标记扩展“StaticResourceExtension”要求在 IServiceProvider 中为 ProvideValue 实现“IXamlSchemaContextProvider”

Question

我已经使用了几年的资源扩展在设计时在一个新的 .Net 4 项目中停止工作，并出现以下错误：

标记扩展“StaticResourceExtension”要求在 IServiceProvider 中为 ProvideValue 实现“IXamlSchemaContextProvider”。

扩展中的相关方法如下：

    public override object ProvideValue(IServiceProvider serviceProvider)
    {
        Style resultStyle = new Style();
        foreach (string currentResourceKey in resourceKeys)
        {
            object key = currentResourceKey;
            if (currentResourceKey == ".")
            {
                IProvideValueTarget service = (IProvideValueTarget)serviceProvider.GetService(typeof(IProvideValueTarget));
                key = service.TargetObject.GetType();
            }
            Style currentStyle = new StaticResourceExtension(key).ProvideValue(serviceProvider) as Style;
            if (currentStyle == null)
                throw new InvalidOperationException("Could not find style with resource key " + currentResourceKey + ".");
            resultStyle.Merge(currentStyle);
        }
        return resultStyle;
    }

据推测，编译器给出了错误，因为当我调用时currentStyle = new StaticResourceExtension(key).ProvideValue(serviceProvider);，我传递的 serviceProvider 缺少 IXamlSchemaContextProvider 信息。不知道它会从哪里来，我什至不知道标记扩展的服务提供者是如何设置的，我只是像这样使用它：

<Style x:Key="ReadOnlyTextCell" TargetType="{x:Type TextBlock}" BasedOn="{util:MultiStyle ReadOnlyCell TextCell}"/>

---

扩展的完整代码在这里：

using System;
using System.Windows;
using System.Windows.Markup;

/* MultiStyleExtension - used to merge multiple existing styles.
 *  
 * Example:
    <Window xmlns:local="clr-namespace:FlagstoneRe.WPF.Utilities.UI">
        <Window.Resources>
            <Style x:Key="ButtonStyle" TargetType="Button">
                <Setter Property="Width" Value="120" />
                <Setter Property="Height" Value="25" />
                <Setter Property="FontSize" Value="12" />
            </Style>
            <Style x:Key="GreenButtonStyle" TargetType="Button">
                <Setter Property="Foreground" Value="Green" />
            </Style>
            <Style x:Key="RedButtonStyle" TargetType="Button">
                <Setter Property="Foreground" Value="Red" />
            </Style>
            <Style x:Key="BoldButtonStyle" TargetType="Button">
                <Setter Property="FontWeight" Value="Bold" />
            </Style>
        </Window.Resources>

        <Button Style="{local:MultiStyle ButtonStyle GreenButtonStyle}" Content="Green Button" />
        <Button Style="{local:MultiStyle ButtonStyle RedButtonStyle}" Content="Red Button" />
        <Button Style="{local:MultiStyle ButtonStyle GreenButtonStyle BoldButtonStyle}" Content="green, bold button" />
        <Button Style="{local:MultiStyle ButtonStyle RedButtonStyle BoldButtonStyle}" Content="red, bold button" />

 * Notice how the syntax is just like using multiple CSS classes.
 * The current default style for a type can be merged using the "." syntax:

        <Button Style="{local:MultiStyle . GreenButtonStyle BoldButtonStyle}" Content="Bold Green Button" />

 */

namespace FlagstoneRe.WPF.Utilities.UI
{
    [MarkupExtensionReturnType(typeof(Style))]
    public class MultiStyleExtension : MarkupExtension
    {
        private string[] resourceKeys;

        /// <summary>
        /// Public constructor.
        /// </summary>
        /// <param name="inputResourceKeys">The constructor input should be a string consisting of one or more style names separated by spaces.</param>
        public MultiStyleExtension(string inputResourceKeys)
        {
            if (inputResourceKeys == null)
                throw new ArgumentNullException("inputResourceKeys");
            this.resourceKeys = inputResourceKeys.Split(new char[] { ' ' }, StringSplitOptions.RemoveEmptyEntries);
            if (this.resourceKeys.Length == 0)
                throw new ArgumentException("No input resource keys specified.");
        }

        /// <summary>
        /// Returns a style that merges all styles with the keys specified in the constructor.
        /// </summary>
        /// <param name="serviceProvider">The service provider for this markup extension.</param>
        /// <returns>A style that merges all styles with the keys specified in the constructor.</returns>
        public override object ProvideValue(IServiceProvider serviceProvider)
        {
            Style resultStyle = new Style();
            foreach (string currentResourceKey in resourceKeys)
            {
                object key = currentResourceKey;
                if (currentResourceKey == ".")
                {
                    IProvideValueTarget service = (IProvideValueTarget)serviceProvider.GetService(typeof(IProvideValueTarget));
                    key = service.TargetObject.GetType();
                }
                Style currentStyle = new StaticResourceExtension(key).ProvideValue(serviceProvider) as Style;
                if (currentStyle == null)
                    throw new InvalidOperationException("Could not find style with resource key " + currentResourceKey + ".");
                resultStyle.Merge(currentStyle);
            }
            return resultStyle;
        }
    }

    public static class MultiStyleMethods
    {
        /// <summary>
        /// Merges the two styles passed as parameters. The first style will be modified to include any 
        /// information present in the second. If there are collisions, the second style takes priority.
        /// </summary>
        /// <param name="style1">First style to merge, which will be modified to include information from the second one.</param>
        /// <param name="style2">Second style to merge.</param>
        public static void Merge(this Style style1, Style style2)
        {
            if(style1 == null)
                throw new ArgumentNullException("style1");
            if(style2 == null)
                throw new ArgumentNullException("style2");
            if(style1.TargetType.IsAssignableFrom(style2.TargetType))
                style1.TargetType = style2.TargetType;
            if(style2.BasedOn != null)
                Merge(style1, style2.BasedOn);
            foreach(SetterBase currentSetter in style2.Setters)
                style1.Setters.Add(currentSetter);
            foreach(TriggerBase currentTrigger in style2.Triggers)
                style1.Triggers.Add(currentTrigger);
            // This code is only needed when using DynamicResources.
            foreach(object key in style2.Resources.Keys)
                style1.Resources[key] = style2.Resources[key];
        }
    }
}

Answer 1

我遇到了同样的问题。一些附加信息：

在运行时，IServiceProvider 值的类型为“MS.Internal.Xaml.ServiceProviderContext”。

在 Visual Studio Xaml 设计器中，IServiceProvider 值的类型为“Microsoft.Expression.DesignModel.Core.InstanceBuilderOperations.InstanceBuilderServiceProvider”。

显然，VS2010 使用 Expression Blend 中的类来提供比 VS2008 更好的设计时行为 - 但要付出一定的代价，因为 Expression Blend 类不具有与实际运行时系统相同的信息。

更多信息：我尝试插入自己的类来实现 IServiceProvider 和 IXamlSchemaContextProvider。一些调用会传递到原始 IServiceProvider，并且我会在请求时提供一个虚拟（空）XamlSchemaContext。但我仍然遇到同样的错误。

WPF 内部的某些内容正在使用另一种 IServiceProvider 类型封装我的 IServiceProvider - 但该类型无法实现 IXamlSchemaContextProvider。我对如何解决这个问题没有进一步的想法。