用surfaceview开发示波器

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:orientation="vertical"
    android:layout_width="match_parent"
    android:layout_height="match_parent">
    <LinearLayout android:orientation="horizontal"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:gravity="center"
        >
        <Button android:id="@+id/sin"
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:text="sin"
            />
        <Button android:id="@+id/cos"
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:text="cos"
            />
    </LinearLayout>
    <SurfaceView android:id="@+id/show"
        android:layout_width="match_parent"
        android:layout_height="match_parent"
        android:gravity="center"
        />
</LinearLayout>

public class MainActivity extends Activity {
    private SurfaceHolder holder;
    private Paint paint;
    final int HEIGHT = 320;
    final int WIDTH = 768;
    final int X_OFFSET = 5;
    private int cx = X_OFFSET;
    // 实际的Y轴的位置
    int centerY = HEIGHT / 2;
    Timer timer = new Timer();
    TimerTask task = null;

    @Override
    public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        final SurfaceView surface = (SurfaceView) findViewById(R.id.show);
        // 初始化SurfaceHolder对象
        holder = surface.getHolder();
        paint = new Paint();
        paint.setColor(Color.GREEN);
        paint.setStrokeWidth(3);
        Button sin = (Button) findViewById(R.id.sin);
        Button cos = (Button) findViewById(R.id.cos);
        View.OnClickListener listener = (new View.OnClickListener() {
            @Override
            public void onClick(final View source) {
                drawBack(holder);//绘制x,y坐标
                cx = X_OFFSET;
                if (task != null) {
                    task.cancel();
                }
                task = new TimerTask() {
                    public void run() {
                        int cy = source.getId() == R.id.sin ? centerY
                                - (int) (100 * Math.sin((cx - 5) * 2
                                * Math.PI / 150))
                                : centerY - (int) (100 * Math.cos((cx - 5)
                                * 2 * Math.PI / 150));
                        Canvas canvas = holder.lockCanvas(new Rect(cx,
                                cy - 2, cx + 2, cy + 2));
                        canvas.drawPoint(cx, cy, paint);
                        cx++;
                        if (cx > WIDTH) {
                            task.cancel();
                            task = null;
                        }
                        holder.unlockCanvasAndPost(canvas);
                    }
                };
                timer.schedule(task, 0, 30);
            }
        });
        sin.setOnClickListener(listener);
        cos.setOnClickListener(listener);
        holder.addCallback(new SurfaceHolder.Callback() {
            @Override
            public void surfaceChanged(SurfaceHolder holder, int format,
                                       int width, int height) {
                drawBack(holder);
            }

            @Override
            public void surfaceCreated(final SurfaceHolder myHolder) {
            }

            @Override
            public void surfaceDestroyed(SurfaceHolder holder) {
                timer.cancel();
            }
        });
    }

    private void drawBack(SurfaceHolder holder) {
        Canvas canvas = holder.lockCanvas();
        // 绘制白色背景
        canvas.drawColor(Color.WHITE);
        Paint p = new Paint();
        p.setColor(Color.BLACK);
        p.setStrokeWidth(2);
        // 绘制坐标轴
        canvas.drawLine(X_OFFSET, centerY, WIDTH, centerY, p);//x轴
        canvas.drawLine(X_OFFSET, 40, X_OFFSET, HEIGHT, p);//y轴
        holder.unlockCanvasAndPost(canvas);
        holder.lockCanvas(new Rect(0, 0, 0, 0));
        holder.unlockCanvasAndPost(canvas);
    }
}