Android事件分发原理分析

MotionEvent.ACTION_DOWN传递

在Android中,触碰控件的时候回产生一个ACTION_DOWN事件并逐层向下传递,首先ACTION_DOWN回先从Activity的dispatchTouchEvent方法开始向下传递:

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

该方法调用了Activity中的Window的superDispatchTouchEvent方法,也就是PhoneWindow中:

@Override
    public boolean superDispatchTouchEvent(MotionEvent event) {
        return mDecor.superDispatchTouchEvent(event);
    }

然后接着调用mDecor的superDispatchTouchEvent方法,而mDecor就是我们熟悉的DecorView类的对象,是一个ViewGroup类型的,这里先大概了解一下Activity布局层级结构:

image.png

从图上可以看出,Activity实际上是包含了一个PhoneWindow,然后在PhoneWindow中又包含了DecorView的ViewGroup,我们通过setContentView为Activity设置的布局文件最终是添加到DecorView下的,也就是我们的xml布局文件最终是DecorView的child,所以当ACTION_DOWN传递到DecorView的superDispatchTouchEvent方法的时候:

public boolean superDispatchTouchEvent(MotionEvent event) {
        return super.dispatchTouchEvent(event);
    }

实际上DecorView的superDispatchTouchEvent就是调用了ViewGroup的dispatchTouchEvent方法继续往子层级继续传递,ViewGroup的dispatchTouchEvent方法源码太长了,这里就不贴上来了,在分析到关键部分的时候只贴关键代码吧。在ViewGroup的dispatchTouchEvent方法里,首先:

// 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();
            }

看注释是出来初始化的ACTION_DOWN事件,为什么要这么作?我的理解是ACTION_DOWN应该作为触摸动作最先发生的事件,一个触摸动作首先发生了ACTION_DOWN事件,然后如果又移动就会发生ACTION_MOVEDMOVE事件,接着再抬手发生了ACTION_UP事件,当然如果你没抬手,只是吧触碰点移动出了控件的范围,那应该是发生ACTION_CANCEL事件(这个有些手机可能不会发生ACTION_CANCEL事件而是发生ACTION_UP事件),这才是一个完整的触摸动作,所以对于一个单点触摸动作来说ACTION_DOWN在这个动作完成之前ACTION_DOWN只会发生一次,因此这里需要吧控件之前发生的一些触摸事件留下来的touch状态信息抛出ACTION_CANCEL事件来结束,然后清空该控件的touch信息与状态恢复到ACTION_DOWN事件发生之前的状态再接着传递ACTION_DOWN事件:

/**
     * Cancels and clears all touch targets.
     */
    private void cancelAndClearTouchTargets(MotionEvent event) {
        if (mFirstTouchTarget != null) {
            boolean syntheticEvent = false;
            if (event == null) {
                final long now = SystemClock.uptimeMillis();
                event = MotionEvent.obtain(now, now,
                        MotionEvent.ACTION_CANCEL, 0.0f, 0.0f, 0);
                event.setSource(InputDevice.SOURCE_TOUCHSCREEN);
                syntheticEvent = true;
            }

            for (TouchTarget target = mFirstTouchTarget; target != null; target = target.next) {
                resetCancelNextUpFlag(target.child);
                dispatchTransformedTouchEvent(event, true, target.child, target.pointerIdBits);
            }
            clearTouchTargets();

            if (syntheticEvent) {
                event.recycle();
            }
        }
    }

dispatchTransformedTouchEvent(event, true, target.child, target.pointerIdBits)就是把当前的ACTION_DOWN先设置成ACTION_CANCEL派发给子控件然后再恢复ACTION_DOWN状态:

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;
        }

清空touch信息只会,继续恢复ACTION_DOWN的传递,在ViewGroup的dispatchTouchEvent方法中,ACTION_DOWN回执行到以下代码:

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;
            }

ACTION_DOWN事件回满足if分支,else暂时不管,在if分支中出现了一个disallowIntercept变量,这个是控制该控件是否允许拦截touch事件用的,由ViewGroup中requestDisallowInterceptTouchEvent方法来控制:

@Override
    public void requestDisallowInterceptTouchEvent(boolean disallowIntercept) {

        if (disallowIntercept == ((mGroupFlags & FLAG_DISALLOW_INTERCEPT) != 0)) {
            // We're already in this state, assume our ancestors are too
            return;
        }

        if (disallowIntercept) {
            mGroupFlags |= FLAG_DISALLOW_INTERCEPT;
        } else {
            mGroupFlags &= ~FLAG_DISALLOW_INTERCEPT;
        }

        // Pass it up to our parent
        if (mParent != null) {
            mParent.requestDisallowInterceptTouchEvent(disallowIntercept);
        }
    }

如果disallowIntercept为true那就是不允许拦截,于是就不会继续调用onInterceptTouchEvent方法,如果为false,就是允许拦截,onInterceptTouchEvent方法将被调用:

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;
    }

这个方法返回true表示触摸事件要被拦截,false表示触摸事件不被拦截,可继续往下传递,如果触摸事件没有被取消或者拦截,会继续执行以下一大段代码:

if (!canceled && !intercepted) {

                // If the event is targeting accessiiblity 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;
                    }
                }
            }

这里面的核心其实就是遍历该ViewGroup下的所有Child,如果当前的ViewGroup没有Child了,那么mFirstTouchTarget == null,接着直接执行:

// 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);
            }

如果ViewGroup有Child,判断Child是否有资格接收触摸事件:

/**
     * Returns true if a child view can receive pointer events.
     * @hide
     */
    private static boolean canViewReceivePointerEvents(@NonNull View child) {
        return (child.mViewFlags & VISIBILITY_MASK) == VISIBLE
                || child.getAnimation() != null;
    }

/**
     * Returns true if a child view contains the specified point when transformed
     * into its coordinate space.
     * Child must not be null.
     * @hide
     */
    protected boolean isTransformedTouchPointInView(float x, float y, View child,
            PointF outLocalPoint) {
        final float[] point = getTempPoint();
        point[0] = x;
        point[1] = y;
        transformPointToViewLocal(point, child);
        final boolean isInView = child.pointInView(point[0], point[1]);
        if (isInView && outLocalPoint != null) {
            outLocalPoint.set(point[0], point[1]);
        }
        return isInView;
    }

子控件必须是可见并且触摸的坐标在控件范围内才能接收触摸事件,这里有一个小细节,我么可以学习如果来把触摸的坐标点是否在控件范围内这个判断:

public boolean pointInView(float localX, float localY, float slop) {
        return localX >= -slop && localY >= -slop && localX < ((mRight - mLeft) + slop) &&
                localY < ((mBottom - mTop) + slop);
    }

注意坐标点的转化。继续来分析触摸事件ACTION_DOWN的传递,在找到能够接收ACTION_DOWN的Child之后,会执行dispatchTransformedTouchEvent(ev, false, child, idBitsToAssign),然后根据返回值决定是否把事件继续往下一个Child传递:

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;
                            }

如果dispatchTransformedTouchEvent返回true表示事件已经被消费,那就会直接break,事件就不会继续传递给下一个Child了,返回false的就会继续循环把事件传递给下一个Child

// 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);
        }

child == null的时候说明ViewGroup没有child,直接会调用到View的dispatchTouchEvent,其实就是ViewGroup本身; child != null的时候就会执行child.dispatchTouchEvent(transformedEvent),child是View类型的,再看View的dispatchTouchEvent方法:

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;
    }

这里就很简单了,判断View是否是enabled的,如果是,就会触发这个View的OnTouchListener的onTouch,然后根据onTouch的返回值决定是否触发View的onTouchEvent,也就是说OnTouchListener会比onTouchEvent先执行,到这ACTION_DOWN事件传递结束,下面来总结以下传递流程与顺序:

image.png

MotionEvent.ACTION_UP的传递

上面提到,一个单点完整的触摸动作是从ACTION_DOWN开始,并以ACTION_UP或者ACTION_CANCEL结束的,ACTION_UP是在ACTION_DOWN已经发生的情况下再去基于当前View的一些特性,例如是否可点击,事件是否被消费来决定ACTION_UP是否能不能到达一些控件的,ACTION_UP依然也是从Activity的dispatchTouchEvent方法开始往下逐层传递,这边可通过对比Button和TextView对于ACTION_UP的不同处理作比较:

  • Button与TextView对于ACTION_UP的区别,Buton是可点击的isClickable方法返回true,而TextView是不可点击的isClickable方法返回false,所以Button在处理ACTION_DOWN的时候,会在View的onTouchEvent返回true:
if (!result && onTouchEvent(event)) {
                result = true;
            }

因此直接导致了View的dispatchTouchEvent方法也返回true,由此逐级继续向上返回这个true,因此Button的父控件,Activity的dispatchTouchEvent方法都会纷纷的返回true,在ViewGroup当中收到View的dispatchTouchEvent返回true的时候会执行以下代码:

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;
                            }

因为View的dispatchTouchEvent返回true,所以也返回true,原因是dispatchTransformedTouchEvent中去分发执行了View的dispatchTouchEvent:

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);
        }

handled就是View的dispatchTouchEvent返回的值,表示事件已经被消费了,dispatchTransformedTouchEvent返回true之后,就执行了newTouchTarget = addTouchTarget(child, idBitsToAssign):

private TouchTarget addTouchTarget(@NonNull View child, int pointerIdBits) {
        final TouchTarget target = TouchTarget.obtain(child, pointerIdBits);
        target.next = mFirstTouchTarget;
        mFirstTouchTarget = target;
        return target;
    }

把子控件赋值给了mFirstTouchTarget,如果mFirstTouchTarget不为null,当下一个事件ACTION_UP传递进入ViewGroup的时候:

// 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;
                }
            }

上面是ViewGroup的dispatchTouchEvent中对于mFirstTouchTarget是否为null的不同处理,对于Button来说,由于ACTION_DOWN被消费了,因此mFirstTouchTarget != null,所以会通过mFirstTouchTarget.child来把ACTION_UP继续分发给子View,前提当然是当前这个ViewGroup满足事件分发条件,例如事件未被拦截,这样ACTION_UP就能顺利的传递到子控件了,因此这就是为什么Button点击后能够收到ACTION_UP,而对于TextView而言,这里就不一样了,由于TextView是不可点击的,因此在执行View的onTouchEvent的时候会返回false,这将导致它的父控件ViewGroup的dispatchTransformedTouchEvent也返回false,所以dispatchTouchEvent返回false,因此mFirstTouchTarget并不会被初始化,即不会执行addTouchTarget方法,所以mFirstTouchTarget为null,当ACTION_UP从Activity传进ViewGroup的时候,发现mFirstTouchTarget == null,就是执行:

if (mFirstTouchTarget == null) {
                // No touch targets so treat this as an ordinary view.
                handled = dispatchTransformedTouchEvent(ev, canceled, null,
                        TouchTarget.ALL_POINTER_IDS);
            }

可以看到dispatchTransformedTouchEvent的child参数(方法的第三个参数)直接传了一个null,这样将导致当前的ViewGroup无法将ACTION_UP传递给它的子控件,而是直接调用了:

if (child == null) {
            handled = super.dispatchTouchEvent(transformedEvent);
        }

由于ViewGroup的父类是View,因此最终执行了View的dispatchTouchEvent,所以ACTION_UP就只传递到了ViewGroup,并不再往下传递,对于Activity的层级结构来说我们通过setContentView设置的布局是嵌套在DecorView中的,DecorView是一个ViewGroup,ACTION_UP是从Activity的dispatchTouchEvent传递进来的,因此ACTION_UP最终只会传递到DecorView这层,而不会传递到我们设置的布局控件了,当把TextView通过setClickable(true)设置成可点击的时候,TextView和它的父控件ViewGroup就能收到ACTION_UP事件,当把Button通过setClickable(false),那么Button就喝TextView一样,无法收到ACTION_UP事件,下面来搞一个Demo,Demo地址:https://github.com/liuhongda/TouchEventDemo,Activity布局文件:

<?xml version="1.0" encoding="utf-8"?>
<android.support.constraint.ConstraintLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:app="http://schemas.android.com/apk/res-auto"
    xmlns:tools="http://schemas.android.com/tools"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    tools:context="com.lhd.touchevent.MainActivity">

    <com.lhd.touchevent.MyRelativeLayout
        android:layout_width="match_parent"
        android:layout_height="match_parent">

        <com.lhd.touchevent.MyTextView
            android:id="@+id/my_tv"
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:text="Hello World!"
            app:layout_constraintBottom_toBottomOf="parent"
            app:layout_constraintLeft_toLeftOf="parent"
            app:layout_constraintRight_toRightOf="parent"
            app:layout_constraintTop_toTopOf="parent" />

        <com.lhd.touchevent.MyButton
            android:id="@+id/my_btn"
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:text="button"
            android:layout_below="@id/my_tv"/>

    </com.lhd.touchevent.MyRelativeLayout>

</android.support.constraint.ConstraintLayout>

MainActivity:

public class MainActivity extends Activity {

    static final String tag = "MainActivity";

    MyButton myButton;

    MyTextView myTextView;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        myTextView = (MyTextView) findViewById(R.id.my_tv);
        myButton = (MyButton) findViewById(R.id.my_btn);
        myTextView.setClickable(true);
        myButton.setOnTouchListener(new View.OnTouchListener() {
            @Override
            public boolean onTouch(View v, MotionEvent event) {
                Log.d(tag, "myButton onTouch:" + event);
                return false;
            }
        });
        myTextView.setOnTouchListener(new View.OnTouchListener() {
            @Override
            public boolean onTouch(View v, MotionEvent event) {
                Log.d(tag, "myTextView onTouch:" + event);
                return false;
            }
        });
        Log.d(tag, "tv:" + myTextView.isClickable());
        Log.d(tag, "btn:" + myButton.isClickable());
    }

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

    @Override
    public boolean dispatchTouchEvent(MotionEvent ev) {
        Log.d(tag, "dispatchTouchEvent:" + ev);
        boolean touch = super.dispatchTouchEvent(ev);
        Log.d(tag, "dispatchTouchEvent:" + touch);
        return touch;
    }
}

MyRelativeLayout:

public class MyRelativeLayout extends RelativeLayout {

    static final String tag = "MyRelativeLayout";

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

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

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

    @RequiresApi(api = Build.VERSION_CODES.LOLLIPOP)
    public MyRelativeLayout(Context context, AttributeSet attrs, int defStyleAttr, int defStyleRes) {
        super(context, attrs, defStyleAttr, defStyleRes);
    }

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

    @Override
    public boolean onInterceptTouchEvent(MotionEvent ev) {
        Log.d(tag, "onInterceptTouchEvent:" + ev.toString());
        boolean touch = super.onInterceptTouchEvent(ev);
        Log.d(tag, "onInterceptTouchEvent:" + touch);
        return touch;
    }

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

    @Override
    public void requestDisallowInterceptTouchEvent(boolean disallowIntercept) {
        Log.d(tag, "requestDisallowInterceptTouchEvent");
        super.requestDisallowInterceptTouchEvent(disallowIntercept);
    }
}

MyTextView:

public class MyTextView extends android.support.v7.widget.AppCompatTextView {

    static final String tag = "MyTextView";

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

    public MyTextView(Context context, @Nullable AttributeSet attrs) {
        super(context, attrs);
    }

    public MyTextView(Context context, @Nullable AttributeSet attrs, int defStyleAttr) {
        super(context, attrs, defStyleAttr);
    }

    @Override
    public boolean dispatchTouchEvent(MotionEvent event) {
        Log.d(tag, "dispatchTouchEvent:" + event);
        return super.dispatchTouchEvent(event);
    }

    @Override
    public boolean onTouchEvent(MotionEvent event) {
        Log.d(tag, "onTouchEvent:" + event);
        boolean touch = super.onTouchEvent(event);
        Log.d(tag, "touch:" + touch);
        return touch;
    }

    @Override
    public boolean isClickable() {
        return super.isClickable();
    }
}

MyButton:

public class MyButton extends android.support.v7.widget.AppCompatButton {

    static final String tag = "MyButton";

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

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

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

    @Override
    public boolean dispatchTouchEvent(MotionEvent event) {
        Log.d(tag, "dispatchTouchEvent:" + event);
        return super.dispatchTouchEvent(event);
    }

    @Override
    public boolean onTouchEvent(MotionEvent event) {
        Log.d(tag, "onTouchEvent:" + event);
        boolean touch = super.onTouchEvent(event);
        Log.d(tag, "touch:" + touch);
        return touch;
    }

    @Override
    public boolean isClickable() {
        return super.isClickable();
    }
}

点击TextView的ACTION_DOWN和ACTION_UP的传递结果打印:

12-06 00:10:27.258 13203-13203/? D/MainActivity: dispatchTouchEvent:MotionEvent { action=ACTION_DOWN, actionButton=0, id[0]=0, x[0]=185.09766, y[0]=105.0, toolType[0]=TOOL_TYPE_FINGER, buttonState=0, metaState=0, flags=0x0, edgeFlags=0x0, pointerCount=1, historySize=0, eventTime=51416868, downTime=51416868, deviceId=0, source=0x1002 }
12-06 00:10:27.258 13203-13203/? D/MyRelativeLayout: dispatchTouchEvent:MotionEvent { action=ACTION_DOWN, actionButton=0, id[0]=0, x[0]=185.09766, y[0]=21.0, toolType[0]=TOOL_TYPE_FINGER, buttonState=0, metaState=0, flags=0x0, edgeFlags=0x0, pointerCount=1, historySize=0, eventTime=51416868, downTime=51416868, deviceId=0, source=0x1002 }
12-06 00:10:27.258 13203-13203/? D/MyRelativeLayout: onInterceptTouchEvent:MotionEvent { action=ACTION_DOWN, actionButton=0, id[0]=0, x[0]=185.09766, y[0]=21.0, toolType[0]=TOOL_TYPE_FINGER, buttonState=0, metaState=0, flags=0x0, edgeFlags=0x0, pointerCount=1, historySize=0, eventTime=51416868, downTime=51416868, deviceId=0, source=0x1002 }
12-06 00:10:27.258 13203-13203/? D/MyRelativeLayout: onInterceptTouchEvent:false
12-06 00:10:27.258 13203-13203/? D/MyTextView: dispatchTouchEvent:MotionEvent { action=ACTION_DOWN, actionButton=0, id[0]=0, x[0]=185.09766, y[0]=21.0, toolType[0]=TOOL_TYPE_FINGER, buttonState=0, metaState=0, flags=0x0, edgeFlags=0x0, pointerCount=1, historySize=0, eventTime=51416868, downTime=51416868, deviceId=0, source=0x1002 }
12-06 00:10:27.258 13203-13203/? D/MainActivity: myTextView onTouch:MotionEvent { action=ACTION_DOWN, actionButton=0, id[0]=0, x[0]=185.09766, y[0]=21.0, toolType[0]=TOOL_TYPE_FINGER, buttonState=0, metaState=0, flags=0x0, edgeFlags=0x0, pointerCount=1, historySize=0, eventTime=51416868, downTime=51416868, deviceId=0, source=0x1002 }
12-06 00:10:27.259 13203-13203/? D/MyTextView: onTouchEvent:MotionEvent { action=ACTION_DOWN, actionButton=0, id[0]=0, x[0]=185.09766, y[0]=21.0, toolType[0]=TOOL_TYPE_FINGER, buttonState=0, metaState=0, flags=0x0, edgeFlags=0x0, pointerCount=1, historySize=0, eventTime=51416868, downTime=51416868, deviceId=0, source=0x1002 }
12-06 00:10:27.259 13203-13203/? D/MyTextView: touch:false
12-06 00:10:27.259 13203-13203/? D/MyRelativeLayout: onTouchEvent:MotionEvent { action=ACTION_DOWN, actionButton=0, id[0]=0, x[0]=185.09766, y[0]=21.0, toolType[0]=TOOL_TYPE_FINGER, buttonState=0, metaState=0, flags=0x0, edgeFlags=0x0, pointerCount=1, historySize=0, eventTime=51416868, downTime=51416868, deviceId=0, source=0x1002 }
12-06 00:10:27.259 13203-13203/? D/MainActivity: onTouchEvent:MotionEvent { action=ACTION_DOWN, actionButton=0, id[0]=0, x[0]=185.09766, y[0]=105.0, toolType[0]=TOOL_TYPE_FINGER, buttonState=0, metaState=0, flags=0x0, edgeFlags=0x0, pointerCount=1, historySize=0, eventTime=51416868, downTime=51416868, deviceId=0, source=0x1002 }
12-06 00:10:27.259 13203-13203/? D/MainActivity: dispatchTouchEvent:false
12-06 00:10:27.361 13203-13203/? D/MainActivity: dispatchTouchEvent:MotionEvent { action=ACTION_UP, actionButton=0, id[0]=0, x[0]=185.09766, y[0]=105.0, toolType[0]=TOOL_TYPE_FINGER, buttonState=0, metaState=0, flags=0x0, edgeFlags=0x0, pointerCount=1, historySize=0, eventTime=51416972, downTime=51416868, deviceId=0, source=0x1002 }
12-06 00:10:27.361 13203-13203/? D/MainActivity: onTouchEvent:MotionEvent { action=ACTION_UP, actionButton=0, id[0]=0, x[0]=185.09766, y[0]=105.0, toolType[0]=TOOL_TYPE_FINGER, buttonState=0, metaState=0, flags=0x0, edgeFlags=0x0, pointerCount=1, historySize=0, eventTime=51416972, downTime=51416868, deviceId=0, source=0x1002 }
12-06 00:10:27.361 13203-13203/? D/MainActivity: dispatchTouchEvent:false

日志打印中MyTextView: touch:false是MyTextView的onTouchEvent方法里面打印的:

@Override
    public boolean onTouchEvent(MotionEvent event) {
        Log.d(tag, "onTouchEvent:" + event);
        boolean touch = super.onTouchEvent(event);
        Log.d(tag, "touch:" + touch);
        return touch;
    }

而ACTION_UP确实只打印了MainActivity级别的,MainActivity以下的就没打印了,ACTION_UP是只传到了DecorView这一层,大家可以通过打断点的方式跟进DecorView的dispatchTouchEvent,而点击Button后ACTION_DOWN与ACTION_UP的传递:

12-06 00:16:39.884 13203-13203/com.lhd.touchevent D/MainActivity: dispatchTouchEvent:MotionEvent { action=ACTION_DOWN, actionButton=0, id[0]=0, x[0]=205.09277, y[0]=220.07812, toolType[0]=TOOL_TYPE_FINGER, buttonState=0, metaState=0, flags=0x0, edgeFlags=0x0, pointerCount=1, historySize=0, eventTime=51789495, downTime=51789495, deviceId=0, source=0x1002 }
12-06 00:16:39.884 13203-13203/com.lhd.touchevent D/MyRelativeLayout: dispatchTouchEvent:MotionEvent { action=ACTION_DOWN, actionButton=0, id[0]=0, x[0]=205.09277, y[0]=136.07812, toolType[0]=TOOL_TYPE_FINGER, buttonState=0, metaState=0, flags=0x0, edgeFlags=0x0, pointerCount=1, historySize=0, eventTime=51789495, downTime=51789495, deviceId=0, source=0x1002 }
12-06 00:16:39.884 13203-13203/com.lhd.touchevent D/MyRelativeLayout: onInterceptTouchEvent:MotionEvent { action=ACTION_DOWN, actionButton=0, id[0]=0, x[0]=205.09277, y[0]=136.07812, toolType[0]=TOOL_TYPE_FINGER, buttonState=0, metaState=0, flags=0x0, edgeFlags=0x0, pointerCount=1, historySize=0, eventTime=51789495, downTime=51789495, deviceId=0, source=0x1002 }
12-06 00:16:39.884 13203-13203/com.lhd.touchevent D/MyRelativeLayout: onInterceptTouchEvent:false
12-06 00:16:39.884 13203-13203/com.lhd.touchevent D/MyButton: dispatchTouchEvent:MotionEvent { action=ACTION_DOWN, actionButton=0, id[0]=0, x[0]=205.09277, y[0]=70.078125, toolType[0]=TOOL_TYPE_FINGER, buttonState=0, metaState=0, flags=0x0, edgeFlags=0x0, pointerCount=1, historySize=0, eventTime=51789495, downTime=51789495, deviceId=0, source=0x1002 }
12-06 00:16:39.885 13203-13203/com.lhd.touchevent D/MainActivity: myButton onTouch:MotionEvent { action=ACTION_DOWN, actionButton=0, id[0]=0, x[0]=205.09277, y[0]=70.078125, toolType[0]=TOOL_TYPE_FINGER, buttonState=0, metaState=0, flags=0x0, edgeFlags=0x0, pointerCount=1, historySize=0, eventTime=51789495, downTime=51789495, deviceId=0, source=0x1002 }
12-06 00:16:39.885 13203-13203/com.lhd.touchevent D/MyButton: onTouchEvent:MotionEvent { action=ACTION_DOWN, actionButton=0, id[0]=0, x[0]=205.09277, y[0]=70.078125, toolType[0]=TOOL_TYPE_FINGER, buttonState=0, metaState=0, flags=0x0, edgeFlags=0x0, pointerCount=1, historySize=0, eventTime=51789495, downTime=51789495, deviceId=0, source=0x1002 }
12-06 00:16:39.885 13203-13203/com.lhd.touchevent D/MyButton: touch:true
12-06 00:16:39.885 13203-13203/com.lhd.touchevent D/MainActivity: dispatchTouchEvent:true
12-06 00:16:40.004 13203-13203/com.lhd.touchevent D/MainActivity: dispatchTouchEvent:MotionEvent { action=ACTION_UP, actionButton=0, id[0]=0, x[0]=205.09277, y[0]=220.07812, toolType[0]=TOOL_TYPE_FINGER, buttonState=0, metaState=0, flags=0x0, edgeFlags=0x0, pointerCount=1, historySize=0, eventTime=51789615, downTime=51789495, deviceId=0, source=0x1002 }
12-06 00:16:40.004 13203-13203/com.lhd.touchevent D/MyRelativeLayout: dispatchTouchEvent:MotionEvent { action=ACTION_UP, actionButton=0, id[0]=0, x[0]=205.09277, y[0]=136.07812, toolType[0]=TOOL_TYPE_FINGER, buttonState=0, metaState=0, flags=0x0, edgeFlags=0x0, pointerCount=1, historySize=0, eventTime=51789615, downTime=51789495, deviceId=0, source=0x1002 }
12-06 00:16:40.004 13203-13203/com.lhd.touchevent D/MyRelativeLayout: onInterceptTouchEvent:MotionEvent { action=ACTION_UP, actionButton=0, id[0]=0, x[0]=205.09277, y[0]=136.07812, toolType[0]=TOOL_TYPE_FINGER, buttonState=0, metaState=0, flags=0x0, edgeFlags=0x0, pointerCount=1, historySize=0, eventTime=51789615, downTime=51789495, deviceId=0, source=0x1002 }
12-06 00:16:40.004 13203-13203/com.lhd.touchevent D/MyRelativeLayout: onInterceptTouchEvent:false
12-06 00:16:40.004 13203-13203/com.lhd.touchevent D/MyButton: dispatchTouchEvent:MotionEvent { action=ACTION_UP, actionButton=0, id[0]=0, x[0]=205.09277, y[0]=70.078125, toolType[0]=TOOL_TYPE_FINGER, buttonState=0, metaState=0, flags=0x0, edgeFlags=0x0, pointerCount=1, historySize=0, eventTime=51789615, downTime=51789495, deviceId=0, source=0x1002 }
12-06 00:16:40.005 13203-13203/com.lhd.touchevent D/MainActivity: myButton onTouch:MotionEvent { action=ACTION_UP, actionButton=0, id[0]=0, x[0]=205.09277, y[0]=70.078125, toolType[0]=TOOL_TYPE_FINGER, buttonState=0, metaState=0, flags=0x0, edgeFlags=0x0, pointerCount=1, historySize=0, eventTime=51789615, downTime=51789495, deviceId=0, source=0x1002 }
12-06 00:16:40.005 13203-13203/com.lhd.touchevent D/MyButton: onTouchEvent:MotionEvent { action=ACTION_UP, actionButton=0, id[0]=0, x[0]=205.09277, y[0]=70.078125, toolType[0]=TOOL_TYPE_FINGER, buttonState=0, metaState=0, flags=0x0, edgeFlags=0x0, pointerCount=1, historySize=0, eventTime=51789615, downTime=51789495, deviceId=0, source=0x1002 }
12-06 00:16:40.005 13203-13203/com.lhd.touchevent D/MyButton: touch:true
12-06 00:16:40.005 13203-13203/com.lhd.touchevent D/MainActivity: dispatchTouchEvent:true

MyButton: touch:true,这是MyButton的onTouchEvent里面的打印,而ACTION_UP确实有被MyButton以及MyRelativeLayout收到,日志证实了我们上面基于源码的分析是正确的

总结

  • 事件触摸机制的几个重要的方法:
  1. ViewGroup中的dispatchTouchEvent方法,负责把事件分发给子View,如果没有子View,就自己处理了
  2. ViewGroup的onInterceptTouchEvent方法,是否拦截触摸事件,控制触摸事件的流向,true表示拦截事件,false表示不拦截
  3. ViewGroup的requestDisallowInterceptTouchEvent方法控制onInterceptTouchEvent是否可以拦截,如果requestDisallowInterceptTouchEvent传进去的方法参数disallowIntercept为true表示不允许拦截,false表示允许拦截
  4. View的dispatchTouchEvent负责把触摸事件进行处理,这里已经是触摸事件传递的终点了,不会再往下传递了,里面回去触发OnTouchListener,onTouchEvent,注意OnTouchListener会比onTouchEvent先触发,如果OnTouchListener返回true,那么事件就会被消费掉,onTouchEvent将不会被触发,对于View来说还有OnClickListener和OnLongClickListener事件,这些都是在onTouchEvent中在ACTION_UP来的时候处理判断的,因此如果OnTouchListener这里把触摸事件拦截了,那OnClickListener和OnLongClickListener事件将无法触发到

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