StrokeStartLineCap not set when PathGeometry is bound

Question

XAML produces the expected result: a line with rounded ends.

However, data binding the same PathGeometry produces flat ends. I'm not sure why this is, can anyone explain?

Here is a simplified example:

XAML:

<Grid>
    <Path Fill="Green" Stroke="Black" StrokeThickness="8"
        Stretch="None" IsHitTestVisible="False"
        Data="{Binding IndicatorGeometry}"
        StrokeStartLineCap="Round" StrokeEndLineCap="Round"/>
    <!--<Path Fill="Green" Stroke="Black" StrokeThickness="8"
        Stretch="None" IsHitTestVisible="False"
        StrokeStartLineCap="Round" StrokeEndLineCap="Round">
        <Path.Data>
            <PathGeometry>
                <PathFigure StartPoint="64,64">
                    <LineSegment Point="128,8"/>
                </PathFigure>
            </PathGeometry>
        </Path.Data>
    </Path>-->
</Grid>

C#:

    private static PathFigure[] ms_figure = new []
                                                {
                                                    new PathFigure(
                                                        new Point(64, 64),
                                                        new[]
                                                            {
                                                                new LineSegment(new Point(128, 8), false)
                                                            },
                                                        true)
                                                };

    public PathGeometry IndicatorGeometry
    {
        get { return (PathGeometry)GetValue(IndicatorGeometryProperty); }
        set { SetValue(IndicatorGeometryProperty, value); }
    }

    public static readonly DependencyProperty IndicatorGeometryProperty =
        DependencyProperty.Register("IndicatorGeometry", typeof(PathGeometry), typeof(MainWindow),
            new FrameworkPropertyMetadata(new PathGeometry(ms_figure)));

    public MainWindow()
    {
        InitializeComponent();
        DataContext = this;
    }

Answer 1

If you compare the Geometry created by the XAML to the one created in code behind, then they are different.

The code-behind one has a number of differences...it uses "z" to close the Path, while your XAML one doesn't...also one had a PathFigureCollection the other didn't....also it set the freezable property to true.

You need to try and build the one in the code-behind to be the same as the XAML produced one...it seems like its a lot of work to build the Geometry to match.

I've come up with an alternative way to build the Geometry which works...hopefully this helps in your case.

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Windows;
using System.Windows.Controls;
using System.Windows.Data;
using System.Windows.Documents;
using System.Windows.Input;
using System.Windows.Media;
using System.Windows.Media.Imaging;
using System.Windows.Navigation;
using System.Windows.Shapes;

namespace WpfApplication4
{
    /// <summary>
    /// Interaction logic for MainWindow.xaml
    /// </summary>
    public partial class MainWindow : Window
    {
        private static Geometry m_DefaultIndicatorGeometry = Geometry.Parse("M 64,64 L 128,8");

        public Geometry IndicatorGeometry
        {
            get { return (Geometry)GetValue(IndicatorGeometryProperty); }
            set { SetValue(IndicatorGeometryProperty, value); }
        }

        public static readonly DependencyProperty IndicatorGeometryProperty =
            DependencyProperty.Register("IndicatorGeometry", typeof(Geometry), typeof(MainWindow),
            new FrameworkPropertyMetadata(m_DefaultIndicatorGeometry));

        public MainWindow()
        {
            InitializeComponent();
            DataContext = this;
        }
    }
}

You could alternatively just use a string as the property, because the Data property has a TypeConverter to convert a string that describes a Path using the Path Markup Syntax into a Geometry.

public partial class MainWindow : Window
{
    private static string m_DefaultIndicatorGeometry = "M 64,64 L 128,8";

    public string IndicatorGeometry
    {
        get { return (string)GetValue(IndicatorGeometryProperty); }
        set { SetValue(IndicatorGeometryProperty, value); }
    }

    public static readonly DependencyProperty IndicatorGeometryProperty =
        DependencyProperty.Register("IndicatorGeometry", typeof(string), typeof(MainWindow),
        new FrameworkPropertyMetadata(m_DefaultIndicatorGeometry));

    public MainWindow()
    {
        InitializeComponent();
        DataContext = this;
    }
}