R – Problems with data binding in ItemContainerStyle in Silverlight 3

data-bindinglistboxsilverlightwpf

I'm unable to use data binding in the ItemContainerStyle for a ListBox in Silverlight 3. It works fine in WPF. This is contrived example to demonstrate my problem. What I really want to is bind to the IsSelected property, but I think that this example is easier to follow.

I have a ListBox that is bound to a ObservableCollection<Item> of Item objects:

public class Item {
  public String Name { get; }
  public Brush Color { get; }
}

Here is the relevant Silverlight XAML:

<ListBox x:Name="listBox" ItemsSource="{Binding .}">
  <ListBox.ItemContainerStyle>
    <Style TargetType="ListBoxItem">
      <Setter Property="Background" Value="{Binding Color}"/>
    </Style>
  </ListBox.ItemContainerStyle>
  <ListBox.ItemTemplate>
    <DataTemplate>
      <TextBlock Text="{Binding Name}"/>
    </DataTemplate>
  </ListBox.ItemTemplate>
</ListBox>

The same XAML can be used in WPF if TargetType="ListBoxItem" is replaced with TargetType="{x:Type ListBoxItem}".

The WPF application will display the items in the list box and set their background color according to the Color property of the Item object. However, the Silverlight application fails with and XamlParseException having the text AG_E_RUNTIME_MANAGED_UNKNOWN_ERROR. Being a stubborn guy I Have even tried to remove the XAML that fails and created my own style instead like this:

  Binding binding = new Binding("Color");
  Setter setter = new Setter(ListBoxItem.BackgroundProperty, binding);
  Style style = new Style(typeof(ListBoxItem));
  style.Setters.Add(setter);
  listBox.ItemContainerStyle = style;

If I try to run this I get an ArgumentException after my Silverlight control has initialized.

What am I doing wrong? How can I bind a property on the ItemContainerStyle to a property of the item?

Best Answer

AFAIK Silverlight (even 3) does not support bindings on style setters. You'd have to do some custom logic to alter the background colour when each item is loaded--probably by getting its parent in the visual tree, which would be the container, and setting it there.

Related Solutions

Wpf border control to span the width of listboxItem

This is probably more to do with the ListBoxItems themselves not taking up the full width of the ListBox. Add the HorizontalContentAlignment="Stretch" attribute to your ListBox and see if it stretches the individual items to fill the width.

C# – Binding a WPF ComboBox to a custom list

You set the DisplayMemberPath and the SelectedValuePath to "Name", so I assume that you have a class PhoneBookEntry with a public property Name.

Have you set the DataContext to your ConnectionViewModel object?

I copied you code and made some minor modifications, and it seems to work fine. I can set the viewmodels PhoneBookEnty property and the selected item in the combobox changes, and I can change the selected item in the combobox and the view models PhoneBookEntry property is set correctly.

Here is my XAML content:

<Window x:Class="WpfApplication6.Window1"
        xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
        xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
        Title="Window1" Height="300" Width="300">
<Grid>
    <StackPanel>
        <Button Click="Button_Click">asdf</Button>
        <ComboBox ItemsSource="{Binding Path=PhonebookEntries}"
                  DisplayMemberPath="Name"
                  SelectedValuePath="Name"
                  SelectedValue="{Binding Path=PhonebookEntry}" />
    </StackPanel>
</Grid>
</Window>

And here is my code-behind:

namespace WpfApplication6
{

    /// <summary>
    /// Interaction logic for Window1.xaml
    /// </summary>
    public partial class Window1 : Window
    {
        public Window1()
        {
            InitializeComponent();
            ConnectionViewModel vm = new ConnectionViewModel();
            DataContext = vm;
        }

        private void Button_Click(object sender, RoutedEventArgs e)
        {
            ((ConnectionViewModel)DataContext).PhonebookEntry = "test";
        }
    }

    public class PhoneBookEntry
    {
        public string Name { get; set; }

        public PhoneBookEntry(string name)
        {
            Name = name;
        }

        public override string ToString()
        {
            return Name;
        }
    }

    public class ConnectionViewModel : INotifyPropertyChanged
    {
        public ConnectionViewModel()
        {
            IList<PhoneBookEntry> list = new List<PhoneBookEntry>();
            list.Add(new PhoneBookEntry("test"));
            list.Add(new PhoneBookEntry("test2"));
            _phonebookEntries = new CollectionView(list);
        }

        private readonly CollectionView _phonebookEntries;
        private string _phonebookEntry;

        public CollectionView PhonebookEntries
        {
            get { return _phonebookEntries; }
        }

        public string PhonebookEntry
        {
            get { return _phonebookEntry; }
            set
            {
                if (_phonebookEntry == value) return;
                _phonebookEntry = value;
                OnPropertyChanged("PhonebookEntry");
            }
        }

        private void OnPropertyChanged(string propertyName)
        {
            if (PropertyChanged != null)
                PropertyChanged(this, new PropertyChangedEventArgs(propertyName));
        }
        public event PropertyChangedEventHandler PropertyChanged;
    }
}

Edit: Geoffs second example does not seem to work, which seems a bit odd to me. If I change the PhonebookEntries property on the ConnectionViewModel to be of type ReadOnlyCollection, the TwoWay binding of the SelectedValue property on the combobox works fine.

Maybe there is an issue with the CollectionView? I noticed a warning in the output console:

System.Windows.Data Warning: 50 : Using CollectionView directly is not fully supported. The basic features work, although with some inefficiencies, but advanced features may encounter known bugs. Consider using a derived class to avoid these problems.

Edit2 (.NET 4.5): The content of the DropDownList can be based on ToString() and not of DisplayMemberPath, while DisplayMemberPath specifies the member for the selected and displayed item only.

Best Answer

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C# – Binding a WPF ComboBox to a custom list

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