Crash and Received memory warning

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()
}

iOS Geek iOS Geek · Accepted Answer · 2017-11-17T04:16:57

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

Crash and Received memory warning

1 Answers