android 关于SurfaceView(二)移动那条线

移动其实就是不停的擦除上一个图画，然后画新的图画，

这里起作用的原因是因为用到了Timer

Timer是定时器，定时的调用某个任务 

SurfaceView的使用是需要在ui线程中，所以这里需要同步synchronized

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.os.Bundle;
import android.view.SurfaceHolder;
import android.view.SurfaceView;
import android.view.View;
import android.widget.Button;

public class SurfaceTest extends Activity {
    private Button mBtn;
    private SurfaceView mSurface;
    private SurfaceHolder mSurfaceHolder;
    private Timer mTimer;
    private MyTimerTask mTimerTask;
    @Override
    public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.surfacetest);
        mBtn=(Button) this.findViewById(R.id.button1);
        mBtn.setOnClickListener(new BtnClick());
        mSurface=(SurfaceView) this.findViewById(R.id.surfaceView1);
        mSurfaceHolder=mSurface.getHolder();
        mTimer=new Timer();
        mTimerTask = new MyTimerTask();  
    }
    
    private class BtnClick implements View.OnClickListener {
        @Override
        public void onClick(View v) {    
            //执行任务在延时多少毫秒后,每隔多少毫秒执行一次
              mTimer.schedule(mTimerTask, 0,1000);
        }      
    }
    
    private void drawLine(float y)
    {
        synchronized(mSurfaceHolder)
        {
        Canvas c=mSurfaceHolder.lockCanvas();
        Paint p=new Paint();
        p.setColor(Color.RED);
        //清除
        c.drawColor(Color.BLACK);
        c.drawLine(10, y, 40, y, p);
        mSurfaceHolder.unlockCanvasAndPost(c);
        }
    }
    
    private int lasty=0;

    class MyTimerTask extends TimerTask {  
        @Override  
        public void run() {
            drawLine(lasty);
            lasty+=20;//向下  
            if (lasty > mSurface.getHeight() ) {//如果到了终点，则清屏重来  
                ClearDraw();  
                lasty = 0;
            }  
        }  
  
    }  
    void ClearDraw() {  
        synchronized(mSurfaceHolder)
        {
        Canvas canvas = mSurfaceHolder.lockCanvas(null);  
        canvas.drawColor(Color.BLACK);// 清除画布  
        mSurfaceHolder.unlockCanvasAndPost(canvas);  
        }
    }  
}

这里直接定义mTimer的间隔时间为1000是不对的，应该定义为一个小值，例如5,然后在实际执行任务的时候，再去判断时间

同时这里对画布的操作都是整块也是不对的,正确情况应该定义一块区域，只画需要画的区域

接下来到了我的目的，编写一个滚动播放图片的类