UIProgressView Crash in swift the message is Thread 6: Fatal error: Unexpectedly found nil while unwrapping an Optional value

Question

I have some issues with UIProgressView, I dont know why It crashes. In my view controller I have outlet like:

   @IBOutlet weak var progressBar: UIProgressView!

and I double checked it connected correctly. In my viewDidLoad I reset the value like:

 progressBar.progress = 0.0

Then when I start to download something, I call it like:

func urlSession(_ session: URLSession, downloadTask: URLSessionDownloadTask, didWriteData bytesWritten: Int64, totalBytesWritten: Int64, totalBytesExpectedToWrite: Int64) {

    let written = byteFormatter.string(fromByteCount: totalBytesWritten)
    print("print the written \(written)")
    let expected = byteFormatter.string(fromByteCount: totalBytesExpectedToWrite)
    self.progressBar.progress = Float(100 * bytesWritten/totalBytesExpectedToWrite)

}

but it crash always in this line:

 self.progressBar.progress = Float(100 * bytesWritten/totalBytesExpectedToWrite)

Any idea?

Outlet connected yes, and the error : Thread 6: Fatal error: Unexpectedly found nil while unwrapping an Optional value — Steven, Jul 04 '18 at 14:33
`bytesWritten/totalBytesExpectedToWrite` is this math working if you debug it ? — GIJOW, Jul 04 '18 at 14:34
if you print its value `self.progressBar.progress` before the error line does it work ? — GIJOW, Jul 04 '18 at 14:37
I don't think that your progressBar is nil because then it should already crash in viewDidLoad(). Please try to split the crashing line in two parts: let myProgress = Float(100 * bytesWritten / totalBytesExpectedToWrite); self.progressBar.progress = myProgress; --> what line is causing the crash now? — ndreisg, Jul 04 '18 at 14:43
it crashed with message: Thread 4: Fatal error: Unexpectedly found nil while unwrapping an Optional value — Steven, Jul 04 '18 at 14:51
Where are you kicking off your download task? Perhaps before `viewDidLoad` is called (e.g. in `perpareForSegue` or in `init`)? In which case, your outlets will be `nil`. — beyowulf, Jul 04 '18 at 15:01

Hussain Chhatriwala · Answer 1 · 2018-07-05T10:07:53.177

1

Try this way

DispatchQueue.main.async {
    if self.progressBar != nil{
       self.progressBar.progress = Float(100 * bytesWritten/totalBytesExpectedToWrite)
     }
}

edited Jul 05 '18 at 10:07

answered Jul 04 '18 at 16:16

Hussain Chhatriwala

820
11
25

Nope, the error message Cannot assign to value: 'progreBar' is a 'let' constant – Steven Jul 04 '18 at 16:29
Try to use above lines now, let me know if it helps – Hussain Chhatriwala Jul 04 '18 at 16:31
1

That will not work, because it will shows always nil. – Steven Jul 05 '18 at 07:40
@Steven I asked to do so because there is crash due to optional handling, so if it dose not go in inner lines then surely there is problem in configuration of progress view. It if it not that case then code would run without any obstacles. – Hussain Chhatriwala Jul 05 '18 at 07:43
I tried but it doesnt work, probably when I run the download with viewWillAppear, the progress not work because the view not set. it can be some bug of apple. when I try with click button when view set, it works. I can run when viewdidappear but in this case will not help me, because make late the download. – Steven Jul 05 '18 at 09:49
@Steven try it on main thread once as mentioned above, let me know if that works. – Hussain Chhatriwala Jul 05 '18 at 10:08
Checking for `nil` is not *swifty*, there is optional chaining: self.progressBar?.progress = ...` and remove the `if` statement. – vadian Jul 05 '18 at 10:18
I tried @Hussain Chhatriwala, it doesnt crash but the progress doesnt work. – Steven Jul 05 '18 at 12:17

UIProgressView Crash in swift the message is Thread 6: Fatal error: Unexpectedly found nil while unwrapping an Optional value

1 Answers1