如何使用Mono.Cecil注入System.Object.Equals?
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; } } }
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,虽然我在这,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 });
如果在阅读程序集时未传递new ReaderParameters { ReadSymbols = true }
,则没有多大意义。
你可以看看KindOfMagic codeplex项目。
它几乎完全相同,但更好一点 – 它不调用Object.Equals(),但在目标类型上定义了相等运算符。