How to get the file content?

Question

I have Obj-C code that looks like this

NSURL * url = [[NSBundle mainBundle] URLForResource:@"MyFile" withExtension:@"txt"];
NSError * err = nil;
NSString * string = [NSString stringWithContentsOfURL:url encoding:NSUTF8StringEncoding error:&err];

This code is working properly. I need to convert it to Swift one, so I did it like this

func getContentOfUrl(by fileName: String) -> String? {
    var result: String?
    guard let pathToFile = Bundle.main.path(forResource: fileName, ofType: "txt")
        else {
            return nil
        }
      
      do {
        result = try String(contentsOf: URL(string: pathToFile)!, encoding: String.Encoding.utf8)
      }
      catch let err{
      }
      
      return result
    }

And I get an error in the catch block

Attempt to get content of URL FAILED, error: Error Domain=NSCocoaErrorDomain Code=256 "The file “MyFile.txt” couldn’t be opened." UserInfo={NSURL=/private/var/containers/Bundle/Application/63FB01-F11-411-B93-6578DEF57B/MyApp.app/MyFile.txt}

what am I doing wrong?

guard let fileURL = Bundle.main.url(forResource: fileName, ofType: "txt") and then then use this url rather than that path, e.g., String(contentsOf: fileURL, encoding: .utf8). — Rob
– Rob, Commented Jul 19, 2021 at 12:44
Never create an URL from a file system path with URL(string:. This is the reason of the error. The proper API is URL(fileURLWithPath. And – as already pointed out – URLForResource:withExtension: exists also in Swift. — vadian
– vadian, Commented Jul 19, 2021 at 12:57
Also, be really careful with all of the contentsOf: url APIs on String, Data, NSDictionary, NSArray, etc. They're synchronous and can block for awhile. — Alexander
– Alexander, Commented Jul 19, 2021 at 13:29

Abizern · Accepted Answer · 2021-07-19 12:51:12Z

2

This works for me.

func getFile(named: String) -> String? {
    guard let url = Bundle.main.url(forResource: named, withExtension: "txt") else { return nil }
    return try? String(contentsOf: url, encoding: .utf8)
}

If it doesn't you need to make sure that the resource file actually exists.

You can test little functions like this in a playground. Add the file you want to use to the Resources folder in the playground. I did this with a file name "MyText.txt" and this worked fine.

answered Jul 19, 2021 at 12:51

Abizern

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Joakim Danielson · Accepted Answer · 2021-07-19 13:09:13Z

2

Apart from the fact that you should use a method that returns a URL instead of a file path as already mentioned is that you are using the wrong init method when creating the URL yourself. URL(string:) expects a string in a url format (file://...) but you have a local path so instead you should use URL(fileURLWithPath:). So this will make your existing code work

result = try String(contentsOf: URL(fileURLWithPath: pathToFile), encoding: .utf8)

Or use the URL directly

func content(of fileName: String) -> String? {
    Bundle.main.url(forResource: fileName, withExtension: "txt")
        .flatMap { try? String.init(contentsOf: $0, encoding: .utf8) }
}

edited Jul 19, 2021 at 13:09

answered Jul 19, 2021 at 13:00

Joakim Danielson

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