View事件分發(fā)（傳遞）機(jī)制

前言：View事件分發(fā)機(jī)制是Android中比較重要和復(fù)雜的部分按价，只有理解了事件分發(fā)除呵，才能更好的自定義控件和解決滑動(dòng)沖突，本篇文章基于API25（7.1）业簿。

相關(guān)方法

• public boolean disptachTouchEvent(MotionEvent ev)

事件分發(fā)方法隔箍，觸控事件從該方法開(kāi)始傳遞，返回true表示分發(fā)完成坎背，返回false則失敗

• public boolean onInterceptTouchEvent(MotionEvent ev)

事件攔截方法替劈，只有ViewGroup中才存在，在dispatchTouchEvent中判斷是否攔截事件由自己處理得滤，或者交給子View（ViewGroup）分發(fā)陨献，返回true表示攔截事件，默認(rèn)返回false

• public boolean onTouchEvent(MotionEvent ev)

事件處理方法懂更，處理事件眨业，返回true表示消耗事件，返回false表示不消耗事件

源碼分析

Activity

 /**
 * 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) {
    if (ev.getAction() == MotionEvent.ACTION_DOWN) {
        onUserInteraction();
    }
    if (getWindow().superDispatchTouchEvent(ev)) {
        return true;
    }
    return onTouchEvent(ev);
}

  /**
 * Retrieve the current {@link android.view.Window} for the activity.
 * This can be used to directly access parts of the Window API that
 * are not available through Activity/Screen.
 *
 * @return Window The current window, or null if the activity is not
 *         visual.
 */
public Window getWindow() {
    return mWindow;
}

事件首先從Activity的disptachTouchEvent的方法開(kāi)始調(diào)用沮协，調(diào)用了Window的superDispatchTouchEvent方法龄捡，至于事件MotionEvent的來(lái)源不在本章討論的范圍內(nèi)

/**
 * 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) {
    if (mWindow.shouldCloseOnTouch(this, event)) {
        finish();
        return true;
    }

    return false;
}

Activity默認(rèn)不會(huì)消耗事件

Window

可以看到這是個(gè)抽象方法，Window是一個(gè)抽象類慷暂，Window的唯一實(shí)現(xiàn)是PhoneWindow

 /**
 * Abstract base class for a top-level window look and behavior policy.  An
 * instance of this class should be used as the top-level view added to the
 * window manager. It provides standard UI policies such as a background, title
 * area, default key processing, etc.
 *
 * <p>The only existing implementation of this abstract class is
 * android.view.PhoneWindow, which you should instantiate when needing a
 * Window.
 */
public abstract class Window {
...
 /**
 * Used by custom windows, such as Dialog, to pass the touch screen event
 * further down the view hierarchy. Application developers should
 * not need to implement or call this.
 *
 */
public abstract boolean superDispatchTouchEvent(MotionEvent event);
...
 }

PhoneWindow

// This is the top-level view of the window, containing the window decor.
private DecorView mDecor;
 @Override
public boolean superDispatchTouchEvent(MotionEvent event) {
    return mDecor.superDispatchTouchEvent(event);
}

PhoneWindow的該方法代碼就一行聘殖，調(diào)用了DecorView的superDisptachTouchEvent方法

DecorView

/** @hide */
public class DecorView extends FrameLayout implements RootViewSurfaceTaker, WindowCallbacks {
...
public boolean superDispatchTouchEvent(MotionEvent event) {
    return super.dispatchTouchEvent(event);
}
...
}

DecorView調(diào)用了父類FrameLayout的disptachTouchEvent，F(xiàn)rameLayout繼承于ViewGroup行瑞，且沒(méi)有重寫該方法奸腺，所以終于到了ViewGroup的dispatchTouchEvent方法，下面開(kāi)始重點(diǎn)

ViewGroup

ViewGroup的dispatchTouchEvent方法比較長(zhǎng)血久，先分開(kāi)看

dispatchTouchEvent#1

        // Handle an initial down.
        if (actionMasked == MotionEvent.ACTION_DOWN) {
            // Throw away all previous state when starting a new touch gesture.
            // The framework may have dropped the up or cancel event for the previous gesture
            // due to an app switch, ANR, or some other state change.
            cancelAndClearTouchTargets(ev);
            resetTouchState();
        }
       // Check for interception.

       final boolean intercepted;
       if (actionMasked == MotionEvent.ACTION_DOWN
               || mFirstTouchTarget != null) {
           final boolean disallowIntercept = (mGroupFlags & FLAG_DISALLOW_INTERCEPT) != 0;
           if (!disallowIntercept) {
               intercepted = onInterceptTouchEvent(ev);
               ev.setAction(action); // restore action in case it was changed
           } else {
               intercepted = false;
           }
       } else {
           // There are no touch targets and this action is not an initial down
           // so this view group continues to intercept touches.
           intercepted = true;
       }

首先在ACTION_DOWN中清除所有的觸摸狀態(tài)和目標(biāo), 然后檢查是否需要攔截事件突照，當(dāng)為ACTION_DOWN事件，首選檢查標(biāo)志位FLAG_DISALLOW_INTERCEPT是否已設(shè)置氧吐，即是否不攔截事件讹蘑，通過(guò)requestDisallowInterceptTouchEvent方法可以設(shè)置該標(biāo)志位末盔，默認(rèn)沒(méi)有設(shè)置，disallowIntercept是false衔肢，如果已設(shè)置該標(biāo)志位庄岖，則不截?cái)嘧覸iew（ViewGroup)事件，否則會(huì)調(diào)用自身的onInterceptTouchEvent方法角骤。

@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);
    }
}

 /**
 * @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;
}

可以看到ViewGroup默認(rèn)情況是不會(huì)攔截事件隅忿，所以接下來(lái)遍歷子View，并調(diào)用disptachTransformedTouchEvent
dispatchTouchEvent#2

         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 (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;
                        }
                    ...     
                    }
                }

如果有符合條件的child（觸摸點(diǎn)和變換后的點(diǎn)在該View內(nèi)）對(duì)應(yīng)于dispatchTransformedTouchEvent返回true的邦尊，則newTouchTraget = addTouchTarget(child, idBitsToAssign)會(huì)走到

/**
 * Adds a touch target for specified child to the beginning of the list.
 * Assumes the target child is not already present.
 */
private TouchTarget addTouchTarget(@NonNull View child, int pointerIdBits) {
    final TouchTarget target = TouchTarget.obtain(child, pointerIdBits);
    target.next = mFirstTouchTarget;
    mFirstTouchTarget = target;
    return target;
}

可以看到如果mFirstTouchTarget賦值了背桐，則后續(xù)事件序列繼續(xù)走進(jìn)第一步事件攔截判斷語(yǔ)句內(nèi)，否則后續(xù)的事件序列都由該ViewGroup攔截

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

    // Canceling motions is a special case.  We don't need to perform any transformations
    // or filtering.  The important part is the action, not the contents.
    final int oldAction = event.getAction();
    if (cancel || oldAction == MotionEvent.ACTION_CANCEL) {
        event.setAction(MotionEvent.ACTION_CANCEL);
        if (child == null) {
            handled = super.dispatchTouchEvent(event);
        } else {
            handled = child.dispatchTouchEvent(event);
        }
        event.setAction(oldAction);
        return handled;
    }

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

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

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

                handled = child.dispatchTouchEvent(event);

                event.offsetLocation(-offsetX, -offsetY);
            }
            return handled;
        }
        transformedEvent = MotionEvent.obtain(event);
    } else {
        transformedEvent = event.split(newPointerIdBits);
    }

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

        handled = child.dispatchTouchEvent(transformedEvent);
    }

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

可以看到如果child為null則會(huì)調(diào)用ViewGroup父類的dispatchTouchEvent,ViewGroup的父類是View則會(huì)走到View的dispatchTouchEvent中蝉揍；否則會(huì)調(diào)用child的dispatchTouchEvent链峭，即事件繼續(xù)傳遞下去

disptachTouchEvent#3

     // 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;
            }
        }

所以如果mFirstTouchTarget為null，即ViewGroup攔截事件或者ViewGroup沒(méi)有child消耗該事件又沾，則調(diào)用super#disptachTouchEvent否則調(diào)用child的dispatchTouchEvent,如果child不消耗ACTION_DOWN除外的事件弊仪，則該事件消失，不會(huì)回傳給父ViewGroup杖刷，最終會(huì)傳給Activity的onTouchEvent励饵，并且后續(xù)的事情此child也能收到。如果ViewGroup在ACTION_MOVE中攔截事件滑燃，則會(huì)走到dispatch(ev,true,target.child,target.pointIdBits)中役听，在該方法中child會(huì)收到一個(gè)ACTION_CANCEL事件，VieGroup不處理該事件表窘，且predecessor == null典予，mFirstTouchTarget = next 最終，mFirstTouchTarget置為null乐严，從下個(gè)事件開(kāi)始都交由ViewGroup處理瘤袖。

View

/**
 * 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);
    }

    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;
}

首先會(huì)檢查是否該View會(huì)設(shè)置OnTouchListener、是否enable昂验、onTouchListener.onTouch(this,event)是否返回true孽椰，如果條件都滿足則標(biāo)識(shí)該View消耗了事件，傳遞完成凛篙，否則會(huì)繼續(xù)調(diào)用onTouchEvent

/**
 * Implement this method to handle touch screen motion events.
 * <p>
 * If this method is used to detect click actions, it is recommended that
 * the actions be performed by implementing and calling
 * {@link #performClick()}. This will ensure consistent system behavior,
 * including:
 * <ul>
 * <li>obeying click sound preferences
 * <li>dispatching OnClickListener calls
 * <li>handling {@link AccessibilityNodeInfo#ACTION_CLICK ACTION_CLICK} when
 * accessibility features are enabled
 * </ul>
 *
 * @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();

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

    if (((viewFlags & CLICKABLE) == CLICKABLE ||
            (viewFlags & LONG_CLICKABLE) == LONG_CLICKABLE) ||
            (viewFlags & CONTEXT_CLICKABLE) == CONTEXT_CLICKABLE) {
        switch (action) {
            case MotionEvent.ACTION_UP:
                boolean prepressed = (mPrivateFlags & PFLAG_PREPRESSED) != 0;
                if ((mPrivateFlags & PFLAG_PRESSED) != 0 || prepressed) {
                    // take focus if we don't have it already and we should in
                    // touch mode.
                    boolean focusTaken = false;
                    if (isFocusable() && isFocusableInTouchMode() && !isFocused()) {
                        focusTaken = requestFocus();
                    }

                    if (prepressed) {
                        // The button is being released before we actually
                        // showed it as pressed.  Make it show the pressed
                        // state now (before scheduling the click) to ensure
                        // the user sees it.
                        setPressed(true, x, y);
                   }

                    if (!mHasPerformedLongPress && !mIgnoreNextUpEvent) {
                        // This is a tap, so remove the longpress check
                        removeLongPressCallback();

                        // Only perform take click actions if we were in the pressed state
                        if (!focusTaken) {
                            // Use a Runnable and post this rather than calling
                            // performClick directly. This lets other visual state
                            // of the view update before click actions start.
                            if (mPerformClick == null) {
                                mPerformClick = new PerformClick();
                            }
                            if (!post(mPerformClick)) {
                                performClick();
                            }
                        }
                    }

                    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:
                mHasPerformedLongPress = false;

                if (performButtonActionOnTouchDown(event)) {
                    break;
                }

                // Walk up the hierarchy to determine if we're inside a scrolling container.
                boolean isInScrollingContainer = isInScrollingContainer();

                // For views inside a scrolling container, delay the pressed feedback for
                // a short period in case this is a scroll.
                if (isInScrollingContainer) {
                    mPrivateFlags |= PFLAG_PREPRESSED;
                    if (mPendingCheckForTap == null) {
                        mPendingCheckForTap = new CheckForTap();
                    }
                    mPendingCheckForTap.x = event.getX();
                    mPendingCheckForTap.y = event.getY();
                    postDelayed(mPendingCheckForTap, ViewConfiguration.getTapTimeout());
                } else {
                    // Not inside a scrolling container, so show the feedback right away
                    setPressed(true, x, y);
                    checkForLongClick(0, x, y);
                }
                break;

            case MotionEvent.ACTION_CANCEL:
                setPressed(false);
                removeTapCallback();
                removeLongPressCallback();
                mInContextButtonPress = false;
                mHasPerformedLongPress = false;
                mIgnoreNextUpEvent = false;
                break;

            case MotionEvent.ACTION_MOVE:
                drawableHotspotChanged(x, y);

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

                        setPressed(false);
                    }
                }
                break;
        }

        return true;
    }

    return false;
}

如果控件不是enable的，但是是可以點(diǎn)擊的clickable栏渺、longClickable或者contextClickable的也會(huì)消耗該事件呛梆；如果控件是enable的，則會(huì)根據(jù)事件的時(shí)間長(zhǎng)短來(lái)執(zhí)行checkForLongClick或者perfomrClick方法,可點(diǎn)擊的View的onTouchEvent默認(rèn)返回true磕诊，如Button填物，不可點(diǎn)擊的則返回false纹腌，如TextView和ImageView

private void checkForLongClick(int delayOffset, float x, float y) {
    if ((mViewFlags & LONG_CLICKABLE) == LONG_CLICKABLE) {
        mHasPerformedLongPress = false;

        if (mPendingCheckForLongPress == null) {
            mPendingCheckForLongPress = new CheckForLongPress();
        }
        mPendingCheckForLongPress.setAnchor(x, y);
        mPendingCheckForLongPress.rememberWindowAttachCount();
        postDelayed(mPendingCheckForLongPress,
                ViewConfiguration.getLongPressTimeout() - delayOffset);
    }
}

private final class CheckForLongPress implements Runnable {
    private int mOriginalWindowAttachCount;
    private float mX;
    private float mY;

    @Override
    public void run() {
        if (isPressed() && (mParent != null)
                && mOriginalWindowAttachCount == mWindowAttachCount) {
            if (performLongClick(mX, mY)) {
                mHasPerformedLongPress = true;
            }
        }
    }

    public void setAnchor(float x, float y) {
        mX = x;
        mY = y;
    }

    public void rememberWindowAttachCount() {
        mOriginalWindowAttachCount = mWindowAttachCount;
    }
}

/**
 * Calls this view's OnLongClickListener, if it is defined. Invokes the
 * context menu if the OnLongClickListener did not consume the event,
 * anchoring it to an (x,y) coordinate.
 *
 * @param x x coordinate of the anchoring touch event, or {@link Float#NaN}
 *          to disable anchoring
 * @param y y coordinate of the anchoring touch event, or {@link Float#NaN}
 *          to disable anchoring
 * @return {@code true} if one of the above receivers consumed the event,
 *         {@code false} otherwise
 */
public boolean performLongClick(float x, float y) {
    mLongClickX = x;
    mLongClickY = y;
    final boolean handled = performLongClick();
    mLongClickX = Float.NaN;
    mLongClickY = Float.NaN;
    return handled;
}

 /**
 * Calls this view's OnLongClickListener, if it is defined. Invokes the
 * context menu if the OnLongClickListener did not consume the event.
 *
 * @return {@code true} if one of the above receivers consumed the event,
 *         {@code false} otherwise
 */
public boolean performLongClick() {
    return performLongClickInternal(mLongClickX, mLongClickY);
}

    
/**
 * Calls this view's OnLongClickListener, if it is defined. Invokes the
 * context menu if the OnLongClickListener did not consume the event,
 * optionally anchoring it to an (x,y) coordinate.
 *
 * @param x x coordinate of the anchoring touch event, or {@link Float#NaN}
 *          to disable anchoring
 * @param y y coordinate of the anchoring touch event, or {@link Float#NaN}
 *          to disable anchoring
 * @return {@code true} if one of the above receivers consumed the event,
 *         {@code false} otherwise
 */
private boolean performLongClickInternal(float x, float y) {
    sendAccessibilityEvent(AccessibilityEvent.TYPE_VIEW_LONG_CLICKED);

    boolean handled = false;
    final ListenerInfo li = mListenerInfo;
    if (li != null && li.mOnLongClickListener != null) {
        handled = li.mOnLongClickListener.onLongClick(View.this);
    }
    if (!handled) {
        final boolean isAnchored = !Float.isNaN(x) && !Float.isNaN(y);
        handled = isAnchored ? showContextMenu(x, y) : showContextMenu();
    }
    if (handled) {
        performHapticFeedback(HapticFeedbackConstants.LONG_PRESS);
    }
    return handled;
}

/**
 * Call this view's OnClickListener, if it is defined.  Performs all normal
 * actions associated with clicking: reporting accessibility event, playing
 * a sound, etc.
 *
 * @return True there was an assigned OnClickListener that was called, false
 *         otherwise is returned.
 */
public boolean performClick() {
    final boolean result;
    final ListenerInfo li = mListenerInfo;
    if (li != null && li.mOnClickListener != null) {
        playSoundEffect(SoundEffectConstants.CLICK);
        li.mOnClickListener.onClick(this);
        result = true;
    } else {
        result = false;
    }

    sendAccessibilityEvent(AccessibilityEvent.TYPE_VIEW_CLICKED);
    return result;
}

結(jié)論

View事件傳遞.png

1. Activity和View中沒(méi)有OnInterceptTouchEvent方法，只有ViewGroup才有
2. 分發(fā)過(guò)程由上到下滞磺，Activity->Window(PhoneWindow)->DecorView->ViewGroup->View,處理過(guò)程由下到上升薯，View->ViewGroup->DecorView->Window(PhoneWindow)->Activity,如果分發(fā)（處理）過(guò)程中有View/ViewGroup消耗事件[返回true]則事件不會(huì)往下傳遞（往上傳遞）
3. 事件分發(fā)序列是有一個(gè)ACTION_DOWN，零或多個(gè)ACTION_MOVE击困，單個(gè)ACTION_UP組成,即ACTION_DOWN->[ACTION_MOVE->...->ACTION_MOVE->]ACTION_UP
4. ViewGroup的ACTION_DOWN事件必定調(diào)用OnInterceptTouchEvent涎劈，如果攔截了ACTION_DOWN事件則后續(xù)的事件序列都不會(huì)再調(diào)用OnInterceptTouchEvent, 事件都由該ViewGroup處理，ViewGroup的Child也不會(huì)再收到后續(xù)的事件序列
5. 如果ViewGroup在ACTION_MOVE中攔截事件阅茶，則會(huì)走到dispatch(ev,true,target.child,target.pointIdBits)中蛛枚，在該方法中child會(huì)收到一個(gè)ACTION_CANCEL事件，ViewGroup不處理該事件脸哀，最終蹦浦，mFirstTouchTarget置為null，從下個(gè)事件開(kāi)始都交由ViewGroup處理
6. 子類可以通過(guò)調(diào)用的父類的requestDisallowInterceptTouchEvent來(lái)改變父類是否攔截事件撞蜂，但是如果ACTION_DOWN事件已被父類攔截盲镶，則無(wú)法改變;且ACTION_DOWN事件不受該方法標(biāo)志位FLAG_DISALLOW_INTERCEPT控制，因?yàn)閂iewGroup的disptachTouchEvent方法在收到ACTION_DOWN事件時(shí)會(huì)調(diào)用resetTouchState方法重置該標(biāo)志位
7. 如果child不消耗ACTION_DOWN,即dispatchTouchEvent返回false蝌诡，則后續(xù)的事件序列都由其父ViewGroup處理溉贿，調(diào)用View#dispatchTouchEvent
8. 如果child不消耗ACTION_DOWN除外的事件，則該事件消失送漠，不會(huì)回傳給父ViewGroup顽照，最終會(huì)傳給Activity的onTouchEvent，但是后續(xù)的事情此child也能收到
9. View#disptachTouchEvent中首先會(huì)判斷是否有設(shè)置OnTouchListener闽寡、控件enable且onTouch返回true代兵，滿足條件則事件分發(fā)完成，否則會(huì)繼續(xù)調(diào)用View#onTouchEvent
10. View#onTouchEvent中爷狈，即使該View不是enable的植影，但是其是clickable、longClickable或者contextClickable的則也消耗事件涎永，如果View是enable的思币，則根據(jù)時(shí)間判斷是執(zhí)行performClick還是performLongClick，可點(diǎn)擊的View的onTouchEvent默認(rèn)返回true羡微，如Button谷饿，不可點(diǎn)擊的則返回false，如TextView和ImageView
11. View方法調(diào)用順序: dispatchTouchEvent->mOnTouchListener#onTouch->onTouchEvent->performLongClick->performClick
12. ViewGroup攔截ACTION_DOWN:dispatchTouchEvent->onInterceptTouchEvent->super.disptachTouchEvent妈倔，后續(xù)事件： dispatchTouchEvent->super.disptachTouchEvent
13. ViewGroup不攔截ACTION_DOWN： child消耗ACTION_DOWN, dispatchTouchEvent->onInterceptTouchEvent->child#disptachTouchEvent->,后續(xù)事件事件dispatchTouchEvent->onInterceptTouchEvent->child#disptachTouchEvent->;child不消耗ACTION_DOWN博投，dispatchTouchEvent->onInterceptTouchEvent->child#disptachTouchEvent->super.disptachTouchEvent，后續(xù)事件
    dispatchTouchEvent->super.disptachTouchEvent
14. ViewGroup攔截ACTION_MOVE： dispatchTouchEvent->onInterceptTouchEvent->child#dispatchTouchEvent(ACTION_CANCEL),后續(xù)事件disptachTouchEvent->super.dispatchTouchEvent

參考文獻(xiàn)

1. Android事件分發(fā)機(jī)制完全解析盯蝴，帶你從源碼的角度徹底理解(上) ,
   Android事件分發(fā)機(jī)制完全解析毅哗，帶你從源碼的角度徹底理解(下)
2. 圖解 Android 事件分發(fā)機(jī)制
3. 十分鐘徹底弄明白 View 事件分發(fā)機(jī)制
4. Android View事件分發(fā)機(jī)制源碼分析
5. Android事件傳遞機(jī)制
6. View 的事件分發(fā)機(jī)制
7. 安卓自定義View進(jìn)階-事件分發(fā)機(jī)制原理,安卓自定義View進(jìn)階-事件分發(fā)機(jī)制詳解
8. Activity, Window, PhoneWindow,ViewGroup,View,MotionEvent
9. 《Android開(kāi)發(fā)藝術(shù)探索》第三章View事件分發(fā)機(jī)制