Android : Set legend margins in an achartEngine library

I'm trying to use the .setMargin(new int[] { 20, 30, 15, 30 }) command to set the margins of the legend of my graph. The problem is that it is not working. Can you please help me?

My code:

public class Graph(){
private DefaultRenderer mRenderer = new DefaultRenderer();

 protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
  (...)
   mRenderer.setLegendTextSize(25);
   mRenderer.setMargins(new int[] { 20, 30, 15, 30 });
  (...)
}