Question

我有一个自定义的MSBuild任务，可以在程序集中查看属性元数据。

Assembly assembly = Assembly.ReflectionOnlyLoadFrom(AssemblyFile)

这是由我们的自动构建/发布过程使用的，并且已经完美地针对类库，控制台应用程序和Web项目使用和引用的程序集。在另一个MSBuild进程编译项目之后调用MSBuild任务。

昨天我添加了一个引用这个特定程序集的WPF项目 - 一个.NET 3.5类库。

System.IO.FileLoadException: API restriction: The assembly 'file:///bogus.dll' has already loaded from a different location. 
It cannot be loaded from a new location within the same appdomain. 
at System.Reflection.Assembly._nLoad(AssemblyName fileName, String codeBase, Evidence assemblySecurity, Assembly locationHint, StackCrawlMark&amp; stackMark, Boolean throwOnFileNotFound, Boolean forIntrospection) 
at System.Reflection.Assembly.nLoad(AssemblyName fileName, String codeBase, Evidence assemblySecurity, Assembly locationHint, StackCrawlMark&amp; stackMark, Boolean throwOnFileNotFound, Boolean forIntrospection) 
at System.Reflection.Assembly.InternalLoad(AssemblyName assemblyRef, Evidence assemblySecurity, StackCrawlMark&amp; stackMark, Boolean forIntrospection) 
at System.Reflection.Assembly.InternalLoadFrom(String assemblyFile, Evidence securityEvidence, Byte[] hashValue, AssemblyHashAlgorithm hashAlgorithm, Boolean forIntrospection, StackCrawlMark&amp; stackMark) 
at System.Reflection.Assembly.ReflectionOnlyLoadFrom(String assemblyFile) 
at RadicaLogic.MSBuild.Tasks.GetAssemblyAttribute.Execute() 
at Microsoft.Build.BuildEngine.TaskEngine.ExecuteInstantiatedTask(EngineProxy engineProxy, ItemBucket bucket, TaskExecutionMode howToExecuteTask, ITask task, Boolean&amp; taskResult)

我知道它与WPF相关，因为如果我将AssemblyFile更改为指向WPF项目未引用的同一解决方案中的另一个程序集，则不会引发异常。

异常消息提及

... already loaded from a different location.

It cannot be loaded from a new location within the same appdomain.

请注意有关相同应用域的部分。

所以我修改了代码来捕获这个特殊的异常并查看CurrentDomain：

Assembly assembly = null;
try
{
    assembly = Assembly.ReflectionOnlyLoadFrom(AssemblyFile);
}
catch (FileLoadException)
{
    List<string> searched = new List<string>();
    foreach (var asm in AppDomain.CurrentDomain.GetAssemblies())
    {
        if (Path.GetFileName(asm.CodeBase).Equals(Path.GetFileName(AssemblyFile), 
            StringComparison.OrdinalIgnoreCase))
        {
            message = string.Format("Found assembly {0} in current domain", 
                asm.CodeBase);
            MSBuildHelper.Log(this, message, MessageImportance.High);
            assembly = asm;
            break;
        }
        else
        {
            searched.Add(Path.GetFileName(asm.CodeBase));
        }
    }
    if (assembly == null)
    {
        message = string.Format(
            "Unable to find {0} after looking in current domain assemblies {1}",
            Path.GetFileName(AssemblyFile), string.Join(", ", searched.ToArray()));
        MSBuildHelper.Log(this, message, MessageImportance.High);                    
    }
}

毫无疑问，有问题的程序集不在当前域中（这可能有意义，因为产生了另一个MSBuild进程进行编译），所以假设错误消息为真，我该如何处理弄清楚它住在哪里？这很令人困惑，因为给我的错误信息表明它应该是CurrentDomain。

或者具有更多WPF经验的人可以解释为什么这个程序集在成功构建后仍然在app域中浮动？

这是来自遇到此异常的其他人的another question。

Answer 1

我的解决方案是开源:)使用Cecil从Attribute获取AssemblyFile：

bool found = false;
string value = string.Empty;
Type attributeType = Type.GetType(Attribute);
AssemblyDefinition assembly = AssemblyFactory.GetAssembly(AssemblyFile);
foreach (CustomAttribute attribute in assembly.CustomAttributes)
{
    if (attribute.Constructor.DeclaringType.Name == attributeType.Name)
    {
        value = attribute.ConstructorParameters[0].ToString();
        found = true;
    }
}

Jays评论更新：

通常我使用：AssemblyFileVersion作为Attribute属性值，并让setter逻辑填充缺少的部分：）

以下是属性的定义方式：

string attribute;
[Required]
public string Attribute
{
    get { return attribute; }
    set
    {
        string tempValue = value;
        if (!tempValue.StartsWith("System.Reflection."))
        {
            tempValue = "System.Reflection." + tempValue;
        }
        if (!value.EndsWith("Attribute"))
        {
            tempValue += "Attribute";
        }
        attribute = tempValue;
    }
}

显示属性属性值的单元测试sans required prefix或suffix：

[Test]
public void Execute_WithoutSystemReflectionPrefixOrAttributeSuffix_ReturnsExpectedResult()
{
    string version = getAssemblyFileVersion();
    Assert.IsNotNull(version, "Expected AssemblyFileVersionAttribute to contain value");

    task.AssemblyFile = assemblyFile;
    task.Attribute = "AssemblyFileVersion";
    task.Value = "Bogus";

    result = task.Execute();

    Assert.IsTrue(result, "Expected execute to pass on valid assembly and attribute name");

    Assert.AreEqual(task.Value, version,
        "Expected task value to match assembly file version attribute value");
}

使用Assembly.ReflectionOnlyLoadFrom加载由WPF项目引用的程序集时出现奇怪的FileLoadException

1 个答案: