How to access file included in app bundle in Swift?

Swift 3, based on Karim’s answer.

Reading

You can read files included in an app’s bundle through the bundle’s resource:

let fileURL = Bundle.main.url(forResource:"filename", withExtension: "txt")

Writing

However, you can’t write there. You will need to create a copy, preferably in the Documents directory:

func makeWritableCopy(named destFileName: String, ofResourceFile originalFileName: String) throws -> URL {
    // Get Documents directory in app bundle
    guard let documentsDirectory = FileManager.default.urls(for: .documentDirectory, in: .userDomainMask).last else {
        fatalError("No document directory found in application bundle.")
    }

    // Get URL for dest file (in Documents directory)
    let writableFileURL = documentsDirectory.appendingPathComponent(destFileName)

    // If dest file doesn’t exist yet
    if (try? writableFileURL.checkResourceIsReachable()) == nil {
        // Get original (unwritable) file’s URL
        guard let originalFileURL = Bundle.main.url(forResource: originalFileName, withExtension: nil) else {
            fatalError("Cannot find original file “\(originalFileName)” in application bundle’s resources.")
        }

        // Get original file’s contents
        let originalContents = try Data(contentsOf: originalFileURL)

        // Write original file’s contents to dest file
        try originalContents.write(to: writableFileURL, options: .atomic)
        print("Made a writable copy of file “\(originalFileName)” in “\(documentsDirectory)\\\(destFileName)”.")

    } else { // Dest file already exists
        // Print dest file contents
        let contents = try String(contentsOf: writableFileURL, encoding: String.Encoding.utf8)
        print("File “\(destFileName)” already exists in “\(documentsDirectory)”.\nContents:\n\(contents)")
    }

    // Return dest file URL
    return writableFileURL
}

Example usage:

let stuffFileURL = try makeWritableCopy(named: "Stuff.txt", ofResourceFile: "Stuff.txt")
try "New contents".write(to: stuffFileURL, atomically: true, encoding: String.Encoding.utf8)

Just a quick update for using this code with Swift 4:

Bundle.main.url(forResource:"YourFile", withExtension: "FileExtension")

And the following has been updated to account for writing the file out:

var myData: Data!

func checkFile() {
    if let documentsDirectory = FileManager.default.urls(for: .documentDirectory, in: .userDomainMask).last {
        let fileURL = documentsDirectory.appendingPathComponent("YourFile.extension")
        do {
            let fileExists = try fileURL.checkResourceIsReachable()
            if fileExists {
                print("File exists")
            } else {
                print("File does not exist, create it")
                writeFile(fileURL: fileURL)
            }
        } catch {
            print(error.localizedDescription)
        }
    }
}

func writeFile(fileURL: URL) {
    do {
        try myData.write(to: fileURL)
    } catch {
        print(error.localizedDescription)
    }
}

This particular example is not the most flexible, but with a little bit of work you can easily pass in your own file names, extensions and data values.

Simply by searching in the app bundle for the resource

var filePath = NSBundle.mainBundle().URLForResource("file", withExtension: "txt")

However you can't write to it because it is in the app resources directory and you have to create it in the document directory to write to it

var documentsDirectory: NSURL?
var fileURL: NSURL?

documentsDirectory = NSFileManager.defaultManager().URLsForDirectory(.DocumentDirectory, inDomains: .UserDomainMask).last!
fileURL = documentsDirectory!.URLByAppendingPathComponent("file.txt")

if (fileURL!.checkResourceIsReachableAndReturnError(nil)) {
    print("file exist")
}else{
    print("file doesnt exist")
    NSData().writeToURL(fileURL!,atomically:true)
}

now you can access it from fileURL

EDIT - 28 August 2018

This is how to do it in Swift 4.2

var filePath = Bundle.main.url(forResource: "file", withExtension: "txt")

To create it in the document directory

if let documentsDirectory = FileManager.default.urls(for: .documentDirectory, in: .userDomainMask).last {
   let fileURL = documentsDirectory.appendingPathComponent("file.txt")
   do {
       if try fileURL.checkResourceIsReachable() {
           print("file exist")
       } else {
           print("file doesnt exist")
           do {
            try Data().write(to: fileURL)
           } catch {
               print("an error happened while creating the file")
           }
       }
   } catch {
       print("an error happened while checking for the file")
   }
}