好记性不如烂笔头，说不如写。备注自己用加深印象
1.事件定义：点击事件 touch 。当用户触摸到view viewgroup会产生事件
2.事件封装：事件的相关信息会（被）封装成 MotionEvent.
3.事件分类： MotionEvent.ACTION_DOWN MotionEvent.ACTION_UP MotionEvent.ACTION_MOVE MotionEvent.ACTION_CANCEL
/**
* Constant for {@link #getActionMasked}: A pressed gesture has started, the
* motion contains the initial starting location.
* <p>
* This is also a good time to check the button state to distinguish
* secondary and tertiary button clicks and handle them appropriately.
* Use {@link #getButtonState} to retrieve the button state.
* </p>
*/
public static final int ACTION_DOWN = 0;
/**
* Constant for {@link #getActionMasked}: A pressed gesture has finished, the
* motion contains the final release location as well as any intermediate
* points since the last down or move event.
*/
public static final int ACTION_UP = 1;
/**
* Constant for {@link #getActionMasked}: A change has happened during a
* press gesture (between {@link #ACTION_DOWN} and {@link #ACTION_UP}).
* The motion contains the most recent point, as well as any intermediate
* points since the last down or move event.
*/
public static final int ACTION_MOVE = 2;
/**
* Constant for {@link #getActionMasked}: The current gesture has been aborted.
* You will not receive any more points in it. You should treat this as
* an up event, but not perform any action that you normally would.
*/
public static final int ACTION_CANCEL = 3;
事件从down 开始到 up结束 中间的 move会有很多 所以很多实时获取位置的计算需要在move中去进行
特殊状态 cancel You should treat this as an up event
将MotionEvent 事件发送到相应的view 并且进行处理 这一个过程就是事件的分发本质
事件传递的对象顺序为： activity --> viewgroup --> view
事件分发涉及到的方法有：
/**
* 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) {
xxx
}
/**
* 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) {
xxxxx
}
以上两个方法在 View 类中
/**
* A helper class to handle touches on the heads-up views.
*/
public class HeadsUpTouchHelper implements Gefingerpoken {
@Override
public boolean onInterceptTouchEvent(MotionEvent event) {
xxxx
}
}
以上就是事件分发的总概念 后面一点点的详细记录
