Question

I have written following simple code to see the behavior of rendering. In this code i’m changing the color of screen.

The thing that I can’t understand is, why this code is running for ever? I didn’t use unlimited loop but this code will run for ever!

Please tell me the reason. Thanks

package kamalan.com.androidbasicstarter;

import java.util.Random;

import android.app.Activity;
import android.content.Context;
import android.graphics.Canvas;
import android.os.Bundle;
import android.view.View;
import android.view.Window;
import android.view.WindowManager;

public class RenderViewTest extends Activity{

    class RenderView extends View{
        Random rand = new Random();

        public RenderView(Context context) {
            super(context);
        }

        protected void onDraw(Canvas canvas){
            canvas.drawRGB(rand.nextInt(256), rand.nextInt(256), rand.nextInt(256));
            invalidate();
        }
    }

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        requestWindowFeature(Window.FEATURE_NO_TITLE);
        getWindow().setFlags(WindowManager.LayoutParams.FLAG_FULLSCREEN, WindowManager.LayoutParams.FLAG_FULLSCREEN);
        setContentView(new RenderView(this));
    }
}

Answer 1

invalidate causes a redraw. It’s usually (always?) a bad idea to call that from onDraw, because it will cause onDraw to be called again immediately. Which is what you are seeing.