---
title: RegisterEvent
summary: Register a Lua callback, interpret its arguments and guard against obsolete contexts.
section: reference
kind: api
status: reference
tags: ["X4","modding","register","event"]
sources: ["https://wiki.egosoft.com/X4%20Foundations%20Wiki/Modding%20Support/"]
---
## Return value

| Type | Meaning |
| --- | --- |
| [`unknown`](wiki:type-results) | Registration return is not established. Callback arguments belong to the specific event, rather than RegisterEvent itself. |

[Types and methods](wiki:types)

## Observed form


Layer: game Lua UI. `name` identifies the received event; `callback` processes its arguments.




```lua
RegisterEvent(name, callback)
```

## Example reply from MD


The first argument is intentionally ignored in the example. The payload is the second argument on this `raise_lua_event` route. Do not apply that signature to every internal game event without checking its contract.




```lua
RegisterEvent("Wiki.Pong", function(_, payload)
    if payload ~= "pong" then
        return
    end
    -- Ответ распознан. При необходимости обновите своё состояние.
end)
```



**What happens:** A callback is registered for Wiki.Pong. With payload = "pong" it reaches the comment; this example has no further action or printed output.

## Lifecycle


Do not install a new handler on every frame. Old adapter callbacks may need a current-instance check after replacement. Instance validity and window cleanup must follow the UI lifecycle: [Lua UI](wiki:lua-ui).