Re: Another userdata question

[Peng Zhicheng <pengzhicheng1986@...>]

于 2013-11-13 4:48, Geoff Smith 写道:

I am really hoping someone could help me with this question please as I am totally stuck on it for now.
 
I am trying to implement a userdata via the C API,  to give me this type of functionality
 
btn1 = graphics.newButton(x,y,width,ht, "pressMe")
btn1:setText("Different Text")
btn1:setFont("Arial")
 
That's OK I think I have got that figured out and largely working, but the next thing I want to do is call a user defined Lua action function on the button instance. For example
 
In Lua
 
function btn1:action(someArbitrayParamBackFromC)
     print("ouch someone just poked btn1")
end
 
How can I call that Lua button instance function from C when I have detected the key is pressed ?
 
I have done something vaguely similar in the past when I have created a custom timer on the Lua side, but the difference was I had a timer create function in Lua such as
 
myNewTimer = createTimer( period, luaFunctionCallback)
 
So I was passed the callback function into the C code which meant I could stash it away in the registry and then when the timer elapsed on the C side, I did this
 
 // push function indexed by registryRef from the registry back onto the stack
// the lua callback function in this case
lua_rawgeti(local_L, LUA_REGISTRYINDEX, registryRef);
/* the first function argument is the timerID */
lua_pushinteger(local_L, myTimerID);
/* call the function with 1 argument, return 0 result */
pcallResult = lua_pcall(local_L,1,0,0);    // pops 2 params from stack

I am guessing the solution is somewhat similar but cant figure it out.
 
Many thanks for any assistance
 
   Geoff
 
 
 

You are right. The solution is similar.

In your Timer example, you retrieved the callback Lua function which was passed to the C side
when the timer was created. While in your button press example, you should retrieve the button
object first, then call the specified method on that object.

Thus said, I assumed you had used some method (e.g. GetWindowLongPtr) to associate the
button object (from Lua) with the *native* button object of the underlying GUI system.

Following is an imaginary example to illustrate this idea to bind Lua to Win32 message system.
Just as an illustration, can't claim the correctness.
----------------------------------------------------------------------------------

[inside the window procedure of the button]
[...]

case WM_LBUTTONUP:
    // first retrive the associated object of the Lua side.
    // the following is just an demo method using GWLP_USERDATA to store L
    // and the registry to store the Lua object (this time a Lua table).
    lua_State * L = GetWindowLongPtr(hwnd, GWLP_USERDATA);
    lua_rawgetp(L, LUA_REGISTRYINDEX, (void*)hwnd);

    // then call the "action" method on the button object
    lua_getfield(L, -1, "action");

    // do some check
    if (!lua_isnil(L, -1)) {
        // push the self parameter
        lua_pushvalue(L, -2);
        lua_pcall(L, 1, 1, 0);
        // check the callback return value and do some processing
        [...]
    }
case WM_XXXX:
[...]
-------------------------------------------------------------------------------------