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Silverlight Tip of the Day #24: How to Apply a XAML Template to a Class

  • Artigo

Let’s say you have a class where you want to declare elements via a XAML template instead of dynamically creating them.

For example, the XAML to declare an image and add it to a canvas would look like this:

 <Canvas x:Name="MyCanvas">

     <Image x:Name="MyImage" Source="Grass.png"></Image>

 </Canvas>

To do the same thing programmatically you would need to declare the following code:

 Image myImage = new Image();

 Uri uri = new Uri("Grass.png", UriKind.Relative);

 ImageSource imgSrc = new System.Windows.Media.Imaging.BitmapImage(uri);

 myImage.SetValue(Image.SourceProperty, imgSrc);

The way to do this via a template in a class is to first put the XAML into a string like this:

 private const string _contentTemplate

        = "<ControlTemplate xmlns=\"https://schemas.microsoft.com/winfx/2006/xaml/presentation\"" +

            "                  xmlns:x=\"https://schemas.microsoft.com/winfx/2006/xaml\">" +

            "<Image x:Name=\"MyImage\" Source=\"Grass.png\"></Image>" +

            "</ControlTemplate>";

Your class will need to inherit from Control:

 public class MyControl : Control

Now, in the constructor of your class you can load this template via the XamlReader.Load() method. You will need to add a using statement first to reference the namespace System.Windows.Markup;

 public MyControl()

 {

     Template = (ControlTemplate)XamlReader.Load(_contentTemplate);

     ApplyTemplate();

 }

ApplyTemplate() is where you can get the elements that are in declared in your XAML code. Override the function OnApplyTemplate like this:

 private _myImage;

  

 public override void OnApplyTemplate()

 {

     _myImage = (Image)GetTemplateChild("MyImage");

 }

Complete class:

 using System;

 using System.Net;

 using System.Windows;

 using System.Windows.Controls;

 using System.Windows.Documents;

 using System.Windows.Ink;

 using System.Windows.Input;

 using System.Windows.Media;

 using System.Windows.Media.Animation;

 using System.Windows.Shapes;

 using System.Windows.Markup;

  

 namespace MapEditor

 {

     public class MyImage : Control

     {

         Image _myImage = null;

  

         private const string _contentTemplate

                = "<ControlTemplate xmlns=\"https://schemas.microsoft.com/winfx/2006/xaml/presentation\"" +

                    "                  xmlns:x=\"https://schemas.microsoft.com/winfx/2006/xaml\">" +

                    "<Image x:Name=\"MyImage\" Source=\"Grass.png\"></Image>" +

                    "</ControlTemplate>";

  

         public override void OnApplyTemplate()

         {

             _myImage = (Image)GetTemplateChild("MyImage");

         }

  

         public MyImage()

         {

             Template = (ControlTemplate)XamlReader.Load(_contentTemplate);

             ApplyTemplate();

         }

  

     }

 }

Thank you,

--Mike Snow

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