为什么'；我的drawBitmap函数在第一次执行后工作（Android、Java）？

MainThread.java

package com.example.myapplication;

import android.graphics.Canvas;
import android.view.SurfaceHolder;

public class MainThread extends Thread {
    private SurfaceHolder surfaceHolder;
    private GameView gameView;
    private boolean running;
    public static Canvas canvas;

    private int targetFPS = 30;
    private double averageFPS;

    public MainThread(SurfaceHolder surfaceHolder, GameView gameView){
        super();

        this.surfaceHolder=surfaceHolder;
        this.gameView=gameView;
    }

    @Override
    public void run(){
        long startTime;
        long timeMillis;
        long waitTime;
        long totalTime = 0;
        int frameCount =0;
        long targetTime = 1000/targetFPS;

        while(running){
            startTime = System.nanoTime();
            canvas = null;

            try{
                canvas=this.surfaceHolder.lockCanvas();

                synchronized (surfaceHolder){
                    this.gameView.update();
                    this.gameView.draw(canvas);
                }
            } catch (Exception e){
                e.printStackTrace();
            } finally {
                if (canvas!=null){
                    try{
                        surfaceHolder.unlockCanvasAndPost(canvas);
                    } catch(Exception e){ e.printStackTrace(); }
                }
            }

            timeMillis = (System.nanoTime() - startTime) / 1000000;
            waitTime = targetTime-timeMillis;

            try{
                this.sleep(waitTime);
            }catch(Exception e){ e.printStackTrace(); }

            totalTime += System.nanoTime()-startTime;
            frameCount++;
            if(frameCount == targetFPS)
            {
                averageFPS = 1000/((totalTime/frameCount)/1000000);
                frameCount =0;
                totalTime = 0;
                System.out.println("AverageFPS: "+averageFPS);
            }
        }
    }

    public void setRunning(boolean isRunning){
        running=isRunning;
    }
}

Number.java

package com.example.myapplication;

import android.graphics.Bitmap;
import android.graphics.Canvas;

public class Number {
    private Bitmap number;
    private int x, y;

    Number(Bitmap num, int x, int y){
       number=num;

       this.x=x;
       this.y=y;
    }

    public void draw(Canvas canvas){
        canvas.drawBitmap(number, x, y, null);
    }

    public void update(){
        x++;
    }
}

GameView.java

package com.example.myapplication;

import android.content.Context;
import android.graphics.BitmapFactory;
import android.graphics.Canvas;
import android.view.SurfaceHolder;
import android.view.SurfaceView;

public class GameView extends SurfaceView implements SurfaceHolder.Callback{
    private MainThread thread;
    private Number One, Two, Three;

    public GameView(Context context){
        super(context);

        getHolder().addCallback(this);

        thread=new MainThread(getHolder(), this);
        setFocusable(true);
    }

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

    }

    @Override
    public void surfaceCreated(SurfaceHolder holder) {
        One=new Number(BitmapFactory.decodeResource(getResources(), R.drawable.one), 50, 50);
        Two=new Number(BitmapFactory.decodeResource(getResources(), R.drawable.ena), 50, 200);
        Three=new Number(BitmapFactory.decodeResource(getResources(), R.drawable.one), 50, 350);

        thread.setRunning(true);
        thread.start();
    }

    @Override
    public void surfaceDestroyed(SurfaceHolder holder) {
        boolean retry=true;
        while (retry){
            try{
                thread.setRunning(false);
                thread.join();
            } catch(InterruptedException e){
                e.printStackTrace();
            }
            retry=false;
        }
    }

    public void update(){
        One.update();
        Two.update();
        Three.update();
    }

    @Override
    public void draw(Canvas canvas) {
        super.draw(canvas);

        if(canvas!=null) {
            One.draw(canvas);
            Two.draw(canvas);
            Three.draw(canvas);
        }
    }
}

第一次绘制精灵，但在第一次绘制之后，它不会移动，除非我取消隐藏并隐藏操作栏

我知道：

• x变量将被更新
• 我的number类中的draw方法被调用
• 线程的循环正常工作

知道怎么修吗