List selection does not increase or decrease in the list when you press the arrow button

Question

Why does the Listbox jump from the last entry to the first when I press the up or down arrow key once?

Here's how to reproduce this problem

Mainwindow

<Window x:Class="WpfApplication1.MainWindow" xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation" xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"> <ListBox x:Name="MyListbox" ItemsSource="{Binding Entities}" SelectedItem="{Binding SelectedEntity}" /> </Window> 

Code for

 public partial class MainWindow { public MainWindow() { InitializeComponent(); DataContext = new MainWindowViewModel(); MyListbox.Focus(); } } 

ViewModel

 public class MainWindowViewModel : NotifyPropertyChanged { public MainWindowViewModel() { Entities = new ObservableCollection<string>() { "Batman", "Superman", "Shrek", "Jack Frost", "Wolverine" }; SelectedEntity = Entities.Last(); } public ObservableCollection<string> Entities { get; set; } private string selectedEntity; public string SelectedEntity { get { return selectedEntity; } set { OnPropertyChanged(ref selectedEntity, value); } } } 

I found this problem in a large application, and I was able to reproduce it in isolation in the above code, so when the window appears, the last item will be selected in Listbox, if I press the arrow key, it goes to the first item no to the previous one. I tried Mode TwoWay , UpdateSourceTriggerPropertyChange etc. On this pair of XAML lines, but nothing worked.

This happens only at the beginning, as soon as it jumps up, it behaves as it should, if I take the mouse and click on an element and then use the keyboard, it also works.

Answer 1

This is because when you set focus on the list box, its dosage sets focus on the selected item, use this code to set focus on the item as well.

 <ListBox.Resources> <Style TargetType="{x:Type ListBoxItem}"> <Style.Triggers> <Trigger Property="IsSelected" Value="True"> <Setter Property="FocusManager.FocusedElement" Value="{Binding RelativeSource={RelativeSource Self}}"></Setter> </Trigger> </Style.Triggers> </Style> </ListBox.Resources> 

Answer 2

I realized that setting IsTabStop = "False" in the ListBoxItem causes the same behavior that you reported.

 <ListBox.ItemContainerStyle> <Style TargetType="ListBoxItem"> <Setter Property="IsTabStop" Value="False"/> </Style> </ListBox.ItemContainerStyle> 

It took me an hour to understand ...