[轉載]Android通過手勢（多點）縮放和拖拽圖片

原文地址:Android通過手勢（多點）縮放和拖拽圖片    作者:望夜

在MotionEvent中有兩個事件值得注意一下，分別是ACTION_DOWN和ACTION_POINTER_DOWN。

       ACTION_DOWN：這個很好理解，當屏幕檢測到有手指按下之後就觸發到這個事件。
       ACTION_POINTER_DOWN：這個是實現多點的關鍵，當屏幕檢測到有多個手指同時按下之後，就觸發了這個事件。
通過getAction()可以獲得當前屏幕的事件類型：ACTION_DOWN, ACTION_MOVE, ACTION_UP, orACTION_CANCEL。但是如果像獲得如上的ACTION_POINTER_DOWN，則得和ACTION_MASK相與才能得到ACTION_POINTER_DOWN事件。

       所以我們運用一個switch-case結構就可以實現對圖片進行拖拽或縮放，而縮放的只要思想是在移動的過程中計算兩個點之間的距離，然後再進行縮放。

      上代碼：

1.       @Override
   
2.        publicboolean onTouch(View v, MotionEvent event) {
   
3.              ImageViewview = (ImageView) v;
   
4.             dumpEvent(event);
   
5.              // Handletouch events here...
   
6.              switch(event.getAction() & MotionEvent.ACTION_MASK){
   
7.              caseMotionEvent.ACTION_DOWN:
   
8.                  matrix.set(view.getImageMatrix());
   
9.                  savedMatrix.set(matrix);
   
10.                  start.set(event.getX(), event.getY());
    
11.                   //Log.d(TAG,"mode=DRAG");
    
12.                   mode =DRAG;
    
13.                   //Log.d(TAG,"mode=NONE");
    
14.                  break;
    
15.              caseMotionEvent.ACTION_POINTER_DOWN:
    
16.                   oldDist =spacing(event);
    
17.                   //Log.d(TAG,"oldDist=" + oldDist);
    
18.                   if (oldDist> 10f) {
    
19.                        savedMatrix.set(matrix);
    
20.                        midPoint(mid,event);
    
21.                        mode =ZOOM;
    
22.                        //Log.d(TAG,"mode=ZOOM");
    
23.                   }//ACTION_DOWN, ACTION_MOVE, ACTION_UP, or ACTION_CANCEL.
    
24.                  break;
    
25.              caseMotionEvent.ACTION_UP:
    
26.              caseMotionEvent.ACTION_POINTER_UP:
    
27.                   mode =NONE;
    
28.                  break;
    
29.              caseMotionEvent.ACTION_MOVE:
    
30.                   if (mode ==DRAG) {
    
31.                        //...
    
32.                        matrix.set(savedMatrix);
    
33.                        matrix.postTranslate(event.getX()- start.x, event.getY()
    
34.                                   -start.y);
    
35.                   } else if(mode == ZOOM) {
    
36.                        float newDist= spacing(event);
    
37.                        //Log.d(TAG,"newDist=" + newDist);
    
38.                        if (newDist> 10f) {
    
39.                             matrix.set(savedMatrix);
    
40.                              float scale= newDist / oldDist;
    
41.                             matrix.postScale(scale, scale, mid.x, mid.y);
    
42.                        }
    
43.                   }
    
44.                  break;
    
45.             }
    
46. 
    
47.             view.setImageMatrix(matrix);
    
48.              returntrue; // indicate event was handled
    
49.        }
    
50. 
    
51.        private voiddumpEvent(MotionEvent event) {
    
52.              Stringnames[] = { "DOWN", "UP", "MOVE", "CANCEL", "OUTSIDE",
    
53.                        "POINTER_DOWN","POINTER_UP", "7?", "8?", "9?" };
    
54.             StringBuilder sb = new StringBuilder();
    
55.              int action= event.getAction();
    
56.              intactionCode = action &MotionEvent.ACTION_MASK;
    
57.             sb.append("event ACTION_").append(names[actionCode]);
    
58.              if(actionCode == MotionEvent.ACTION_POINTER_DOWN
    
59.                        || actionCode== MotionEvent.ACTION_POINTER_UP) {
    
60.                  sb.append("(pid ").append(
    
61.                              action>>MotionEvent.ACTION_POINTER_ID_SHIFT);
    
62.                  sb.append(")");
    
63.             }
    
64.             sb.append("[");
    
65.              for (int i= 0; i < event.getPointerCount(); i++) {
    
66.                  sb.append("#").append(i);
    
67.                  sb.append("(pid").append(event.getPointerId(i));
    
68.                  sb.append(")=").append((int)event.getX(i));
    
69.                  sb.append(",").append((int)event.getY(i));
    
70.                   if (i + 1< event.getPointerCount())
    
71.                        sb.append(";");
    
72.             }
    
73.             sb.append("]");
    
74.             //Log.d(TAG, sb.toString());
    
75.        }

複製代碼

求兩點間距離：

1. private float spacing(MotionEvent event) {
   
2.              float x =event.getX(0) - event.getX(1);
   
3.              float y =event.getY(0) - event.getY(1);
   
4.              returnFloatMath.sqrt(x * x + y * y);
   
5.        }

複製代碼

求兩點間中點：

1.        private voidmidPoint(PointF point, MotionEvent event) {
   
2.              float x =event.getX(0) + event.getX(1);