Question

I’ve created an XNA application that utilizes LuaInterface (via Lua) to control many aspects of the application itself.

I added an extension to an XNA class (specifically the KeyboardState object). The problem is, if I call the extended function with Lua, I get an error: Attempt to call field ‘KeyDown’ (a userdata value.

Here is my Lua script:

Game.Updated:Add(function(t)
    if Players.LocalPlayer.Controller.KeyboardState:KeyDown(KeyboardKey.W) then
        print("W key down")
    end
end)

And here is my module extending the class:

Imports System.Runtime.CompilerServices
Module XNAExtensions
    <Extension()> _
    Public Function KeyDown(ByVal this As Microsoft.Xna.Framework.Input.KeyboardState, ByVal e As Integer) As Boolean
        Return this.IsKeyDown(e)
    End Function
End Module

What am I doing wrong?

Answer 1

Extension methods are a function of the compiler, not the framework. In order to call this from Lua, you will need to call your XNAExtensions module directly as a static method. Lua doesn’t understand extension methods.

XNAExtensions:KeyDown(Players.LocalPlayer.Controller.KeyboardState, KeyboardKey.W)