[MonoTouch] Access a property of an outlet in a new method

[Salmo Junior]

Hello,

I'm having trouble getting access a property of an 
outlet in a new method, for example:

        public partial class ViewApresentacao : UIViewController
	{
		...
                ...
		public override void ViewDidLoad ()
		{
			base.ViewDidLoad ();

			//my ImageView 
			imgModelo.Image = UIImage.FromBundle ("Image/car.png");
		}

		public void ImagemModelo(string caminho)
		{
                        imgModelo.Image = UIImage.FromBundle (caminho);
		}
                ....
        }

At viewDidLoad functions normally, but the second did not, 
wanted to use it to update when a selected 
row in a table, it's all working but when I call the method of 
the error "object reference not set to an 
instance of an object", can someone help me?

Sorry if I was not very clear, I'm from Brazil and I'm 
using google translate!

Hugs