ComboBox binding using DoubleCollection throwing ArgumentException

I am developing using Silverlight 3 and I have the following xaml:

<Application.Resources>        
    <DataTemplate x:Key="LineCombo">
        <StackPanel Orientation="Horizontal" Margin="2">
            <Line X1="0" Y1="0" X2="50" Y2="0" VerticalAlignment="Center" Stroke="Blue" StrokeThickness="1" StrokeDashArray="{Binding}" />               
        </StackPanel>
    </DataTemplate>
</Application.Resources>

<StackPanel>开发者_运维问答;
    <ComboBox x:Name="ComboBoxTest1" ItemTemplate="{StaticResource LineCombo}" Width="200" Height="30">
    </ComboBox>
    <ComboBox x:Name="ComboBoxTest2" ItemTemplate="{StaticResource LineCombo}" Width="200" Height="30">
    </ComboBox>           
</StackPanel>

And code behind:

    public ObservableCollection<DoubleCollection> strokeDashArrays1 = new ObservableCollection<DoubleCollection>();
    public ObservableCollection<Double[]> strokeDashArrays2 = new ObservableCollection<Double[]>();

    public MainPage()
    {
        InitializeComponent();

        strokeDashArrays1.Add(new DoubleCollection { 2, 4 });
        strokeDashArrays1.Add(new DoubleCollection { 3, 6 });
        strokeDashArrays1.Add(new DoubleCollection { 4, 8 });

        strokeDashArrays2.Add(new double[] { 2, 4 });
        strokeDashArrays2.Add(new double[] { 3, 6 });
        strokeDashArrays2.Add(new double[] { 4, 8 });

        ComboBoxTest1.ItemsSource = strokeDashArrays1;
        ComboBoxTest2.ItemsSource = strokeDashArrays2;            

    }

Selecting an item from ComboBoxTest1 throws an ArgumentException:

"Value does not fall within the expected range".

Both display OK and ComboBoxTest2 works OK when selecting an item.

What is causing this behaviour?

I have only been working with Silverlight for a couple of weeks and am trying to display a ComboBox of StrokeDashArrays to allow line customisation.

Binding to the StrokeDashArray property works when using a string of values so I worked around this problem by implementing the following IValueConverter:

public class DoubleCollectionConverter : IValueConverter
{
    public object Convert(object value, Type targetType, object parameter, CultureInfo culture)
    {
        DoubleCollection doubleCollection = (DoubleCollection)value;
        return string.Join(",", doubleCollection.Select(x => x.ToString()).ToArray());
    }

    public object ConvertBack(object value, Type targetType, object parameter, CultureInfo culture)
    {
        throw new NotImplementedException();
    }
}

Used like this:

<src:DoubleCollectionConverter x:Key="doubleCollectionConverter"/>

 <DataTemplate x:Key="LineCombo">
    <StackPanel Orientation="Horizontal" Margin="2">
        <Line X1="0" Y1="0" X2="50" Y2="0" VerticalAlignment="Center" Stroke="Blue" StrokeThickness="1" StrokeDashArray="{Binding Converter={StaticResource doubleCollectionConverter}}" />
    </StackPanel>
 </DataTemplate>

Never figured out why the exception was being thrown though...

I have run into a similar problem using DoubleCollections. Typically, this "Value does not fall within the expected range" error indicates that "two objects having the same name in the same parent."

When using a DoubleCollection, I found that if I was certain I didn't use a common instance, I didn't get this error. Silverlight didn't like me trying to use the same instance of a DoubleCollection for between the different children.

Give this a try!