How do I duplicate a resource reference in code behind in WPF?如何在WPF后台代码中中复制引用的资源？

原文 https://stackoverflow.com/questions/28240528/how-do-i-duplicate-a-resource-reference-in-code-behind-in-wpf

如何在WPF后台代码中中复制引用的资源？

In my application, I have a color resources. I have one element that uses that color as a dynamic resource in xaml.

  <Window x:Class="ResourcePlay.MainWindow"

          xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"

          xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"

          Title="MainWindow" Height="" Width="">

     <Window.Resources>

        <Color x:Key="MyColor">Red</Color>

     </Window.Resources>

     <Grid>

        <Rectangle VerticalAlignment="Top" Width="" Height="" Margin="">

           <Rectangle.Fill>

              <SolidColorBrush x:Name="TopBrush" Color="{DynamicResource MyColor}"/>

           </Rectangle.Fill>

        </Rectangle>

        <Rectangle VerticalAlignment="Bottom" Width="" Height="" Margin="">

           <Rectangle.Fill>

              <SolidColorBrush x:Name="BottomBrush"/>

           </Rectangle.Fill>

        </Rectangle>

     </Grid>

  </Window>

In the code, I want to duplicate this resource reference.

  using System.Windows;

  using System.Windows.Media;

  namespace ResourcePlay {

     public partial class MainWindow : Window {

        public MainWindow() {

           InitializeComponent();

           // I want to copy the resource reference, not the color.

           BottomBrush.Color = TopBrush.Color;

           // I'd really rather do something like this.

           var reference = TopBrush.GetResourceReference(SolidColorBrush.ColorProperty);

           BottomBrush.SetResourceReference(reference);

           // I want this to change the colors of both elements

           Resources["MyColor"] = Colors.Green;

        }

     }

  }

However, SetResourceReference only works for FrameworkElements or FrameworkContentElements. SolidColorBrush is just a Freezable. Also, I have no idea how to get a resource reference in code behind.

Is there a way to do this in WPF so that both of the colors change at the same time? In my real application, the problem isn't quite so simple, so I can't just add a second DynamicResource in xaml.

Il Vic suggested using reflection. Expanding on that, I was able to build some extension methods for DependencyObject that do what I want. I don't really like using reflection in code, and if someone else knows a better way to implement this, I'd love to see it. At least this will be helpful whenever I'm trying to debug DynamicResources from code behind.

  public static class DependencyObjectExtensions

  {

     public static object GetDynamicResourceKey(this DependencyObject obj, DependencyProperty prop)

     {

        // get the value entry from the depencency object for the specified dependency property

        var dependencyObject = typeof(DependencyObject);

        var dependencyObject_LookupEntry = dependencyObject.GetMethod("LookupEntry", BindingFlags.NonPublic | BindingFlags.Instance);

        var entryIndex = dependencyObject_LookupEntry.Invoke(obj, new object[] { prop.GlobalIndex });

        var effectiveValueEntry_GetValueEntry = dependencyObject.GetMethod("GetValueEntry", BindingFlags.NonPublic | BindingFlags.Instance);

        var valueEntry = effectiveValueEntry_GetValueEntry.Invoke(obj, new object[] { entryIndex, prop, null, 0x10 });

        // look inside the value entry to find the ModifiedValue object

        var effectiveValueEntry = valueEntry.GetType();

        var effectiveValueEntry_Value = effectiveValueEntry.GetProperty("Value", BindingFlags.Instance | BindingFlags.NonPublic);

        var effectiveValueEntry_Value_Getter = effectiveValueEntry_Value.GetGetMethod(nonPublic: true);

        var rawEntry = effectiveValueEntry_Value_Getter.Invoke(valueEntry, new object[]);

        // look inside the ModifiedValue object to find the ResourceReference

        var modifiedValue = rawEntry.GetType();

        var modifiedValue_BaseValue = modifiedValue.GetProperty("BaseValue", BindingFlags.Instance | BindingFlags.NonPublic);

        var modifiedValue_BaseValue_Getter = modifiedValue_BaseValue.GetGetMethod(nonPublic: true);

        var resourceReferenceValue = modifiedValue_BaseValue_Getter.Invoke(rawEntry, new object[]);

        // check the ResourceReference for the original ResourceKey

        var resourceReference = resourceReferenceValue.GetType();

        var resourceReference_resourceKey = resourceReference.GetField("_resourceKey", BindingFlags.NonPublic | BindingFlags.Instance);

        var resourceKey = resourceReference_resourceKey.GetValue(resourceReferenceValue);

        return resourceKey;

     }

     public static void SetDynamicResourceKey(this DependencyObject obj, DependencyProperty prop, object resourceKey)

     {

        var dynamicResource = new DynamicResourceExtension(resourceKey);

        var resourceReferenceExpression = dynamicResource.ProvideValue(null);

        obj.SetValue(prop, resourceReferenceExpression);

     }

  }

The second method uses DynamicResourceExtension to avoid some nastiness with Activator, but the first method feels incredibly brittle.

I can use these methods in my original example as follows:

  public MainWindow() {

     InitializeComponent();

     var key = TopBrush.GetDynamicResourceKey(SolidColorBrush.ColorProperty);

     BottomBrush.SetDynamicResourceKey(SolidColorBrush.ColorProperty, key);

     Resources["MyColor"] = Colors.Green;

  }

This will work for any DependencyProperty, provided it is set to a DynamicResource when we try to get the resource key. A little more finesse would be needed for production code.