Re: loadfile callback?

[Duncan Cross <duncan.cross@...>]

On Tue, Jun 14, 2011 at 9:49 AM, Han Zhao <abrash_han@hotmail.com> wrote:
> hi,
>
> I'm using lua table to store my app data and load the data
> back via loadfile().
>
> When the table is big, I'd like a callback in loadfile() to
> display some progress info in the UI.
>
> Is it possible?
>
> Best Regards,
> hz
>
>
>

Not with loadfile() itself, but if you pass a custom coroutine-based
loader function to load() it's quite possible, something like this:


 -- variation on loadfile() that calls [callback] every [nlines] lines
 function loadfile_callback(path, nlines, callback)
   local f = io.open(path, 'rb')
   if not f then
     return nil, 'file not found: ' .. path
   end
   return load(coroutine.wrap(function()
     -- get the total length of the file in bytes
     local length = f:seek('end')
     f:seek('set', 0)
     local linecount = 0
     for line in f:lines() do
       linecount = linecount + 1
       coroutine.yield(line)
       if ((linecount % nlines) == 0) then
         callback(f:seek('cur') / length)
       end
     end
     return nil
   end))
 end


An example of using this to display the percentage loaded from a file
every 1000 lines:


 local chunk = assert(loadfile_callback('largefile.lua', 1000, function(ratio)
   print(string.format('%d%% complete...', ratio * 100))
 end))


Of course, if your app data file is not split up into lines, this may
need to be adjusted a bit...

-Duncan