Manual Patching

Previous chapters used [HarmonyPatch] attributes with PatchAll for automatic application. Some scenarios require manual patching with code.

When to Use Manual Patching

• The target method can only be determined at runtime (e.g. dynamically generated, name from a string)
• You need to conditionally apply patches (only when a condition is met)
• Multiple patch methods in the same class need flexible combinations

Basic API

var harmony = MyMod.Harmony;   // Existing Harmony instance

var target = AccessTools.Method(typeof(SomeGameClass), "SomeMethod");
var prefix = AccessTools.Method(typeof(MyPatches), nameof(MyPatches.Prefix));

harmony.Patch(target, prefix: new HarmonyMethod(prefix));

Harmony.Patch parameters:

Parameter	Purpose
target	Target MethodBase (obtained via AccessTools.Method)
prefix	Prefix patch method (wrapped in HarmonyMethod)
postfix	Postfix patch method
finalizer	Finalizer patch method
transpiler	Transpiler patch method

Conditional Patches

Only apply a patch when a condition is met:

private static bool applied;

public static void Apply()
{
    if (applied) return;
    if (MyMod.Settings.Enabled)   // Condition check
    {
        var target = AccessTools.Method(typeof(SomeGameClass), "SomeMethod");
        var prefix = AccessTools.Method(typeof(MyPatches), nameof(MyPatches.Prefix));
        MyMod.Harmony.Patch(target, prefix: new HarmonyMethod(prefix));
        applied = true;
    }
}

Dynamic Targets: String Method Names

var target = AccessTools.Method("SomeGameClass:SomeMethod");
// Or
var target = AccessTools.TypeByName("SomeGameClass")
    .GetMethod("SomeMethod", BindingFlags.Public | BindingFlags.Instance);

Locating methods by string is fragile across game version updates — prefer the strongly-typed API when possible.

Removing Manual Patches

// Remove a specific patch
MyMod.Harmony.Unpatch(target, HarmonyPatchType.Prefix, MyMod.Harmony.Id);

Unpatch parameter meanings:

• Remove all patches: UnpatchAll(modEntry.Info.Id)
• Remove a specific patch type: specify HarmonyPatchType.Prefix etc.
• Remove to original state: Unpatch(target, HarmonyPatchType.All, Harmony.Id)

Attributes vs Manual: Mixing Notes

• PatchAll applies all classes with [HarmonyPatch]
• Manual Patch doesn't go through PatchAll — it patches the Harmony instance directly
• Both are controlled by UnpatchAll(modEntry.Info.Id) (as long as the Harmony instance Id matches)

What You Learned

• Why manual patching is needed
• Using Harmony.Patch and AccessTools.Method
• Conditional patches and dynamic targets
• Various ways to remove patches

Next Step

Learn Reverse Patch to call game methods in reverse → Reverse Patch