Always select first item from listbox when binding is changed - wpf

Question

There is a ListBox that its ItemsSource is bind to a collection,
we need always selected first item when binding is changed, for example at first ListBox has 3 items, second item is selected from ListBox by user, after that binding is changed and ListBox has 1 items, but second item is selected yet.( and also second item is emty but is not hidden)
<ListBoxItem x:Name="item1">
<Border Margin="0" >
<Image Source="{Binding Selected.List[2].Image,NotifyOnTargetUpdated=True}" ></Image>
</Border>
</ListBoxItem>
<ListBoxItem x:Name="item2">
<Border Margin="0">
<Image Source="{Binding Selected.List[1].Image,NotifyOnTargetUpdated=True}"></Image>
</Border>
</ListBoxItem>
<ListBoxItem x:Name="item3">
<Border Margin="0">
<Image Source="{Binding Selected.List[0].Image,NotifyOnTargetUpdated=True}"></Image>
</Border>
</ListBoxItem>
Can anyone help that how can resolve this issue?

Answer 1

You are adding items inside the xaml statically. Please create a collection property in your view model, bind it to the items source and bind the SelectedItem property of the listbox in the view model like this:
<ListBox ItemsSource="{Binding ItemCollection}"
SelectedItem="{Binding SelectedItem}">
<ListBox.ItemTemplate>
<DataTemplate>
<!-- bind to item properties here -->
</DataTemplate>
</ListBox.ItemTemplate>
</ListBox>
Whenever the ItemCollection property is set, the view model could also set its SelectedItem property:
public class Item { ... }
public class ViewModel : INotifyPropertyChanged
{
public event PropertyChangedEventHandler PropertyChanged;
private IEnumerable<Item> itemCollection;
public IEnumerable<Item> ItemCollection
{
get { return itemCollection; }
set
{
itemCollection = value;
PropertyChanged?.Invoke(this,
new PropertyChangedEventArgs(nameof(ItemCollection)));
SelectedItem = itemCollection.FirstOrDefault(); // here
}
}
private Item selectedItem;
public Item SelectedItem
{
get { return selectedItem; }
set
{
selectedItem = value;
PropertyChanged?.Invoke(this,
new PropertyChangedEventArgs(nameof(SelectedItem)));
}
}
}

Answer 2

first make an event for change binding and set the index in the change_event funciton
private void AddEventHandler()
{
myListBox.BindingContextChanged += new EventHandler(BindingContext_Changed);
}
private void BindingContext_Changed(object sender, EventArgs e)
{
myListBox.SelectedIndex = 0;
}

Answer 3

Firstly do you have any specific reason to add ListBoxItem in xaml itself.
If not please use observable collection to binding to Itemsource property of your listbox.
Also bind the selected item property of your ListBox to the property from your viewmodel.
Once your collection is changed set binded selected item property of your viewmodel to first item.
Also set,
IsSynchronizedWithCurrentItem="True" on your listbox in xaml.
This should work !