title: Drawing on canvas and refreshing image
body: <p>Hello and sorry for my bad English.
  On my application, onDraw() method draws 10x10 field with lines using canvas.
  Then, in other method I want some cells to be painted in yellow for example. </p>
  
  <p>The code is: </p>
  
  <pre><code>    Paint ship = new Paint();
      ship.setColor(getResources().getColor(R.color.ship_color));
      Canvas canvas = new Canvas();
      Rect r = new Rect(x*(rebro_piece),y*rebro_piece, x*(rebro_piece+1), y*(rebro_piece+1));
      canvas.drawRect(r, ship);
  </code></pre>
  
  <p>but nothing happens. What shall I do?</p>
  
  <p><strong>UPD</strong>: am I right, that Canvas only draws within onDraw() method and from nothing else?</p>