Maintenance script: UI Lua API import (WAR 1.4.8)

2026-10-16T19:51:45Z

UI Lua API import (WAR 1.4.8)

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{{LuaApi|group=Window}}
Makes a window call a Lua function whenever a game event is broadcast.

<pre>
WindowRegisterEventHandler(windowName, eventId, functionName)
</pre>

== Arguments ==
;windowName : <code>string</code> – Name of the window that owns the handler.
;eventId : <code>number</code> – The event, usually a <code>SystemData.Events.*</code> value.
;functionName : <code>string</code> – Name of the Lua function to call, as a dotted path such as <code>"MyAddon.OnEvent"</code>.

== Returns ==
Nothing.

== Details ==
* A window can have one handler per event. Registering a second handler for the same event raises the ''already has an event handler'' error, which names the existing handler. Remove the old one first with [[API:WindowUnregisterEventHandler|WindowUnregisterEventHandler]].
* <code>eventId</code> is truncated to a whole number. It is not checked against the known events.
* The handler belongs to the window. Many stock windows register on <code>"Root"</code> for events that do not belong to a particular window.
* For a window's own events, such as mouse clicks, use [[API:WindowRegisterCoreEventHandler|WindowRegisterCoreEventHandler]].
* <code>easystem_dialogmanager/source/dialogs.lua</code> calls <code>WindowRegisterEventHandler( "GROUP_INVITE_ID", "GroupInviteCallback" )</code>. That call passes only two arguments, with a string where the event number belongs, so it does not register anything.

== Errors ==
* <code>Error in function call 'WindowRegisterEventHandler': Window %s does not exist</code>
* <code>Error in function call 'WindowRegisterEventHandler': Window %s already has an event handler (%s) for event %d.</code>

== Example ==
From <code>easystem_windowutils/source/windowutils.lua</code>:
<pre>
WindowRegisterEventHandler( "Root", SystemData.Events.ESCAPE_KEY_PROCESSED, "WindowUtils.EscapeKeyProcessed")
</pre>

From <code>ea_abilitieswindow/source/abilitieswindow.lua</code>:
<pre>
WindowRegisterEventHandler( "AbilitiesWindow", SystemData.Events.PLAYER_ABILITIES_LIST_UPDATED, "AbilitiesWindow.UpdateIfNotLoading")
</pre>

== See also ==
* [[API:WindowUnregisterEventHandler|WindowUnregisterEventHandler]]
* [[API:WindowRegisterCoreEventHandler|WindowRegisterCoreEventHandler]]

API:WindowRegisterEventHandler - Revision history

Maintenance script: UI Lua API import (WAR 1.4.8)