Android学习笔记——View的Touch事件

1、Touch事件
（1）事件分发／事件消费
（2）案例分析
2、滑动事件
（1）滑动冲突
3、参考文档

1、Touch事件

官方文档：Manage touch events in a ViewGroup
https://developer.android.com/training/gestures/viewgroup

ACTION_CANCEL触发时机
If you return true from onInterceptTouchEvent(), the child view that was previously handling touch events receives an ACTION_CANCEL, and the events from that point forward are sent to the parent’s onTouchEvent() method for the usual handling

TouchDelegate: Extend a child view’s touchable area

多指触控：
https://developer.android.com/training/gestures/multi
https://developer.android.com/training/gestures/scale

ACTION_DOWN—For the first pointer that touches the screen. This starts the gesture. The pointer data for this pointer is always at index 0 in the MotionEvent.
ACTION_POINTER_DOWN—For extra pointers that enter the screen beyond the first. The pointer data for this pointer is at the index returned by getActionIndex().
ACTION_MOVE—A change has happened during a press gesture.
ACTION_POINTER_UP—Sent when a non-primary pointer goes up.
ACTION_UP—Sent when the last pointer leaves the screen.

ACTION_POINTER_UP事件处理：
In the ACTION_POINTER_UP case, the example extracts this index and ensures that the active pointer ID is not referring to a pointer that is no longer touching the screen. If it is, the app selects a different pointer to be active and saves its current X and Y position. Since this saved position is used in the ACTION_MOVE case to calculate the distance to move the onscreen object, the app will always calculate the distance to move using data from the correct pointer.

参考ScrollView的源码。

（1）事件分发／事件消费

（2）案例分析

2、滑动事件

（1）滑动冲突

PS：之前写过一篇View事件分发及消费源码分析，缺少流程图，导致整个流程不够清晰。

3、参考文档

（1）Android事件分发机制
（2）Android 事件分发机制源码和实例解析
（3）Android View体系之Touch事件传递源码解析(8.0)
（4）Android事件分发机制 详解攻略，您值得拥有

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