Program on Swift Crashes when first compiling - swift

Question

So I ran this code using swift and the issue that I am having is that it's not working on the first try it compiles the project. However, when I stop the project and run it again it works perfectly fine and I do repeat this several times and the issue doesn't occur anymore. More specifically, when the project opens and I press a button on the app it goes to the error that I show below:
This is the error that I get when I run it for the first time
"Thread 1: Fatal error: 'try!' expression unexpectedly raised an
error: Error Domain=NSCocoaErrorDomain Code=260 "The file “.tmp”
couldn’t be opened because there is no such file."
UserInfo={NSFilePath=/.tmp, NSUnderlyingError=0x60000335d9b0 {Error
Domain=NSPOSIXErrorDomain Code=2 "No such file or directory"}}"
This error shows up on the line where let contentstring is created. I check the value of contentstring and I get that contentstring = (NSString) 0x0000000000000000. When running the program multiple times it gives me a valid value and it works perfectly fine.
I am not sure why this error occurs only once when the button is pressed and what is a solid approach to this problem.
import UIKit
class KresgePorter: UIViewController, UITableViewDataSource, UITableViewDelegate {
var printString: String!
var array: [String] = []
var count: Int = 0
override func viewWillAppear(_ animated: Bool) {
super.viewWillAppear(animated)
navigationController?.setNavigationBarHidden(true, animated: false)
}
override func viewDidLoad() {
super.viewDidLoad()
/*-------------------------------------------------------------------------------------------------------------------------------------------------*/
var nameTXT = ""
var documentsDir = ""
let website = some string url
guard let url1 = URL(string: website) else { return }
//This portion of the code focuses on creating a download task with a completion handler
//Completion handler moves the downloaded file to the app's directory
let downloadTask = URLSession.shared.downloadTask(with: url1) {
urlOrNil, responseOrNil, errorOrNil in
// check for and handle errors:
// * errorOrNil should be nil
// * responseOrNil should be an HTTPURLResponse with statusCode in 200..<299
print("Went into the let\n")
guard let fileURL = urlOrNil else { return }
do {
let documentsURL = try
FileManager.default.url(for: .documentDirectory,
in: .userDomainMask,
appropriateFor: nil,
create: true)
let savedURL = documentsURL.appendingPathComponent(fileURL.lastPathComponent)
let filename = fileURL.lastPathComponent
let fileName2 = URL(fileURLWithPath: filename).deletingPathExtension().lastPathComponent
nameTXT = fileName2
print("the content of nameTXT is: \(nameTXT)")
try FileManager.default.moveItem(at: fileURL, to: savedURL)
} catch {
print ("file error: \(error)")
}
let paths = NSSearchPathForDirectoriesInDomains(.documentDirectory, .userDomainMask, true) as NSArray
documentsDir = paths.firstObject as! String
print("Path to the Documents directory\n\(documentsDir)")
}
downloadTask.resume()
//If you want to receive progress updates as the download proceeds, you must use a delegate.
var urlSession = URLSession(configuration: .default, delegate: self as? URLSessionDelegate, delegateQueue: nil)
func startDownload(url1: URL){
print("Went into the startDownload function\n")
let downloadTask = urlSession.downloadTask(with: url1)
//let fname = downloadTask.response?.suggestedFilename
downloadTask.resume()
}
startDownload(url1: url1)
/*-----------------------------------------------------------------------------------------------------*/
usleep(270000)
let directPath = documentsDir + "/" + nameTXT + ".tmp"
let url = URL(fileURLWithPath: directPath)
let contentString = try! NSString(contentsOf: url, encoding: String.Encoding.utf8.rawValue)
printString = contentString as String
let fullName = printString
array = fullName!.components(separatedBy: "\n")
// Do any additional setup after loading the view.
}
func tableView(_ tableView: UITableView, numberOfRowsInSection section: Int) -> Int {
return array.count
}
func tableView(_ tableView: UITableView, cellForRowAt indexPath: IndexPath) -> UITableViewCell {
let cell = tableView.dequeueReusableCell(withIdentifier: "breakfast", for: indexPath)
cell.textLabel?.text = array[indexPath.row]
return cell
}
}

Answer 1

I shouldn't use try! in production code!
let contentString = try! NSString(contentsOf: url, encoding: String.Encoding.utf8.rawValue)
convert to this:
do {
let contentString = try? String( url, encoding: .utf8)
} catch {
print(error)
}
The actual problem is that:
let directPath = documentsDir + "/" + nameTXT + ".tmp"
let url = URL(fileURLWithPath: directPath)
yields "/.tmp". this is an invalid URL.
This is because of both documentsDir and nameTXT are empty.
So, the core reason is that you call
let directPath = documentsDir + "/" + nameTXT + ".tmp"
let url = URL(fileURLWithPath: directPath)
outside of the server response callback.
Just move your code from
// If you want to receive progress updates as the download until
array = fullName!.components(separatedBy: "\n")
into closure right after this line:
print("Path to the Documents directory\n\(documentsDir)")
your closure is launched asynchronously.