Question

When I try to bind a ResourceDictionary item against Rectangle.Child, I get an exception:

ArgumentException: Value does not fall within the expected range.

Here is an example:

<UserControl.Resources>
    <local:PersonConverter x:Key="MyConverter"/>
</UserControl.Resources>

<ListBox ItemsSource="{Binding Persons}">
    <ListBox.ItemTemplate>
        <DataTemplate>
            <Border Child="{Binding Gender, Converter={StaticResource MyConverter}}"/>
        </DataTemplate>
    </ListBox.ItemTemplate>
</ListBox>

And the code behind:

public class MainViewModel : ViewModelBase
{
    public MainViewModel()
    {
        Persons = new List<Person> {new Person("Female"), new Person("Male")};
    }

    public List<Person> Persons { get; private set; }
}

public class PersonConverter : IValueConverter
{
    private ResourceDictionary Items { get; set; }

    public PersonConverterRes()
    {
        Items = new ResourceDictionary
            {
                {"Male", new Canvas() {
                                 Background = new SolidColorBrush(Colors.Blue),
                                 Height = 100, Width = 100}},
                {"Female", new Canvas() {
                                 Background = new SolidColorBrush(Colors.Magenta),
                                 Height = 100, Width = 100}}
            };
    }

    public object Convert(object value, Type targetType, object parameter,
                          System.Globalization.CultureInfo culture)
    {
        return Items[value.ToString()];
    }

    ...
}

public class Person
{
    public Person(String gender)
    {
        Gender = gender;
    }

    public String Gender { get; private set; }
}

But if I replace the ResourceDictionary with a plain Dictionary<String, UIElement> the binding works fine:

public class PersonConverter : IValueConverter
{
    private Dictionary<String, UIElement> Items { get; set; }

    public PersonConverterRes()
    {
        Items = new Dictionary<String, UIElement>
            {
                {"Male", new Canvas() {
                                 Background = new SolidColorBrush(Colors.Blue),
                                 Height = 100, Width = 100}},
                {"Female", new Canvas() {
                                 Background = new SolidColorBrush(Colors.Magenta),
                                 Height = 100, Width = 100}}
            };
    }

    ...
}

Does anybody know what is causing this exception?

Note:
I have tried this under WinRT as well. There, the code doesn’t throw an exception, but the binding still doesn’t work if I use a ResourceDictionary. I guess it’s probably failing silently.

Answer 1

You can not use databinding to bind to the Child property of a Border since it is not a DependencyProperty. This is why your ResourceDictionary approach does not work.

Also, databinding in WPF/Silvelight/WinRT fails silently by design (it’s a feature, and a very useful one if used correctly), so your guess would be right on that.