如何使用Mono.Cecil注入System.Object.Equals？

Question

使用Mono.Cecil我想重写以下属性:

public string FirstName
{
    get { return _FirstName; }
    set
    {
        _FirstName = value;
    }
}

对此:

public string FirstName
{
    get { return _FirstName; }
    set
    {
        if (System.Object.Equals(_FirstName, value))
        {
            return;
        }
        _FirstName = value;
    }
}

这只是重写的内容,但它是我遇到问题的地方.

使用Reflector我可以看到以下代码根据需要重写属性,除了调用System.Object.Equals().如果期望IL代码是:

call bool [mscorlib]System.Object::Equals(object, object)

但它被写成:

call instance void RewriteSharp.Person::.ctor()

写入对System.Object.Equals的调用的代码是:

setMethodWriter.InsertBefore(
    firstExistingInstruction, 
    setMethodWriter.Create(OpCodes.Call, objectEqualsMethodReference));

用于初始化objectEqualsMethodReference的方法是:

private static MethodReference GetSystemObjectEqualsMethodReference(
    AssemblyDefinition assembly
)
{

    var typeReference = assembly.MainModule.GetTypeReferences()
        .Single(t => t.FullName == "System.Object");

    var typeDefinition = typeReference.Resolve();

    var methodDefinition = typeDefinition.Methods.Single(
                            m => m.Name == "Equals"
                                && m.Parameters.Count == 2
                                && m.Parameters[0].ParameterType.Name == "Object"
                                && m.Parameters[1].ParameterType.Name == "Object"
    );

    return methodDefinition;
}

在我看来,setMethodWriter.Create()或GetSystemObjectEqualsMethodReference()是不正确的,没有多少调试解决了这个问题.

正在编写的属性和重写属性的代码具有相同的框架目标.3.5和4.0都失败了.

我正在使用主分支https://github.com/jbevain/cecil来构建Mono.Cecil.

完整的代码清单

using Mono.Cecil;
using Mono.Cecil.Cil;
using System;
using System.Linq;

namespace RewriteNotifyPropertyChanged
{
class Program
{
static void Main(string[] args)
{
    var rewrite = "..\\RewriteSharp.dll";
    var rewritten  = "..\\RewritenSharp.dll";

    var typeName = "Person";
    var propertyName = "FirstName";

    var assembly = AssemblyDefinition.ReadAssembly(rewrite);
    var typeDefinition = assembly.MainModule.Types.Single(t => t.Name == typeName);
    var propertyDefintion = typeDefinition.Properties
        .Single(p => p.Name == propertyName);

    var setMethodWriter = propertyDefintion.SetMethod.Body.GetILProcessor();
    var backingFieldReference = GetBackingFieldReference(typeDefinition, propertyName);
    var objectEqualsMethodReference = GetSystemObjectEqualsMethodReference(assembly);
    var firstExistingInstruction = setMethodWriter.Body.Instructions[0];

    setMethodWriter.InsertBefore(
        firstExistingInstruction, 
        setMethodWriter.Create(OpCodes.Ldarg_0));

    setMethodWriter.InsertBefore(
        firstExistingInstruction, 
        setMethodWriter.Create(OpCodes.Ldfld, backingFieldReference));

    setMethodWriter.InsertBefore(
        firstExistingInstruction, 
        setMethodWriter.Create(OpCodes.Ldarg_1));

    setMethodWriter.InsertBefore(
        firstExistingInstruction, 
        setMethodWriter.Create(OpCodes.Call, objectEqualsMethodReference));

    setMethodWriter.InsertBefore(
        firstExistingInstruction, 
        setMethodWriter.Create(OpCodes.Brfalse_S, firstExistingInstruction));

    setMethodWriter.InsertBefore(
        firstExistingInstruction, 
        setMethodWriter.Create(OpCodes.Ret));

    assembly.Write(rewritten, new WriterParameters { WriteSymbols = true });

    Console.WriteLine("Done.");
    Console.ReadKey();
}

private static MethodReference GetSystemObjectEqualsMethodReference(
    AssemblyDefinition assembly
)
{

    var typeReference = assembly.MainModule.GetTypeReferences()
        .Single(t => t.FullName == "System.Object");

    var typeDefinition = typeReference.Resolve();

    var methodDefinition = typeDefinition.Methods.Single(
                            m => m.Name == "Equals"
                                && m.Parameters.Count == 2
                                && m.Parameters[0].ParameterType.Name == "Object"
                                && m.Parameters[1].ParameterType.Name == "Object"
    );

    return methodDefinition;
}

private static FieldReference GetBackingFieldReference(
    TypeDefinition typeDefinition, 
    string propertyName
)
{
    var fieldName = "_" + propertyName;
    var fieldReference = typeDefinition.Fields.Single(f => f.Name == fieldName);

    return fieldReference;
}
}
}

Answer 1

与System.Reflection不同,Cecil对引用和定义进行区分,并且每个模块都有一个范围.这意味着您不能简单地使用自己内部另一个模块的MethodDefinition.你必须创建一个适当的引用.这是一个名为Cecil术语导入的过程.

具体来说,GetSystemObjectEqualsMethodReference返回corlib中定义的方法,您需要在模块中创建对它的引用:

更换:

var objectEqualsMethodReference = GetSystemObjectEqualsMethodReference(assembly);

通过:

var objectEqualsMethodReference = assembly.MainModule.Import (GetSystemObjectEqualsMethodReference(assembly));

修复IL应该可以使它工作.

此外,虽然我在,它的方法:

private static MethodReference GetSystemObjectEqualsMethodReference(AssemblyDefinition assembly)
{
    var typeReference = assembly.MainModule.GetTypeReferences()
        .Single(t => t.FullName == "System.Object");

    var typeDefinition = typeReference.Resolve();

    var methodDefinition = typeDefinition.Methods.Single(
                            m => m.Name == "Equals"
                                && m.Parameters.Count == 2
                                && m.Parameters[0].ParameterType.Name == "Object"
                                && m.Parameters[1].ParameterType.Name == "Object"
    );

    return methodDefinition;
}

会写得更好:

private static MethodReference GetSystemObjectEqualsMethodReference(AssemblyDefinition assembly)
{
    var @object = assembly.MainModule.TypeSystem.Object.Resolve ();

    return @object.Methods.Single(
        m => m.Name == "Equals"
            && m.Parameters.Count == 2
            && m.Parameters[0].ParameterType.MetadataType == MetadataType.Object
            && m.Parameters[1].ParameterType.MetadataType == MetadataType.Object);
}

和

assembly.Write(rewritten, new WriterParameters { WriteSymbols = true });

如果你new ReaderParameters { ReadSymbols = true }在阅读装配时没有通过,那没有多大意义.