深入浅出Android中的事件分发机制

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从输入硬件到Android窗口

这里直接从底层硬件分析到事件传递到View的流程,具体的调用链查看源码,这里是基于Android 10 的源码分析的.

主要流程如下:

输入设备产生信号,比如手触摸屏幕,触摸屏产生电流或者电压信号,传递给设备固件

设备固件对信号进行编码和处理,比如产生中断,比如发送USB HID报告

Linux内核驱动程序接收到信号,并按照input.h中定义的协议,将信号转换成事件

EventHub通过libevdev读取各个设备(如/dev/input/event4)的事件,并传递给InputReader

InputReader将事件封装成Android事件流,传递给InputDispatcher进行分发

InputDispatcher通过InputChannel与Java层的InputEventReceiver联系上,并调用它的方法进行事件分发

最终会进入到ViewRootImpl中,根据输入阶段不同,进行不同的处理,最终会调用到DecorView的dispatchTouchEvent()方法

再之后就是我们熟悉的View/ViewGroup事件分发流程了

View/ViewGroup事件分发

进入到DecorView中的dispatchTouchEvent(event)方法:


    @Override
    public boolean dispatchTouchEvent(MotionEvent ev) {
        // 这里的callback实现类有Activity,Dialog等,这里只分析Activity的
        final Window.Callback cb = mWindow.getCallback();
        return cb != null && !mWindow.isDestroyed() && mFeatureId < 0
                ? cb.dispatchTouchEvent(ev) : super.dispatchTouchEvent(ev);
    }

Activity中:


    public boolean dispatchTouchEvent(MotionEvent ev) {
        if (ev.getAction() == MotionEvent.ACTION_DOWN) {
            onUserInteraction();
        }
        // 调用window的事件分发
        if (getWindow().superDispatchTouchEvent(ev)) {
            return true;
        }
        return onTouchEvent(ev);
    }

Window的实现类是PhoneWindow中,因此:


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

DecorView中:


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

ViewGroup中:


    @Override
    public boolean dispatchTouchEvent(MotionEvent ev) {
        boolean handled = false;
        //如果window做了模糊处理,则不处理事件分发
        if (onFilterTouchEventForSecurity(ev)) {
            final int action = ev.getAction();
            final int actionMasked = action & MotionEvent.ACTION_MASK;

            // 重制状态
            if (actionMasked == MotionEvent.ACTION_DOWN) {
                cancelAndClearTouchTargets(ev);
                resetTouchState();
            }

            // 拦截处理
            final boolean intercepted;
            if (actionMasked == MotionEvent.ACTION_DOWN
                    || mFirstTouchTarget != null) {
                // View有方法可以设置
                final boolean disallowIntercept = (mGroupFlags & FLAG_DISALLOW_INTERCEPT) != 0;
                if (!disallowIntercept) {
                    // 关键点: 拦截
                    intercepted = onInterceptTouchEvent(ev);
                    ev.setAction(action); // restore action in case it was changed
                } else {
                    intercepted = false;
                }
            } else {
                // mFirstTouchTarget == null && action != ACTION_DOWN
                intercepted = true;
            }

            // 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;
            // 不是取消事件,也没有拦截
            if (!canceled && !intercepted) {
                if (actionMasked == MotionEvent.ACTION_DOWN
                        || (split && actionMasked == MotionEvent.ACTION_POINTER_DOWN)
                        || actionMasked == MotionEvent.ACTION_HOVER_MOVE) {

                    final int childrenCount = mChildrenCount;
                    if (newTouchTarget == null && childrenCount != 0) {
                        final float x = ev.getX(actionIndex);
                        final float y = ev.getY(actionIndex);
                        // 根据z重新排序子View
                        final ArrayList<View> preorderedList = buildTouchDispatchChildList();
                        final boolean customOrder = preorderedList == null
                                && isChildrenDrawingOrderEnabled();
                        final View[] children = mChildren;
                        for (int i = childrenCount - 1; i >= 0; i--) {
                            // 关键
                            if (dispatchTransformedTouchEvent(ev, false, child, idBitsToAssign)) {
                                // 为mFirstTouchTarget赋值
                                newTouchTarget = addTouchTarget(child, idBitsToAssign);
                                alreadyDispatchedToNewTouchTarget = true;
                                break;
                            }
                        }
                        if (preorderedList != null) preorderedList.clear();
                    }
                }
            }

            // Dispatch to touch targets.
            if (mFirstTouchTarget == null) {
               // 关键
                handled = dispatchTransformedTouchEvent(ev, canceled, null,
                        TouchTarget.ALL_POINTER_IDS);
            } else {

                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;
                        // 关键
                        if (dispatchTransformedTouchEvent(ev, cancelChild,
                                target.child, target.pointerIdBits)) {
                            handled = true;
                        }
                    }

                }
            }
        }

        return handled;
    }

这里会进行一些判断(比如触摸点是否在对应的View内,避免无效计算),然后:


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

        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);
                    // 关键
                    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) {
            // 关键
            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());
            }
            //关键
            handled = child.dispatchTouchEvent(transformedEvent);
        }

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

这里就将事件分发给子View了.

View#dispatchTouchEvent():


    public boolean dispatchTouchEvent(MotionEvent event) {
        boolean result = false;
        if (onFilterTouchEventForSecurity(event)) {
            if ((mViewFlags & ENABLED_MASK) == ENABLED && handleScrollBarDragging(event)) {
                result = true;
            }
            // 关键
            ListenerInfo li = mListenerInfo;
            if (li != null && li.mOnTouchListener != null
                    && (mViewFlags & ENABLED_MASK) == ENABLED
                    // OnTouchListener回调
                    && li.mOnTouchListener.onTouch(this, event)) {
                result = true;
            }
            // 如果OnTouchListener消耗了事件,则不会执行后面的onTouchEvent()
            if (!result && onTouchEvent(event)) {
                result = true;
            }
        }
        return result;
    }

这里可以看到OnTouchListener#onTouch() 优先级高于 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;

        // 关键
        if (mTouchDelegate != null) {
            if (mTouchDelegate.onTouchEvent(event)) {
                return true;
            }
        }

        if (clickable || (viewFlags & TOOLTIP) == TOOLTIP) {
            switch (action) {
                case MotionEvent.ACTION_UP:
                    boolean prepressed = (mPrivateFlags & PFLAG_PREPRESSED) != 0;
                    if ((mPrivateFlags & PFLAG_PRESSED) != 0 || prepressed) {
                        boolean focusTaken = false;
                        if (isFocusable() && isFocusableInTouchMode() && !isFocused()) {
                            focusTaken = requestFocus();
                        }
                        if (!mHasPerformedLongPress && !mIgnoreNextUpEvent) {
                            // This is a tap, so remove the longpress check
                            removeLongPressCallback();

                            // 处理点击事件
                            if (!focusTaken) {
                                if (mPerformClick == null) {
                                    // 一个Runnbale
                                    mPerformClick = new PerformClick();
                                }
                                if (!post(mPerformClick)) {
                                    //一般不会进入这个分支
                                    performClickInternal();
                                }
                            }
                        }
                        removeTapCallback();
                    }
                    mIgnoreNextUpEvent = false;
                    break;

                case MotionEvent.ACTION_DOWN:
                    mHasPerformedLongPress = false;

                    if (!clickable) {
                        // 处理长按点击事件
                        checkForLongClick(
                                ViewConfiguration.getLongPressTimeout(),
                                x,
                                y,
                                TOUCH_GESTURE_CLASSIFIED__CLASSIFICATION__LONG_PRESS);
                        break;
                    }
                    if (isInScrollingContainer) {
                        mPrivateFlags |= PFLAG_PREPRESSED;
                        // 检查点击事件
                        if (mPendingCheckForTap == null) {
                            mPendingCheckForTap = new CheckForTap();
                        }
                        mPendingCheckForTap.x = event.getX();
                        mPendingCheckForTap.y = event.getY();
                        postDelayed(mPendingCheckForTap, ViewConfiguration.getTapTimeout());
                    } else {
                        // 长按
                        setPressed(true, x, y);
                        checkForLongClick(
                                ViewConfiguration.getLongPressTimeout(),
                                x,
                                y,
                                TOUCH_GESTURE_CLASSIFIED__CLASSIFICATION__LONG_PRESS);
                    }
                    break;

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

                case MotionEvent.ACTION_MOVE:
                    if (ambiguousGesture && hasPendingLongPressCallback()) {
                        if (!pointInView(x, y, touchSlop)) {
                            removeLongPressCallback();
                            long delay = (long) (ViewConfiguration.getLongPressTimeout()
                                    * mAmbiguousGestureMultiplier);
                            // Subtract the time already spent
                            delay -= event.getEventTime() - event.getDownTime();
                            checkForLongClick(
                                    delay,
                                    x,
                                    y,
                                    TOUCH_GESTURE_CLASSIFIED__CLASSIFICATION__LONG_PRESS);
                        }
                        touchSlop *= mAmbiguousGestureMultiplier;
                    }
                    if (!pointInView(x, y, touchSlop)) {
                        // Outside button
                        // Remove any future long press/tap checks
                        removeTapCallback();
                        removeLongPressCallback();
                        if ((mPrivateFlags & PFLAG_PRESSED) != 0) {
                            setPressed(false);
                        }
                        mPrivateFlags3 &= ~PFLAG3_FINGER_DOWN;
                    }

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

                    break;
            }

            return true;
        }

        return false;
    }

View#onTouchEvent()中的逻辑也比较复杂,需要注意几个要点:

TouchDelegate具有很高的优先级,会最先进行判断,它是用来拓展View的可点击区域的(适合于View尺寸有限,但是需要扩大点击区域的场景)

点击事件和长安事件目前都封装成了Runnable,在DOWN,MOVE,UP,CANCEL等几种事件里都有逻辑,本质就是通过view的延时post方法,即Handler的延时发送来进行调度的

基本流程如下:

DecorView -> Activity -> Window ->ViewGroup#dispatchTouchEvent()

ViewGroup#onInterceptTouchEvent(ev),返回true,表示拦截,否则表示不拦截

如果不拦截,则调用dispatchTransformedTouchEvent(),child为null,则调用super.dispatchTouchEvent(),super是什么,是View,因此把当前ViewGroup当作View,并执行它的dispatchTouchEvent()方法;如果child不为null,则直接执行child的dispatchTouchEvent()方法,进入循环,遇到没有子View的时候执行View的dispatchTouchEvent()方法;

如果拦截,则调用自己的dispatchTransformedTouchEvent(),传入的child为null,因此会执行super.dispatchTouchEvent(),把自己当作View,执行View的dispatchTouchEvent()方法;

View#dispatchTouchEvent()方法中会执行onTouchEvent()方法;

到这里整个流程其实就走通了,唯一可能导致疑惑的地方其实就是ViewGroup如何调用自身的onTouchEvent(),其实这里记住一点即可:

ViewGroup的super就是View,View中才有默认实现的onTouchEvent().

优先级问题

从上面的源码分析可以看到:

OnTouchListener#onTouch() 大于 View#onTouchEvent() 大于 OnClickListener#onClick()

View#onTouchEvent()返回值问题

View如果消费了ACTION_DOWN,则后续的一系列ACTION都会传给这个View的onTouchEvent()来处理; View如果不消费ACTION_DOWN,则后续的一系列ACTION都不会交给它的onTouchEvent()处理;如果当前View和它的兄弟View都无法消费ACTION_DOWN,则会找它的父布局的onTouchEvent()去消费

所谓消费,指的就是View#onTouchEvent()的返回值,返回true,表示消费了,否则表示没消费

ViewGroup#onInterceptTouchEvent(ev)的问题


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 {
                intercepted = true;
            }

从dispatchTouchEvent()开始,一层层的调用,直到View#onTouchEvent(),返回值其实是ViewGroup#dispatchTouchEvent()最终使用的:

如果返回fasle,则不会为mFirstTouchTarget赋值,否则将child赋值给mFristTouchTarget.那这又影响了什么呢?

如果不调用API请求不拦截事件,则只有两种情况下的任意一种,才会触发拦截:

当前事件是ACTION_DOWN

mFirstTouchTarget != null (当前ViewGroup的所有子View的onTouchEvent()均返回false)

因此得出结论:

只有ViewGroup才有onInterceptTouchEvent(ev)方法

只要是ACTION_DOWN事件,ViewGroup都会执行onInterceptTouchEvent(ev)方法

如果不是ACTION_DOWN事件,则要判断该ViewGroup的所有子View中是否能消耗ACTION_DOWN事件,即子View中是否有onTouchEvent()返回为true,如果有,则还会执行onInterceptTouchEvent(ev)方法,如果一个都没有,则不会执行onInterceptTouchEvent(ev)方法

如果ViewGroup的onInterceptTouchEvent(ev)返回了true,则其子View一种事件都获取不到,因为不会执行子View的dispatchTouchEvent()方法,就算仅仅是拦截了ACTION_DOWN;如果不拦截ACTION_DOWN,而拦截ACTION_MOVE,则子View可以正常捕获到ACTION_DOWN,但是后面会主动执行一个ACTION_CANCEL,就不再接收其他事件了.

adb查看工具

getevent : 输出所有event设备的基本信息


130|cmi:/dev/input $ getevent
add device 1: /dev/input/event7
  name:     "kona-mtp-snd-card USB_3_5 Jack"   #声音
add device 2: /dev/input/event6
  name:     "kona-mtp-snd-card Button Jack"    #
add device 3: /dev/input/event5
  name:     "kona-mtp-snd-card Headset Jack"  #耳机
add device 4: /dev/input/event4
  name:     "fts"                             #触摸屏
add device 5: /dev/input/event1
  name:     "uinput-goodix"                   #指纹传感器
add device 6: /dev/input/event3               # 音量上按键
  name:     "gpio-keys"
add device 7: /dev/input/event0               #高通按键驱动
  name:     "qpnp_pon"
add device 8: /dev/input/event2
  name:     "aw8697_haptic"                  #电机驱动

此时如果触摸屏幕或者按键,会输出:


/dev/input/event4: 0003 0039 ffffffff

格式为: 设备名: 事件type 事件code 事件value (这里的数字是16进制的)

如果使用getevent -l,则会输出具体的常量名称,比较易于理解:


/dev/input/event4: EV_SYN       SYN_REPORT           00000000

这些常量是定义在sysroot/usr/include/linux/input.h中的.

sendevent: 模拟发送事件 (可能需要权限)

格式为:


sendevent DEVICE TYPE CODE VALUE

如:


sendevent /dev/input/event0 0001 0114 00000001

这里面的值是由16进制转换而成的10进制数.

getevent -p: 查看详细的交互设备信息

输出如下:


1|cmi:/dev/input $ getevent -p
add device 1: /dev/input/event7
  name:     "kona-mtp-snd-card USB_3_5 Jack"
  events:
    SW  (0005): 0002  0004  0013
  input props:
    <none>
add device 2: /dev/input/event6
  name:     "kona-mtp-snd-card Button Jack"
  events:
    KEY (0001): 00e2  0101  0102  0103  0104  0105
  input props:
    <none>
add device 3: /dev/input/event5
  name:     "kona-mtp-snd-card Headset Jack"
  events:
    SW  (0005): 0002  0004  0006  0007  0010  0011  0012  0013
  input props:
    <none>
add device 4: /dev/input/event4
  name:     "fts"
  events:
    KEY (0001): 0011  0012  0018  001a  001b  001f  0021  0026
                002c  002e  002f  0032  003b  003c  003d  003e
                003f  0067  0069  006a  006c  008f  0096  0145
                014a  0152  0162
    ABS (0003): 002f  : value 0, min 0, max 9, fuzz 0, flat 0, resolution 0
                0030  : value 0, min 0, max 1080, fuzz 0, flat 0, resolution 0
                0031  : value 0, min 0, max 2340, fuzz 0, flat 0, resolution 0
                0032  : value 0, min 0, max 127, fuzz 0, flat 0, resolution 0
                0033  : value 0, min 0, max 127, fuzz 0, flat 0, resolution 0
                0034  : value 0, min -90, max 90, fuzz 0, flat 0, resolution 0
                0035  : value 0, min 0, max 1079, fuzz 0, flat 0, resolution 0
                0036  : value 0, min 0, max 2339, fuzz 0, flat 0, resolution 0
                0039  : value 0, min 0, max 65535, fuzz 0, flat 0, resolution 0
                003b  : value 0, min 0, max 127, fuzz 0, flat 0, resolution 0
  input props:
    INPUT_PROP_DIRECT
add device 5: /dev/input/event1
  name:     "uinput-goodix"
  events:
    KEY (0001): 0066  0067  0069  006a  006c  0072  0073  0074
                008b  009e  00d4  00d8  00d9
  input props:
    <none>
add device 6: /dev/input/event3
  name:     "gpio-keys"
  events:
    KEY (0001): 0073
    SW  (0005): 0000
  input props:
    <none>
add device 7: /dev/input/event0
  name:     "qpnp_pon"
  events:
    KEY (0001): 0072  0074
  input props:
    <none>
add device 8: /dev/input/event2
  name:     "aw8697_haptic"
  events:
    FF  (0015): 0050  0051  0052  005d  0060
  input props:
    <none>

getevent -lp或者 getevent -lp /dev/input/event4 : 输出交互设备信息文字标签信息


add device 1: /dev/input/event4
  name:     "fts"
  events:
    KEY (0001): KEY_W                 KEY_E                 KEY_O                 KEY_LEFTBRACE
                KEY_RIGHTBRACE        KEY_S                 KEY_F                 KEY_L
                KEY_Z                 KEY_C                 KEY_V                 KEY_M
                KEY_F1                KEY_F2                KEY_F3                KEY_F4
                KEY_F5                KEY_UP                KEY_LEFT              KEY_RIGHT
                KEY_DOWN              KEY_WAKEUP            KEY_WWW               BTN_TOOL_FINGER
                BTN_TOUCH             0152                  KEY_GOTO
    ABS (0003): ABS_MT_SLOT           : value 0, min 0, max 9, fuzz 0, flat 0, resolution 0
                ABS_MT_TOUCH_MAJOR    : value 0, min 0, max 1080, fuzz 0, flat 0, resolution 0
                ABS_MT_TOUCH_MINOR    : value 0, min 0, max 2340, fuzz 0, flat 0, resolution 0
                ABS_MT_WIDTH_MAJOR    : value 0, min 0, max 127, fuzz 0, flat 0, resolution 0
                ABS_MT_WIDTH_MINOR    : value 0, min 0, max 127, fuzz 0, flat 0, resolution 0
                ABS_MT_ORIENTATION    : value 0, min -90, max 90, fuzz 0, flat 0, resolution 0
                ABS_MT_POSITION_X     : value 0, min 0, max 1079, fuzz 0, flat 0, resolution 0
                ABS_MT_POSITION_Y     : value 0, min 0, max 2339, fuzz 0, flat 0, resolution 0
                ABS_MT_TRACKING_ID    : value 0, min 0, max 65535, fuzz 0, flat 0, resolution 0
                ABS_MT_DISTANCE       : value 0, min 0, max 127, fuzz 0, flat 0, resolution 0
  input props:
    INPUT_PROP_DIRECT

getevent -i: 显示更加详细的信息

getevent -t: 显示时间戳

参考文件

https://source.android.com/devices/input