SurfaceView的绘图机制

public class SurfaceViewTest extends Activity {

    //SurfaceHolder负责维护SurfaceView上绘制的内容
    private SurfaceHolder holder;
    private Paint paint;
    @Override
    protected void onCreate(Bundle savedInstanceState) {
        // TODO Auto-generated method stub
        super.onCreate(savedInstanceState);
        setContentView(R.layout.surface);
        paint=new Paint();
        SurfaceView surface=(SurfaceView) findViewById(R.id.surface);
        //初始化SurfaceView对象
        holder=surface.getHolder();
        holder.addCallback(new Callback() {
            @Override
            public void surfaceDestroyed(SurfaceHolder arg0) {
                // TODO Auto-generated method stub
            }
            @Override
            public void surfaceCreated(SurfaceHolder arg0) {
                // TODO Auto-generated method stub
                //锁定整个SurfaceView
                Canvas canvas=holder.lockCanvas();
                //绘制背景
                Bitmap back=BitmapFactory.decodeResource(SurfaceViewTest.this.getResources(), 
                        R.drawable.ic_launcher);
                canvas.drawBitmap(back, 0,0, null);
                //绘制完成，释放画布，提交修改
                holder.unlockCanvasAndPost(canvas);
                //重新锁一次，“持久化”上次所绘制的内容
                holder.lockCanvas(new Rect(0, 0, 0, 0));
                holder.unlockCanvasAndPost(canvas);
            }
            @Override
            public void surfaceChanged(SurfaceHolder arg0, int arg1, int arg2, int arg3) {
                // TODO Auto-generated method stub
            }
        });
        //为SurfaceView绑定监听事件
        surface.setOnTouchListener(new OnTouchListener() {
            
            @Override
            public boolean onTouch(View arg0, MotionEvent arg1) {
                // TODO Auto-generated method stub
                //按下的事件
                if(arg1.getAction()==MotionEvent.ACTION_DOWN){
                    int cx=(int) arg1.getX();
                    int cy=(int) arg1.getY();
                    //锁定SurfaceView的局部区域，只更新局部
                    Canvas canvas=holder.lockCanvas(new Rect(cx-50, cy-50, cx+50, cy+50));
                    //保存当前的状态
                    canvas.save();
                    canvas.rotate(30, cx, cy);
                    paint.setColor(Color.GREEN);
                    canvas.drawRect(cx-40, cy-40, cx, cy, paint);
                    canvas.restore();
                    paint.setColor(Color.RED);
                    canvas.drawRect(cx, cy, cx+40, cy+40, paint);
                    holder.unlockCanvasAndPost(canvas);
                }
                return false;
            }
        });
    }
}

    SurfaceView一般会与SurfaceHolder结合使用，SurfaceHolder用于向与之关联的SurfaceView上绘图，调用SurfaceView的getHolder()方法即可获取SurfaceView关联的SurfaceHolder。

  SurfaceHolder提供了如下方法来获取Canvas对象。

   Canvas lockCanvas():锁定SurfaceView对象，获取Surface上的Canvas。

   Canvas lockCanvas(Rect dirty):锁定SurfaceView上Rect划分的区域，获取该Surface上的Canvas。

   unlockCanvasAndPost（canva）；

  需要指出的是，当调用SurfaceHolder的 unlockCanvasAndPost方法之后，该方法之前绘制的图形还处于缓冲之中，下一次lockCanvas（）方法锁定的区域可能会“遮挡”它。