IL2CPP tips

Game classes are exposed through generated interop assemblies. They look like normal C# classes but are wrappers around native objects, which causes a few surprises.

Casting

as and is work on the wrapper type, not on the native type. A Transform.parent is returned as a Transform wrapper, so transform.parent as RectTransform gives null. Use the interop cast:

var rect = transform.parent.TryCast<RectTransform>();
if (rect != null) { /* ... */ }

Delegates and callbacks

A C# delegate cannot be passed to the game directly. Convert it, and keep both objects alive for as long as the game may call it; otherwise the garbage collector frees it and the game crashes later.

Action handler = OnClick;
var native = DelegateSupport.ConvertDelegate<UnityEngine.Events.UnityAction>(handler);
button.onClick.AddListener(native);
keepAlive.Add(handler); keepAlive.Add(native);    // e.g. a list owned by the same Unity object

Your own MonoBehaviours

A MonoBehaviour that the game must instantiate (for example to receive Update) has to be registered first, and needs a constructor taking an IntPtr:

ClassInjector.RegisterTypeInIl2Cpp<MyBehaviour>();   // once, in Load()
public MyBehaviour(IntPtr ptr) : base(ptr) { }

The BepInEx log prints Registered mono type ... in il2cpp domain for each registered type.

Cloning game UI

• Clone with Object.Instantiate under an inactive parent, strip what you do not want, configure it, then move it to the real parent. The game's Awake and OnEnable run when the clone becomes active, so they see the final setup.
• Remove the donor's click listeners and tooltip text, otherwise a cloned "Rules" button would still open the Rules screen.
• Do not clear a button's sprite: BaseButton.Update maps the shown sprite to a state and throws every frame for an unknown one.
• Font asset and material must be copied together from a live game text; a mismatched pair draws garbage glyphs.
• A TMP text cut with "..." shows nothing at all if its box is shorter than one line. Size the box from the font's line height.

Debugging

• Read BepInEx/LogOutput.log first; ErrorLog.log usually holds little (launcher and crash-reporter lines).
• Dump a game object hierarchy once (name, rect, anchors, components) when you need the structure of a screen, and log it with a "log once" helper so it does not spam every frame.
• Il2CppDumper's dump.cs and Ghidra with the game's GameAssembly.dll loaded give names, fields and method bodies. See Reverse-engineering notes.
• If the build says succeeded very quickly and nothing changed in the game, the DLL was not recompiled. Run dotnet build -c Release --no-incremental and copy the new DLL (check its timestamp).