title: add UIImage in CALayer
body: <p>I must add a UIImageView as subview of MapView. To do this I created a layer above the MapView. In this layer I want to put my image, but I get a white rectangle and nothing else. My image is not visible.</p>
  
  <p>This is the code:</p>
  
  <pre><code>- (void)viewDidLoad
  {
      //......
  
      CALayer *layer = [CALayer layer];
      layer.backgroundColor = [[UIColor whiteColor] CGColor];
  
      if(UI_USER_INTERFACE_IDIOM() == UIUserInterfaceIdiomPhone)
      {
          layer.bounds = CGRectMake(self.mapView.bounds.origin.x,
                                    self.mapView.bounds.origin.y, 80, 300);
      }
      else
      {
          layer.bounds = CGRectMake(self.mapView.frame.origin.x,
                                    self.mapView.frame.origin.y, 150, 700);
      }
  
      layer.contents = (id)[UIImage imageNamed:@"myImage.png"];
      //the name is correct but  in the output the image is not visible
  
      [[self.mapView layer] addSublayer:layer];
      [layer setNeedsDisplay];
  }
  </code></pre>