引言

Android 事件详细总结。

该文章基于android-28，仅分析Framework java层代码逻辑，仅供参考，不敢保证百分百正确无误。

一、Android 事件分发概述

一般说来当用户触摸屏幕或者按键操作，首次触发的是底层硬件驱动，驱动收到事件后并将该相应事件写入到输入设备节点， 便产生最原生态的内核事件。接着，输入（Input）系统取出原生态的事件再经过层层封装后成为KeyEvent或者MotionEvent ，最后交付给相应的目标窗口(Window)来消费该输入事件。其中Input模块的主要组成有：

• Native层的InputReader负责从EventHub取出事件并处理，再交给InputDispatcher；
• Native层的InputDispatcher接收来自InputReader的输入事件，并记录WMS（WindowManagerService）的窗口信息，用于派发事件到合适的窗口；
• Java层的InputManagerService跟WMS交互，WMS记录所有窗口信息，并同步更新到IMS，为InputDispatcher正确派发事件到ViewRootImpl提供保障。

简而言之，Android 中事件传递按照从上到下进行层级传递，事件处理从 Activity 开始到 ViewGroup 再到 View。事件传递方法包括dispatchTouchEvent、onTouchEvent、onInterceptTouchEvent，其中前两个是 View 和 ViewGroup 都有的，最后一个是只有 ViewGroup 才有的方法。其中onTouch 方法要先于 onClick 触发执行，onTouch 在 dispatchTouchEvent 中被调用，而 onClick 在 onTouchEvent 方法中被调用，因此onTouchEvent 要后于 dispatchTouchEvent 方法的调用。

二、Touch事件分发的对象MotionEvent

MotionEvent 继承自InputEvent并实现Parcelable接口，作为事件分发机制的核心对象，在Android中当用户触摸屏幕上的View 或 ViewGroup（及其子View），将产生点击事件（Touch事件）并根据Touch事件的发生时触摸的位置、时间、类型等相关细节封装不同类型的MotionEvent对象进行传递，该对象用于记录所有与移动相关的事件信息（事件分发和处理由Activity去调用native层完成），比较典型的有以上四种：

事件ACTION	触发场景	单次事件流中触发的次数
MotionEvent.ACTION_DOWN	在屏幕被按下时（所有事件的源头）	1次
MotionEvent.ACTION_MOVE	在屏幕上进行滑动时	0次或者多次
MotionEvent.ACTION_UP	从屏幕上抬起时	0次或者1次
MotionEvent.ACTION_CANCEL	结束事件（非人为原因）	0或者1次

所以一次完整的MotionEvent事件，是从用户触摸屏幕到离开屏幕。整个过程的动作序列：ACTION_DOWN(1次) —> ACTION_MOVE(N次) -> ACTION_UP(1次)。

而对于多点触摸，每一个触摸点Pointer会有一个id和index。对于多指操作，通过pointerindex来获取指定Pointer的触屏位置。比如单点操作时通过getX()获取x坐标，而多点操作时通过getX(pointerindex)获取x坐标。

MotionEvent 还有很多的ACTION类型，MotionEvent需要继承native 层InputEvent（其实是内核层的Input机制），因为Android Framework 通过JNI 进行处理，同时需要跨进程因而MotionEvent实现了Parcelable序列化接口。

三、分发事件的核心对象及方法

1、分发事件的核心对象

• Activity——作为Android四大基本组件之一，当手指触摸到屏幕时，屏幕硬件逐行不断地扫描每个像素点，获取到触摸事件后，从底层产生中断上报。再通过native层调用Java层InputEventReceiver中的dispatchInputEvent方法。最后经过层层调用交由Activity的dispatchTouchEvent方法来处理。

• View——作为所有视图对象的父类，实现了Drawable.Callback（动画相关的接口）、KeyEvent.Callback（按键相关的接口）和AccessibilityEventSource（交互相关的接口）。

• ViewGroup——ViewGroup是一个继承了View并实现了ViewParent（用于与父视图交互的接口）， ViewManager（用于添加、删除、更新子视图到Activity的接口）的抽象类，作为盛放其他View的容器，可以包含View和ViewGroup，是所有布局的父类或间接父类。

2、事件分发的核心方法

Touch事件都源自按下屏幕里Activity中的View或者ViewGroup（及其子View），所以事件的处理都是由Activity、View或ViewGroup对象完成的，换言之，只在Activity、View或ViewGroup里拥有处理事件系列方法如下表所示：

从源码中可以得知在Activity、 ViewGroup 和View中都存在 dispatchTouchEvent 和 onTouchEvent 方法（但是在 ViewGroup 中还有一个 onInterceptTouchEvent 方法），他们都接受了一个MotionEvent类型的参数用于标记各种动作事件且返回值都是boolean型，true则代表不往下传递，false则表示继续往下传递，那么这些方法有何功能的呢？

• boolean dispatchTouchEvent(MotionEvent event)——负责Touch事件的分发，Android 中所有的事件都必须经过此方法的分发，然后决定是自身消费当前事件还是继续往下分发给子View返回 true 则表示不继续分发，反之返回 false 则继续往下分发；而如果ViewGroup 则是先分发给 onInterceptTouchEvent 进行判断是否拦截该事件。

• boolean onTouchEvent(MotionEvent event)—— 负责Touch事件的处理，返回 true 则表示消费当前事件，反之返回 false 则不处理交给子View继续进行分发。

• boolean onInterceptTouchEvent(MotionEvent event)—— 负责Touch事件的拦截 返回 true 则表示拦截当前事件就不继续往下分发，交给自身的 onTouchEvent 进行处理；而返回 false 则不拦截，继续往下传。这是 ViewGroup 特有的方法，因为 ViewGroup 作为容器可以存放其他子 View，而View 则不能，换言之，只有 ViewGroup才有拦截事件的能力。

事件分发的核心流程都是围绕这些方法进行的，由不同的对象直接或者间接调用进行处理。

四、Touch事件分发的流程

事件分发有多种类型, 以下是Touch相关的事件分发大致流程：
Activity——>Window（PhoneWindow）——>DecorView——>ViewGroup——>View。

1、Activity的事件处理流程

事件的分发是由Activity开始的，当用户点击屏幕的时候首先接触到的就是Activity，从而触发Activity#dispatchTouchEvent方法，

    /**
     * android.app.Activity#dispatchTouchEvent
     * Called to process touch screen events.  You can override this to
     * intercept all touch screen events before they are dispatched to the
     * window.  Be sure to call this implementation for touch screen events
     * that should be handled normally.
     * @param ev The touch screen event.
     * @return boolean Return true if this event was consumed.
     */
    public boolean dispatchTouchEvent(MotionEvent ev) {
		//如果是DOWN类型则说明是一个全新的事件
        if (ev.getAction() == MotionEvent.ACTION_DOWN) {
			//默认为空实现，可以被重写，如果你想要知道用户已经与Activity进行交互
            onUserInteraction();
        }
		//调用Window的dispatchTouchEvent方法,并把事件分发至PhoneWindow（获取当前Activity的顶层窗口是PhoneWindow），返回false表示当前事件没有被消费。
        if (getWindow().superDispatchTouchEvent(ev)) {
            return true;
        }
        //如果PhoneWindow消费了事件则把事件分发至Activity的onTouchEvent
        return onTouchEvent(ev);
    }

Activity#dispatchTouchEvent返回结果之前，会先分发到ViewGroup&View，而最终的执行分为两个分支（抛开中间细节）：

• getWindow().superDispatchTouchEvent(ev)返回flase时，代表当前事件没有被Activity中的任何View或者ViewGroup处理（即DecorView #dispatchTouchEvent方法返回false），则此次事件最终是由Activity#onTouchEvent 去处理的。

    /**
     *	android.app.Activity#onTouchEvent
     * Called when a touch screen event was not handled by any of the views
     * under it.  This is most useful to process touch events that happen
     * outside of your window bounds, where there is no view to receive it.
     * @param event The touch screen event being processed.
     * @return Return true if you have consumed the event, false if you haven't.
     * The default implementation always returns false.
     */
    public boolean onTouchEvent(MotionEvent event) {
	    //判断是否屏幕出界，比如说点击到屏幕的非有效区域时，当窗口需要关闭时，消费掉当前event
        if (mWindow.shouldCloseOnTouch(this, event)) {
            finish();
            return true;
        }
        return false;
    }

• getWindow().superDispatchTouchEvent(ev)返回true时，代表事件已被Activity中的View或者ViewGroup消费了。

再回到分发流程，Activity#dispatchTouchEvent执行后，接着会通过getWindow()方法得到当前Activity的顶层窗口（即PhoneWindow）并调用它的superDispatchTouchEvent方法把事件分发到PhoneWindow，执行PhoneWindow#superDispatchTouchEvent方法传入到DecorView（根ViewGroup）…

DecorView继承自 FrameLayout 并实现了RootViewSurfaceTaker和WindowCallbacks接口，是当前界面的最外（顶）层容器，即setContentView方法所设置的View的父容器根ViewGroup。

//com.android.internal.policy.PhoneWindow#superDispatchTouchEvent
@Override
public boolean superDispatchTouchEvent(MotionEvent event) {
	//分发至DecorView
    return mDecor.superDispatchTouchEvent(event);
}

分发到DecorView，再通过DecorView#superDispatchTouchEvent方法

//com.android.internal.policy.DecorView#superDispatchTouchEvent
public boolean superDispatchTouchEvent(MotionEvent event) {
   return super.dispatchTouchEvent(event);//实际上调用的是ViewGroup#dispatchTouchEvent
}

接下来分发到了ViewGroup中，ViewGroup的分发流程比较复杂，篇幅有限会省略部分逻辑。

2、ViewGroup&View的事件分发流程

ViewGroup&View的事件分发流程的起点是从PhoneWindow#superDispatchTouchEvent开始的，首先分发至根ViewGroup（DecorView）并执行ViewGroup#dispatchTouchEvent方法。

//android.view.ViewGroup#dispatchTouchEvent
public boolean dispatchTouchEvent(MotionEvent ev) {
    //辅助功能跨进程调用，是当前应用与系统层进行交互的，模拟的点击事件
    if (mInputEventConsistencyVerifier != null) {
        mInputEventConsistencyVerifier.onTouchEvent(ev, 1);
    }
	...
	//是否消费了当前事件的标识，最终的返回值
    boolean handled = false;
    //根据隐私策略而来决定是否过滤本次触摸事件,相当于是检测当前事件，功能类似检测操作UI时是否在主线程中
    if (onFilterTouchEventForSecurity(ev)) {
        final int action = ev.getAction();
        final int actionMasked = action & MotionEvent.ACTION_MASK;

        if (actionMasked == MotionEvent.ACTION_DOWN) {
            // 发生ACTION_DOWN事件, 则取消并清除之前所有的触摸targets，可能是由于App切换、ANR或者其他原因抛弃了上一次的UP或者CANCEL，需要取消并移除所有目标
            cancelAndClearTouchTargets(ev);
            resetTouchState(); // 重置触摸状态为下一次循环做准备
        }

        // 发生ACTION_DOWN事件或者已经发生过ACTION_DOWN;才进入此区域，主要功能是拦截器
        //第一次触摸屏幕时是DOWN，只有发生过ACTION_DOWN事件，则mFirstTouchTarget != null;
        final boolean intercepted;
        if (actionMasked == MotionEvent.ACTION_DOWN
                || mFirstTouchTarget != null) {
            //可以通过在其子View中去调用父ViewGroup的requestDisallowInterceptTouchEvent方法设置是否允许拦截，让父View是否拦截事件
            final boolean disallowIntercept = (mGroupFlags & FLAG_DISALLOW_INTERCEPT) != 0;
            //判断是否允许调用拦截器
            if (!disallowIntercept) {
                //！！调用拦截逻辑的方法！！
                intercepted = onInterceptTouchEvent(ev);
                ev.setAction(action);
            } else {
                intercepted = false;
            }
        } else {
            // 当没有触摸targets，且不是down事件时，开始持续拦截触摸。
            intercepted = true;
        }
        ...

        //不取消事件，同时不拦截事件, 并且是Down事件时
        if (!canceled && !intercepted) {
            //把事件分发给所有的子视图，寻找可以获取焦点的视图。
            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(); // down事件等于0
                final int idBitsToAssign = split ? 1 << ev.getPointerId(actionIndex)
                        : TouchTarget.ALL_POINTER_IDS;

                removePointersFromTouchTargets(idBitsToAssign); //清空早先的触摸对象

                final int childrenCount = mChildrenCount;
                //第一次down事件，同时子视图不会空时
                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.
					//创建可以接收事件的子View，并按照z轴值对子View进行排序，因为子View可能存在相互重叠的部分，从顶层到底层排序
                    final ArrayList<View> preorderedList = buildTouchDispatchChildList();
                    final boolean customOrder = preorderedList == null
                            && isChildrenDrawingOrderEnabled();
					//当前ViewGroup 中所有的子View数组
                    final View[] children = mChildren;

                    /* 倒序遍历，从底层到顶层，从最底层的父视图开始遍历， ** 找寻newTouchTarget，并赋予view与 pointerIdBits； ** 如果已经存在找寻newTouchTarget，说明正在接收触摸事件，则跳出循环。 */
                    for (int i = childrenCount - 1; i >= 0; i--) {
                         final int childIndex = getAndVerifyPreorderedIndex(
                                childrenCount, i, customOrder);
						//获取当前ViewGroup中的子View
                        final View child = getAndVerifyPreorderedView(
                                preorderedList, children, childIndex);

                        // 如果当前视图无法获取用户焦点，则跳过本次循环
                        if (childWithAccessibilityFocus != null) {
                            if (childWithAccessibilityFocus != child) {
                                continue;
                            }
                            childWithAccessibilityFocus = null;
                            i = childrenCount - 1;
                        }
                        //如果view不可见或正在执行动画，或者触摸的坐标点不在view的范围内，则跳过本次循环
                        if (!canViewReceivePointerEvents(child)
                                || !isTransformedTouchPointInView(x, y, child, null)) {
                            ev.setTargetAccessibilityFocus(false);
                            continue;
                        }
						//获取当前的View的包装对象
                        newTouchTarget = getTouchTarget(child);
                        // 已经开始接收触摸事件,并退出整个循环。
                        if (newTouchTarget != null) {
                            newTouchTarget.pointerIdBits |= idBitsToAssign;
                            break;
                        }

                        //重置取消或抬起标志位
						resetCancelNextUpFlag(child);
                        //如果触摸位置在child的区域内，则把事件分发给子View或ViewGroup，开始事件分发，child为null时传递到View#dispatchTouchEvent,而child不为null时则调用child自身的dispatchTouchEvent
                        if (dispatchTransformedTouchEvent(ev, false, child, idBitsToAssign)) { // [见小节2.4.4]
                            // 获取TouchDown的时间点
                            mLastTouchDownTime = ev.getDownTime();
                            // 获取TouchDown的Index
                            if (preorderedList != null) {
                                for (int j = 0; j < childrenCount; j++) {
                                    if (children[childIndex] == mChildren[j]) {
                                        mLastTouchDownIndex = j;
                                        break;
                                    }
                                }
                            } else {
                                mLastTouchDownIndex = childIndex;
                            }

                            //获取TouchDown的x,y坐标
                            mLastTouchDownX = ev.getX();
                            mLastTouchDownY = ev.getY();
                            //添加TouchTarget,则mFirstTouchTarget != null，给mFirstTouchTarget赋值
                            newTouchTarget = addTouchTarget(child, idBitsToAssign);
                            //表示以及分发给NewTouchTarget
                            alreadyDispatchedToNewTouchTarget = true;
                            break;
                        }
                        ev.setTargetAccessibilityFocus(false);
                    }
                    // 清除视图列表
                    if (preorderedList != null) preorderedList.clear();
                }

                if (newTouchTarget == null && mFirstTouchTarget != null) {
                    //将mFirstTouchTarget的链表最后的touchTarget赋给newTouchTarget
                    newTouchTarget = mFirstTouchTarget;
                    while (newTouchTarget.next != null) {
                        newTouchTarget = newTouchTarget.next;
                    }
                    newTouchTarget.pointerIdBits |= idBitsToAssign;
                }
            }
        }///#endif  if (!canceled && !intercepted)
        
		//ViewGroup进行事件拦截之后直接越过前面的逻辑，执行到这里，mFirstTouchTarget赋值是在通过addTouchTarget方法获取的；
        // 只有处理ACTION_DOWN事件，才会进入addTouchTarget方法。这也正是当View没有消费ACTION_DOWN事件，则不会接收其他MOVE,UP等事件的原
        if (mFirstTouchTarget == null) {
            //没有触摸target,则由当前ViewGroup来处理
            handled = dispatchTransformedTouchEvent(ev, canceled, null,
                    TouchTarget.ALL_POINTER_IDS);
        } else {
            //如果View消费ACTION_DOWN事件，那么MOVE,UP等事件相继开始执行
            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;
            }
        }

        //当发生抬起或取消事件，更新触摸targets
        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);
        }
    } //此处大括号，是if (onFilterTouchEventForSecurity(ev))的结尾

    //通知verifier由于当前时间未处理，那么该事件其余的都将被忽略
    if (!handled && mInputEventConsistencyVerifier != null) {
        mInputEventConsistencyVerifier.onUnhandledEvent(ev, 1);
    }
    return handled;
}

在ViewGroup每次调用ViewGroup#dispatchTouchEvent方法时，当requestDisallowInterceptTouchEvent方法返回true时则说明允许事件拦截，就会先执行ViewGroup#onInterceptTouchEvent判断是否进行事件拦截，

    /**
     * Implement this method to intercept all touch screen motion events. 
     *
     * @param ev The motion event being dispatched down the hierarchy.
     * @return Return true to steal motion events from the children and have
     * them dispatched to this ViewGroup through onTouchEvent().
     * The current target will receive an ACTION_CANCEL event, and no further
     * messages will be delivered here.
     */
    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;
    }

返回true则进行拦截，就会越过 if (!canceled && !intercepted)分支，直接执行ViewGroup#dispatchTransformedTouchEvent方法

/**
 * Transforms a motion event into the coordinate space of a particular child view,
 * filters out irrelevant pointer ids, and overrides its action if necessary.
 * If child is null, assumes the MotionEvent will be sent to this ViewGroup instead.
* ViewGroup 真正分发事件的逻辑
* @param child null则调用View#dispatchTouchEvent;反之则调用child里的dispatchTouchEvent方法
 */
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) {
// 第一次触发Touch事件时执行到这里，去调用父类的dispatchTouchEvent
        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;
}

其核心逻辑取决于传入的child，当child =null则调用View#dispatchTouchEvent;反之则调用child自身（有可能是View或ViewGroup）的dispatchTouchEvent方法，假设调用的是View#dispatchTouchEvent方法

  /**
     * Pass the touch screen motion event down to the target view, or this view if it is the target.
     * @param event The motion event to be dispatched.
     * @return True if the event was handled by the view, false otherwise.
     */
    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);
        }
		//是否消费此事件标识，最终的返回值
        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;
            }
            //ListenerInfo（可从View#getListenerInfo方法获取）为所有View的事件监听封装类，包含了所有常见事件的监听接口
            ListenerInfo li = mListenerInfo;
			//如果外部调用了setOnTouchListener方法时，会先执行OnTouchListener#onTouch，当onTouch返回true时则不会执行View#onTouchEvent方法
            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;
    }

如果外部调用了setOnTouchListener方法时设置onTouchListener监听时，会先执行View$$OnTouchListener#onTouch，当OnTouchListener#onTouch返回true时则不会执行View#onTouchEvent方法;反之还会去调用View#onTouchEvent方法

/**
 * Implement this method to handle touch screen motion events.
 *
 * @param event The motion event.
 * @return True if the event was handled, false otherwise.
 */
public boolean onTouchEvent(MotionEvent event) {
    final float x = event.getX();
    final float y = event.getY();
    final int viewFlags = mViewFlags;
    final int action = event.getAction();
// 是否可点击的标志
    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) {
					//PerformClick实现了Runnable接口
                                mPerformClick = new PerformClick();
                            }
                            if (!post(mPerformClick)) {
					//在该方法内处理Click事件触发OnClickListener.onClick方法
                                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);
		//处理OnLongClickListener.onLongClick方法
                    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;
}

所以基本就是在View#onTouchEvent方法的处理onClickListener

private final class PerformClick implements Runnable {
    @Override
    public void run() {
        performClickInternal();
    }
}

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);
       //处理OnClickListener接口
       li.mOnClickListener.onClick(this);
       result = true;
   } else {
       result = false;
   }
   sendAccessibilityEvent(AccessibilityEvent.TYPE_VIEW_CLICKED);
   notifyEnterOrExitForAutoFillIfNeeded(true);
   return result;
}

onLongClickListener等其他监听接口也类似。

五、事件分发的应用

1、事件拦截

拦截事件可以通过两种形式：

• 继承ViewGroup或其子类重写onInterceptTouchEvent方法并返回true。

• 在子View中调用父ViewGroup的requestDisallowInterceptTouchEvent方法并返回true。

2、响应点击事件