Question

Say i have a tab control that displays data of various types, eg EditorTabViewModel, PreviewTabViewModel both inheriting from TabViewModel. The implementation is similar to the tutorial on MSDN

I want to enable buttons depending on the active tab, whether its an EditorTabViewModel or a PreviewTabViewModel. How can I achieve this?

UPDATE

public ICommand EditorCommand
{
    get
    {
        if (_editorCommand == null) {
            _editorCommand = new RelayCommand(() =>
            {
                MessageBox.Show("Editor");
            }, () =>
            {
                var enabled = true;
                var viewSource = CollectionViewSource.GetDefaultView(Tabs);
                viewSource.CurrentChanged += (o, e) =>
                {
                    if (viewSource.CurrentItem is EditorTabViewModel)
                    {
                        enabled = false;
                    }
                };
                return enabled;
            });
        }
        return _editorCommand;
    }
}

UPDATE 2

public ICommand PreviewCommand
{
    get
    {
        if (_previewCommand == null) {
            _previewCommand = new RelayCommand(() =>
            {
                MessageBox.Show("Preview");
            }, () =>
            {
                var viewSource = CollectionViewSource.GetDefaultView(Tabs);
                var enabled = viewSource.CurrentItem is EditorTabViewModel;
                viewSource.CurrentChanged += (o, e) =>
                {
                    CommandManager.InvalidateRequerySuggested();
                };
                return enabled;
            });
        }
        return _previewCommand;
    }
}

Answer 1

I would suggest that you create an ICommand implementation that constructs on the ICollectionView that contains the 2 tab controls. The command can then react to the CurrentChanged event from the collection view to determine whether or not it should be enabled, and raise a CanExecuteChanged event to indicate a change.

class MyCommand : ICommand
{
    private bool _isEnabled = true;

    public MyCommand(MyTopLevelViewModel viewModel)
    {
        var viewSource = CollectionViewSource.GetDefaultView(viewModel.Tabs);
        viewSource.CurrentChanged += (o,e) =>
            {
                _isEnabled = (viewSource.CurrentItem is EditorTabViewModel); //or however you want to decide

                if (this.CanExecuteChanged != null) 
                     this.CanExecuteChanged(this, EventArgs.Empty);

            };
    }

    public void Execute(object parameter) { /*...*/ }

    public bool CanExecute(object parameter) { return _isEnabled; }

    public event EventHandler CanExecuteChanged;
}

Note: you will need to set the IsSyncronizedWithCurrentItem property on the tab control:

<TabControl IsSynchronizedWithCurrentItem="True" />