File access in a sandboxed Mac app with swift

Here is my answer that I've just got working in Swift 3 with a little help from http://swiftrien.blogspot.com/2015/07/persisting-file-access-rights-between.html

import Foundationimport Cocoavar bookmarks = [URL: Data]()func bookmarkPath() -> String{    var url = app.applicationDocumentsDirectory    url = url.appendingPathComponent("Bookmarks.dict")    return url.path}func loadBookmarks(){    let path = bookmarkPath()    bookmarks = NSKeyedUnarchiver.unarchiveObject(withFile: path) as! [URL: Data]    for bookmark in bookmarks    {        restoreBookmark(bookmark)    }}func saveBookmarks(){    let path = bookmarkPath()    NSKeyedArchiver.archiveRootObject(bookmarks, toFile: path)}func storeBookmark(url: URL){    do    {        let data = try url.bookmarkData(options: NSURL.BookmarkCreationOptions.withSecurityScope, includingResourceValuesForKeys: nil, relativeTo: nil)        bookmarks[url] = data    }    catch    {        Swift.print ("Error storing bookmarks")    }}func restoreBookmark(_ bookmark: (key: URL, value: Data)){    let restoredUrl: URL?    var isStale = false    Swift.print ("Restoring \(bookmark.key)")    do    {        restoredUrl = try URL.init(resolvingBookmarkData: bookmark.value, options: NSURL.BookmarkResolutionOptions.withSecurityScope, relativeTo: nil, bookmarkDataIsStale: &isStale)    }    catch    {        Swift.print ("Error restoring bookmarks")        restoredUrl = nil    }    if let url = restoredUrl    {        if isStale        {            Swift.print ("URL is stale")        }        else        {            if !url.startAccessingSecurityScopedResource()            {                Swift.print ("Couldn't access: \(url.path)")            }        }    }}func allowFolder() -> URL?{    let openPanel = NSOpenPanel()    openPanel.allowsMultipleSelection = false    openPanel.canChooseDirectories = true    openPanel.canCreateDirectories = true    openPanel.canChooseFiles = false    openPanel.begin        { (result) -> Void in            if result == NSFileHandlingPanelOKButton            {                let url = openPanel.url                storeBookmark(url: url!)            }    }    return openPanel.url}

Swift 4 (update):

import Foundationimport Cocoavar bookmarks = [URL: Data]()func fileExists(_ url: URL) -> Bool{    var isDir = ObjCBool(false)    let exists = FileManager.default.fileExists(atPath: url.path, isDirectory: &isDir)    return exists}func bookmarkURL() -> URL{    let urls = FileManager.default.urls(for: .applicationSupportDirectory, in: .userDomainMask)    let appSupportURL = urls[urls.count - 1]    let url = appSupportURL.appendingPathComponent("Bookmarks.dict")    return url}func loadBookmarks(){    let url = bookmarkURL()    if fileExists(url)    {        do        {            let fileData = try Data(contentsOf: url)            if let fileBookmarks = try NSKeyedUnarchiver.unarchiveTopLevelObjectWithData(fileData) as! [URL: Data]?            {                bookmarks = fileBookmarks                for bookmark in bookmarks                {                    restoreBookmark(bookmark)                }            }        }        catch        {            print ("Couldn't load bookmarks")        }    }}func saveBookmarks(){    let url = bookmarkURL()    do    {        let data = try NSKeyedArchiver.archivedData(withRootObject: bookmarks, requiringSecureCoding: false)        try data.write(to: url)    }    catch    {        print("Couldn't save bookmarks")    }}    func storeBookmark(url: URL){    do    {        let data = try url.bookmarkData(options: NSURL.BookmarkCreationOptions.withSecurityScope, includingResourceValuesForKeys: nil, relativeTo: nil)        bookmarks[url] = data    }    catch    {        Swift.print ("Error storing bookmarks")    }}func restoreBookmark(_ bookmark: (key: URL, value: Data)){    let restoredUrl: URL?    var isStale = false    Swift.print ("Restoring \(bookmark.key)")    do    {        restoredUrl = try URL.init(resolvingBookmarkData: bookmark.value, options: NSURL.BookmarkResolutionOptions.withSecurityScope, relativeTo: nil, bookmarkDataIsStale: &isStale)    }    catch    {        Swift.print ("Error restoring bookmarks")        restoredUrl = nil    }    if let url = restoredUrl    {        if isStale        {            Swift.print ("URL is stale")        }        else        {            if !url.startAccessingSecurityScopedResource()            {                Swift.print ("Couldn't access: \(url.path)")            }        }    }}func allowFolder() -> URL?{    let openPanel = NSOpenPanel()    openPanel.allowsMultipleSelection = false    openPanel.canChooseDirectories = true    openPanel.canCreateDirectories = true    openPanel.canChooseFiles = false    openPanel.begin        { (result) -> Void in            if result == NSFileHandlingPanelOKButton            {                let url = openPanel.url                storeBookmark(url: url!)            }    }    return openPanel.url}

To use this code you must first call NSOpenPanel so the user can select which folders to give you access to. The NSOpenPanel must be stored as a bookmark and saved to disk.

let url = allowFolder()saveBookmarks()

When you restart the application you must call

loadBookmarks()

then your app will have the same level of access as it did when the user selected the folder. Hope this helps someone.

Here's more clean solution with SWIFT 5.0:

import Foundationimport Cocoa    class BookmarkManager {        static let manager = BookmarkManager()        // Save bookmark for URL. Use this inside the NSOpenPanel `begin` closure        func saveBookmark(for url: URL){            guard let bookmarkDic = self.getBookmarkData(url: url),                let bookmarkURL = getBookmarkURL() else{                    print("Error getting data or bookmarkURL")                    return            }            do            {                let data = try NSKeyedArchiver.archivedData(withRootObject: bookmarkDic, requiringSecureCoding: false)                try data.write(to: bookmarkURL)                print("Did save data to url")            }            catch            {                print("Couldn't save bookmarks")            }        }        // Load bookmarks when your app launch for example        func loadBookmarks()        {            guard let url = self.getBookmarkURL() else {                return            }            if self.fileExists(url)            {                do                {                    let fileData = try Data(contentsOf: url)                    if let fileBookmarks = try NSKeyedUnarchiver.unarchiveTopLevelObjectWithData(fileData) as! [URL: Data]?                    {                        for bookmark in fileBookmarks{                            self.restoreBookmark(key: bookmark.key, value: bookmark.value)                        }                    }                }                catch                {                    print ("Couldn't load bookmarks")                }            }        }        private func restoreBookmark(key: URL, value: Data){            let restoredUrl: URL?            var isStale = false            Swift.print ("Restoring \(key)")            do            {                restoredUrl = try URL.init(resolvingBookmarkData: value, options: NSURL.BookmarkResolutionOptions.withSecurityScope, relativeTo: nil, bookmarkDataIsStale: &isStale)            }            catch            {                Swift.print ("Error restoring bookmarks")                restoredUrl = nil            }            if let url = restoredUrl            {                if isStale                {                    Swift.print ("URL is stale")                }                else                {                    if !url.startAccessingSecurityScopedResource()                    {                        Swift.print ("Couldn't access: \(url.path)")                    }                }            }        }        private func getBookmarkData(url: URL) -> [URL: Data]?{            let data = try? url.bookmarkData(options: NSURL.BookmarkCreationOptions.withSecurityScope, includingResourceValuesForKeys: nil, relativeTo: nil)            if let data = data{                return [url: data]            }            return nil        }        private func getBookmarkURL() -> URL? {            let urls = FileManager.default.urls(for: .applicationSupportDirectory, in: .userDomainMask)            if let appSupportURL = urls.last{                let url = appSupportURL.appendingPathComponent("Bookmarks.dict")                return url            }            return nil        }        private func fileExists(_ url: URL) -> Bool        {            var isDir = ObjCBool(false)            let exists = FileManager.default.fileExists(atPath: url.path, isDirectory: &isDir)            return exists        }    }

security scoped bookmarks is exactly the way to go. good starting point is apple documentation on AppStore sandbox (which includes sample code) and class reference of NSFileManager.

you then will not store the path in user defaults but the binary data of the bookmark.