Nikita B Nikita B - 3 months ago 78
C# Question

How to cancel tab change in WPF TabControl

I have found multiple questions about this problem on SO, however I still can't quite get a realiable solution. Here is what I came up with after reading the answers.

Xaml:

<Window x:Class="WpfApplication1.MainWindow"
xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml" Title="MainWindow" Height="300" Width="300" x:Name="this">
<TabControl IsSynchronizedWithCurrentItem="True" ItemsSource="{Binding Tabs, ElementName=this}" x:Name="TabControl"/>
</Window>


Code behind:

public partial class MainWindow : Window
{
public MainWindow()
{
InitializeComponent();
var tabs = new ObservableCollection<string> {"Tab1", "Tab2", "Tab3"};
Tabs = CollectionViewSource.GetDefaultView(tabs);
Tabs.CurrentChanging += OnCurrentChanging;
Tabs.CurrentChanged += OnCurrentChanged;
Tabs.MoveCurrentToFirst();
CurrentTab = tabs.First();
}

private void OnCurrentChanging(object sender, CurrentChangingEventArgs e)
{
//only show message box when tab is changed by user input
if (!_cancelTabChange)
{
if (MessageBox.Show("Change tab?", "Message", MessageBoxButton.YesNo) == MessageBoxResult.No)
{
_cancelTabChange = true;
return;
}
}
_cancelTabChange = false;
}

private void OnCurrentChanged(object sender, EventArgs e)
{
if (!_cancelTabChange)
{
//Update current tab property, if user did not cancel transition
CurrentTab = (string)Tabs.CurrentItem;
}
else
{
//navigate back to current tab otherwise
Dispatcher.BeginInvoke(new Action(() => Tabs.MoveCurrentTo(CurrentTab)));
}
}

public string CurrentTab { get; set; }

public static readonly DependencyProperty TabsProperty = DependencyProperty.Register("Tabs", typeof(ICollectionView), typeof(MainWindow), new FrameworkPropertyMetadata(default(ICollectionView)));
public ICollectionView Tabs
{
get { return (ICollectionView)GetValue(TabsProperty); }
set { SetValue(TabsProperty, value); }
}

private bool _cancelTabChange;
}


Basically I want to display a confirmation message, when user navigates to different tab, and if he clicks "no" - abort the transition. This code does not work though. If you click multiple times on "Tab2", each time choosing "no" in message box, at some point it stops working: events stop triggering. Event will trigger again if you click on "Tab3", but if you choose "yes" it opens second tab and not third. I am having trouble figuring out wtf is going on. :)

Does anyone see a bug in my solution? Or is there an easier way to display a confirmation message, when user switches tabs? I am also willing to use any opensource tab control, which does have a proper
SelectionChanging
event. I could not find any though.

I am using .Net 4.0.

Edit:
If I comment the message box out:

private void OnCurrentChanging(object sender, CurrentChangingEventArgs e)
{
//only show message box when tab is changed by user input
if (!_cancelTabChange)
{
//if (MessageBox.Show("Change tab?", "Message", MessageBoxButton.YesNo) == MessageBoxResult.No)
//{
Debug.WriteLine("Canceled");
_cancelTabChange = true;
return;
//}
}
_cancelTabChange = false;
}


Everything works fine. Weird.

Answer

This solution http://coderelief.net/2011/11/07/fixing-issynchronizedwithcurrentitem-and-icollectionview-cancel-bug-with-an-attached-property/

seems to work quite well with

<TabControl ... yournamespace:SelectorAttachedProperties.IsSynchronizedWithCurrentItemFixEnabled="True" .../>

private void OnCurrentChanging(object sender, CurrentChangingEventArgs e)
{                   
    if (MessageBox.Show("Change tab?", "Message", MessageBoxButton.YesNo) == MessageBoxResult.No)
    {
        e.Cancel = true;                    
    }                     
}



public static class SelectorAttachedProperties
{
    private static Type _ownerType = typeof(SelectorAttachedProperties);

    #region IsSynchronizedWithCurrentItemFixEnabled

    public static readonly DependencyProperty IsSynchronizedWithCurrentItemFixEnabledProperty =
        DependencyProperty.RegisterAttached("IsSynchronizedWithCurrentItemFixEnabled", typeof(bool), _ownerType,
        new PropertyMetadata(false, OnIsSynchronizedWithCurrentItemFixEnabledChanged));

    public static bool GetIsSynchronizedWithCurrentItemFixEnabled(DependencyObject obj)
    {
        return (bool)obj.GetValue(IsSynchronizedWithCurrentItemFixEnabledProperty);
    }

    public static void SetIsSynchronizedWithCurrentItemFixEnabled(DependencyObject obj, bool value)
    {
        obj.SetValue(IsSynchronizedWithCurrentItemFixEnabledProperty, value);
    }

    private static void OnIsSynchronizedWithCurrentItemFixEnabledChanged(DependencyObject d, DependencyPropertyChangedEventArgs e)
    {
        Selector selector = d as Selector;
        if (selector == null || !(e.OldValue is bool && e.NewValue is bool) || e.OldValue == e.NewValue)
            return;

        bool enforceCurrentItemSync = (bool)e.NewValue;
        ICollectionView collectionView = null;

        EventHandler itemsSourceChangedHandler = null;
        itemsSourceChangedHandler = delegate
        {
            collectionView = selector.ItemsSource as ICollectionView;
            if (collectionView == null)
                collectionView = CollectionViewSource.GetDefaultView(selector);
        };

        SelectionChangedEventHandler selectionChangedHanlder = null;
        selectionChangedHanlder = delegate
        {
            if (collectionView == null)
                return;

            if (selector.IsSynchronizedWithCurrentItem == true && selector.SelectedItem != collectionView.CurrentItem)
            {
                selector.IsSynchronizedWithCurrentItem = false;
                selector.SelectedItem = collectionView.CurrentItem;
                selector.IsSynchronizedWithCurrentItem = true;
            }
        };

        if (enforceCurrentItemSync)
        {
            TypeDescriptor.GetProperties(selector)["ItemsSource"].AddValueChanged(selector, itemsSourceChangedHandler);
            selector.SelectionChanged += selectionChangedHanlder;
        }
        else
        {
            TypeDescriptor.GetProperties(selector)["ItemsSource"].RemoveValueChanged(selector, itemsSourceChangedHandler);
            selector.SelectionChanged -= selectionChangedHanlder;
        }
    }

    #endregion IsSynchronizedWithCurrentItemFixEnabled
}
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