Crash and Received memory warning - ios

Question

I have below for loop to download files from server to my iPad 3 device.
Running hundred of files, I got error and app crash. The console shown me "Received memory warning. Same logic running on my iPad Air was passed. Anyone can adivse how to resolve the problem.
iPad 3 -> iOS 9.3.5
iPad Air -> iOS 10.3.3
func download() {
for (index, subJson): (String, JSON) in serverJson! {
for (_, subJson): (String, JSON) in subJson {
let filepath = subJson["path"].stringValue
let nUpdated = subJson["updated"].stringValue
if let oUpdated = localJson?[index].array?.filter({ $0["path"].string == filepath}).first?["updated"].stringValue {
if (oUpdated == nUpdated)
{
DispatchQueue.main.async { () -> Void in
self.progressView.progress = Float(self.count) / Float(self.totalCount)
}
count += 1
continue
}
}
var absPath = filepath
let strIdx = absPath.index(absPath.startIndex, offsetBy: 2)
if (absPath.hasPrefix("./"))
{
absPath = absPath.substring(from: strIdx)
}
let sourceUrl = URL(string: self.sourceUrl.appending(absPath))
do {
let fileData = try NSData(contentsOf: sourceUrl!, options: NSData.ReadingOptions())
try writeFileToLocal(absPath, fileData)
} catch {
print(error)
}
DispatchQueue.main.async { () -> Void in
self.progressView.progress = Float(self.count) / Float(self.totalCount)
}
//print("Path: \(absPath)")
//print("%: \(Float(count) / Float(totalCount))")
count += 1
}
}
do {
// Remove temp json file first if exists.
if fileManager.fileExists(atPath: oldManifestPath) {
try? fileManager.removeItem(atPath: oldManifestPath)
}
// Write temp json file to local.
try data?.write(to: oldManifestUrl)
self.defaults.set(hashes, forKey: "LastHash")
} catch {
print(error)
}
DispatchQueue.main.async {
self.progressView.isHidden = true
self.changeViewProperties(2)
}
}
}
private func writeFileToLocal(_ url:String, _ data:NSData) throws {
let url = URL(string: url)
let path = url?.deletingLastPathComponent().relativePath
let file = url?.lastPathComponent
let documentsPath = NSURL(fileURLWithPath: NSSearchPathForDirectoriesInDomains(.documentDirectory, .userDomainMask, true)[0])
let filePath = documentsPath.appendingPathComponent(path!)
var isDir: ObjCBool = false
if !FileManager.default.fileExists(atPath: (filePath?.path)!, isDirectory:&isDir) {
try FileManager.default.createDirectory(atPath: filePath!.path, withIntermediateDirectories: true, attributes: nil)
}
FileManager.default.changeCurrentDirectoryPath((filePath?.path)!)
try data.write(toFile: file!, options: .atomicWrite)
print("Update: \(filePath!), \(file!)")
FileManager.default.changeCurrentDirectoryPath(documentsPath.path!)
}
Then I call the function "download" in DispatchQueue.
DispatchQueue.global().async {
self.downloadFiles()
}

Answer 1

Memory waring is occuring as you are processing hundreds of Things on main thread just a Trick that you can try out if it helps you take that function in background queue instead of main Queue , you may get some ui warnings which you need to manage as updating ui in background thread
I do not know if it will help you or not but you an just give it a try for once
DispatchQueue.global(qos: .background).async
{
//BackGround Queue Update
self.downloadFiles()
DispatchQueue.main.async
{
//Main Queue Update With All UI
}
}
as background thread is always good to manage huge processing for example kingfisher library take data on main thread and return on main thread but process it in background thread