no route to host Chromium网页输入事件捕捉和手势检测过程分析(11)

这个滑动手势操作也是通过调用GestureDetector类的成员变量listener_描写叙述的一个GestureListener对象的成员函数OnScroll进行处理。

接下来我们主要关注滑动手势操作的处理过程。GestureDetector类的成员变量listener_指向的实际上是一个GestureListenerImpl对象。no route to host

这个GestureListenerImpl对象就是前面提到的GestureProvider类的成员变量gesture_listener_所指向的GestureListenerImpl对象。这意味着GestureDetector类的成员函数OnTouchEvent检测到的滑动手势操作将由这个GestureListenerImpl对象的成员函数OnScroll进行处理。

GestureListenerImpl类的成员函数OnScroll的实现例如以下所看到的：

class GestureProvider::GestureListenerImpl
    : public GestureDetector::GestureListener,
      public GestureDetector::DoubleTapListener {
 public:
  ......

  virtual bool OnScroll(const MotionEvent& e1,
                        const MotionEvent& e2,
                        float raw_distance_x,
                        float raw_distance_y) OVERRIDE {
    float distance_x = raw_distance_x;
    float distance_y = raw_distance_y;
    ......

    if (!provider_->IsScrollInProgress()) {
      // Note that scroll start hints are in distance traveled, where
      // scroll deltas are in the opposite direction.
      GestureEventDetails scroll_details(
          ET_GESTURE_SCROLL_BEGIN, -raw_distance_x, -raw_distance_y);

      // Use the co-ordinates from the touch down, as these co-ordinates are
      // used to determine which layer the scroll should affect.
      provider_->Send(CreateGesture(scroll_details,
                                    e2.GetId(),
                                    e2.GetEventTime(),
                                    e1.GetX(),
                                    e1.GetY(),
                                    e1.GetRawX(),
                                    e1.GetRawY(),
                                    e2.GetPointerCount(),
                                    GetBoundingBox(e2)));
    }


    if (distance_x || distance_y) {
      const gfx::RectF bounding_box = GetBoundingBox(e2);
      const gfx::PointF center = bounding_box.CenterPoint();
      const gfx::PointF raw_center =
          center + gfx::Vector2dF(e2.GetRawOffsetX(), e2.GetRawOffsetY());
      GestureEventDetails scroll_details(
          ET_GESTURE_SCROLL_UPDATE, -distance_x, -distance_y);
      provider_->Send(CreateGesture(scroll_details,
                                    e2.GetId(),
                                    e2.GetEventTime(),
                                    center.x(),
                                    center.y(),
                                    raw_center.x(),
                                    raw_center.y(),
                                    e2.GetPointerCount(),
                                    bounding_box));
    }

    return true;
  }

  ......
};

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