File System and Documents in Mobile Development: What It Is, Principles, and How It Works

import Foundation

let fileManager = FileManager.default
guard let documentsURL = fileManager.urls(
    for: .documentDirectory,
    in: .userDomainMask
).first else { return }

let fileURL = documentsURL.appendingPathComponent("notes.txt")
let text = "Содержимое файла"

// Atomic write with encryption
try text.write(
    to: fileURL,
    atomically: true,
    encoding: .utf8
)

func readDocumentsFile(named fileName: String) -> String? {
    guard let docsURL = FileManager.default.urls(
        for: .documentDirectory,
        in: .userDomainMask
    ).first else { return nil }

    let fileURL = docsURL.appendingPathComponent(fileName)
    return try? String(contentsOf: fileURL)
}

val contentValues = ContentValues().apply {
    put(MediaStore.MediaColumns.DISPLAY_NAME, "report.pdf")
    put(MediaStore.MediaColumns.MIME_TYPE, "application/pdf")
    put(MediaStore.MediaColumns.RELATIVE_PATH, "Documents/Reports")
}

val uri = contentResolver.insert(
    MediaStore.Files.getContentUri("external"),
    contentValues
)

uri?.let {
    contentResolver.openOutputStream(it)?.use { stream ->
        stream.write(pdfBytes)
    }
}

val intent = Intent(Intent.ACTION_OPEN_DOCUMENT).apply {
    addCategory(Intent.CATEGORY_OPENABLE)
    type = "*/*"
    putExtra(Intent.EXTRA_MIME_TYPES, arrayOf(
        "application/pdf",
        "text/plain"
    ))
}
startActivityForResult(intent, REQUEST_CODE)

let picker = UIDocumentPickerViewController(
    forOpeningContentTypes: [.pdf, .plainText]
)
picker.allowsMultipleSelection = true
picker.delegate = self
present(picker, animated: true)

// Releasing access in the delegate
func documentPicker(
    _ controller: UIDocumentPickerViewController,
    didPickDocumentsAt urls: [URL]
) {
    guard let url = urls.first else { return }
    url.startAccessingSecurityScopedResource()
    defer { url.stopAccessingSecurityScopedResource() }
}