An ItemsControl is inconsistent with its items source - WPF Listbox

Question

I have a WPF window containing a ListBox control that is populated when a button click method is executed.

XAML:

<ListBox Name="ThirdPartyListBox" ItemsSource="{Binding}" Margin="0,70,0,0">                                           <ListBox.ItemTemplate>                         <DataTemplate>                             <StackPanel Orientation="Horizontal">                                 <Image Source="C:\Users\Test\Desktop\Project\ACME-WPF\ACME-WPF\window-new-3.ico" Margin="5" Width="50"/>                                 <Button Name="ThirdPartyInstallButton" Content="Install" Click="InstallThirdPartyUpdatesButton_Click" Margin="5,5,0,0" Height="25"></Button>                                 <Button Name="ThirdPartyPostoneButton" Content="Postpone" Click ="PostponeThirdPartyUpdatesButton_Click" Margin="5,5,0,0" Height="25"></Button>                                 <TextBlock FontWeight="Bold" Text="{Binding Item2.Name}" Margin="12,25,0,0"/>                                 <TextBlock FontWeight="Bold" Text="{Binding Item2.RequiredVersion}" Margin="3,25,0,0"/>                                 <TextBlock Text="{Binding Item2.CustomUIMessage}" Margin="10,25,0,0" TextWrapping="Wrap" Foreground="Red"/>                                 <TextBlock Text="You have used " Margin="3,25,0,0"/>                                 <TextBlock Text="{Binding Item3.UsedDeferrals}" Margin="3,25,0,0"/>                                 <TextBlock Text=" of " Margin="3,25,0,0"/>                                 <TextBlock Text="{Binding Item2.MaxDefferals}" Margin="3,25,0,0"/>                                 <TextBlock Text=" deferrals for this update." Margin="3,25,0,0"/>                             </StackPanel>                         </DataTemplate>                     </ListBox.ItemTemplate>                 </ListBox> 

C#:

 private void CheckforThirdPartyUpdatesButton_Click(object sender, RoutedEventArgs e)     {         CheckforThirdPartyUpdatesButton.IsEnabled = false;          worker = new BackgroundWorker();         worker.WorkerReportsProgress = true;         worker.WorkerSupportsCancellation = true;          worker.DoWork += delegate(object s, DoWorkEventArgs args)         {             MainEntry.checkFor3PUpdates();         };          worker.ProgressChanged += delegate(object s, ProgressChangedEventArgs args)         {          };          worker.RunWorkerCompleted += delegate(object s, RunWorkerCompletedEventArgs args)         {              ThirdPartyListBox.DataContext = RegScan_ThirdParty.comparisonListWithState;             CheckforThirdPartyUpdatesButton.IsEnabled = true;         };          worker.RunWorkerAsync();     } 

Everything up to this point functions as expected and the listbox is populated with multiple rows of items depending on how many items are in list ThirdPartyListBox.DataContext = RegScan_ThirdParty.comparisonListWithState;. However, if I interact with the listbox items at all, an InvalidOperationException is thrown with inner exception "An ItemsControl is inconsistent with its items source."

Can someone help me understand what's happening?

Answer 1

Such exceptions are thrown when an item's source has changed from another thread and ListBox doesn't receive a notification (CollectionChanged event) about ItemsSource being changed; so when it starts to do some work (like updating layout) it will see that Items are not equal to ItemsSource and throws an exception.

Since .NET 4.5, WPF provides a way to enable synchronization with a collection that changes from different threads. Try to use the EnableCollectionSynchronization method on your ItemsSource. See an example usage in this answer to a similar question