正弦余弦曲线的绘制动画

使用SurfaceView实现正弦余弦曲线的绘制动画！
主要代码如下：
  1 package com.example.surfaceviewtest;
  2 
  3 import java.util.Timer;
  4 import java.util.TimerTask;
  5 
  6 import android.app.Activity;
  7 import android.graphics.Canvas;
  8 import android.graphics.Color;
  9 import android.graphics.Paint;
 10 import android.graphics.Rect;
 11 import android.os.Bundle;
 12 import android.util.Log;
 13 import android.view.Menu;
 14 import android.view.MenuItem;
 15 import android.view.SurfaceHolder;
 16 import android.view.SurfaceHolder.Callback;
 17 import android.view.SurfaceView;
 18 
 19 public class ShowWave extends Activity {
 20 
 21     SurfaceView surfaceView;
 22     SurfaceHolder holder;
 23     Paint paint;
 24     final int HEIGHT = 320;
 25     final int WIDTH = 320;
 26     final int X_OFFSET = 5;
 27     private int cx = X_OFFSET;
 28     int CenterY = HEIGHT / 2;
 29     Timer timer;
 30     TimerTask task = null;
 31 
 32     @Override
 33     protected void onCreate(Bundle savedInstanceState) {
 34 
 35         super.onCreate(savedInstanceState);
 36         setContentView(R.layout.activity_main);
 37         surfaceView = (SurfaceView) findViewById(R.id.show);
 38 
 39         holder = surfaceView.getHolder();
 40         holder.addCallback(new Callback() {
 41 
 42             @Override
 43             public void surfaceDestroyed(SurfaceHolder holder) {
 44                 Log.i("csx", "surfaceDestroyed");
 45                 timer.cancel();
 46             }
 47 
 48             @Override
 49             public void surfaceCreated(SurfaceHolder holder) {
 50                 Log.i("csx", "surfaceCreated");
 51                 timer = new Timer();
 52                 drawBack(holder);
 53 
 54             }
 55 
 56             @Override
 57             public void surfaceChanged(SurfaceHolder holder, int format, int width, int height) {
 58                 Log.i("csx", "surfaceChanged");
 59 
 60             }
 61         });
 62 
 63         paint = new Paint();
 64         paint.setColor(Color.GREEN);
 65         paint.setStrokeWidth(3);
 66 
 67     }
 68 
 69     @Override
 70     public boolean onCreateOptionsMenu(Menu menu) {
 71 
 72         getMenuInflater().inflate(R.menu.main, menu);
 73         return true;
 74     }
 75 
 76     @Override
 77     public boolean onOptionsItemSelected(MenuItem item) {
 78 
 79         int id = item.getItemId();
 80         drawWave(id);
 81         return super.onOptionsItemSelected(item);
 82     }
 83 
 84     public void drawWave(final int item_id) {
 85         if (task != null) {
 86             task.cancel();
 87         }
 88         drawBack(holder);
 89         cx = X_OFFSET;
 90 
 91         task = new TimerTask() {
 92 
 93             @Override
 94             public void run() {
 95                 int cy = item_id == R.id.sin ? CenterY
 96                         - (int) (100 * Math.sin((cx - 5) * 2 * Math.PI / 150)) : CenterY
 97                         - (int) (100 * Math.cos((cx - 5) * 2 * Math.PI / 150));
 98 
 99                 try {
100                     Canvas canvas = holder.lockCanvas(new Rect(cx, cy - 2, cx + 2, cy + 2));
101                     canvas.drawPoint(cx, cy, paint);
102                     cx++;
103                     if (cx > WIDTH) {
104                         task.cancel();
105                         task = null;
106                     }
107                     holder.unlockCanvasAndPost(canvas);
108                 } catch (NullPointerException e) {
109                     return;
110                 }
111 
112             }
113         };
114 
115         timer.schedule(task, 0, 30);
116 
117     }
118 
119     private void drawBack(SurfaceHolder holder) {
120         Canvas canvas = holder.lockCanvas();
121         canvas.drawColor(Color.WHITE);
122         Paint p = new Paint();
123         p.setColor(Color.BLACK);
124         p.setStrokeWidth(3);
125         canvas.drawLine(X_OFFSET, CenterY, WIDTH, CenterY, p);
126         canvas.drawLine(X_OFFSET, 40, X_OFFSET, HEIGHT, p);
127         holder.unlockCanvasAndPost(canvas);
128         holder.lockCanvas(new Rect(0, 0, 0, 0));
129         holder.unlockCanvasAndPost(canvas);
130 
131     }
132 
133 }