Cast the returned Control reference to the real control's type. For example:
oTxt = (TextBox)SourceControl;
Some controls have access limitation and have to be called directly from the control's running thread. For such controls, you can access only Get properties.To invoke methods in the same thread as the control, use the indirect mechanism, ControlInvokeMethod.
If there are no threading issues, use the simple obj.Member syntax:
string txt = oTxt.Text;