meisw's blog

 我们曾就《Android手势识别ViewFlipper触摸动画》做过详细的讲解，其实，Android应用程序开发中，多点触摸（Multitouch）不是那么遥不可及，实现起来也很简单。如果您对开发多点触摸程序感兴趣的话，那么本文将是一个很好的开始，本例只需要两个类就能实现多点触摸。
首先来看看我们的视图类MTView.java:

1. package com.ideasandroid.demo;  
2.   
3. import android.content.Context;  
4. import android.graphics.Canvas;  
5. import android.graphics.Color;  
6. import android.graphics.Paint;  
7. import android.view.MotionEvent;  
8. import android.view.SurfaceHolder;  
9. import android.view.SurfaceView;  
10.   
11. public class MTView extends SurfaceView implements SurfaceHolder.Callback {  
12.   
13.     private static final int MAX_TOUCHPOINTS = 10;  
14.     private static final String START_TEXT = "请随便触摸屏幕进行测试";  
15.     private Paint textPaint = new Paint();  
16.     private Paint touchPaints[] = new Paint[MAX_TOUCHPOINTS];  
17.     private int colors[] = new int[MAX_TOUCHPOINTS];  
18.   
19.     private int width, height;  
20.     private float scale = 1.0f;  
21.   
22.     public MTView(Context context) {  
23.         super(context);  
24.         SurfaceHolder holder = getHolder();  
25.         holder.addCallback(this);  
26.         setFocusable(true); // 确保我们的View能获得输入焦点  
27.         setFocusableInTouchMode(true); // 确保能接收到触屏事件  
28.         init();  
29.     }  
30.   
31.     private void init() {  
32.         // 初始化10个不同颜色的画笔  
33.         textPaint.setColor(Color.WHITE);  
34.         colors[0] = Color.BLUE;  
35.         colors[1] = Color.RED;  
36.         colors[2] = Color.GREEN;  
37.         colors[3] = Color.YELLOW;  
38.         colors[4] = Color.CYAN;  
39.         colors[5] = Color.MAGENTA;  
40.         colors[6] = Color.DKGRAY;  
41.         colors[7] = Color.WHITE;  
42.         colors[8] = Color.LTGRAY;  
43.         colors[9] = Color.GRAY;  
44.         for (int i = 0; i < MAX_TOUCHPOINTS; i++) {  
45.             touchPaints[i] = new Paint();  
46.             touchPaints[i].setColor(colors[i]);  
47.         }  
48.     }  
49.   
50.     /*  
51.      * 处理触屏事件  
52.      */  
53.     @Override  
54.     public boolean onTouchEvent(MotionEvent event) {  
55.         // 获得屏幕触点数量  
56.         int pointerCount = event.getPointerCount();  
57.         if (pointerCount > MAX_TOUCHPOINTS) {  
58.             pointerCount = MAX_TOUCHPOINTS;  
59.         }  
60.         // 锁定Canvas,开始进行相应的界面处理  
61.         Canvas c = getHolder().lockCanvas();  
62.         if (c != null) {  
63.             c.drawColor(Color.BLACK);  
64.             if (event.getAction() == MotionEvent.ACTION_UP) {  
65.                 // 当手离开屏幕时，清屏  
66.             } else {  
67.                 // 先在屏幕上画一个十字，然后画一个圆  
68.                 for (int i = 0; i < pointerCount; i++) {  
69.                     // 获取一个触点的坐标，然后开始绘制  
70.                     int id = event.getPointerId(i);  
71.                     int x = (int) event.getX(i);  
72.                     int y = (int) event.getY(i);  
73.                     drawCrosshairsAndText(x, y, touchPaints[id], i, id, c);  
74.                 }  
75.                 for (int i = 0; i < pointerCount; i++) {  
76.                     int id = event.getPointerId(i);  
77.                     int x = (int) event.getX(i);  
78.                     int y = (int) event.getY(i);  
79.                     drawCircle(x, y, touchPaints[id], c);  
80.                 }  
81.             }  
82.             // 画完后，unlock  
83.             getHolder().unlockCanvasAndPost(c);  
84.         }  
85.         return true;  
86.     }  
87.   
88.     /**  
89.      * 画十字及坐标信息  
90.      *  
91.      * @param x  
92.      * @param y  
93.      * @param paint  
94.      * @param ptr  
95.      * @param id  
96.      * @param c  
97.      */  
98.     private void drawCrosshairsAndText(int x, int y, Paint paint, int ptr,  
99.             int id, Canvas c) {  
100.         c.drawLine(0, y, width, y, paint);  
101.         c.drawLine(x, 0, x, height, paint);  
102.         int textY = (int) ((15 + 20 * ptr) * scale);  
103.         c.drawText("x" + ptr + "=" + x, 10 * scale, textY,
104.         c.drawText("y" + ptr + "=" + y, 70 * scale, textY,
105.         c.drawText("id" + ptr + "=" + id, width - 55 * sc
106.     }  
107.   
108.     /**  
109.      * 画圆  
110.      *  
111.      * @param x  
112.      * @param y  
113.      * @param paint  
114.      * @param c  
115.      */  
116.     private void drawCircle(int x, int y, Paint paint, Canvas c
117.         c.drawCircle(x, y, 40 * scale, paint);  
118.     }  
119.   
120.     /*  
121.      * 进入程序时背景画成黑色，然后把“START_TEXT”写到屏幕  
122.      */  
123.     public void surfaceChanged(SurfaceHolder holder, int format, i
124.             int height) {  
125.         this.width = width;  
126.         this.height = height;  
127.         if (width > height) {  
128.             this.scale = width / 480f;  
129.         } else {  
130.             this.scale = height / 480f;  
131.         }  
132.         textPaint.setTextSize(14 * scale);  
133.         Canvas c = getHolder().lockCanvas();  
134.         if (c != null) {  
135.             // 背景黑色  
136.             c.drawColor(Color.BLACK);  
137.             float tWidth = textPaint.measureText(START_TEXT);
138.             c.drawText(START_TEXT, width / 2 - tWidth / 2
139.                     textPaint);  
140.             getHolder().unlockCanvasAndPost(c);  
141.         }  
142.     }  
143.   
144.     public void surfaceCreated(SurfaceHolder holder) {  
145.     }  
146.   
147.     public void surfaceDestroyed(SurfaceHolder holder) {  
148.     }  
149.   
150. }  

接下来看看我们的Activity，MultitouchVisible.java

1. package com.ideasandroid.demo;  
2.   
3. import android.app.Activity;  
4. import android.os.Bundle;  
5. import android.view.Window;  
6. import android.view.WindowManager;  
7.   
8. public class MultitouchVisible extends Activity {  
9.     @Override  
10.     public void onCreate(Bundle savedInstanceState) {  
11.         super.onCreate(savedInstanceState);  
12.         //隐藏标题栏  
13.         requestWindowFeature(Window.FEATURE_NO_TITLE);  
14.         //设置成全屏  
15.         getWindow().setFlags(WindowManager.LayoutParams.FLAG_FULLSCREEN,  
16.                 WindowManager.LayoutParams.FLAG_FULLSCREEN);  
17.         //设置为上面的MTView  
18.         setContentView(new MTView(this));  
19.     }  
20. }