原文連結：http://blog.sina.com.cn/s/blog_82f01d350101gbbf.html

看到下面程式碼中用了AND位運算是為了什麼呢？

public boolean onTouchEvent(MotionEvent event) {
int action = event.getAction();
switch (action & MotionEvent.ACTION_MASK) {
case MotionEvent.ACTION_DOWN:
showMsg("ACTION_DOWN" + action);
break;
case MotionEvent.ACTION_UP:
showMsg("ACTION_UP" + action);
break;
case MotionEvent.ACTION_POINTER_UP:
showMsg("ACTION_POINTER_UP" + action);
break;
case MotionEvent.ACTION_POINTER_DOWN:
showMsg("ACTION_POINTER_DOWN" + action);
break;
}
return super.onTouchEvent(event);
}
 

ACTION_MASK     0x000000ff
ACTION_DOWN     0x00000000         ACTION_UP      0x00000001        ACTION_MOVE      0x00000002
ACTION_POINTER_DOWN       0x00000005            ACTION_POINTER_UP        0x00000006
ACTION_POINTER_1_DOWN     0x00000005            ACTION_POINTER_1_UP      0x00000006
ACTION_POINTER_2_DOWN     0x00000105            ACTION_POINTER_2_UP      0x00000106
 

例如：ACTION_MASK & ACTION_POINTER_2_DOWN 即0x000000ff & 0×00000105=0x0000005

可以看到，and運算的結果總是小於等於0x000000ff，那就是說and之後，無論你多少根手指加進來，都是會ACTION_POINTER_DOWN或者ACTION_POINTER_UP