事件處理機制(一) 一、事件接收流程 二、View繼承關係調用

Android知識總結

一、事件接收流程

首先我們在ViewRootImpl#setView創建View的接收事件

    public void setView(View view, WindowManager.LayoutParams attrs, View panelParentView, int userId) {
        ...
        if (inputChannel != null) {
            if (mInputQueueCallback != null) {
                mInputQueue = new InputQueue();
                mInputQueueCallback.onInputQueueCreated(mInputQueue);
            }
            //接收事件
            mInputEventReceiver = new WindowInputEventReceiver(inputChannel,
                    Looper.myLooper());
        }
        ...
    }

然後我們看ViewRootImpl的內部類WindowInputEventReceiver

    final class WindowInputEventReceiver extends InputEventReceiver {
        public WindowInputEventReceiver(InputChannel inputChannel, Looper looper) {
            super(inputChannel, looper);
        }

        @Override
        public void onInputEvent(InputEvent event) {
            Trace.traceBegin(Trace.TRACE_TAG_VIEW, "processInputEventForCompatibility");
            List<InputEvent> processedEvents;
            try {
                processedEvents =
                    mInputCompatProcessor.processInputEventForCompatibility(event);
            } finally {
                Trace.traceEnd(Trace.TRACE_TAG_VIEW);
            }
            if (processedEvents != null) {
                if (processedEvents.isEmpty()) {
                    // InputEvent consumed by mInputCompatProcessor
                    finishInputEvent(event, true);
                } else {
                    for (int i = 0; i < processedEvents.size(); i++) {
                        //派發事件
                        enqueueInputEvent(
                                processedEvents.get(i), this,
                                QueuedInputEvent.FLAG_MODIFIED_FOR_COMPATIBILITY, true);
                    }
                }
            } else {
                enqueueInputEvent(event, this, 0, true);
            }
        }

        @Override
        public void onBatchedInputEventPending(int source) {
            // mStopped: There will be no more choreographer callbacks if we are stopped,
            // so we must consume all input immediately to prevent ANR
            final boolean unbuffered = mUnbufferedInputDispatch
                    || (source & mUnbufferedInputSource) != SOURCE_CLASS_NONE
                    || mStopped;
            if (unbuffered) {
                if (mConsumeBatchedInputScheduled) {
                    unscheduleConsumeBatchedInput();
                }
                // Consume event immediately if unbuffered input dispatch has been requested.
                consumeBatchedInputEvents(-1);
                return;
            }
            scheduleConsumeBatchedInput();
        }

        @Override
        public void onFocusEvent(boolean hasFocus, boolean inTouchMode) {
            windowFocusChanged(hasFocus, inTouchMode);
        }

        @Override
        public void dispose() {
            unscheduleConsumeBatchedInput();
            super.dispose();
        }
    }
    WindowInputEventReceiver mInputEventReceiver;

然後在onInputEvent中調用enqueueInputEvent獲取事件

    void enqueueInputEvent(InputEvent event,
            InputEventReceiver receiver, int flags, boolean processImmediately) {
        QueuedInputEvent q = obtainQueuedInputEvent(event, receiver, flags);
        // the time stamp of injected events are monotonic.
        QueuedInputEvent last = mPendingInputEventTail;
        if (last == null) {
            mPendingInputEventHead = q;
            mPendingInputEventTail = q;
        } else {
            last.mNext = q;
            mPendingInputEventTail = q;
        }
        mPendingInputEventCount += 1;
        Trace.traceCounter(Trace.TRACE_TAG_INPUT, mPendingInputEventQueueLengthCounterName,
                mPendingInputEventCount);

        if (processImmediately) {
            doProcessInputEvents();
        } else {
            scheduleProcessInputEvents();
        }
    }

    void doProcessInputEvents() {
        // Deliver all pending input events in the queue.
        while (mPendingInputEventHead != null) {
            QueuedInputEvent q = mPendingInputEventHead;
            mPendingInputEventHead = q.mNext;
            if (mPendingInputEventHead == null) {
                mPendingInputEventTail = null;
            }
            q.mNext = null;

            mPendingInputEventCount -= 1;
            Trace.traceCounter(Trace.TRACE_TAG_INPUT, mPendingInputEventQueueLengthCounterName,
                    mPendingInputEventCount);

            long eventTime = q.mEvent.getEventTimeNano();
            long oldestEventTime = eventTime;
            if (q.mEvent instanceof MotionEvent) {
                MotionEvent me = (MotionEvent)q.mEvent;
                if (me.getHistorySize() > 0) {
                    oldestEventTime = me.getHistoricalEventTimeNano(0);
                }
            }
            mChoreographer.mFrameInfo.updateInputEventTime(eventTime, oldestEventTime);
            //處理事件
            deliverInputEvent(q);
        }
        // so we can clear the pending flag immediately.
        if (mProcessInputEventsScheduled) {
            mProcessInputEventsScheduled = false;
            //移出事件
            mHandler.removeMessages(MSG_PROCESS_INPUT_EVENTS);
        }
    }

    private void deliverInputEvent(QueuedInputEvent q) {
            ...
            InputStage stage;
            if (q.shouldSendToSynthesizer()) {
                stage = mSyntheticInputStage;
            } else {
                stage = q.shouldSkipIme() ? mFirstPostImeInputStage : mFirstInputStage;
            }
            if (stage != null) {
                handleWindowFocusChanged();
                //處理事件
                stage.deliver(q);
            } else {
              //結束事件
                finishInputEvent(q);
            }
    }

在這個方法中調用InputStage的各個方法deliver， 處理完事件後就會finishInputEvent來完成事件分發操作。

1.1、各個InputStage

public void setView(View view, WindowManager.LayoutParams attrs, View panelParentView, int userId) {
    mSyntheticInputStage = new SyntheticInputStage();
    InputStage viewPostImeStage = new ViewPostImeInputStage(mSyntheticInputStage);
    InputStage nativePostImeStage = new NativePostImeInputStage(viewPostImeStage,
            "aq:native-post-ime:" + counterSuffix);
    InputStage earlyPostImeStage = new EarlyPostImeInputStage(nativePostImeStage);
    InputStage imeStage = new ImeInputStage(earlyPostImeStage,
            "aq:ime:" + counterSuffix);
    InputStage viewPreImeStage = new ViewPreImeInputStage(imeStage);
    InputStage nativePreImeStage = new NativePreImeInputStage(viewPreImeStage,
            "aq:native-pre-ime:" + counterSuffix);
}

構造了7個InputStage實現類，

• NativePreImeInputStage: 主要是爲了將消息放到NativeActivity中去處理, NativeActivity和普通Acitivty的功能區別不大,只是很多代碼都在native層去實現,這樣執行效率更高,並且NativeActivity在遊戲開發中很實用。
• ViewPreImeInputStage: 從名字中就可得知,最後會調用Acitivity的所有view的onkeyPreIme方法,這樣就給View在輸入法處理key事件之前先得到消息並處理的機會。
• ImeInputStage: ImeInputStage的onProcess方法會調用InputMethodManager的dispatchInputEvent方法處理消息。
• EarlyPostImeInputStage: 屏幕上有焦點的View會高亮顯示,用來提示用戶焦點所在。
• NativePostImeInputStage: 爲了讓IME處理完消息後能先於普通的Activity處理消息。
• ViewPostImeInputStage: Acitivity和view處理各種消息。
• SyntheticInputStage: 流水線的最後一級,經過層層過濾之後,到達這裏的消息已經不多了,例如手機上的虛擬按鍵消息。

那麼Activity和View的事件處理主要對應的InputStage是ViewPostImeInputStage。

1.2、ViewPostImeInputStage

調用ViewPostImeInputStage的父類InputStage#deliver方法

abstract class InputStage {
    public final void deliver(QueuedInputEvent q) {
        if ((q.mFlags & QueuedInputEvent.FLAG_FINISHED) != 0) {
            forward(q);
        } else if (shouldDropInputEvent(q)) {
            finish(q, false);
        } else {
            traceEvent(q, Trace.TRACE_TAG_VIEW);
            final int result;
            try {
                result = onProcess(q);
            } finally {
                Trace.traceEnd(Trace.TRACE_TAG_VIEW);
            }
            apply(q, result);
        }
    }

    protected int onProcess(QueuedInputEvent q) {
         return FORWARD;
    }
}

接下來看 ViewPostImeInputStage的onProcess方法

    final class ViewPostImeInputStage extends InputStage {
        public ViewPostImeInputStage(InputStage next) {
            super(next);
        }

        @Override
        protected int onProcess(QueuedInputEvent q) {
            if (q.mEvent instanceof KeyEvent) {
                return processKeyEvent(q);
            } else {
                final int source = q.mEvent.getSource();
                if ((source & InputDevice.SOURCE_CLASS_POINTER) != 0) {
                      //處理點擊事件
                    return processPointerEvent(q);
                } else if ((source & InputDevice.SOURCE_CLASS_TRACKBALL) != 0) {
                    return processTrackballEvent(q);
                } else {
                    return processGenericMotionEvent(q);
                }
            }
        }
  }

    private int processPointerEvent(QueuedInputEvent q) {
        final MotionEvent event = (MotionEvent) q.mEvent;

        mAttachInfo.mUnbufferedDispatchRequested = false;
        mAttachInfo.mHandlingPointerEvent = true;
        //mView ==> DecorView
        boolean handled = mView.dispatchPointerEvent(event);
        maybeUpdatePointerIcon(event);
        maybeUpdateTooltip(event);
        mAttachInfo.mHandlingPointerEvent = false;
        if (mAttachInfo.mUnbufferedDispatchRequested && !mUnbufferedInputDispatch) {
            mUnbufferedInputDispatch = true;
            if (mConsumeBatchedInputScheduled) {
                scheduleConsumeBatchedInputImmediately();
            }
        }
        return handled ? FINISH_HANDLED : FORWARD;
    }

會調用到DecorView 的 dispatchTouchEvent

二、View繼承關係調用

2.1、我們先看DecorView 的繼承關係

private final class DecorView extends FrameLayout implements RootViewSurfaceTaker{...}
public class FrameLayout extends ViewGroup {...}
public abstract class ViewGroup extends View implements ViewParent, ViewManager{..}

2.2、事件處理

最後回調到父類View的dispatchPointerEvent

    public final boolean dispatchPointerEvent(MotionEvent event) {
        if (event.isTouchEvent()) {
            //分發事件
            return dispatchTouchEvent(event);
        } else {
            return dispatchGenericMotionEvent(event);
        }
    }

然後再回到頂層DecorView中執行dispatchTouchEvent

    public boolean dispatchTouchEvent(MotionEvent ev) {
        //cb==> Activity
        final Window.Callback cb = mWindow.getCallback();
        //mWindow ==> PhoneWindow
        return cb != null && !mWindow.isDestroyed() && mFeatureId < 0
                ? cb.dispatchTouchEvent(ev) : super.dispatchTouchEvent(ev);
    }

調用Activity的dispatchTouchEvent，先調用各個DispatchTouchEvent，最後才調用 onTouchEvent。因此最早 dispatchTouchEvent，應用最晚 onTouchEvent。

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

調用PhoneWindow#superDispatchTouchEvent

    public boolean superDispatchTouchEvent(MotionEvent event) {
      //mDecor ==> DecorView
        return mDecor.superDispatchTouchEvent(event);
    }

調用DecorView#superDispatchTouchEvent

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

調用ViewGoup#superDispatchTouchEvent

    public boolean dispatchTouchEvent(MotionEvent ev) {
        ...
    }

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

最後調用View#dispatchTouchEvent

public boolean dispatchTouchEvent(MotionEvent event) { ... }

在調用 onTouchEvent處理事件

public boolean onTouchEvent(MotionEvent event) { ... }

具體事件怎麼處理見下章