Question about Network.download

Hi guys

I am making an apps which will download some photo from the server, then play with the photo

I found that if i run the apps in the simulator, it find not problems not problems.

but when i put it into iphone/Ipad, it will crash and shut down the apps automatically before showing the photo.

first step, I try to use the photo from my computer, instead of download from server. then it works on both IPAD IPHONE.

So, i conclude that there are some wrong in the download process.

Can anyone tell me how to download a photo then store with a specific name i give?

here is my download function.[lua]function networkListener( event )

if ( event.isError ) then
print( “Network error - download failed” )
elseif ( event.phase == “began” ) then
print( “Progress Phase: began” )
elseif ( event.phase == “ended” ) then
print( “displaying response image file” )
myImage = display.newImage( event.response.filename, event.response.baseDirectory, 1, 1 )
myImage.alpha = 1
–myImage.Isvisble=flase
myImage.x =-20
myImage.y =-20
myImage.height= 20
myImage.width= 20
transition.to( myImage, { alpha = 1 } )
end
end

function download()

local params = {}
params.progress = true

network.download(
http://54.254.181.71/image/”…math.random(1,5)…".png",
“GET”,
networkListener,
params,
“helloCopy.png”,
system.DocumentsDirectory
)

end
[/lua]

I am new to Lua

In my code above, I can only use the photo when I declare some variable for

A=myImage

also, the download photo will show on the screen, so i just be  a silly guys to move it out of the screen.

I really want to know how to download a photo without show on the screen and I can use it for my apps?