Android自定义控件之事件分发机制表现与实现原理

事件分发机制表现与实现原理

http://blog.csdn.net/qq_23547831/article/details/51530671
表现图片来源: http://blog.csdn.net/chunqiuwei/article/details/41084921

• 事件拦截表现
  

  • 不拦截不处理时
    
  • C拦截但不处理时
    
  • D处理时
    

• 事件拦截原理
  

ViewGroup # dispatchTouchEvent()

// 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);//清除之前的所有其他动作,使mFirstTouchTarget=null
             resetTouchState();//重置Touch状态标识。
         }

// 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);//默认不拦截
                 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;
         }

1. 每个MotionEvent.ACTION_DOWN发生时会清除之前所有连续的动作并作为一系列动作的开端；
2. 当MotionEvent.ACTION_DOWN或存在动作接收对象时,默认不拦截动作；否则拦截动作；

---

View # dispatchTouchEvent(event)

ViewGroup # dispatchTouchEvent(event) 倒序循环判断当前从上方到下方的直接子View/ViewGroup, 判断当前事件是否存在消费对象,递归判断,最终调用的是已经定义过的child # dispatchTouchEvent()或者是View # dispatchTouchEvent(event)

• View # dispatchTouchEvent(event) 返回true的情况
  • 处理内部滚动事件
  • View # isEnabled()==true,添加View $ OnTouchListener并在OnTouchListener # onTouch()返回true;
  • View # onTouchEvent()返回true;

如果控件（View）是enable且onTouch返回true情况下，dispatchTouchEvent直接返回true，不会调用onTouchEvent方法。

完整代码如下:

/**
    * View # dispatchTouchEvent(event)
    * 
    * 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;
   }

---

View # onTouchEvent(event)

• 点击和长按事件都会消耗当前事件返回true

全部代码如下:

/**
 * 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();

>>>    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) {
                                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:
                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);
                    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;
}

---