常见的动作常量：
public static final int ACTION_DOWN = 0;单点触摸动作
public static final int ACTION_UP = 1;单点触摸离开动作
public static final int ACTION_MOVE = 2;触摸点移动动作
public static final int ACTION_CANCEL = 3;触摸动作取消
public static final int ACTION_OUTSIDE = 4;触摸动作超出边界
public static final int ACTION_POINTER_DOWN = 5;多点触摸动作
public static final int ACTION_POINTER_UP = 6;多点离开动作
以下是一些非touch事件
public static final int ACTION_HOVER_MOVE = 7;
public static final int ACTION_SCROLL = 8;
public static final int ACTION_HOVER_ENTER = 9;
public static final int ACTION_HOVER_EXIT = 10;
掩码常量
ACTION_MASK = 0X000000ff
动作掩码
ACTION_POINTER_INDEX_MASK = 0X0000ff00
触摸点索引掩码
ACTION_POINTER_INDEX_SHIFT = 8 获取触摸点索引需要移动的位数
ACTION_POINTER_INDEX_SHIFT = 8 获取触摸点索引需要移动的位数