Easy C#.NET databinding question (to bind a string to a textbox) - very simple

C#.NET Visual Studio 2005 DataBinding  simple question. I have a class called TextParms and it has a get method and a field that returns a string.  I am using data binding to bind this to a text box, but what should be the value of the third parameter to get this to work?
TextParms tp = new TextParms(200, "Casablanca", Color.Beige);
Inside of the TextParms class I have a string holding "Casablanca"   public string m_strText;
Inside of the TextParms class I have a get method to return this string:  public string getString()

In order to bind the value of the string which will be Casablanca to this text box, what is the value I should place in the third parameter for the databinding.add method?  I can get this to work with null in the value and the ToString() method returning the string, but I need to figure out another way.
 textBox1.DataBindings.Add("Text", tbList, null);