How to save the tab order of tabcontrol items which are bound to an ObservableCollection in wpf?

Question

I have a ObservableCollection which is bound to a tabcontrol .

<TabControl
    ItemsSource="{Binding Steps}"
    SelectedItem="{Binding SelectedStep}"
    CanUserReorder="{Binding EditMode}"
</TabControl>

The user can reorder the tab items, if he is in EditMode. When I am leaving the view with the tabcontrol, I lose the tab order, which was modified by the user. How can I prevent this?

Thanks for your help!

Answer 1

I got it! This solution is implemented in mvvm-pattern.

Every time the collection Steps is changing add or remove the items and afterwards reorder their positions. The TabItems of the TabControl in the View could be reordered by the user through using TabControl of ComponentOne or by using Bea Stollnitz's Drag/Drop functionality.

ViewModel:

public class MyViewModel
{
    public MyModel Model {/*get... set*/}
    public ObservableCollection<StepViewModel> Steps {/*get... set...*/}
    public StepViewModel SelectedStep {/*get... set...*/}

    public MyViewModel()
    {
        Model = new MyModel();
        Steps = new ObservableCollection<StepViewModel>();
        Model.Steps = new ObservableCollection<StepModel>();
        // Load the saved Model with the steps and their positions
        Model.Steps = LoadFromXml();

        Steps.CollectionChanged += Steps_OnCollectionChanged;
        // Add the Steps in the right order
        for (int i = 0; i < Steps.Count; i++)
        {
             var item = Steps.First(x => x.Position == i);
             var vm = new StepViewModel();
             Steps.Add(vm);
        }
    }

    private void Steps_OnCollectionChanged(object sender, NotifyCollectionChangedEventArgs e)
    {
        if (e.Action == NotifyCollectionChangedAction.Add)
        {
            foreach (StepViewModel vm in e.NewItems)
            {
                if (!Model.Steps.Contains(vm.Model))
                    Model.Steps.Add(vm.Model);
            }
        }
        else if (e.Action == NotifyCollectionChangedAction.Remove)
        {
            foreach (StepViewModel vm in e.OldItems)
            {
                if (Model.Steps.Contains(vm.Model))
                    Model.Steps.Remove(vm.Model);
            }
        }
        // Match the temporary collectionindex to a position-property
        foreach (StepViewModel item in Steps)
        {
            item.Position = Steps.IndexOf(item);
        }
    }

}