To get these nice, L-shaped corners in WPF you'll have to draw the horizontal and vertical borders separately since the StrokeDashArray will not (always) be the same for both.
Your requirements for the StrokeDashArray are:
- Each line should start and end with a full dash
- The length of the dashes should stay the same
- excess/missing distance should be filled by stretching the space between dashes
To get the precise length needed to draw a line like that you have to calculate the number of lines (+1) and spaces in your dashes line, e.g. like this:
private IEnumerable<double> GetDashArray(double length)
{
double useableLength = length - StrokeDashLine;
int lines = (int)Math.Round(useableLength/(StrokeDashLine + StrokeDashSpace));
useableLength -= lines*StrokeDashLine;
double actualSpacing = useableLength/lines;
yield return StrokeDashLine / StrokeThickness;
yield return actualSpacing / StrokeThickness;
}
Wrap that up in a custom control and you will get something like this:
![Dashed Rectangle with L-shaped corners]()
<local:NiceCornersControl Fill="LightGray" Stroke="Black"
StrokeThickness="2" StrokeDashLine="5" StrokeDashSpace="5">
<TextBlock HorizontalAlignment="Center" VerticalAlignment="Center"
Text="Drop files here"/>
</local:NiceCornersControl>
A couple of things you should be aware of:
- To have your line "inside" of the rectangle you need to offset them by
StrokeThickness / 2
- The
DashStyle will scale with your StrokeThickness
- This will probably look odd for semi-transparent stroke colors
Full code for the control:
using System;
using System.Collections.Generic;
using System.Windows;
using System.Windows.Controls;
using System.Windows.Media;
namespace InsertNamespaceHere
{
public class NiceCornersControl : ContentControl
{
public static readonly DependencyProperty StrokeProperty = DependencyProperty.Register(
"Stroke", typeof(Brush), typeof(NiceCornersControl), new PropertyMetadata(default(Brush), OnVisualPropertyChanged));
public Brush Stroke
{
get { return (Brush)GetValue(StrokeProperty); }
set { SetValue(StrokeProperty, value); }
}
public static readonly DependencyProperty StrokeThicknessProperty = DependencyProperty.Register(
"StrokeThickness", typeof(double), typeof(NiceCornersControl), new PropertyMetadata(default(double), OnVisualPropertyChanged));
public double StrokeThickness
{
get { return (double)GetValue(StrokeThicknessProperty); }
set { SetValue(StrokeThicknessProperty, value); }
}
public static readonly DependencyProperty StrokeDashLineProperty = DependencyProperty.Register(
"StrokeDashLine", typeof(double), typeof(NiceCornersControl), new PropertyMetadata(default(double), OnVisualPropertyChanged));
public double StrokeDashLine
{
get { return (double)GetValue(StrokeDashLineProperty); }
set { SetValue(StrokeDashLineProperty, value); }
}
public static readonly DependencyProperty StrokeDashSpaceProperty = DependencyProperty.Register(
"StrokeDashSpace", typeof(double), typeof(NiceCornersControl), new PropertyMetadata(default(double), OnVisualPropertyChanged));
public double StrokeDashSpace
{
get { return (double)GetValue(StrokeDashSpaceProperty); }
set { SetValue(StrokeDashSpaceProperty, value); }
}
public static readonly DependencyProperty FillProperty = DependencyProperty.Register(
"Fill", typeof(Brush), typeof(NiceCornersControl), new PropertyMetadata(default(Brush), OnVisualPropertyChanged));
public Brush Fill
{
get { return (Brush)GetValue(FillProperty); }
set { SetValue(FillProperty, value); }
}
private static void OnVisualPropertyChanged(DependencyObject d, DependencyPropertyChangedEventArgs e)
{
((NiceCornersControl)d).InvalidateVisual();
}
public NiceCornersControl()
{
SnapsToDevicePixels = true;
UseLayoutRounding = true;
}
protected override void OnRender(DrawingContext drawingContext)
{
double w = ActualWidth;
double h = ActualHeight;
double x = StrokeThickness / 2.0;
Pen horizontalPen = GetPen(ActualWidth - 2.0 * x);
Pen verticalPen = GetPen(ActualHeight - 2.0 * x);
drawingContext.DrawRectangle(Fill, null, new Rect(new Point(0, 0), new Size(w, h)));
drawingContext.DrawLine(horizontalPen, new Point(x, x), new Point(w - x, x));
drawingContext.DrawLine(horizontalPen, new Point(x, h - x), new Point(w - x, h - x));
drawingContext.DrawLine(verticalPen, new Point(x, x), new Point(x, h - x));
drawingContext.DrawLine(verticalPen, new Point(w - x, x), new Point(w - x, h - x));
}
private Pen GetPen(double length)
{
IEnumerable<double> dashArray = GetDashArray(length);
return new Pen(Stroke, StrokeThickness)
{
DashStyle = new DashStyle(dashArray, 0),
EndLineCap = PenLineCap.Square,
StartLineCap = PenLineCap.Square,
DashCap = PenLineCap.Flat
};
}
private IEnumerable<double> GetDashArray(double length)
{
double useableLength = length - StrokeDashLine;
int lines = (int)Math.Round(useableLength / (StrokeDashLine + StrokeDashSpace));
useableLength -= lines * StrokeDashLine;
double actualSpacing = useableLength / lines;
yield return StrokeDashLine / StrokeThickness;
yield return actualSpacing / StrokeThickness;
}
}
}
