How to set the default value of a DependencyProperty of type Brush

Question

I have the following DependencyProperty which is of type Brush. I am trying to set the default value for the PatternBrushProperty.

    public Brush PatternBrush
    {
        get => (Brush)GetValue(PatternBrushProperty);
        set => SetValue(PatternBrushProperty, value);
    }

    public static readonly DependencyProperty PatternBrushProperty =
        DependencyProperty.Register("PatternBrush", typeof(Brush), typeof(MyCustomControl),
            new UIPropertyMetadata(defaultPatternBrush));

    private static SolidColorBrush defaultPatternBrush 
       =  new((Color)ColorConverter.ConvertFromString("#C5D4E3"));

When I try to execute the application, I get the following error:

System.InvalidOperationException Message='#FFC5D4E3' is not a valid value for property 'Color'.

I have tried different methods to specify the default brush but have had no success.

Is there a way to reference a SolidColorBrush in a resource dictionary to set the value?

accoording to MS docs, ColorConverter.ConvertFromString doesn't throw InvalidOperationException. that means exception happens somewhere else (e.g in binding). — ASh, Jun 07 '22 at 20:03

score 1 · Accepted Answer · answered Jun 08 '22 at 09:48

Declare the defaultPatternBrush as readonly static field before you register the property. The following code work just fine for me:

public partial class MyCustomControl : UserControl
{
    private static readonly SolidColorBrush s_defaultPatternBrush = 
        new SolidColorBrush((Color)ColorConverter.ConvertFromString("#C5D4E3"));

    public MyCustomControl()
    {
        InitializeComponent();
    }

    public Brush PatternBrush
    {
        get => (Brush)GetValue(PatternBrushProperty);
        set => SetValue(PatternBrushProperty, value);
    }

    public static readonly DependencyProperty PatternBrushProperty =
        DependencyProperty.Register(nameof(PatternBrush), typeof(Brush), typeof(MyCustomControl),
            new PropertyMetadata(s_defaultPatternBrush));
}

Mark Feldman · Answer 2 · 2022-06-07T23:13:55.310

You're effectively trying to cast a Color to a SolidColorBrush, try this instead:

private static SolidColorBrush defaultPatternBrush = new SolidColorBrush((Color)ColorConverter.ConvertFromString("#C5D4E3"));

Also, storing the brush in a static field like this isn't safe, because you can't guarentee that it will be initialized prior to the intialization of PatternBrushProperty (in fact, in the code you've posted, it probably won't unless you declare defaultPatternBrush first). Turn it into a static method instead:

private static SolidColorBrush defaultPatternBrush => new SolidColorBrush((Color)ColorConverter.ConvertFromString("#C5D4E3"));

OP uses target-typed new expressions for defaultPatternBrush and so `new((Color)ColorConverter.ConvertFromString("#C5D4E3"))` produces a SolidColorBrush. — emoacht, Jun 08 '22 at 02:33

How to set the default value of a DependencyProperty of type Brush

2 Answers2