Question

I have a TabControl with two items.

<TabControl x:Name="tab" SelectionChanged="TabControl_SelectionChanged">
    <TabItem Header="TabItem1">
    <Grid />
</TabItem>
<TabItem Header="TabItem2">
    <Grid />
</TabItem>
</TabControl>

private void TabControl_SelectionChanged(object sender, SelectionChangedEventArgs e)
{
    Debug.WriteLine("Selected Index: " + tab.SelectedIndex);

    if (tab.SelectedIndex == 1)
    {
        tab.SelectedIndex = 0;
    }
}

when click 2nd item, 1st item have focus and print below.

Selected Index: 1
Selected Index: 0

but retry clicking 2nd item, no output!
SelectionChanged event do not fire.

what’s wrong?
Is there work around?

Answer 1

This is because you are changing the selectedIndex within the SelcetedIndexChanged event which will call itself in sycnhronous manner. Instead try to put it on UI dispatcher in an aysnchronous manner like this –

private void TabControl_SelectionChanged(object sender, SelectionChangedEventArgs e)
{
   Debug.WriteLine("Selected Index: " + tab.SelectedIndex);

   if (tab.SelectedIndex == 1)
   {
      Application.Current.Dispatcher.BeginInvoke
          ((Action)delegate { tab.SelectedIndex = 0; }, DispatcherPriority.Render, null);
   }
}

It will give you the desired output.