Web应用程序的GetEntryAssembly

Question

Assembly.GetEntryAssembly()不适用于Web应用程序.

但是......我真的需要这样的东西.我使用了一些在Web和非Web应用程序中使用的深层嵌套代码.

我目前的解决方案是浏览StackTrace以找到第一个被调用的程序集.

/// <summary>
/// Version of 'GetEntryAssembly' that works with web applications
/// </summary>
/// <returns>The entry assembly, or the first called assembly in a web application</returns>
public static Assembly GetEntyAssembly()
{
    // get the entry assembly
    var result = Assembly.GetEntryAssembly();

    // if none (ex: web application)
    if (result == null)
    {
        // current method
        MethodBase methodCurrent = null;
        // number of frames to skip
        int framestoSkip = 1;


        // loop until we cannot got further in the stacktrace
        do
        {
            // get the stack frame, skipping the given number of frames
            StackFrame stackFrame = new StackFrame(framestoSkip);
            // get the method
            methodCurrent = stackFrame.GetMethod();
            // if found
            if ((methodCurrent != null)
                // and if that method is not excluded from the stack trace
                && (methodCurrent.GetAttribute<ExcludeFromStackTraceAttribute>(false) == null))
            {
                // get its type
                var typeCurrent = methodCurrent.DeclaringType;
                // if valid
                if (typeCurrent != typeof (RuntimeMethodHandle))
                {
                    // get its assembly
                    var assembly = typeCurrent.Assembly;

                    // if valid
                    if (!assembly.GlobalAssemblyCache
                        && !assembly.IsDynamic
                        && (assembly.GetAttribute<System.CodeDom.Compiler.GeneratedCodeAttribute>() == null))
                    {
                        // then we found a valid assembly, get it as a candidate
                        result = assembly;
                    }
                }
            }

            // increase number of frames to skip
            framestoSkip++;
        } // while we have a working method
        while (methodCurrent != null);
    }
    return result;
}

为了确保组装符合我们的要求,我们有三个条件:

• 该程序集不在GAC中
• 组装没有动态
• 未生成程序集(以避免临时的asp.net文件

我遇到的最后一个问题是何时在单独的程序集中定义基页.(我使用ASP.Net MVC,但ASP.Net也是如此).在这种特殊情况下,它是返回的单独程序集,而不是包含页面的程序集.

我现在正在寻找的是:

1)我的装配验证条件是否足够？(我可能已经忘记了案件)

2)从ASP.Net临时文件夹中的给定代码生成的程序集中,是否有一种方法可以获取有关包含该页面/视图的项目的信息？(我想不是,但谁知道......)

Answer 1

这似乎是一种可靠,简单的方法来获取Web应用程序的"入口"或主要程序集.

如果你把控制器放在一个单独的项目中,你可能会发现ApplicationInstance的基类与包含Views的MVC项目不在同一个程序集中 - 但是,这个设置似乎很少见(我提到它因为我试过这个设置在一个点,一段时间后,一些博客支持这个想法).

    static private Assembly GetWebEntryAssembly()
    {
        if (System.Web.HttpContext.Current == null ||
            System.Web.HttpContext.Current.ApplicationInstance == null) 
        {
            return null;
        }

        var type = System.Web.HttpContext.Current.ApplicationInstance.GetType();
        while (type != null && type.Namespace == "ASP") {
            type = type.BaseType;
        }

        return type == null ? null : type.Assembly;
    }

Answer 2

在我的情况下,我需要在初始化System.Web.HttpContext.Current.ApplicationInstance之前获取Web应用程序的"入口程序集".此外,我的代码需要适用于各种应用程序类型(窗口服务,桌面应用程序等),我不喜欢用Web问题污染我的常用代码.

我创建了一个自定义程序集级属性,可以在要指定为入口点程序集的程序集的AssembyInfo.cs文件中声明.然后,您只需调用属性的静态GetEntryAssembly方法来获取条目程序集.如果Assembly.GetEntryAssembly返回非null,则使用该null,否则它将在已加载的程序集中搜索具有custom属性的程序集.结果缓存在Lazy <T>中.

using System;
using System.Collections.Generic;
using System.Linq;
using System.Reflection;

namespace EntryAssemblyAttributeDemo
{
    /// <summary>
    /// For certain types of apps, such as web apps, <see cref="Assembly.GetEntryAssembly"/> 
    /// returns null.  With the <see cref="EntryAssemblyAttribute"/>, we can designate 
    /// an assembly as the entry assembly by creating an instance of this attribute, 
    /// typically in the AssemblyInfo.cs file.
    /// <example>
    /// [assembly: EntryAssembly]
    /// </example>
    /// </summary>
    [AttributeUsage(AttributeTargets.Assembly)]
    public sealed class EntryAssemblyAttribute : Attribute
    {
        /// <summary>
        /// Lazily find the entry assembly.
        /// </summary>
        private static readonly Lazy<Assembly> EntryAssemblyLazy = new Lazy<Assembly>(GetEntryAssemblyLazily);

        /// <summary>
        /// Gets the entry assembly.
        /// </summary>
        /// <returns>The entry assembly.</returns>
        public static Assembly GetEntryAssembly()
        {
            return EntryAssemblyLazy.Value;
        }

        /// <summary>
        /// Invoked lazily to find the entry assembly.  We want to cache this value as it may 
        /// be expensive to find.
        /// </summary>
        /// <returns>The entry assembly.</returns>
        private static Assembly GetEntryAssemblyLazily()
        {
            return Assembly.GetEntryAssembly() ?? FindEntryAssemblyInCurrentAppDomain();
        }

        /// <summary>
        /// Finds the entry assembly in the current app domain.
        /// </summary>
        /// <returns>The entry assembly.</returns>
        private static Assembly FindEntryAssemblyInCurrentAppDomain()
        {
            var assemblies = AppDomain.CurrentDomain.GetAssemblies();
            var entryAssemblies = new List<Assembly>();
            foreach (var assembly in assemblies)
            {
                // Note the usage of LINQ SingleOrDefault.  The EntryAssemblyAttribute's AttrinuteUsage 
                // only allows it to occur once per assembly; declaring it more than once results in 
                // a compiler error.
                var attribute =
                    assembly.GetCustomAttributes().OfType<EntryAssemblyAttribute>().SingleOrDefault();
                if (attribute != null)
                {
                    entryAssemblies.Add(assembly);
                }
            }

            // Note that we use LINQ Single to ensure we found one and only one assembly with the 
            // EntryAssemblyAttribute.  The EntryAssemblyAttribute should only be put on one assembly 
            // per application.
            return entryAssemblies.Single();
        }
    }
}