Android点击事件派发机制源码分析

   /**   * 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) {      //这个函数其实是个空函数，啥也没干，如果你没重写的话，不用关心      onUserInteraction();    }    //这里事件开始交给Activity所附属的Window进行派发，如果返回true，整个事件循环就结束了    //返回false意味着事件没人处理，所有人的onTouchEvent都返回了false，那么Activity就要来做最后的收场。    if (getWindow().superDispatchTouchEvent(ev)) {      return true;    }    //这里，Activity来收场了，Activity的onTouchEvent被调用    return onTouchEvent(ev);  } 

  /**   * 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);

@Override  public boolean superDispatchTouchEvent(MotionEvent event) {    return mDecor.superDispatchTouchEvent(event);  }这个逻辑很清晰了，PhoneWindow将事件传递给DecorView了，这个DecorView是啥呢，请看下面   private final class DecorView extends FrameLayout implements RootViewSurfaceTaker  // This is the top-level view of the window, containing the window decor.  private DecorView mDecor;  @Override  public final View getDecorView() {    if (mDecor == null) {      installDecor();    }    return mDecor;  }

  @Override  public boolean dispatchTouchEvent(MotionEvent ev) {    if (mInputEventConsistencyVerifier != null) {      mInputEventConsistencyVerifier.onTouchEvent(ev, 1);    }    boolean handled = false;    if (onFilterTouchEventForSecurity(ev)) {      final int action = ev.getAction();      final int actionMasked = action & MotionEvent.ACTION_MASK;      // 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) {       //这里判断是否拦截点击事件，如果拦截，则intercepted=true          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;      }      // 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;       //这里面一大堆是派发事件到子View，如果intercepted是true，则直接跳过      if (!canceled && !intercepted) {        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 View[] children = mChildren;            final boolean customOrder = isChildrenDrawingOrderEnabled();            for (int i = childrenCount - 1; i >= 0; i--) {              final int childIndex = customOrder ?                  getChildDrawingOrder(childrenCount, i) : i;              final View child = children[childIndex];              if (!canViewReceivePointerEvents(child)                  || !isTransformedTouchPointInView(x, y, child, null)) {                continue;              }              newTouchTarget = getTouchTarget(child);              if (newTouchTarget != null) {                // Child is already receiving touch within its bounds.                // Give it the new pointer in addition to the ones it is handling.                newTouchTarget.pointerIdBits |= idBitsToAssign;                break;              }              resetCancelNextUpFlag(child);              if (dispatchTransformedTouchEvent(ev, false, child, idBitsToAssign)) {                // Child wants to receive touch within its bounds.                mLastTouchDownTime = ev.getDownTime();                mLastTouchDownIndex = childIndex;                mLastTouchDownX = ev.getX();                mLastTouchDownY = ev.getY();                //注意下面两句，如果有子View处理了点击事件，则newTouchTarget会被赋值，                //同时alreadyDispatchedToNewTouchTarget也会为true，这两个变量是直接影响下面的代码逻辑的。                newTouchTarget = addTouchTarget(child, idBitsToAssign);                alreadyDispatchedToNewTouchTarget = true;                break;              }            }          }          if (newTouchTarget == null && mFirstTouchTarget != null) {            // Did not find a child to receive the event.            // Assign the pointer to the least recently added target.            newTouchTarget = mFirstTouchTarget;            while (newTouchTarget.next != null) {              newTouchTarget = newTouchTarget.next;            }            newTouchTarget.pointerIdBits |= idBitsToAssign;          }        }      }      // Dispatch to touch targets.     //这里如果当前ViewGroup拦截了事件，或者其子View的onTouchEvent都返回了false，则事件会由ViewGroup处理      if (mFirstTouchTarget == null) {        // No touch targets so treat this as an ordinary view.       //这里就是ViewGroup对点击事件的处理        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;        }      }      // Update list of touch targets for pointer up or cancel, if needed.      if (canceled          || actionMasked == MotionEvent.ACTION_UP          || actionMasked == MotionEvent.ACTION_HOVER_MOVE) {        resetTouchState();      } else if (split && actionMasked == MotionEvent.ACTION_POINTER_UP) {        final int actionIndex = ev.getActionIndex();        final int idBitsToRemove = 1 << ev.getPointerId(actionIndex);        removePointersFromTouchTargets(idBitsToRemove);      }    }    if (!handled && mInputEventConsistencyVerifier != null) {      mInputEventConsistencyVerifier.onUnhandledEvent(ev, 1);    }    return handled;  }

   /**   * 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) {     //这里就是ViewGroup对点击事件的处理，其调用了View的dispatchTouchEvent方法        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;  }

  /**   * 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 (mInputEventConsistencyVerifier != null) {      mInputEventConsistencyVerifier.onTouchEvent(event, 0);    }    if (onFilterTouchEventForSecurity(event)) {      //noinspection SimplifiableIfStatement      ListenerInfo li = mListenerInfo;      if (li != null && li.mOnTouchListener != null && (mViewFlags & ENABLED_MASK) == ENABLED          && li.mOnTouchListener.onTouch(this, event)) {        return true;      }      if (onTouchEvent(event)) {        return true;      }    }    if (mInputEventConsistencyVerifier != null) {      mInputEventConsistencyVerifier.onUnhandledEvent(event, 0);    }    return false;  }