Redraw Canvas by calling invalidate method

import android.app.Activity;
import android.content.Context;
import android.graphics.Canvas;
import android.graphics.Paint;
import android.os.Bundle;
import android.view.View;
/*from   w  ww  .j ava2s .co  m*/
import java.util.Random;

public class MainActivity extends Activity {

   @Override
   public void onCreate(Bundle savedInstanceState) {
      super.onCreate(savedInstanceState);

      setContentView(new CanvasView(this));
   }

   class CanvasView extends View {
      Paint paint;
      Random random = new Random();

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

      @Override
      protected void onDraw(Canvas canvas) {
         canvas.drawRGB(0, 0, 0);
         for (int i = 0; i < 10; i++) {
            paint = new Paint();
            paint.setARGB(random.nextInt(256), random.nextInt(256), random.nextInt(256), random.nextInt(256));
            canvas.drawLine(random.nextInt(canvas.getWidth()), random.nextInt(canvas.getHeight()),
                     random.nextInt(canvas.getWidth()), random.nextInt(canvas.getHeight()), paint);
            canvas.drawCircle(random.nextInt(canvas.getWidth() - 30), random.nextInt(canvas.getHeight() - 30),
                     random.nextInt(30), paint);
            canvas.drawRect(random.nextInt(canvas.getWidth()), random.nextInt(canvas.getHeight()),
                     random.nextInt(canvas.getWidth()), random.nextInt(canvas.getHeight()), paint);
         }
         invalidate();
      }
   }
}