DynamicResource binding to Color not working

Question

I have a style being created in the xaml for my window which contains bindings to a DynamicResource:

<Window.Resources>
    <local:RowColorConverter x:Key="RowColorConverter" />
        <Style x:Key="OddEvenRowStyle">
            <Setter Property="DataGridRow.Background">
                <Setter.Value>
                    <Binding RelativeSource="{RelativeSource AncestorType=GroupItem}" Path="(ItemsControl.AlternationIndex)" Converter="{StaticResource RowColorConverter}">
                        <Binding.ConverterParameter>
                            <x:Array Type="Brush">
                                <SolidColorBrush Color="{DynamicResource RowPrimaryBrush}" />
                                <SolidColorBrush Color="{DynamicResource RowSecondaryBrush}" />
                            </x:Array>
                        </Binding.ConverterParameter>
                    </Binding>
                </Setter.Value>
            </Setter>
        </Style>
</Window.Resources>

I then assign the style to a RowStyle for a DataGrid:

<DataGrid Name="dataGrid" AutoGenerateColumns="False" Height="Auto" Width="Auto" ItemsSource="{Binding}" RowStyle="{StaticResource OddEvenRowStyle}">

In the initialization of my window I'm assigning these DynamicResource values:

Resources["RowPrimaryBrush"] = Colors.LightGray;
Resources["RowSecondaryBrush"] = Colors.DarkGray;

However when I load up the window the colors aren't working correctly:

I'm pretty sure the rest of my code is okay because when I change the Color values in xaml to color values:

<x:Array Type="Brush">
    <SolidColorBrush Color="LightGray" />
    <SolidColorBrush Color="DarkGray" />
</x:Array>

The colors get assigned correctly:

Which is why I'm led to believe it's something to do with the bindings. Is there something wrong with the way I'm binding my colors?

Answer 1

Make sure you set your resources before your window initializes.

public MainWindow()
{
    Resources["RowPrimaryBrush"] = Colors.LightGray;
    Resources["RowSecondaryBrush"] = Colors.DarkGray;
    InitializeComponent();
}

A dynamic resource won't update when changed, like a Binding. Its just deferred until runtime rather than evaluated at compile time.

---

Not familiar with the limitation, but its not surprising. You might have to rewrite your RowColorConverter to take its argument directly and then update it from codebehind via

(Resources["RowColorConverter"] as RowColorConverter).Parameter = 
    new Brush[]
    {
        Brushes.LightGray, 
        Brushes.DarkGray
    }

Or define an attached property within your RowColorConverter

#region Brushes Attached DependencyProperty
public static readonly DependencyProperty BrushesProperty = DependencyProperty.RegisterAttached(
    BrushesPropertyName,
    typeof(SolidColorBrush[]),
    typeof(RowColorConverter),
    new FrameworkPropertyMetadata(null)
);
public const string BrushesPropertyName = "Brushes";
public static void SetBrushes(DependencyObject element, SolidColorBrush[] value)
{
    element.SetValue(BrushesProperty, value);
}
public static SolidColorBrush[] GetBrushes(DependencyObject element)
{
    return (SolidColorBrush[])element.GetValue(BrushesProperty);
}
#endregion

that you can set differently on each grid

<DataGrid Name="dataGrid" SnipPointlessAttributes="True">
    <local:RowColorConverter.Colors>
        <x:Array Type="Brush">
            <SolidColorBrush Color="LightGray" />
            <SolidColorBrush Color="DarkGray" />
        </x:Array>
    </local:RowColorConverter.Colors>
</DataGrid>

Answer 2

Binding.ConverterParameter is not part of WPF's logical tree, so performing dynamic resource lookups within it won't work.

Answer 3

Use a MultiBinding instead of a binding with a converter parameter.