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Android 事件分发

7月前 作者：夏沫琅琊 分类：Toy博客 阅读(49) 违法举报

这篇具有很好参考价值的文章主要介绍了Android 事件分发。希望对大家有所帮助。如果存在错误或未考虑完全的地方，请大家不吝赐教，您也可以点击"举报违法"按钮提交疑问。

Android 事件分发

本篇文章主要简单介绍下Android中的事件分发,和大家一起学习,进步,有问题也希望大家及时指证修改.

1: onClick和OnTouch

首先我们在单独的activity中添加个按钮button.增加点击事件setOnClickListener:

button.setOnClickListener(v -> Log.i(TAG, "onClick: "));

接着添加OnTouch:

button.setOnTouchListener((v, event) -> {
    Log.i(TAG, "onTouch: " + event.getAction());
    return false;
});

我们执行下点击事件.可以看到输出如下:

2024-04-09 20:54:11.219 17770-17770/? I/testxxx: onTouch: 0
2024-04-09 20:54:11.234 17770-17770/? I/testxxx: onTouch: 2
2024-04-09 20:54:11.294 17770-17770/? I/testxxx: onTouch: 2
2024-04-09 20:54:11.299 17770-17770/? I/testxxx: onTouch: 2
2024-04-09 20:54:11.300 17770-17770/? I/testxxx: onTouch: 1
2024-04-09 20:54:11.306 17770-17770/? I/testxxx: onClick:

OnTouch的事件比较多一些,包含了按下,移动,抬起事件.

事件执行的顺序我们可以看到是OnTouch->onClick.

我们在修改下OnTouch方法:

2024-04-10 10:03:53.245 19437-19437/? I/testxxx: onTouch: 0
2024-04-10 10:03:53.264 19437-19437/? I/testxxx: onTouch: 2
2024-04-10 10:03:53.298 19437-19437/? I/testxxx: onTouch: 2
2024-04-10 10:03:53.304 19437-19437/? I/testxxx: onTouch: 2
2024-04-10 10:03:53.305 19437-19437/? I/testxxx: onTouch: 1

可以看到这里已经没有onCLick事件的执行了.

原因是:onTouch返回true,就代表了该点击事件被onTouch消费掉了,不会继续向下执行. 具体的源码分析可以继续往下看.

2: onInterceptTouchEvent/dispatchTouchEvent/onTouchEvent

首先我们自定义下relationlayout以及button:

package com.test.touchtest;

import android.content.Context;
import android.util.AttributeSet;
import android.util.Log;
import android.view.MotionEvent;
import android.widget.RelativeLayout;

/**
 * @Author: zh
 * @Time: 24-4-10.
 * @Describe:
 */
public class CustomLayout extends RelativeLayout {
    private static final String TAG = "CustomLayout";

    public CustomLayout(Context context) {
        super(context);
    }

    public CustomLayout(Context context, AttributeSet attrs) {
        super(context, attrs);
    }

    public CustomLayout(Context context, AttributeSet attrs, int defStyleAttr) {
        super(context, attrs, defStyleAttr);
    }

    @Override
    public boolean onInterceptTouchEvent(MotionEvent ev) {
        Log.i(TAG, "onInterceptTouchEvent: " + ev.getAction());
        return super.onInterceptTouchEvent(ev);
    }

    @Override
    public boolean dispatchTouchEvent(MotionEvent ev) {
        Log.i(TAG, "dispatchTouchEvent: " + ev.getAction());
        return super.dispatchTouchEvent(ev);
    }

    @Override
    public boolean onTouchEvent(MotionEvent event) {
        Log.i(TAG, "onTouchEvent: " + event.getAction());
        return super.onTouchEvent(event);
    }
}

package com.test.touchtest;

import android.content.Context;
import android.util.AttributeSet;
import android.util.Log;
import android.view.MotionEvent;

/**
 * @Author: zh
 * @Time: 24-4-10.
 * @Describe:
 */
public class CustomButton extends androidx.appcompat.widget.AppCompatButton {
    private static final String TAG = "CustomButton";

    public CustomButton(Context context) {
        super(context);
    }

    public CustomButton(Context context, AttributeSet attrs) {
        super(context, attrs);
    }

    public CustomButton(Context context, AttributeSet attrs, int defStyleAttr) {
        super(context, attrs, defStyleAttr);
    }


    @Override
    public boolean dispatchTouchEvent(MotionEvent ev) {
        Log.i(TAG, "dispatchTouchEvent: " + ev.getAction());
        return super.dispatchTouchEvent(ev);
    }

    @Override
    public boolean onTouchEvent(MotionEvent event) {
        Log.i(TAG, "onTouchEvent: " + event.getAction());
        return super.onTouchEvent(event);
    }
}

执行下button的点击.

2024-04-10 10:16:57.059 25026-25026/com.test.touchtest I/CustomLayout: dispatchTouchEvent: 0
2024-04-10 10:16:57.059 25026-25026/com.test.touchtest I/CustomLayout: onInterceptTouchEvent: 0

2024-04-10 10:16:57.060 25026-25026/com.test.touchtest I/CustomButton: dispatchTouchEvent: 0
2024-04-10 10:16:57.060 25026-25026/com.test.touchtest I/CustomButton: onTouchEvent: 0

2024-04-10 10:16:57.077 25026-25026/com.test.touchtest I/CustomLayout: dispatchTouchEvent: 2
2024-04-10 10:16:57.077 25026-25026/com.test.touchtest I/CustomLayout: onInterceptTouchEvent: 2

2024-04-10 10:16:57.077 25026-25026/com.test.touchtest I/CustomButton: dispatchTouchEvent: 2
2024-04-10 10:16:57.077 25026-25026/com.test.touchtest I/CustomButton: onTouchEvent: 2

2024-04-10 10:16:57.116 25026-25026/com.test.touchtest I/CustomLayout: dispatchTouchEvent: 1
2024-04-10 10:16:57.116 25026-25026/com.test.touchtest I/CustomLayout: onInterceptTouchEvent: 1

2024-04-10 10:16:57.117 25026-25026/com.test.touchtest I/CustomButton: dispatchTouchEvent: 1
2024-04-10 10:16:57.117 25026-25026/com.test.touchtest I/CustomButton: onTouchEvent: 1

2024-04-10 10:16:57.126 25026-25026/com.test.touchtest I/custom: onClick:

可以看到大概的执行顺序如下:

  1. ViewGroup: dispatchTouchEvent
  2. ViewGroup: onInterceptTouchEvent
  3. Button: dispatchTouchEvent
  4. Button: onTouchEvent
  5. Button: onClick

我们在增加下button的setOnToucnListener,打印输出如下:

2024-04-10 11:01:38.824 2160-2160/? I/CustomLayout: dispatchTouchEvent: 0
2024-04-10 11:01:38.825 2160-2160/? I/CustomLayout: onInterceptTouchEvent: 0
2024-04-10 11:01:38.825 2160-2160/? I/CustomButton: dispatchTouchEvent: 0
2024-04-10 11:01:38.826 2160-2160/? I/customActivity: onTouch: 0
2024-04-10 11:01:38.826 2160-2160/? I/CustomButton: onTouchEvent: 0

2024-04-10 11:01:38.843 2160-2160/? I/CustomLayout: dispatchTouchEvent: 2
2024-04-10 11:01:38.843 2160-2160/? I/CustomLayout: onInterceptTouchEvent: 2
2024-04-10 11:01:38.843 2160-2160/? I/CustomButton: dispatchTouchEvent: 2
2024-04-10 11:01:38.843 2160-2160/? I/customActivity: onTouch: 2
2024-04-10 11:01:38.843 2160-2160/? I/CustomButton: onTouchEvent: 2

2024-04-10 11:01:38.902 2160-2160/? I/CustomLayout: dispatchTouchEvent: 1
2024-04-10 11:01:38.902 2160-2160/? I/CustomLayout: onInterceptTouchEvent: 1
2024-04-10 11:01:38.902 2160-2160/? I/CustomButton: dispatchTouchEvent: 1
2024-04-10 11:01:38.902 2160-2160/? I/customActivity: onTouch: 1
2024-04-10 11:01:38.902 2160-2160/? I/CustomButton: onTouchEvent: 1

2024-04-10 11:01:38.908 2160-2160/? I/customActivity: onClick:

可以看到大概的执行顺序如下:

  1. ViewGroup: dispatchTouchEvent
  2. ViewGroup: onInterceptTouchEvent
  3. Button: dispatchTouchEvent
  4. Button: onTouch
  5. Button: onTouchEvent
  6. Button: onClick

3: 源码分析

我们简单看下源码:

  1. View的onTouchEvent:

    public boolean onTouchEvent(MotionEvent event) {
    final float x = event.getX();
    final float y = event.getY();
    final int viewFlags = mViewFlags;
    final int action = event.getAction();

    final boolean clickable = ((viewFlags & CLICKABLE) == CLICKABLE
            || (viewFlags & LONG_CLICKABLE) == LONG_CLICKABLE)
            || (viewFlags & CONTEXT_CLICKABLE) == CONTEXT_CLICKABLE;

    if ((viewFlags & ENABLED_MASK) == DISABLED) {
        if (action == MotionEvent.ACTION_UP && (mPrivateFlags & PFLAG_PRESSED) != 0) {
            setPressed(false);
        }
        mPrivateFlags3 &= ~PFLAG3_FINGER_DOWN;
        // A disabled view that is clickable still consumes the touch
        // events, it just doesn't respond to them.
        return clickable;
    }
    if (mTouchDelegate != null) {
        if (mTouchDelegate.onTouchEvent(event)) {
            return true;
        }
    }

    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)) {
                                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(0, x, y);
                    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(0, x, y);
                }
                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);
                }

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

        return true;
    }

    return false;
}

    我们关注下MotionEvent.ACTION_UP事件,可以看到在事件处理的最后有这么一段代码:

    if (mPerformClick == null) {
    mPerformClick = new PerformClick();
}
if (!post(mPerformClick)) {
    performClickInternal();
}

  2. performClickInternal() 源码如下:

    private boolean performClickInternal() {
    // Must notify autofill manager before performing the click actions to avoid scenarios where
    // the app has a click listener that changes the state of views the autofill service might
    // be interested on.
    notifyAutofillManagerOnClick();

    return performClick();
}

  3. performClick()源码:

    public boolean performClick() {
    // We still need to call this method to handle the cases where performClick() was called
    // externally, instead of through performClickInternal()
    notifyAutofillManagerOnClick();

    final boolean result;
    final ListenerInfo li = mListenerInfo;
    if (li != null && li.mOnClickListener != null) {
        playSoundEffect(SoundEffectConstants.CLICK);
        li.mOnClickListener.onClick(this);
        result = true;
    } else {
        result = false;
    }

    sendAccessibilityEvent(AccessibilityEvent.TYPE_VIEW_CLICKED);

    notifyEnterOrExitForAutoFillIfNeeded(true);

    return result;
}

    可以看到在li != null && li.mOnClickListener != null条件下,执行了:

    li.mOnClickListener.onClick(this);

所以也可以解释了:

事件onTouchEvent()->onClick()的执行顺序.

然后我们看下View的dispathTouchEvent()的源码:

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;
        }
        //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;
}

可以看到源码中的这段代码:

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;
}

这里调用了mOnTouchListener.onTouch事件.

所以也就证明了之前事件执行的顺序:

view的dispatchTouchEvent()->mOnTouchListener.onTouch()->onTouchEent()->onClick().

并且如果li.mOnTouchListener.onTouch(this, event)返回true,也可以看到onTouchEvent(event)并不会执行.

也就解释了我们前面如果修改了onTouch返回值为true,并不会执行onClick事件的原因.

接着我们在看下ViewGroup的dispatchTouchEvent()源码:

public boolean dispatchTouchEvent(MotionEvent ev) {
    if (mInputEventConsistencyVerifier != null) {
        mInputEventConsistencyVerifier.onTouchEvent(ev, 1);
    }

    // If the event targets the accessibility focused view and this is it, start
    // normal event dispatch. Maybe a descendant is what will handle the click.
    if (ev.isTargetAccessibilityFocus() && isAccessibilityFocusedViewOrHost()) {
        ev.setTargetAccessibilityFocus(false);
    }

    boolean handled = false;
    if (onFilterTouchEventForSecurity(ev)) {
        final int action = ev.getAction();
        final int actionMasked = action & MotionEvent.ACTION_MASK;

        // 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();
        }

        // Check for interception.
        final boolean intercepted;
        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;
            }
        } else {
            // There are no touch targets and this action is not an initial down
            // so this view group continues to intercept touches.
            intercepted = true;
        }

        // If intercepted, start normal event dispatch. Also if there is already
        // a view that is handling the gesture, do normal event dispatch.
        if (intercepted || mFirstTouchTarget != null) {
            ev.setTargetAccessibilityFocus(false);
        }

        // Check for cancelation.
        final boolean canceled = resetCancelNextUpFlag(this)
                || actionMasked == MotionEvent.ACTION_CANCEL;

        // Update list of touch targets for pointer down, if needed.
        final boolean split = (mGroupFlags & FLAG_SPLIT_MOTION_EVENTS) != 0;
        TouchTarget newTouchTarget = null;
        boolean alreadyDispatchedToNewTouchTarget = false;
        if (!canceled && !intercepted) {

            // If the event is targeting accessibility focus we give it to the
            // view that has accessibility focus and if it does not handle it
            // we clear the flag and dispatch the event to all children as usual.
            // We are looking up the accessibility focused host to avoid keeping
            // state since these events are very rare.
            View childWithAccessibilityFocus = ev.isTargetAccessibilityFocus()
                    ? findChildWithAccessibilityFocus() : null;

            if (actionMasked == MotionEvent.ACTION_DOWN
                    || (split && actionMasked == MotionEvent.ACTION_POINTER_DOWN)
                    || actionMasked == MotionEvent.ACTION_HOVER_MOVE) {
                final int actionIndex = ev.getActionIndex(); // always 0 for down
                final int idBitsToAssign = split ? 1 << ev.getPointerId(actionIndex)
                        : TouchTarget.ALL_POINTER_IDS;

                // Clean up earlier touch targets for this pointer id in case they
                // have become out of sync.
                removePointersFromTouchTargets(idBitsToAssign);

                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.
                    final ArrayList<View> preorderedList = buildTouchDispatchChildList();
                    final boolean customOrder = preorderedList == null
                            && isChildrenDrawingOrderEnabled();
                    final View[] children = mChildren;
                    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;
                        }

                        if (!canViewReceivePointerEvents(child)
                                || !isTransformedTouchPointInView(x, y, child, null)) {
                            ev.setTargetAccessibilityFocus(false);
                            continue;
                        }

                        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);
                        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 = 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;
                }
            }
        }

        // Dispatch to touch targets.
        if (mFirstTouchTarget == null) {
            // No touch targets so treat this as an ordinary view.
            handled = dispatchTransformedTouchEvent(ev, canceled, null,
                    TouchTarget.ALL_POINTER_IDS);
        } else {
            // Dispatch to touch targets, excluding the new touch target if we already
            // dispatched to it.  Cancel touch targets if necessary.
            TouchTarget predecessor = null;
            TouchTarget target = mFirstTouchTarget;
            while (target != null) {
                final TouchTarget next = target.next;
                if (alreadyDispatchedToNewTouchTarget && target == newTouchTarget) {
                    handled = true;
                } else {
                    final boolean cancelChild = resetCancelNextUpFlag(target.child)
                            || intercepted;
                    if (dispatchTransformedTouchEvent(ev, cancelChild,
                            target.child, target.pointerIdBits)) {
                        handled = true;
                    }
                    if (cancelChild) {
                        if (predecessor == null) {
                            mFirstTouchTarget = next;
                        } else {
                            predecessor.next = next;
                        }
                        target.recycle();
                        target = next;
                        continue;
                    }
                }
                predecessor = target;
                target = next;
            }
        }

        // Update list of touch targets for pointer up or cancel, if needed.
        if (canceled
                || actionMasked == MotionEvent.ACTION_UP
                || actionMasked == MotionEvent.ACTION_HOVER_MOVE) {
            resetTouchState();
        } else if (split && actionMasked == MotionEvent.ACTION_POINTER_UP) {
            final int actionIndex = ev.getActionIndex();
            final int idBitsToRemove = 1 << ev.getPointerId(actionIndex);
            removePointersFromTouchTargets(idBitsToRemove);
        }
    }

    if (!handled && mInputEventConsistencyVerifier != null) {
        mInputEventConsistencyVerifier.onUnhandledEvent(ev, 1);
    }
    return handled;
}

  1. actionMasked == MotionEvent.ACTION_DOWN 条件触发时,将mFirstTouchTarget置为null.

  2. disallowIntercept定义了是否禁用事件拦截.可以通过requestDisallowInterceptTouchEvent修改.默认情况下为false.

  3. 接着进入if条件,默认情况下,执行onInterceptTouchEvent.

    public boolean onInterceptTouchEvent(MotionEvent ev) {
    if (ev.isFromSource(InputDevice.SOURCE_MOUSE)
            && ev.getAction() == MotionEvent.ACTION_DOWN
            && ev.isButtonPressed(MotionEvent.BUTTON_PRIMARY)
            && isOnScrollbarThumb(ev.getX(), ev.getY())) {
        return true;
    }
    return false;
}

  4. 在顺序执行可以看到dispatchTransformedTouchEvent()

    private boolean dispatchTransformedTouchEvent(MotionEvent event, boolean cancel,
        View child, int desiredPointerIdBits) {
    final boolean handled;

    // Canceling motions is a special case.  We don't need to perform any transformations
    // or filtering.  The important part is the action, not the contents.
    final int oldAction = event.getAction();
    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;
    }

    // Calculate the number of pointers to deliver.
    final int oldPointerIdBits = event.getPointerIdBits();
    final int newPointerIdBits = oldPointerIdBits & desiredPointerIdBits;

    // If for some reason we ended up in an inconsistent state where it looks like we
    // might produce a motion event with no pointers in it, then drop the event.
    if (newPointerIdBits == 0) {
        return false;
    }

    // If the number of pointers is the same and we don't need to perform any fancy
    // irreversible transformations, then we can reuse the motion event for this
    // dispatch as long as we are careful to revert any changes we make.
    // Otherwise we need to make a copy.
    final MotionEvent transformedEvent;
    if (newPointerIdBits == oldPointerIdBits) {
        if (child == null || child.hasIdentityMatrix()) {
            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);
            }
            return handled;
        }
        transformedEvent = MotionEvent.obtain(event);
    } else {
        transformedEvent = event.split(newPointerIdBits);
    }

    // Perform any necessary transformations and dispatch.
    if (child == null) {
        handled = super.dispatchTouchEvent(transformedEvent);
    } else {
        final float offsetX = mScrollX - child.mLeft;
        final float offsetY = mScrollY - child.mTop;
        transformedEvent.offsetLocation(offsetX, offsetY);
        if (! child.hasIdentityMatrix()) {
            transformedEvent.transform(child.getInverseMatrix());
        }

        handled = child.dispatchTouchEvent(transformedEvent);
    }

    // Done.
    transformedEvent.recycle();
    return handled;
}

    可以看到主要会执行child.dispatchTouchEvent()方法.

这里其实也就验证了我们先前的调用顺序.

ViewGroup的dispatchTouchEvent->ViewGroup的onInterceptTouchEvent->子view的dispatchTouchEvent.文章来源地址https://www.toymoban.com/news/detail-847613.html

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