Corona SDK JSON usage - json

Question

I have an operating JSON library which I use to load an array of tile IDs. When I double click main.lua directly from file explorer, it runs great, but when I open Corona Simulator and open my project from there or build my project and run it on my testing device, it gives me a null reference error when I attempt to use the data I loaded.
Here is the function to load a table from a JSON file:
function fileIO.loadJSONFile (fileName)
local path = fileName
local contents = ""
local loadingTable = {}
local file = io.open (path, "r")
print (file)
if file then
local contents = file:read ("*a")
loadingTable = json.decode (contents)
io.close (file)
return loadingTable
end
return nil
end
Here is the usage:
function wr:renderChunkFile (path)
local data = fileIO.loadJSONFile (path)
self:renderChunk (data)
end
function wr:renderChunk (data)
local a, b = 1
if (self.img ~= nil) then
a = #self.img + 1
self.img[a] = {}
else
self.img[1] = {}
end
if (self.chunks ~= nil) then
b = #self.chunks + 1
self.chunks[b] = display.newGroup ()
else
self.chunks[1] = display.newGroup ()
end
for i = 1, #data do -- Y axis ERROR IS HERE
self.img[a][i] = {}
for j = 1, #data[i] do -- Z axis
self.img[a][i][j] = {}
for k = 1, #data[i][j] do -- X axis
if (data[i + 1] ~= nil) then
if (data[i + 1][j][k] < self.transparentLimit) then
self.img[a][i][j][k] = display.newImage ("images/tiles/"..data[i][j][k]..".png", k*self.tileWidth, display.contentHeight -j*self.tileDepth - i*self.tileThickness)
self.chunks[b]:insert (self.img[a][i][j][k])
elseif(data[i + 1] == nil) then
self.img[a][i][j][k] = display.newImage ("images/tiles/"..data[i][j][k]..".png", k*self.tileWidth, display.contentHeight -j*self.tileDepth - i*self.tileThickness)
self.chunks[b]:insert (self.img[a][i][j][k])
end
end
end
end
end
end
When it gets to the line for i = 1, #data do it tells me it is trying to access the length of a nil field. Where did I go wrong here?
EDIT: I feel the need to give a more clear explanation of what my problem is. I am getting inconsistent results from this program. When I select main.lua in file explorer and open it with Corona Simulator, it works. When I open Corona Simulator and internally navigate to main.lua, it does not work. When I build the project and test it on my device, it does not work. What I really need is some insight into Corona's JSON library and APK internal directory structure requirements (directory nesting limits, naming restrictions, etc.). If someone thinks of something else that might cause the issue I am having, please bring it up! I am open to anything.

Answer 1

Without seeing the entire error message and not knowing what the value of "path" is it's going to be hard to speculate. But Corona SDK uses four base directories:
system.ResourceDirectory -- Same folder as main.lua and is read-only
system.DocumentsDirectory -- Your writable folder where your data lives
system.CachesDirectory -- for downloaded files
system.TemporaryDirectory -- for temp files.
The last three, while in the simulator are in the project's Sandbox master folder. On device who knows where the folders really are.
In your case, if your JSON file is going to be included in with your downloadble app, your .json file should be in the same folder with your main.lua (or a sub folder) and referenced in system.ResourceDirectory.