Android事件分发机制浅谈（三）--源码分析（View篇）

写事件分发源码分析的时候很纠结，网上的许多博文都是先分析的View，后分析ViewGroup。因为我一开始理解的时候是按我的流程图往下走的，感觉方向很对，单是具体分析的时候总是磕磕绊绊的，老要跳到View中去分析，很多方法理解不了，但毕竟流程清楚了许多，算是有得有失吧，不多说，开始分析。

继续根据流程，先分析View的dispatchTouchEvent()方法，看源码。

 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, );
        }

        final int actionMasked = event.getActionMasked();
        if (actionMasked == MotionEvent.ACTION_DOWN) {
            // Defensive cleanup for new gesture
            stopNestedScroll();
        }

        if (onFilterTouchEventForSecurity(event)) {
            //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, );
        }

        // 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;
    }

不得不说，比起ViewGroup这个方法真的很短。

        if (onFilterTouchEventForSecurity(event)) 

略过不必要的看这个判断中的方法判断当前View是否没被遮住等，接下来的就是我们曾在上一节中讲解过的

   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;
             }

这里不分析情景了，这里主要看下上一次没分析的onTouch方法和onTouchEvent方法

首先进入onTouch方法的源码

 boolean onTouch(View v, MotionEvent event);

才发现这只是个接口方法，看来是要重写的，那没什么好看的了，看onTouchEvent()方法

  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) != ) {
                 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) != ;
                     if ((mPrivateFlags & PFLAG_PRESSED) !=  || 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();
                     }
                     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) != ) {
                             // Remove any future long press/tap checks
                             removeLongPressCallback();

                             setPressed(false);
                         }
                     }
                     break;
             }

             return true;
         }

         return false;
     }

突然发现好长，那么咱们分开看　　

7-16 我们可以看到如果控件是disabled的同时是可以clickable的则onTouchEvent直接消费事件返回true，反之如果控件（View）是disenable状态，同时是disclickable的则onTouchEvent直接false。

24、137看到如果是disclickable的那么返回false

27-134是一个switch判断event的类型，对每个类型进行了适当的分析，有兴趣的可以自己了解一下

我们可以看到当ACTION_UP执行时，执行了一个perforClick方法

 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;
     }

这下我们可以看到if判断句中熟悉的方法了onCLick，原来onClick()方法是在这里调用的，同样的li.mOnClickListener是通过setOnClickListener方法设置的，现在是知道了为什么onClik方法的优先级较低了吧

好了，现在android的事件分析就告一段落了，写的时候因为很多，所以有些地方可能写的比较糊涂，有错误的话请指出。