Editing WoW:UI XML tutorial (section)

=== Handling UI Events ===

To handle UI events, you must include event handler elements in your XML code. You do this by having a Scripts element, inside of which you have one or more Onxxxx event handler elements. For example:

 <Frame name="MyFrame">
  <Scripts>
   <OnShow>
    message("Hello!");
   </OnShow>
  </Scripts>
 </Frame>

This frame has one event handler only, which is executed every time this Frame becomes visible. The contents of the OnShow element can be any valid Lua code. In this example, it's a single statement, which calls the function '''message''', which causes a dialog box to pop up with "Hello" inside it. ('''message''' is a function defined in BasicControls.xml and is available by default.)

Here is a more complete example of how you include Lua code and then reference it from the event handlers.

'''mymod.xml''':

 <Ui ... >
   <Script file="mymod.lua"/>
   <Frame name="MyModMainFrame">
     <Scripts>
       <OnLoad>
         MyMod_ShowMessage();
       </OnLoad>
     </Scripts>
   </Frame>
 </Ui>

'''mymod.lua''':

 function MyMod_ShowMessage()
   message("Hello World!");
 end

When '''MyModMainFrame''' gets loaded (which happens once, at the start of the game, when all the XML files are read in), the OnLoad handler gets executed. In this case, the single Lua statement there simply calls the MyMod_ShowMessage function.

It is recommended that you prefix the names of all of your functions, UI objects and global variables with the name of your AddOn like above; all data is shared between Blizzard's own UI and all your addons, so picking a unique prefix helps avoid clashes with other people's code.

''For the above example to actually work, you must either create an AddOn with the mymod.lua and mymod.xml files, or include them in the FrameXML directory and reference myframe.xml from FrameXML.toc.'' See [[AddOns]] on how to combine these files into an AddOn.