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StreamGeometry.Open Method

Opens a StreamGeometryContext that can be used to describe this StreamGeometry object's contents.

Namespace:  System.Windows.Media
Assembly:  PresentationCore (in PresentationCore.dll)

public StreamGeometryContext Open()
You cannot use methods in XAML.

Return Value

Type: System.Windows.Media.StreamGeometryContext
A StreamGeometryContext that can be used to describe this StreamGeometry object's contents.

StreamGeometry is light-weight alternative to PathGeometry for creating geometric shapes. Use a StreamGeometry when you need to describe a complex geometry but do not want the overhead of supporting data binding, animation, or modification. For example, because of its efficiency, the StreamGeometry class is a good choice for describing adorners.

The following example uses attribute syntax to create a triangular StreamGeometry in XAML.

<Page xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
  xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml">
  <StackPanel>

    <Path Data="F0 M10,100 L100,100 100,50Z" 
      StrokeThickness="1" Stroke="Black"/>

  </StackPanel>
</Page>

For more information about StreamGeometry attribute syntax, see the Path Markup Syntax page.

The next example uses a StreamGeometry to define a triangle in code. First, the example creates a StreamGeometry, then obtains a StreamGeometryContext and uses it to describe the triangle.

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

namespace SDKSample
{
    // Use StreamGeometry with StreamGeometryContext to define a triangle shape. 
    public partial class StreamGeometryTriangleExample : Page
    {
        public StreamGeometryTriangleExample()
        {
            // Create a path to draw a geometry with.
            Path myPath = new Path();
            myPath.Stroke = Brushes.Black;
            myPath.StrokeThickness = 1;

            // Create a StreamGeometry to use to specify myPath.
            StreamGeometry geometry = new StreamGeometry();
            geometry.FillRule = FillRule.EvenOdd;

            // Open a StreamGeometryContext that can be used to describe this StreamGeometry  
            // object's contents. 
            using (StreamGeometryContext ctx = geometry.Open())
            {

                // Begin the triangle at the point specified. Notice that the shape is set to  
                // be closed so only two lines need to be specified below to make the triangle.
                ctx.BeginFigure(new Point(10, 100), true /* is filled */, true /* is closed */);

                // Draw a line to the next specified point.
                ctx.LineTo(new Point(100, 100), true /* is stroked */, false /* is smooth join */);

                // Draw another line to the next specified point.
                ctx.LineTo(new Point(100, 50), true /* is stroked */, false /* is smooth join */);
            }

            // Freeze the geometry (make it unmodifiable) 
            // for additional performance benefits.
            geometry.Freeze();

            // Specify the shape (triangle) of the Path using the StreamGeometry.
            myPath.Data = geometry;

            // Add path shape to the UI.
            StackPanel mainPanel = new StackPanel();
            mainPanel.Children.Add(myPath);
            this.Content = mainPanel;
        }
    }
}

The next example creates a method that uses a StreamGeometry and StreamGeometryContext to define a geometric shape based on specified parameters.

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

namespace SDKSample
{
    public partial class StreamGeometryExample : Page
    {
        public StreamGeometryExample()
        {
            // Create a path to draw a geometry with.
            Path myPath = new Path();
            myPath.Stroke = Brushes.Black;
            myPath.StrokeThickness = 1;

            // Create a StreamGeometry to use to specify myPath.
            StreamGeometry theGeometry = BuildRegularPolygon(new Point(200, 200), 200, 8, 0);
            theGeometry.FillRule = FillRule.EvenOdd;

            // Freeze the geometry (make it unmodifiable) 
            // for additional performance benefits.
            theGeometry.Freeze();

            // Use the StreamGeometry returned by the BuildRegularPolygon to  
            // specify the shape of the path.
            myPath.Data = theGeometry;

            // Add path shape to the UI.
            StackPanel mainPanel = new StackPanel();
            mainPanel.Children.Add(myPath);
            this.Content = mainPanel;
        }

        StreamGeometry BuildRegularPolygon(Point c, double r, int numSides, double offsetDegree)
        {
            // c is the center, r is the radius, 
            // numSides the number of sides, offsetDegree the offset in Degrees. 
            // Do not add the last point.

            StreamGeometry geometry = new StreamGeometry();

            using (StreamGeometryContext ctx = geometry.Open())
            {
                ctx.BeginFigure(new Point(), true /* is filled */, true /* is closed */);

                double step = 2 * Math.PI / Math.Max(numSides, 3);
                Point cur = c;

                double a = Math.PI * offsetDegree / 180.0;
                for (int i = 0; i < numSides; i++, a += step)
                {
                    cur.X = c.X + r * Math.Cos(a);
                    cur.Y = c.Y + r * Math.Sin(a);
                    ctx.LineTo(cur, true /* is stroked */, false /* is smooth join */);
                }
            }

            return geometry;
        }
    }
}

Windows 7, Windows Vista, Windows XP SP2, Windows Server 2008 R2, Windows Server 2008, Windows Server 2003

The .NET Framework and .NET Compact Framework do not support all versions of every platform. For a list of the supported versions, see .NET Framework System Requirements.

.NET Framework

Supported in: 3.5, 3.0

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