Harmony是一个开放源代码库，旨在在运行时替换、修饰或修改任何现有C＃方法。它的主要用在用Mono语言编写的游戏和插件，但是该技术可以与任何.NET版本一起使用。它还照顾对同一方法的多次更改（它们累积而不是覆盖）。

它为每个原始方法创建DynamicMethod方法，并向其织入代码，该代码在开始和结束时调用自定义方法。它还允许您编写过滤器来处理原始的IL代码，从而可以对原始方法进行更详细的操作。

文档可以在这里找到。

• 最新2.0版本终于支持.net core.

• Harmony支持手动（Patch）和自动（PatchAll）织入

• 织入位置可以是执行前（Prefix）、执行后（Postfix）和终结嚣（Finalizer），也可以更详细的手动修改IL（Transpiler）

• 支持构造函数、Getter/Setter、虚/非虚方法、静态方法

手动模式

class NoneGenericClass
{
    private readonly bool _isRunning = true;
    private int _counter = 1;


    public int DoSomething()
    {
        Console.WriteLine(nameof(DoSomething));


        if (_isRunning)
        {
            _counter++;
        }
        return _counter * 10;
    }


    public static int DoSomething2()
    {
        Console.WriteLine(nameof(DoSomething2));


        return 3333;
    }


    public IEnumerable<int> GetNumbers()
    {
        Console.WriteLine(nameof(GetNumbers));


        yield return 1;
        yield return 2;
        yield return 3;
    }
}


static class NoneGenericClassPatcher
{
    public static void Patch()
    {
        var harmony = new Harmony(nameof(NoneGenericClassPatcher));


        harmony.Patch(typeof(NoneGenericClass).GetMethod(nameof(NoneGenericClass.DoSomething)),
            new HarmonyMethod(GetMethod(nameof(MyPrefix))),
            new HarmonyMethod(GetMethod(nameof(MyPostfix))),
            new HarmonyMethod(GetMethod(nameof(MyTranspiler))),
            new HarmonyMethod(GetMethod(nameof(MyFinalizer))));


        Console.WriteLine(new NoneGenericClass().DoSomething());
        Console.WriteLine();


        harmony.Patch(typeof(NoneGenericClass).GetMethod(nameof(NoneGenericClass.GetNumbers)),
            new HarmonyMethod(GetMethod(nameof(MyPrefix))),
            new HarmonyMethod(GetMethod(nameof(PassthroughPostfix))),
            new HarmonyMethod(GetMethod(nameof(MyTranspiler))),
            new HarmonyMethod(GetMethod(nameof(MyFinalizer))));


        Console.WriteLine(string.Join(", ", new NoneGenericClass().GetNumbers())); //BUG：有Finalizer方法时PassthroughPostfix不生效
        Console.WriteLine();


        harmony.Patch(typeof(NoneGenericClass).GetMethod(nameof(NoneGenericClass.DoSomething2)),
            new HarmonyMethod(GetMethod(nameof(StaticPrefix))),
            new HarmonyMethod(GetMethod(nameof(MyPostfix))),
            new HarmonyMethod(GetMethod(nameof(MyTranspiler))),
            new HarmonyMethod(GetMethod(nameof(MyFinalizer))));


        Console.WriteLine(NoneGenericClass.DoSomething2());
    }


    static MethodInfo GetMethod(string name) => typeof(NoneGenericClassPatcher).GetMethod(name, BindingFlags.Static | BindingFlags.Public);


    public static bool MyPrefix(out Stopwatch __state, ref bool ____isRunning)
    {
        __state = Stopwatch.StartNew();
        Console.WriteLine($"{nameof(MyPrefix)} {____isRunning}");


        return true;
    }


    public static bool StaticPrefix(out Stopwatch __state)
    {
        __state = Stopwatch.StartNew();
        Console.WriteLine($"{nameof(StaticPrefix)}");


        return true;
    }


    public static void MyPostfix(Stopwatch __state, ref int __result, MethodBase __originalMethod)
    {
        Console.WriteLine($"{__state.ElapsedMilliseconds} {__result++}");
        Console.WriteLine(nameof(MyPostfix));
    }


    public static IEnumerable<int> PassthroughPostfix(IEnumerable<int> values)
    {
        yield return 0;
        foreach (var value in values)
            if (value > 1)
                yield return value * 10;
        yield return 99;
        Console.WriteLine(nameof(PassthroughPostfix));
    }


    // looks for STDFLD someField and inserts CALL MyExtraMethod before it
    public static IEnumerable<CodeInstruction> MyTranspiler(IEnumerable<CodeInstruction> instructions)
    {
        Console.WriteLine(nameof(MyTranspiler));
        //var found = false;
        foreach (var instruction in instructions)
        {
            //if (instruction.opcode == OpCodes.Stfld && instruction.operand == f_someField)
            //{
            //    yield return new CodeInstruction(OpCodes.Call, m_MyExtraMethod);
            //    found = true;
            //}
            yield return instruction;
        }
        //if (found == false)
        //    ReportError("Cannot find <Stdfld someField> in OriginalType.OriginalMethod");
    }


    public static void MyFinalizer(Exception __exception)
    {
        Console.WriteLine($"{nameof(MyFinalizer)} {__exception}");
    }
}

自动模式

public class Annotations
{
    private readonly bool _isRunning;


    public IEnumerable<int> GetNumbers()
    {
        Console.WriteLine(nameof(GetNumbers));


        yield return 1;
        yield return 2;
        yield return 3;
    }
}


[HarmonyPatch(typeof(Annotations))]
[HarmonyPatch(nameof(Annotations.GetNumbers))]
public class AnnotationsPatcher
{
    static AccessTools.FieldRef<Annotations, bool> isRunningRef =
        AccessTools.FieldRefAccess<Annotations, bool>("_isRunning");


    public static void Patch()
    {
        var harmony = new Harmony(nameof(AnnotationsPatcher));


        harmony.PatchAll();


        Console.WriteLine(string.Join(", ", new Annotations().GetNumbers()));
    }


    static bool Prefix(Annotations __instance)
    {
        Console.WriteLine("Prefix");


        return true;
    }


    /// <summary>Not working</summary>
    static IEnumerable<int> Postfix(IEnumerable<int> values)
    {
        yield return 0;
        foreach (var value in values)
            if (value > 1)
                yield return value * 10;
        yield return 99;
        Console.WriteLine(nameof(Postfix));
    }


    // looks for STDFLD someField and inserts CALL MyExtraMethod before it
    public static IEnumerable<CodeInstruction> Transpiler(IEnumerable<CodeInstruction> instructions)
    {
        Console.WriteLine(nameof(Transpiler));
        //var found = false;
        foreach (var instruction in instructions)
        {
            //if (instruction.opcode == OpCodes.Stfld && instruction.operand == f_someField)
            //{
            //    yield return new CodeInstruction(OpCodes.Call, m_MyExtraMethod);
            //    found = true;
            //}
            yield return instruction;
        }
        //if (found == false)
        //    ReportError("Cannot find <Stdfld someField> in OriginalType.OriginalMethod");
    }
}

运行代码

static void Main(string[] args)
{
    NoneGenericClassPatcher.Patch();
    Console.WriteLine();
    AnnotationsPatcher.Patch();
}

输出结果

MyTranspiler
MyPrefix True
DoSomething
20
MyPostfix
MyFinalizer


MyTranspiler
MyPrefix True
MyFinalizer
GetNumbers
1, 2, 3


MyTranspiler
StaticPrefix
DoSomething2
3333
MyPostfix
MyFinalizer


Transpiler
Prefix
GetNumbers
Postfix
0, 20, 30, 99