How do I convert a Color to a Brush in XAML?

I want to convert a System.Windows.Media.Color value to a System.Windows.Media.Brush. The color value is databound to a Rectangle object's Fill property. The Fill property takes a Brush object, so I need an IValueConverter object to perform the conversion.

Is there a built-in converter in WPF or do I need to create my own? How do I go about creating my own if it becomes necessary?

I know I am really late to the party, but you don't need a converter for this.

You could do

<Rectangle>
    <Rectangle.Fill>
        <SolidColorBrush Color="{Binding YourColorProperty}" />
    </Rectangle.Fill>
</Rectangle>

It seems that you have to create your own converter. Here a simple example to start:

public class ColorToSolidColorBrushValueConverter : IValueConverter {

    public object Convert(object value, Type targetType, object parameter, System.Globalization.CultureInfo culture) {
        if (null == value) {
            return null;
        }
        // For a more sophisticated converter, check also the targetType and react accordingly..
        if (value is Color) {
            Color color = (Color)value;
            return new SolidColorBrush(color);
        }
        // You can support here more source types if you wish
        // For the example I throw an exception
        
        Type type = value.GetType();
        throw new InvalidOperationException("Unsupported type ["+type.Name+"]");            
    }

    public object ConvertBack(object value, Type targetType, object parameter, System.Globalization.CultureInfo culture) {
        // If necessary, here you can convert back. Check if which brush it is (if its one),
        // get its Color-value and return it.

        throw new NotImplementedException();
    }
}

To use it, declare it in the resource-section.

<local:ColorToSolidColorBrushValueConverter  x:Key="ColorToSolidColorBrush_ValueConverter"/>

And the use it in the binding as a static resource:

Fill="{Binding Path=xyz,Converter={StaticResource ColorToSolidColorBrush_ValueConverter}}"

I have not tested it. Make a comment if its not working.

A Converter is not needed here. You can define a Brush in XAML and use it. It would be better to define the Brush as a Resource so it can be used other places required.

XAML is as below:

<Window.Resources>
    <SolidColorBrush Color="{Binding ColorProperty}" x:Key="ColorBrush" />
</Window.Resources>
<Rectangle Width="200" Height="200" Fill="{StaticResource ColorBrush}" />

I wanted to do this HCL's way rather than Jens' way because I have a lot of things bound to the Color, so there's less duplication and boiler-plate .Fill nodes.

However when trying to write it, ReSharper pointed me to the WPF Toolkit's implementation of the ColorToSolidColorBrushConverter. You need to include the following namespace declaration in the main Window/UserControl node:

xmlns:Toolkit="clr-namespace:Microsoft.Windows.Controls.Core.Converters;assembly=WPFToolkit.Extended"

Then a static resource in the Window/UserControl resources:

<Toolkit:ColorToSolidColorBrushConverter x:Key="colorToSolidColorBrushConverter" />

Then you can do it like HCL's answer:

<Rectangle Fill="{Binding Color, Converter={StaticResource colorToSolidColorBrushConverter}}" />

With some more enhancment to HCL answer, I tested it - it works.

public class ColorToSolidColorBrushValueConverter : IValueConverter
{
    public object Convert(object value, Type targetType, object parameter, System.Globalization.CultureInfo culture)
    {
        if (value == null)
            return null;

        if (value is Color)
            return new SolidColorBrush((Color)value);

        throw new InvalidOperationException("Unsupported type [" + value.GetType().Name + "], ColorToSolidColorBrushValueConverter.Convert()");
    }

    public object ConvertBack(object value, Type targetType, object parameter, System.Globalization.CultureInfo culture)
    {
        if (value == null)
            return null;

        if (value is SolidColorBrush)
            return ((SolidColorBrush)value).Color;

        throw new InvalidOperationException("Unsupported type [" + value.GetType().Name + "], ColorToSolidColorBrushValueConverter.ConvertBack()");
    }

}

Converter:

[ValueConversion(typeof(SolidColorBrush), typeof(Color))]
public class SolidBrushToColorConverter : IValueConverter
{
    public object Convert(object value, Type targetType, object parameter, CultureInfo culture)
    {
        if (!(value is SolidColorBrush)) return null;
        var result = (SolidColorBrush)value;
        return result.Color;
    }

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

XAML:

//...
<converters:SolidBrushToColorConverter x:Key="SolidToColorConverter" />
//...
<Color>
	<Binding Source="{StaticResource YourSolidColorBrush}"
			 Converter="{StaticResource SolidToColorConverter}">
	</Binding>
</Color>
//...

In addition to HCLs answer: If you don't want to care if System.Windows.Media.Color is used or System.Drawing.Color you can use this converter, which accepts both:

public class ColorToSolidColorBrushValueConverter : IValueConverter
{
    public object Convert(object value, Type targetType, object parameter, CultureInfo culture)
    {
        switch (value)
        {
            case null:
                return null;
            case System.Windows.Media.Color color:
                return new SolidColorBrush(color);
            case System.Drawing.Color sdColor:
                return new SolidColorBrush(System.Windows.Media.Color.FromArgb(sdColor.A, sdColor.R, sdColor.G, sdColor.B));
        }

        Type type = value.GetType();
        throw new InvalidOperationException("Unsupported type [" + type.Name + "]");
    }

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