Question

我遇到的情况是我需要能够根据部分名称在GAC中加载程序集。为此，我将以下内容添加到app.config文件中：

<runtime>
  <assemblyBinding xmlns="urn:schemas-microsoft-com:asm.v1">
    <qualifyAssembly partialName="MyAssembly"
                     fullName= "MyAssembly, Version=1.0.0.0, Culture=neutral, PublicKeyToken=0123456789abcdef"/>
  </assemblyBinding>
</runtime>

这完全符合我的要求。但是，如果我将相同的元素放在我的machine.config文件中，它似乎被忽略了，并且在尝试加载MyAssembly时我得到了FileNotFoundExceptions。

当元素在我的app.config中时，以下是程序集绑定日志，并且绑定成功：

LOG: This bind starts in default load context.
LOG: Using application configuration file: C:\Documents and Settings\jon_scheiding\My Documents\Source\Testing\Test Projects 1\Cmd\bin\Debug\Testers.Cmd.vshost.exe.config
LOG: Using machine configuration file from C:\WINDOWS\Microsoft.NET\Framework\v2.0.50727\config\machine.config.
LOG: Partial reference qualified from config file. New reference: MyAssembly, Version=1.0.0.0, Culture=neutral, PublicKeyToken=0123456789abcdef.
LOG: Post-policy reference: MyAssembly, Version=1.0.0.0, Culture=neutral, PublicKeyToken=0123456789abcdef
LOG: Found assembly by looking in the GAC.
LOG: Binding succeeds. Returns assembly from C:\WINDOWS\assembly\GAC_MSIL\MyAssembly\1.0.0.0__b20f4683c1030dbd\MyAssembly.dll.
LOG: Assembly is loaded in default load context.

当我的配置在machine.config中时，与日志形成对比，并且绑定失败：

LOG: This bind starts in default load context.
LOG: Using application configuration file: C:\Documents and Settings\jon_scheiding\My Documents\Source\Testing\Test Projects 1\Cmd\bin\Debug\Testers.Cmd.vshost.exe.config
LOG: Using machine configuration file from C:\WINDOWS\Microsoft.NET\Framework\v2.0.50727\config\machine.config.
LOG: Policy not being applied to reference at this time (private, custom, partial, or location-based assembly bind).
LOG: Attempting download of new URL file:///C:/Documents and Settings/jon_scheiding/My Documents/Source/Testing/Test Projects 1/Cmd/bin/Debug/MyAssembly.DLL.
LOG: Attempting download of new URL file:///C:/Documents and Settings/jon_scheiding/My Documents/Source/Testing/Test Projects 1/Cmd/bin/Debug/MyAssembly/MyAssembly.DLL.
LOG: Attempting download of new URL file:///C:/Documents and Settings/jon_scheiding/My Documents/Source/Testing/Test Projects 1/Cmd/bin/Debug/MyAssembly.EXE.
LOG: Attempting download of new URL file:///C:/Documents and Settings/jon_scheiding/My Documents/Source/Testing/Test Projects 1/Cmd/bin/Debug/MyAssembly/MyAssembly.EXE.
LOG: All probing URLs attempted and failed.

这个问题似乎是第四行，“政策目前尚未应用于参考”。但是，我几乎找不到关于此消息的含义或如何解决它的文档。

如何让框架识别我的＆lt; runtime＆gt;元件？

提前致谢！

Answer 1

框架不会从machine.config读取qualifyAssebmly配置，它只从应用程序配置文件中读取它。

框架确实识别你的runtim元素，但是它不识别qualifyAssembly元素。

Answer 2

我很久以后就回到了这个需求，因为我们在GAC中有一些程序集，像NHibernate这样的东西需要解决它们。以下代码不是将所有这些qualifyAssembly元素添加到每个app.config，而是允许我们将它们添加到machine.config中。

using System;
using System.Collections.Generic;
using System.Configuration;
using System.IO;
using System.Reflection;
using System.Xml;
using System.Xml.XPath;

namespace MyNamespace {

    /// <summary>
    /// Implements <see cref="IDisposable"/> to provide a scope for resolving
    /// assemblies described in the machine.config file with 
    /// &lt;qualifyAssembly&gt; elements.
    /// </summary>
    /// <remarks>
    /// Because the framework only respects &lt;qualifyAssembly&gt; at the
    /// application configuration level, this class provides similar
    /// functionality for this element at the machine configuration level.
    /// You can wrap a new instance of this class in a <b>using</b> statement
    /// to get resolution within a specific scope; or, you can call the 
    /// <see cref="AssemblyResolver.Attach()"/> method to get 
    /// resolution for the lifetime of the current <see cref="AppDomain"/>.
    /// </remarks>
    public sealed class AssemblyResolver : IDisposable {

        #region Private fields and implementation

        private static Dictionary<string, string> _qualifiedNames;

        private static Assembly ResolveAssembly(object sender, ResolveEventArgs args) {
            if(_qualifiedNames == null) {
                //
                // Lazily initialize short/long name mappings.
                //
                _qualifiedNames = BuildQualifiedNameList();
            }

            if(!_qualifiedNames.ContainsKey(args.Name)) {
                return null;
            }

            try {
                return Assembly.Load(_qualifiedNames[args.Name]);
            }
            catch(FileNotFoundException) {
                //
                // TODO: Should this exception be propogated?
                // It probably should not be hidden from the consumer
                // since it likely indicates a configuration error.
                //
                return null;
            }
        }

        private static Dictionary<string, string> BuildQualifiedNameList() {
            var dict = new Dictionary<string, string>(StringComparer.InvariantCultureIgnoreCase);

            //
            // Get runtime XML data
            //
            var xml = GetConfigXml(GetMachineRuntimeSection());
            if(xml == null) {
                return dict;
            }

            //
            // Iterate the qualifyAssembly elements and register in the list
            //
            var navigator = xml.CreateNavigator();
            foreach(XPathNavigator qualifyAssembly in navigator.Select("runtime/asm:assemblyBinding/asm:qualifyAssembly", CreateNamespaceManager())) {
                dict.Add(
                    qualifyAssembly.GetAttribute("partialName", string.Empty),
                    qualifyAssembly.GetAttribute("fullName", string.Empty));
            }

            return dict;
        }

        private static ConfigurationSection GetMachineRuntimeSection() {
            System.Configuration.Configuration machineConfig = ConfigurationManager.OpenMachineConfiguration();
            return machineConfig.GetSection("runtime") as ConfigurationSection;
        }

        private static IXPathNavigable GetConfigXml(ConfigurationSection runtimeSection) {
            var ignoreSection = runtimeSection as IgnoreSection;
            if(ignoreSection == null) {
                return null;
            }

            //
            // Cheat via Reflection to get the XML content of the config
            // section.
            //
            FieldInfo field = typeof(IgnoreSection).GetField("_rawXml", BindingFlags.Instance | BindingFlags.NonPublic);
            string rawXml = (string)field.GetValue(ignoreSection);
            return new XPathDocument(new StringReader(rawXml));
        }
        private static IXmlNamespaceResolver CreateNamespaceManager() {
            var nsmgr = new XmlNamespaceManager(new NameTable());
            nsmgr.AddNamespace("asm", "urn:schemas-microsoft-com:asm.v1");
            return nsmgr;
        }

        #endregion

        /// <summary>
        /// Creates a new <see cref="AssemblyResolver"/>.
        /// </summary>
        public AssemblyResolver() {
            AppDomain.CurrentDomain.AssemblyResolve += new ResolveEventHandler(ResolveAssembly);
        }

        /// <summary>
        /// Removes the current <see cref="AssemblyResolver"/>
        /// from the <see cref="AppDomain"/>.
        /// </summary>
        public void Dispose() {
            AppDomain.CurrentDomain.AssemblyResolve -= new ResolveEventHandler(ResolveAssembly);
            GC.SuppressFinalize(this);
        }

        /// <summary>
        /// Provides qualified assembly resolution for the lifetime of the
        /// current <see cref="AppDomain"/>.
        /// </summary>
        public static void Attach() {
            Attach(AppDomain.CurrentDomain);
        }

        /// <summary>
        /// Provides qualified assembly resolution for the lifetime of an
        /// <see cref="AppDomain"/>.
        /// </summary>
        /// <param name="appDomain">
        /// The <see cref="AppDomain"/> to service.
        /// </param>
        public static void Attach(AppDomain appDomain) {
            appDomain.AssemblyResolve += new ResolveEventHandler(ResolveAssembly);
        }

    }
}

在大多数情况下，我们通过使用它来限制它的范围：

using(new AssemblyResolver()) {
    //
    // NHibernate initialization or whatever
    //
}

它也可以在app启动代码或global.asax中使用，并在应用程序的生命周期内持续存在，如下所示：

AssemblyResolver.Attach();
//
// or
//
AssemblyResolver.Attach(AppDomain.CurrentDomain);

在machine.config中忽略.NET assemblyBinding配置

2 个答案: