如何解决如何用DynamicMethod
在帖子Replacing C# method of declaring type which implements an interface and inherits from base中，我知道如何将方法指针更改为方法的另一个指针或Action / Func。但是我需要将其替换为指向DynamicMethod的指针。
提到的帖子中的工作示例，其中添加了一种方法，稍后将使用该方法检查其是否与DynamicMethod一起使用：
using System;
using System.Diagnostics;
using System.Reflection;
using System.Runtime.CompilerServices;
namespace Foo.Bar {
public interface IFoo {
string Apple();
}
public class Bar {
protected virtual object One() {
return null;
}
protected virtual object Two() {
return null;
}
protected virtual object Three() {
return null;
}
// New
public override int VirtualTestMethod()
{
return 10;
}
/* Uncomment this to generate a null reference */
//protected virtual object Four() {
// return null;
//}
}
public class Foo : Bar,IFoo {
public string Apple() {
return "Apple";
}
public string Orange() {
return "Orange";
}
// New
public override int VirtualTestMethod()
{
return 0;
}
/* Uncommenting this fixes the null reference */
//public override int GetHashCode() {
// throw new NotImplementedException();
//}
public void ReplaceMethod(Delegate targetMethod,Delegate replacementMethod) {
MethodInfo methodToReplace = targetMethod.Method;
MethodInfo methodToInject = replacementMethod.Method;
RuntimeHelpers.PrepareMethod(methodToReplace.MethodHandle);
RuntimeHelpers.PrepareMethod(methodToInject.MethodHandle);
if (methodToReplace.IsVirtual)
ReplaceVirtualInner(methodToReplace,methodToInject);
else
ReplaceStandard(methodToReplace,methodToInject);
}
// New
public void ReplaceMethod(MethodInfo methodToReplace,MethodInfo methodToInject)
{
RuntimeHelpers.PrepareMethod(methodToReplace.MethodHandle);
RuntimeHelpers.PrepareMethod(methodToInject.MethodHandle);
if (methodToReplace.IsVirtual)
ReplaceVirtualInner(methodToReplace,methodToInject);
}
private void ReplaceStandard(MethodInfo methodToReplace,MethodInfo methodToInject) {
IntPtr targetPtr = methodToInject.MethodHandle.Value;
IntPtr replacePtr = methodToReplace.MethodHandle.Value;
unsafe
{
if (IntPtr.Size == 4) {
int* inj = (int*)replacePtr.ToPointer() + 2;
int* tar = (int*)targetPtr.ToPointer() + 2;
if (Debugger.IsAttached) {
byte* injInst = (byte*)*inj;
byte* tarInst = (byte*)*tar;
int* injSrc = (int*)(injInst + 1);
int* tarSrc = (int*)(tarInst + 1);
*tarSrc = (((int)injInst + 5) + *injSrc) - ((int)tarInst + 5);
}
else {
*tar = *inj;
}
}
else {
long* inj = (long*)replacePtr.ToPointer() + 1;
long* tar = (long*)targetPtr.ToPointer() + 1;
if (Debugger.IsAttached) {
byte* injInst = (byte*)*inj;
byte* tarInst = (byte*)*tar;
long* injSrc = (long*)(injInst + 1);
long* tarSrc = (long*)(tarInst + 1);
*tarSrc = (((long)injInst + 5) + *injSrc) - ((long)tarInst + 5);
}
else {
*tar = *inj;
}
}
}
}
private void ReplaceVirtualInner(MethodInfo methodToReplace,MethodInfo methodToInject) {
unsafe
{
UInt64* methodDesc = (UInt64*)(methodToReplace.MethodHandle.Value.ToPointer());
int index = (int)(((*methodDesc) >> 32) & 0xFF);
if (IntPtr.Size == 4) {
uint* classStart = (uint*)methodToReplace.DeclaringType.TypeHandle.Value.ToPointer();
classStart += 10;
classStart = (uint*)*classStart;
uint* tar = classStart + index;
uint* inj = (uint*)methodToInject.MethodHandle.Value.ToPointer() + 2;
if (Debugger.IsAttached) {
byte* injInst = (byte*)*inj;
byte* tarInst = (byte*)*tar;
uint* injSrc = (uint*)(injInst + 1);
uint* tarSrc = (uint*)(tarInst + 1);
*tarSrc = (((uint)injInst + 5) + *injSrc) - ((uint)tarInst + 5);
}
else {
*tar = *inj;
}
}
else {
ulong* classStart = (ulong*)methodToReplace.DeclaringType.TypeHandle.Value.ToPointer();
classStart += 8;
classStart = (ulong*)*classStart;
ulong* tar = classStart + index;
ulong* inj = (ulong*)methodToInject.MethodHandle.Value.ToPointer() + 1;
if (Debugger.IsAttached) {
byte* injInst = (byte*)*inj;
byte* tarInst = (byte*)*tar;
ulong* injSrc = (ulong*)(injInst + 1);
ulong* tarSrc = (ulong*)(tarInst + 1);
*tarSrc = (((ulong)injInst + 5) + *injSrc) - ((ulong)tarInst + 5);
}
else {
*tar = *inj;
}
}
}
}
}
}
工作用法示例（也可与其他ReplaceMethod-过载一起使用
Foo.Bar.Foo foo = new Foo.Bar.Foo();
foo.ReplaceMethod(
((Func<string>)foo.Apple),((Func<string>)foo.Orange)
);
var result = foo.Apple(); // this is "Orange" :)
不起作用的示例：
Foo.Bar.Foo foo = new Foo.Bar.Foo();
var methodInfo = foo.GetType().GetMethod("VirtualTestMethod",(BindingFlags)(-1));
var dm = new DynamicMethod("",typeof(int),new Type[]{});
var il = dm.GetILGenerator();
il.Emit(OpCodes.Ldc_I4,25);
il.Emit(OpCodes.Ret);
foo.ReplaceMethod(
methodInfo,dm.Method
);
var result = foo.VirtualTestMethod(); // this should be 25
但是，如果我尝试将其替换为DynamicMethod，那么它将不起作用，因为它没有MethodHandle。如果我使用以下代码片段从MethodHandle获取DynamicMethod并将其用于方法中，则该方法将无效。摘录摘自该SO answer。
private static readonly Func<DynamicMethod,RuntimeMethodHandle> getDynamicHandle = Delegate.CreateDelegate(
typeof(Func<DynamicMethod,RuntimeMethodHandle>),typeof(DynamicMethod).GetMethod("GetMethodDescriptor",BindingFlags.Instance | BindingFlags.NonPublic)
) as Func<DynamicMethod,RuntimeMethodHandle>;
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