Question

I have a ListBox and a class with strings. Each time that a user clicks add button in the application, I create a new instance of the class and add it to the list which is binded to the ListBox. The first time I click the add button, the list box shows the first item, but the next time it doesn’t show two items.

XAML – this is the ListBox:

<ListBox Name="ListBox_BinsRegion" Height="181" Margin="233,16,6,94" Width="253" Background="Transparent" BorderThickness="1" BorderBrush="Black" ScrollViewer.VerticalScrollBarVisibility="Auto" ItemsSource="{Binding}"/> 

The code behind:

List<Class_ListViewItem> List_ListBoxItems = new List<Class_ListViewItem>();

 private void Button_Add_Click(object sender, RoutedEventArgs e)
    {
        Class_ListViewItem item = new Class_ListViewItem();
        item.WH = this.comboBox_WareHouseBinsRegionDefinition.SelectedItem.ToString();
        item.XXFrom = textBox_XXFrom.Text;
        item.XXTo = textBox_XXTo.Text;
        item.YYFrom = textBox_YYFrom.Text;
        item.YYTo = textBox_YYTO.Text;
        item.Z = textBox_ZFrom.Text;

        List_ListBoxItems.Add(item);

        ListBox_BinsRegion.DataContext = List_ListBoxItems;
    }

Where is my mistake?

Answer 1

WPF does not know when your collection is changing. The problem is here:

List<Class_ListViewItem> List_ListBoxItems = new List<Class_ListViewItem>();

you need to change the list to

ObservableCollection<Class_ListViewItem> List_ListBoxItems = new ObservableCollection<Class_ListViewItem>();

ObservableCollection (System.Collections.ObjectModel) throws an event when the collection is changed, so that WPF can update the listbox.

Also, you can remove the following line, or move it to the constructor of your control.

ListBox_BinsRegion.DataContext = List_ListBoxItems;