Androin学习笔记五十六： android多点触控统一的原理(使用 event.getAction()&MotionEvent.ACTION_MASK的原因)

水深无声 2022-08-22 12:21 96阅读 0赞

出处：[http://blog.csdn.net/fancylovejava/article/details/38582983][http_blog.csdn.net_fancylovejava_article_details_38582983]

看到下面代码中用了AND位运算是为了什么呢？

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);

首先来看看这些常量的值

ACTION\_MASK 0x000000ff

ACTION\_DOWN 0x00000000ACTION\_UP0x00000001ACTION\_MOVE0x00000002

ACTION\_POINTER\_DOWN0x00000005ACTION\_POINTER\_UP0x00000006

ACTION\_POINTER\_1\_DOWN 0x00000005ACTION\_POINTER\_1\_UP0x00000006

ACTION\_POINTER\_2\_DOWN 0x00000105ACTION\_POINTER\_2\_UP0x00000106

例如：ACTION\_MASK & ACTION\_POINTER\_2\_DOWN 即0x000000ff & 0×00000105=0x0000005

可以看到，and运算的结果总是小于等于0x000000ff，那就是说and之后，无论你多少根手指加进来，都是会ACTION\_POINTER\_DOWN或者ACTION\_POINTER\_UP

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1.  imgitem.setOnTouchListener(**new** OnTouchListener() \{ 
2.  
3.   PointF start = **new** PointF(); 
4.   PointF mid = **new** PointF(); 
5.  **float** oldDist = 1f; 
6.   Matrix matrix = **new** Matrix(); 
7.   Matrix savedMatrix = **new** Matrix(); 
8.  **static****final****int** NONE = 0; 
9.  **static****final****int** DRAG = 1; 
10. **static****final****int** ZOOM = 2; 
11. **int** mode = NONE; 
12. 
13. **long** startTime; 
14. 
15. **public****boolean** onTouch(View v, MotionEvent event) \{ 
16.  ImageView view = (ImageView) v; 
17.  view.setScaleType(ScaleType.MATRIX); 
18. 
19. **switch** (event.getAction() & MotionEvent.ACTION\_MASK) \{ 
20. 
21. **case** MotionEvent.ACTION\_DOWN: 
22.  matrix.set(view.getImageMatrix()); 
23.  savedMatrix.set(matrix); 
24.  start.set(event.getX(), event.getY()); 
25.  mode = DRAG; 
26. // isclick = true;
27.  startTime = System.currentTimeMillis(); 
28. **break**; 
29. 
30. **case** MotionEvent.ACTION\_POINTER\_DOWN: 
31. // isclick = false;
32.  oldDist = spacing(event); 
33. **if** (oldDist > 10f) \{ 
34.  savedMatrix.set(matrix); 
35.  midPoint(mid, event); 
36.  mode = ZOOM; 
37.  \} 
38. **break**; 
39. 
40. **case** MotionEvent.ACTION\_UP: 
41. /\*if (mode == DRAG && System.currentTimeMillis() - startTime < 150) \{ 
42.  finish();
43.  overridePendingTransition(android.R.anim.fade\_in, android.R.anim.fade\_out);
44.  \}\*/
45. **break**; 
46. **case** MotionEvent.ACTION\_POINTER\_UP: 
47.  mode = NONE; 
48. **break**; 
49. **case** MotionEvent.ACTION\_MOVE: 
50. // isclick = false;
51. **if** (mode == DRAG) \{ 
52.  matrix.set(savedMatrix); 
53.  matrix.postTranslate(event.getX() - start.x, event.getY() - start.y); 
54.  \} **else****if** (mode == ZOOM) \{ 
55. **float** newDist = spacing(event); 
56. **if** (newDist > 10f) \{ 
57.  matrix.set(savedMatrix); 
58. **float** scale = newDist / oldDist; 
59.  matrix.postScale(scale, scale, mid.x, mid.y); 
60.  \} 
61.  \} 
62. **break**; 
63.  \} 
64. 
65.  view.setImageMatrix(matrix); 
66. 
67. **return****true**; 
68.  \} 
69. 
70. **private****float** spacing(MotionEvent event) \{ 
71. **float** x = event.getX(0) - event.getX(1); 
72. **float** y = event.getY(0) - event.getY(1); 
73. **return** FloatMath.sqrt(x \* x + y \* y); 
74.  \} 
75. 
76. **private****void** midPoint(PointF point, MotionEvent event) \{ 
77. **float** x = event.getX(0) + event.getX(1); 
78. **float** y = event.getY(0) + event.getY(1); 
79.  point.set(x / 2, y / 2); 
80.  \} 
81. 
82.  \});

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