Why do these tabs seem to share the same textbox?

Question

I defined my UI in xaml and below is my code:

Answer 1

It seems like your Model implement

ObservableCollection<MyHomeworkModel>.

Remove this Base class and it should work.

Edit:

Your need to change:

       AddCourseCommand = new AddCourseCommand(this);

To

Download DelegateCommand

       AddCourseCommand = new DelegateCommand(AddNewTab);

Edit:

You Cut your ViewModel from your UI. You Copy an Instance into your Command and than call on that Copy add. This is wrong and Property your Fault. I realy advice you to use DelegateCommand this will maybe fix it.

To your guess:

think I know why it's complaining. My Text property is is MyHomeworkModel not MyHomeworkViewModel...but why it's fine with me binding the header to the Header property in MyHomeworkModel ?

It is right that your Property is in MyHomeworkModel and not in MyHomeworkViewModel you Bind onto a List that contains MyHomeworkModels. Now is you add a new item your Binding will set in the Lowest level. In this case in your insance of MyHomeworkModel and not in MyHomeworkViewModel