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：

package com.example.surfaceviewtest;

import java.util.Timer;
import java.util.TimerTask;

import android.app.Activity;
import android.graphics.Canvas;
import android.graphics.Color;
import android.graphics.Paint;
import android.graphics.Rect;
import android.os.Bundle;
import android.util.Log;
import android.view.Menu;
import android.view.MenuItem;
import android.view.SurfaceHolder;
import android.view.SurfaceHolder.Callback;
import android.view.SurfaceView;

public class ShowWave extends Activity {

    SurfaceView surfaceView;
    SurfaceHolder holder;
    Paint paint;
    final int HEIGHT = 320;
    final int WIDTH = 320;
    final int X_OFFSET = 5;
    private int cx = X_OFFSET;
    int CenterY = HEIGHT / 2;
    Timer timer;
    TimerTask task = null;

    @Override
    protected void onCreate(Bundle savedInstanceState) {

        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        surfaceView = (SurfaceView) findViewById(R.id.show);

        holder = surfaceView.getHolder();
        holder.addCallback(new Callback() {

            @Override
            public void surfaceDestroyed(SurfaceHolder holder) {
                Log.i("csx", "surfaceDestroyed");
                timer.cancel();
            }

            @Override
            public void surfaceCreated(SurfaceHolder holder) {
                Log.i("csx", "surfaceCreated");
                timer = new Timer();
                drawBack(holder);

            }

            @Override
            public void surfaceChanged(SurfaceHolder holder, int format, int width, int height) {
                Log.i("csx", "surfaceChanged");

            }
        });

        paint = new Paint();
        paint.setColor(Color.GREEN);
        paint.setStrokeWidth(3);

    }

    @Override
    public boolean onCreateOptionsMenu(Menu menu) {

        getMenuInflater().inflate(R.menu.main, menu);
        return true;
    }

    @Override
    public boolean onOptionsItemSelected(MenuItem item) {

        int id = item.getItemId();
        drawWave(id);
        return super.onOptionsItemSelected(item);
    }

    public void drawWave(final int item_id) {
        if (task != null) {
            task.cancel();
        }
        drawBack(holder);
        cx = X_OFFSET;

        task = new TimerTask() {

            @Override
            public void run() {
                int cy = item_id == 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));

                try {
                    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);
                } catch (NullPointerException e) {
                    return;
                }

            }
        };

        timer.schedule(task, 0, 30);

    }

    private void drawBack(SurfaceHolder holder) {
        Canvas canvas = holder.lockCanvas();
        canvas.drawColor(Color.WHITE);
        Paint p = new Paint();
        p.setColor(Color.BLACK);
        p.setStrokeWidth(3);
        canvas.drawLine(X_OFFSET, CenterY, WIDTH, CenterY, p);
        canvas.drawLine(X_OFFSET, 40, X_OFFSET, HEIGHT, p);
        holder.unlockCanvasAndPost(canvas);
        holder.lockCanvas(new Rect(0, 0, 0, 0));
        holder.unlockCanvasAndPost(canvas);

    }

}