Databinding - Refresh Problem

I want to bind a control to a dataset that is inside
another object. When the dataset in the object changes
the changes are not reflected in my control. See the code
below for more details...

public class WinForm : System.Windows.Forms.Form
{
MyClass myObj;
public WinForm()
{ ...
myObj = new MyClass();
txt.DataBindings.Add(new System.Windows.Forms.Binding
("Text", myObj.myDS, "MyTable.MyField"));
...
}
// if changes are made to myObj.myDS the text inside
the textbox won't change...
}

public class MyClass
{
public MyDS myDS;
public MyClass()
{
myDS = new MyDS();
myDA.Fill(myDS);
}
}

Any idea of what is wrong?

Thanks a lot!
Marc