLongPressTimeout()
                                    * ambiguousMultiplier);
                            // Subtract the time already spent
                            delay -= event.getEventTime() - event.getDownTime();
                            checkForLongClick(
                                    delay,
                                    x,
                                    y,
                                    TOUCH_GESTURE_CLASSIFIED__CLASSIFICATION__LONG_PRESS);
                        }
                        touchSlop *= ambiguousMultiplier;
                    }

                    // Be lenient about moving outside of buttons
                    if (!pointInView(x, y, touchSlop)) {
                        // Outside button
                        // Remove any future long press/tap checks
                        removeTapCallback();
                        removeLongPressCallback();
                        if ((mPrivateFlags & PFLAG_PRESSED) != 0) {
                            setPressed(false);
                        }
                        mPrivateFlags3 &= ~PFLAG3_FINGER_DOWN;
                    }

                    final boolean deepPress =
                            motionClassification == MotionEvent.CLASSIFICATION_DEEP_PRESS;
                    if (deepPress && hasPendingLongPressCallback()) {
                        // process the long click action immediately
                        removeLongPressCallback();
                        checkForLongClick(
                                0 /* send immediately */,
                                x,
                                y,
                                TOUCH_GESTURE_CLASSIFIED__CLASSIFICATION__DEEP_PRESS);
                    }

                    break;
            }
			//如果这个view 是可点击的clickable为true,则处理事件
            return true;
        }
   //此方法默认值false,不消费事件
   return false;

总结

  1. ViewGroup包涵多个子view的时候,按Z轴(也就是层)我们是从最底层遍历,判断当前view是否可以点击,然后分发给需要处理的子view。
  2. 我们可以在onInterceptTouchEvent中进行事件拦截。
  3. 我们可以发现ViewGroup没有onTouchEvent事件,说明他的处理逻辑和View是一样的。
  4. 子view如果消耗了事件,那么ViewGroup就不会在接受到事件了。

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