[問題] surfaceView如何清空上一次的畫面?

[uzoo (coding....coding)]

先感謝進來看文章的各位大大!!

這問題小弟已經GOOGLE過

大部分都是建議畫一個全畫面的矩形來覆蓋上一次的畫面

小弟也有實做看看，不過 為什麼沒有效果阿啊啊啊啊啊!!

小弟是每3秒跟系統要一次時間 然後用drawText畫在畫面上!

結果畫出來的文字都一直重疊 嗚嗚

附上完整程式碼:
public class SurfaceVewTestActivity extends Activity implements
SurfaceHolder.Callback {
        private SurfaceView sv;
        private SurfaceHolder svHolder;
        private String time;
        private int width,height;
    /** Called when the activity is first created. */
    @Override
    public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);

        sv=new SurfaceView(this);
        WindowManager manager=(WindowManager)
getSystemService(WINDOW_SERVICE);
                Display display=manager.getDefaultDisplay();
                width=display.getWidth();
                height=display.getHeight();
                Log.d("uzoo", "width:"+width+" height:"+height);
        svHolder=sv.getHolder();
        svHolder.addCallback(this);
        setContentView(sv);
    }
        @Override
        protected void onResume() {
                // TODO Auto-generated method stub
                super.onResume();

        }
        @Override
        public void surfaceChanged(SurfaceHolder holder, int format, int width,
                        int height) {
                // TODO Auto-generated method stub

        }
        @Override
        public void surfaceCreated(SurfaceHolder holder) {
                // TODO Auto-generated method stub
                Log.d("uzoo", "ready to draw");

                handler.post(r);
        }
        @Override
        public void surfaceDestroyed(SurfaceHolder holder) {
                // TODO Auto-generated method stub

        }
    public void letsGoDrawing(String time){

        Paint paint=new Paint();
                paint.setColor(Color.RED);
                paint.setTextSize(25);
                Canvas vas=svHolder.lockCanvas();
                vas.drawText(time, 130, 130, paint);
                svHolder.unlockCanvasAndPost(vas);

    }
    Handler handler=new Handler();
    Runnable r=new Runnable() {

                @Override
                public void run() {
                        // TODO Auto-generated method stub
                        Canvas vas=svHolder.lockCanvas();
                        Paint paint=new Paint();
                        paint.setColor(Color.BLACK);
                        paint.setAntiAlias(true);
                        Rect rec=new Rect(0, 0, width, height);
                        vas.drawRect(rec, paint);
                        svHolder.unlockCanvasAndPost(vas);
                        String time=""+System.currentTimeMillis();
                        letsGoDrawing(time);
                        handler.postDelayed(r, 3000);
                }
        };
}

希望有大大能幫我解答 先謝過了!

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推 chrisho:不是每幀都畫嗎? 為什麼3秒才畫一次?
→ uzoo:恩~因為我在除錯 所以讓他更新頻率慢一點 不然跳超快的
→ uzoo:解決了~分享一下解法
→ uzoo:就是在畫出下次的時間之前要先畫一個全畫面的背景
→ uzoo:然後在畫上時間的字串
→ uzoo:重點是 畫這兩個圖是在一次的lockCanvas()中執行
→ uzoo:然後在unlockCanvas