Custom MethodPatcher

The core benefit of HarmonyX is the ability to extend the patching backend to support patching alternative methods. This allows to use Harmony's attribute-based patching on methods that are not managed by default.

Some use cases for specifying the custom patching backend:

• Ability to patch mono internal calls and DllImport methods. A basic implementation already exists in HarmonyX: NativeDetourMethodPatcher
• Ability to patch Il2Cpp methods like managed methods. An example implementation with Il2CppUnhollower: IL2CPPDetourMethodPatcher

Basic usage

To implement a custom method patcher:

1. Create a new class that inherits MethodPatcher and implement the required methods. Refer to the documentation that explains each method in detail. In addition, refer to two example implementations:

   • ManagedMethodPatcher (patched normal managed methods);
   • NativeDetourMethodPatcher (patches icalls and DllImports)

2. Implement a resolver method. This is a simple static method with the following signature:

   public static void TryResolve(object sender, PatchManager.PatcherResolverEventArgs args)
   {
   }

   The method will be called by HarmonyX when a method is to be patched. The resolver should check the method passed in the args and initialize the instance of the custom MethodPatcher if there is a match. In most cases the body of TryResolve is:

   if (/* some logic to check if args.Original should be patched with the custom patcher */)
       args.MethodPatcher = new MyCustomMethodPatcher(args.Original);

3. Register your resolver with PatchManager.ResolvePatcher event. You simply register your resolver as an event handler before applying your patches:

   PatchManager.ResolvePatcher += TryResolve;