WPF/DashedBorder

DashedBorder.cs

using System.Windows;
using System.Windows.Controls;
using System.Windows.Data;
using System.Windows.Media;
using System.Windows.Shapes;


/// <summary>
/// <see href="https://stackoverflow.com/a/72138376/4380178">How can I achieve a dashed or dotted border in WPF?</see>
/// </summary>
public class DashedBorder : Border
{
    public static readonly DependencyProperty DashedBorderBrushProperty =
        DependencyProperty.Register(
            nameof(DashedBorderBrush),
            typeof(Brush),
            typeof(DashedBorder),
            new FrameworkPropertyMetadata(null));

    public static readonly DependencyProperty StrokeDashArrayProperty =
        DependencyProperty.Register(
            nameof(StrokeDashArray),
            typeof(DoubleCollection),
            typeof(DashedBorder),
            new FrameworkPropertyMetadata(EmptyDoubleCollection()));

    public static readonly DependencyProperty UseDashedBorderProperty =
        DependencyProperty.Register(
            nameof(UseDashedBorder),
            typeof(bool),
            typeof(DashedBorder),
            new FrameworkPropertyMetadata(false, OnUseDashedBorderChanged));

    private static DoubleCollection? _emptyDoubleCollection;

    public Brush DashedBorderBrush
    {
        get => (Brush)GetValue(DashedBorderBrushProperty);
        set => SetValue(DashedBorderBrushProperty, value);
    }

    public DoubleCollection StrokeDashArray
    {
        get => (DoubleCollection)GetValue(StrokeDashArrayProperty);
        set => SetValue(StrokeDashArrayProperty, value);
    }

    public bool UseDashedBorder
    {
        get => (bool)GetValue(UseDashedBorderProperty);
        set => SetValue(UseDashedBorderProperty, value);
    }

    private static DoubleCollection EmptyDoubleCollection()
    {
        if (_emptyDoubleCollection == null)
        {
            DoubleCollection doubleCollection = [];
            doubleCollection.Freeze();
            _emptyDoubleCollection = doubleCollection;
        }

        return _emptyDoubleCollection;
    }

    private static void OnUseDashedBorderChanged(DependencyObject target, DependencyPropertyChangedEventArgs e)
    {
        var dashedBorder = (DashedBorder)target;
        dashedBorder.UseDashedBorderChanged();
    }

    private VisualBrush CreateDashedBorderBrush()
    {
        var dashedBorderBrush = new VisualBrush();
        var grid = new Grid();
        var backgroundRectangle = GetBackgroundRectangle();
        var dashedRectangle = GetDashedRectangle();
        grid.Children.Add(backgroundRectangle);
        grid.Children.Add(dashedRectangle);
        dashedBorderBrush.Visual = grid;

        return dashedBorderBrush;
    }

    private Rectangle GetBackgroundRectangle()
    {
        var rectangle = GetBoundRectangle();
        rectangle.SetBinding(Rectangle.StrokeProperty, new Binding() { Source = this, Path = new PropertyPath(BackgroundProperty) });

        return rectangle;
    }

    private Rectangle GetBoundRectangle()
    {
        var rectangle = new Rectangle();

        rectangle.SetBinding(Rectangle.StrokeThicknessProperty, new Binding() { Source = this, Path = new PropertyPath("BorderThickness.Left") });
        rectangle.SetBinding(Rectangle.RadiusXProperty, new Binding() { Source = this, Path = new PropertyPath("CornerRadius.TopLeft") });
        rectangle.SetBinding(Rectangle.RadiusYProperty, new Binding() { Source = this, Path = new PropertyPath("CornerRadius.TopLeft") });
        rectangle.SetBinding(Rectangle.WidthProperty, new Binding() { Source = this, Path = new PropertyPath(ActualWidthProperty) });
        rectangle.SetBinding(Rectangle.HeightProperty, new Binding() { Source = this, Path = new PropertyPath(ActualHeightProperty) });

        return rectangle;
    }

    private Rectangle GetDashedRectangle()
    {
        var rectangle = GetBoundRectangle();
        rectangle.SetBinding(Rectangle.StrokeDashArrayProperty, new Binding() { Source = this, Path = new PropertyPath(StrokeDashArrayProperty) });
        rectangle.SetBinding(Rectangle.StrokeProperty, new Binding() { Source = this, Path = new PropertyPath(DashedBorderBrushProperty) });
        Panel.SetZIndex(rectangle, 2);

        return rectangle;
    }

    private void UseDashedBorderChanged()
    {
        if (UseDashedBorder)
        {
            BorderBrush = CreateDashedBorderBrush();
        }
        else
        {
            ClearValue(BorderBrushProperty);
        }
    }
}