Question

我正在尝试使用Reflection Emit（IL代码）制作自定义代理。一切都工作正常，但是当我调用第二种方法时，我总是得不到结果，并且我得到一个尝试取消装箱空值的执行（NullReferenceException）。

这是使用Emit动态生成的IL代码。（我评论了重要的部分）

.method public hidebysig newslot virtual final 
        instance int32  TestCall(int32 A_1,
                                 int32 A_2) cil managed
{
  // Code size       155 (0x9b)
  .maxstack  5
  .locals init (class [mscorlib]System.Reflection.MethodInfo V_0,
           class [BaseProxy.Console]BaseProxy.Console.TestClass V_1,
           object[] V_2,
           bool V_3,
           object V_4)
  IL_0000:  ldc.i4     0x2
  IL_0005:  newarr     [mscorlib]System.Object
  IL_000a:  stloc.2
  IL_000b:  ldloc.2
  IL_000c:  ldc.i4     0x0
  IL_0011:  ldarg      A_1
  IL_0015:  nop
  IL_0016:  nop
  IL_0017:  box        [mscorlib]System.Int32
  IL_001c:  stelem.ref
  IL_001d:  ldloc.2
  IL_001e:  ldc.i4     0x1
  IL_0023:  ldarg      A_2
  IL_0027:  nop
  IL_0028:  nop
  IL_0029:  box        [mscorlib]System.Int32
  IL_002e:  stelem.ref
  IL_002f:  ldtoken    [BaseProxy.Console]BaseProxy.Console.TestClass
  IL_0034:  call       class [mscorlib]System.Type [mscorlib]System.Type::GetTypeFromHandle(valuetype [mscorlib]System.RuntimeTypeHandle)
  IL_0039:  ldstr      "TestCall"
  IL_003e:  call       instance class [mscorlib]System.Reflection.MethodInfo [mscorlib]System.Type::GetMethod(string)
  IL_0043:  stloc.0
  IL_0044:  ldarg.0
  IL_0045:  ldfld      class [BaseProxy.Console]BaseProxy.Console.TestClass TestClassProxy::wrappedObject
  IL_004a:  stloc.1
  IL_004b:  ldc.i4.1
  IL_004c:  stloc.3
  IL_004d:  ldarg.0
  IL_004e:  ldfld      class [BaseProxy.Console]BaseProxy.Console.BasicInterceptor TestClassProxy::interception
  IL_0053:  ldloc.0
  IL_0054:  ldloc.2
  IL_0055:  ldloc.1
  IL_0056:  ldloca.s   V_3
  IL_0058:  callvirt   instance object [BaseProxy.Console]BaseProxy.Console.BasicInterceptor::Before(class [mscorlib]System.Reflection.MethodInfo,
                                                                                                     object[],
                                                                                                     object,
                                                                                                     bool&) 
  **//Here everything is ok, i can get the result.**
  IL_005d:  box        [mscorlib]System.Object
  IL_0062:  stloc.s    V_4
  IL_0064:  nop
  IL_0065:  ldloc.3
  IL_0066:  brfalse.s  IL_0093
  IL_0068:  ldarg.0
  IL_0069:  ldfld      class [BaseProxy.Console]BaseProxy.Console.TestClass TestClassProxy::wrappedObject
  IL_006e:  ldloc.2
  IL_006f:  ldc.i4     0x0
  IL_0074:  ldelem.ref
  IL_0075:  unbox.any  [mscorlib]System.Int32
  IL_007a:  ldloc.2
  IL_007b:  ldc.i4     0x1
  IL_0080:  ldelem.ref
  IL_0081:  unbox.any  [mscorlib]System.Int32
  IL_0086:  callvirt   instance int32 [BaseProxy.Console]BaseProxy.Console.TestClass::TestCall(int32,
                                                                                               int32)
  **\\This Call Always return nothing (null)**
  IL_008b:  box        [mscorlib]System.Object
  IL_0090:  stloc.s    V_4
  IL_0092:  nop
  IL_0093:  ldloc.s    V_4
  **\\And i get a Exception here because loc 4 is null**
  IL_0095:  unbox.any  [mscorlib]System.Int32
  IL_009a:  ret
} // end of method TestClassProxy::TestCall

TestCall方法是一个返回int32值的非常简单的方法。我已经在TestCall中设置了一个断点并且它很好。

PEVerify给我回复了以下错误：

[IL]: Error: [GeneratedProxyModule.dll : TestClassProxy::TestCall][offset 0x0000008B][found Int32][expected ref 'System.Object'] Unexpected type on the stack.

任何有用的帮助。提前谢谢。

Answer 1

PEVerify输出可以准确地告诉您问题所在。 8B处的盒子指令预期在堆栈上Object，但当时Int32就在那里。但是我们希望Int32在那里，这就是我们想要的东西。那么为什么box期望Object？因为你这么说。 The parameter to box tells it from what type to box, not to what type to box.

所以，将代码更改为：

IL_008b:  box        [mscorlib]System.Int32

应该解决你的问题。

尽管8B和95之间的所有指令看起来都像是一种复杂的方式（盒子，存储，加载，取消装箱）给我。如果你没有任何特殊的理由让它们在那里，你应该删除它们。

IL方法调用始终返回null

1 个答案: