Why do I get an error of "index out of bounds" in Swift when appending a new file?

Question

I'm very new with swift and I have a function on my app which sets a schedule for an audio recording to happen automatically. The recording successfully starts and stops at the given times. However, I get a runtime error when I hit the button “recordings” to check for the created recording file.

Would you happen to know why that's the case?

I didn't think it should be a problem as I'm only automating a pre-existing function. I initially have a function which sucessfully records when start and stop button for the function is manually pressed and the file is created within the folder "recordings"

Here's my code:

/*
 This will change recordings to fileitmes and add to an array, this array is used by the table view, which will then show the recordings
 */
func addToRecordings(folder: String) {
    let documentsDirectory = FileManager.default.urls(for: .documentDirectory, in: .userDomainMask).first!
    let path = documentsDirectory.appendingPathComponent(folder).absoluteURL
    do {
        let directoryContents = try FileManager.default.contentsOfDirectory(at: path, includingPropertiesForKeys: nil, options: [])
        //only want the wav files
        let wavFiles = directoryContents.filter{ $0.pathExtension == "wav" }
        for file in wavFiles{
            let fileName = file.lastPathComponent
            let start = fileName.index(fileName.startIndex, offsetBy: 26)
            let end = fileName.index(fileName.endIndex, offsetBy: -4)
            let range = start..<end
            //create id to help sort the wav files 
            let id = Int(fileName[range]) ?? 0
            if let fileAttributes = try? FileManager.default.attributesOfItem(atPath: file.path) {
                if let bytes = fileAttributes[.size] as? Int64 {
                    let fileSize = fileByteCountFormatter.string(fromByteCount: bytes)
                    let recording = FileItem(id: id, fileName: fileName, fileSizeSpecific: fileSize, fileSizeBytes: bytes, fileLocation: folder+fileName)
                    self.recordings.append(recording!)
                }
            }
        }
        self.recordings = self.recordings.sorted(by: {$0.id < $1.id})
        self.tableView.reloadData()
    } catch {
        print(error)
    }
    if recordings.isEmpty{
        recordingsActionButton.isHidden = true
        self.selectAllButton.isHidden = true
        progressBar.isHidden = true
    }else {
        recordingsActionButton.isHidden = false
        self.selectAllButton.isHidden = false
    }
}

   

The error is here: let start = fileName.index(fileName.startIndex, offsetBy: 26)

Thank you so much in advance!

Answer 1

This line will give index out of bounds if fileName is shorter than 26 characters:

let start = fileName.index(fileName.startIndex, offsetBy: 26)