一个关于android surfaceView的问题，求大神回答

Question

surfaceView据说双缓存，两画布换来换去，但是我post后画布有时候还有有时候就没了
surfaceCreated方法里，最后的
canvas=sfh.lockCanvas();
sfh.unlockCanvasAndPost(canvas);
多加几个少加几个出现不同的情况，这个是怎么回事，大神求帮忙TT

下面是代码 clock.java

 package com.app.jtj.clock;

import android.content.Context;
import android.graphics.Canvas;
import android.graphics.Color;
import android.graphics.Paint;
import android.graphics.Rect;
import android.text.format.Time;
import android.util.Log;
import android.view.SurfaceHolder;
import android.view.SurfaceView;

/**
 * Created by Administrator on 2015/11/18.
 */
public class Clock extends SurfaceView implements SurfaceHolder.Callback,Runnable{

    private int w,h=0;
    private int mCP=0;
    private int xxxR=0;
    private int xxR=0;
    private int xR=0;
    private int R=0;
    private int mR=0;
    private float du=0;
    private Time t=new Time();
    private Time tP=new Time();

    private SurfaceHolder sfh;
    private Paint paint;
    private Canvas canvas;
    private boolean flag=true;
    private Thread th;

    public Clock(Context context) {
        super(context);
        sfh = this.getHolder();
        sfh.addCallback(this);
    }

    private void init() {
        mCP= (int) (w * 0.5);
        xxxR = (int) ( w * 0.93 * 0.5);
        xxR = (int) ( w * 0.90 * 0.5);
        xR = (int) ( w * 0.85 * 0.5);
        R = (int) ( w * 0.80 * 0.5);
        mR = (int) ( w * 0.75 * 0.5);
    }

    private void initView() {
        //canvas.drawColor(Color.WHITE);

        //画圆
        paint.setStyle(Paint.Style.STROKE);
        paint.setStrokeWidth(5);
        paint.setARGB(255, 150, 150, 150);
        canvas.drawCircle(mCP, mCP, xR, paint);

        paint.setStrokeWidth(1);
        paint.setARGB(255, 150, 150, 150);
        canvas.drawCircle(mCP, mCP, R, paint);

        //刻度
        paint.setStrokeWidth(10);
        for (int i=0;i<12;i++){
            canvas.drawLine(mCP,mCP-xR,mCP,mCP-xxR,paint);
            canvas.rotate(30,mCP,mCP);
        }

        paint.setStrokeWidth(10);
        paint.setARGB(255, 20, 20, 20);
        for (int i=0;i<4;i++){
            canvas.drawLine(mCP,mCP-xR,mCP,mCP-xxxR,paint);
            canvas.rotate(90,mCP,mCP);
        }

        //日期时间
        tP.setToNow();
        t.setToNow();
        paint.setStyle(Paint.Style.FILL_AND_STROKE);
        paint.setTextSize((float) (w * 0.05));
        paint.setStrokeWidth(1);
        int month=tP.month+1;
        String str1=tP.year + "."+month+"."+tP.monthDay;
        float numb1=paint.measureText(str1);
        canvas.drawText(str1, mCP-numb1/2, (float) (w*0.30), paint);
        str1=getWeek(tP);
        numb1=paint.measureText(str1);
        canvas.drawText(str1, mCP-numb1/2, (float) (w*0.70), paint);

    }

    private String getWeek(Time t) {
        String str2="";
        switch (t.weekDay){
            case 0:str2="星期日";break;
            case 1:str2="星期一";break;
            case 2:str2="星期二";break;
            case 3:str2="星期三";break;
            case 4:str2="星期四";break;
            case 5:str2="星期五";break;
            case 6:str2="星期六";break;
        }
        return str2;
    }

    @Override
    public void run() {

        }

    @Override
    public void surfaceCreated(SurfaceHolder holder) {

        w=this.getWidth();
        h = this.getHeight();
        flag=true;
        paint =new Paint();
        paint.setColor(Color.WHITE);
        paint.setAntiAlias(true);

        for (int i=0;i<2;){
            canvas=sfh.lockCanvas(new Rect(0,0,w,h));
            if (canvas!=null){
                i++;
                canvas.drawColor(Color.WHITE);
                sfh.unlockCanvasAndPost(canvas);
            }
        }

        for (int i=0;i<2;) {
            canvas = sfh.lockCanvas();
            if (canvas!=null) {
                init();
                Log.i("ttt", "1");
                initView();

                i++;
                sfh.unlockCanvasAndPost(canvas);
            }
        }
        canvas=sfh.lockCanvas();
        sfh.unlockCanvasAndPost(canvas);
        canvas=sfh.lockCanvas();
        sfh.unlockCanvasAndPost(canvas);
        canvas=sfh.lockCanvas();
        sfh.unlockCanvasAndPost(canvas);
        canvas=sfh.lockCanvas();
        sfh.unlockCanvasAndPost(canvas);

        //th = new Thread(this);
        //th.start();
    }

    @Override
    public void surfaceChanged(SurfaceHolder holder, int format, int width, int height) {

    }

    @Override
    public void surfaceDestroyed(SurfaceHolder holder){
        flag=false;
    }

}

activity里就加了
requestWindowFeature(Window.FEATURE_NO_TITLE);
setContentView(new Clock(this));

Answer 1

无报错，log.i,"ttt"有打印，也就是方法有执行