DataBound tabs: Selected index -1 after datacontext changes

[Karl B]

I am dynamically generating tabs based on databinding.  After I change the datacontext I get the tabs I expect but none of the tabs are selected. I am expecting a tab (likely the first one) to be selected when this happens.   I should mention I am using an older version R2 2017

 

<CheckBox x:Name="cbox" Click="CheckBox_Checked">Click Me</CheckBox>
<telerik:RadTabControl x:Name="tabCtrl" DisplayMemberPath="Name" ItemsSource="{Binding TabItems}" Height="250"/>

private void TabCtrl_DataContextChanged (object sender, DependencyPropertyChangedEventArgs e)
    {
    // Attempting to fixt the problem here. Tabs are still unselected when changing data context
    this.tabCtrl.SelectedIndex = 0;
    }

/// <summary>
/// Simulating a data context change in a complicated MVVM scenario here
/// </summary>
/// <param name="sender"></param>
/// <param name="e"></param>
private void CheckBox_Checked (object sender, RoutedEventArgs e)
    {

    if ( cbox.IsChecked == true )
        {
        this.tabCtrl.DataContext = m_mainVm.TabViewModelA;
        }
    else
        {
        this.tabCtrl.DataContext = m_mainVm.TabViewModelB;
        }
    }

 

[Karl B]

Here are my data classes I used-

public class MyData
    {
    public String Name { get; set; }
    }

public class TabControlViewModel
    {
    public List<MyData> TabItems { get; set; } = new List<MyData>();
    }

public class MainViewModel
    {
    public TabControlViewModel TabViewModelA { get; set; } = new TabControlViewModel();
    public TabControlViewModel TabViewModelB { get; set; } = new TabControlViewModel();

    public MainViewModel ()
        {

        for ( int i = 0; i < 2; i++ )
            {
            TabViewModelA.TabItems.Add(new MyData { Name = "First" + i });
            }

        for ( int i = 0; i < 3; i++ )
            {
            TabViewModelB.TabItems.Add(new MyData { Name = "Other" + i });
            }
        }
    }

[Martin Ivanov]

Hello Karl,

Thank you for the code. To achieve your requirement you can set the SelectedIndex to 0 in the Checked/Unchecked event handler. I've prepared a small example showing this. Can you please try it and let me know how it goes?

Regards,
Martin Ivanov
Progress Telerik

[Karl B]

[quote]Martin Ivanov said:Hello Karl,

Thank you for the code. To achieve your requirement you can set the SelectedIndex to 0 in the Checked/Unchecked event handler. I've prepared a small example showing this. Can you please try it and let me know how it goes?

Regards,
Martin Ivanov
Progress Telerik

[/quote]

 

Going off of the checkbox handler will not work for me. As mentioned in the comments this is just simulating a complicated MVVM scenario. In my real scenario the data context of my view is changing based on treeview selections made in a separate view.

 

[Karl B]

Do I need to create a sample project and submit a support ticket?

[Martin Ivanov]

Hello Karl,

In this case you can use a dispatcher the delay the SelectedIndex setting in the DataContextChanged event handler. This will give the tabcontrol time to load its tabs before the selection appears. Here is an example in code:

private void TabCtrl_DataContextChanged(object sender, DependencyPropertyChangedEventArgs e)
{
    Dispatcher.BeginInvoke(new Action(() =>
    {
        this.tabCtrl.SelectedIndex = 0;
    }));
}

About the support ticket, if this doesn't help it would be very helpful to open a support ticket with a project. Also, the support ticket will guarantee you a reply within the 24h timeframe.

Regards,
Martin Ivanov
Progress Telerik