Maintenance script: UI Lua API import (WAR 1.4.8)

2026-10-16T19:41:04Z

UI Lua API import (WAR 1.4.8)

New page

{{LuaApi|group=Trade}}
Changes the player's side of the current trade (items or money) and sends the update to the server.

<pre>
ChangeTrade(tradeSlot, inventorySlot, backpackType, money)
</pre>

== Arguments ==
;tradeSlot : <code>number</code> – What to change. <code>0</code> updates the money offer only. <code>1</code>–<code>9</code> adds or removes an item (see Details).
;inventorySlot : <code>number</code> – Slot of the item to add, inside its backpack. <code>0</code> removes the item in trade slot <code>tradeSlot</code> instead.
;backpackType : <code>number</code> – Backpack that <code>inventorySlot</code> belongs to (the <code>EA_Window_Backpack.TYPE_*</code> values: 1 quest, 2 inventory, 3 currency, 4 crafting).
;money : <code>number</code> – Money offered. Only read when <code>tradeSlot</code> is <code>0</code>.

== Returns ==
Nothing.

== Details ==
* The client keeps a list of the items the player offers (up to 9) and the money amount. After changing that list it sends a trade update with the full list and money to the current trade partner.
* <code>tradeSlot = 0</code>: stores <code>money</code> as the money offer and sends the update. The item list is unchanged.
* <code>tradeSlot</code> 1–9 and <code>inventorySlot = 0</code>: removes the item in that trade slot. Later items move up one slot.
* <code>tradeSlot</code> 1–9 and <code>inventorySlot</code> not 0: appends the item to the end of the list. The actual value of <code>tradeSlot</code> does not matter here; the stock UI always passes <code>1</code>. <code>inventorySlot</code> and <code>backpackType</code> are turned into the item's absolute inventory slot before it is stored.
* Any other <code>tradeSlot</code> value sends the update without changing anything.
* The money value is only stored when <code>tradeSlot</code> is <code>0</code>; in the other cases the last stored amount is sent again.
* The stock UI calls <code>ChangeTrade(0, 0, 0, money)</code> to take back an acceptance (<code>EA_Window_Trade.UnacceptTrade</code>).
* The client does not check for duplicate items or for more than 9 items, and removing an empty trade slot still shortens the list by one. Keep track of the offer in Lua, as the stock trade window does.
* Does nothing if the player object does not exist yet.
* The function needs at least four arguments and only reads the last four. All must be numbers.

== Errors ==
None besides the generic ''Invalid Parameters'' message when an argument is not a number.

== Example ==
From <code>default/ea_tradewindow/source/tradewindow.lua</code>:
<pre>
-- which trade slot we're requesting doesn't matter so just hardcoding 1,
-- since server is just putting it in first available slot
ChangeTrade( 1, invSlotNum, backpackType, EA_Window_Trade.myOfferMoney )
</pre>
<pre>
-- tell server we're removing item from trade
ChangeTrade( slot, 0, 0, EA_Window_Trade.myOfferMoney )
</pre>

== See also ==
* [[API:InitiateTrade|InitiateTrade]]
* [[API:AcceptTrade|AcceptTrade]]
* [[API:CancelTrade|CancelTrade]]

API:ChangeTrade - Revision history

Maintenance script: UI Lua API import (WAR 1.4.8)