… how do I get the content of the nstextfield and assign it to the name property ?
Translate that directly into Objective-C:
NSString *contentOfTheNSTextField = [myTextField stringValue];
myNewTask.name = contentOfTheNSTextField;
You'd do that in the action method that you've set both the button and the field to call.
I tried creating an outlet from the Todoitem class to the textfield, but xcode won't let me connect it....
To do this, the Todoitem would need to reside in the nib.
But, even if you could do that, why should the model object know about the text field? Carrying values between model and view is a controller's job.