当我按下按钮时，出现错误ViewRootImpl $ CalledFromWrongThreadException

Question

I tried to make a simple game on Android. The player is a blue ball and is supposed to avoid the moving objects. Once it hits it, the game is over. The game also ends if the player catches all the food objects. I got the collision detection working but when I tried to add a button afterwards to give the user the option to restart, I got the ViewRootImpl$CalledFromWrongThreadException error. The button is already declared in the onCreate method and the visibility is set to invisible, but when I change it to visible, I get the error. I have no idea how to fix it. I tried looking online and it wasn't much help. I understood that the error occcurs when you modify the UI in a non-UI thread, but how would you fix that? Any help would be appreciated. (:

Here is the run method:

@Override
public void run() {
    // TODO Auto-generated method stub
    while(locker==true){
        //checks if the lockCanvas() method will be success,and if not, will check this statement again
        if(!holder.getSurface().isValid()){
            continue;
        }
        /** Start editing pixels in this surface.*/
        Canvas canvas = holder.lockCanvas();
        draw(canvas);

        if (up==true){
            y=y-3;
        }
        else if(down==true){
            y=y+3;
        }
        else if (left==true){
            x=x-3;
        }
        else if (right==true){
            x=x+3;
        }

        int counter=0;

        for(int i=0;i<listOfFs.length;i++)
        {
            foodCaught [i] = listOfFs [i].check (x,y,radiusBlack);
            if (foodCaught [i] == true)
            {
                alive [i] = listOfFs [i].kill ();
            }
            else{
                counter++;
            }
        }
        if (counter==0){
            win=true;
            playAgain.setVisibility(View.VISIBLE);
        }
        for(int i=0;i<listOfCs.length;i++)
        {
            if (i<3){
                listOfCs[i].changeX(listOfCs[i].getX()+increment[i]);
            }
            else{
                listOfCs[i].changeY(listOfCs[i].getY()+increment[i]);
            }
        }

        for(int i=0;i<listOfCs.length;i++){
            if   (y+radiusBlack>listOfCs[i].getY()&& y-radiusBlack<listOfCs[i].getY()+listOfCs[i].getSize()&& x-radiusBlack<listOfCs[i].getX()+listOfCs[i].getSize()&& x+radiusBlack>listOfCs[i].getX())
            {
                chaserCaught = true;
                playAgain.setVisibility(View.VISIBLE);
            }
        }
        // End of painting to canvas. system will paint with this canvas,to the surface.
        holder.unlockCanvasAndPost(canvas);
    }
}

Answer 1

You can't touch views outside UI thread (and your SurfaceView drawning happens on non-UI thread). Just instead of doing this:

playAgain.setVisibility(View.VISIBLE);

do this:

playAgain.post(new Runnable() {
    @Override
    public void run() {
        playAgain.setVisibility(View.VISIBLE);
    }
});