Harmony Introduction

Harmony is the most essential capability for ADOFAI Mods: intercepting and modifying game methods without touching the game source code.

Why Harmony?

The game is a compiled Unity program — we can't directly edit its source. Harmony rewrites methods at runtime, letting our code execute before, after, or even inside game methods.

Four Patch Types

Type	Timing	Purpose
Prefix	Before method execution	Modify parameters, early return (intercept)
Postfix	After method execution	Read / modify return value
Finalizer	After method ends (regardless of exceptions)	Exception handling
Transpiler	IL level	Deep modification of method internals

This series covers each in 11 chapters:

Chapter	Content
Prefix Patch	Intercept methods, modify parameters
Postfix Patch	Read / modify return values
Finalizer Patch	Exception handling
Magic Parameters	__instance / __result / __state etc.
HarmonyPatch Details	Target syntax and priorities
Patch Lifecycle	How patches are applied and removed
Transpiler Introduction	What IL is, how to write patches
Transpiler Practice	CodeMatcher advanced usage
Manual Patching	Dynamic patching with code
Reverse Patch	Call game methods in reverse

What a Complete Patch Looks Like

using HarmonyLib;

namespace MyFirstMod
{
    [HarmonyPatch(typeof(SomeGameClass), nameof(SomeGameClass.SomeMethod))]
    public static class SomeMethod_Prefix
    {
        public static bool Prefix()
        {
            // Returning false skips the original method (interception)
            return false;
        }
    }
}

Three essential elements:

1. [HarmonyPatch] — declares the patch target (class + method)
2. Patch method name — Prefix / Postfix / Finalizer / Transpiler; Harmony identifies by name
3. Patch class — must be a static class; PatchAll scans automatically

Finding the Target Method

Finding the target method is one of the hardest parts of Mod development. We recommend using dnSpy or ILSpy to decompile the game assembly. See the full guide in Finding Target Methods.

What You Learned

• Why Harmony exists
• The four patch types and their timing
• The three essential elements of a patch

Next Step

Learn the most common Prefix patch → Prefix Patch