File System Access

1. File System Access Access to known folders, using pickers, writing to and reading from files, caching files for future access George Georgiev Telerik Software Academy academy.telerik.com Technical Trainer itgeorge.net

2. Table of Contents • Store Apps File Access • Capabilities, Prompting for Access • Accessing "Known Folders" • Documents, pictures, etc. • Pickers • Folder Picker • File Open Picker • Reading and writing to a file • File Save Picker • Storing Files in the Access Cache

3. Store Apps File Access Restrictions, Capabilities, Prompting for Access

4. Store Apps File Access • Store Apps don't have typical access to files • Only to the per-app virtual file system • Several ways of accessing the file system • Through known folders • Documents, Pictures, Removable Storage, etc. • Need to add capabilities in app manifest • Through file/folder pickers • System-controlled dialogs/prompts to the user • Through other apps • Participating in file picker or share contracts

5. Store Apps File Access • WinRT Storage APIs • Provide file pickers & file picker contracts • Provide KnownFolders enumeration • Provide file input/output operations, file/folder creation, renaming, deleting, etc. • Other storage locations and options • Namespace – Windows.Storage

6. Accessing Known Folders Adding capabilities, using the storage API

7. Accessing Known Folders • Known folders are typical folders in Windows • Documents library, Music library, etc. • Apps can access them directly • If they define this capability in the app manifest • Adding known folders capabilities • Go to the manifest, under Capabilities • Pick the folder(s) needed for the app • Under declarations, add File Type Associations • Customize for files your app will access in the known folders

8. Accessing Known Folders • After editing the manifest, use the storage API • E.g. Windows.Storage.KnownFolders.documentsLibrary • The API returns a StorageFolder object • Once you have a StorageFolder, you can: • Access file types declared in the manifest • Read, write, rename, delete, etc. • Create any file type • Open & create subfolders

9. Accessing Known Folders Live Demo

10. Pickers Winows.Storage.Pickers

11. Pickers • Pickers are special views in Store Apps • Controlled and styled by the system • Limited customization options for apps • Button text, file display mode, visible files (by extension), suggestedStartLocation etc. • Asynchronously pick files/folders • Visualize picking UI for the user • App keeps running as if on-screen • On successful pick, app gets access to picked item • App can store the file for future access • Windows.Storage.Pickers

12. Folder Picker Introduction to pickers, picking a folder

13. Folder Picker • Folder pickers provide UI for picking folders • Result is received asynchronously • pickSingleFolderAsync() returns a promise • Result value is a StorageFolder • like when using Known Folders • Requires a FileTypeFilterto be set • Files listed to the user when navigating • List/array of strings (extensions, e.g. ".txt", "*") • Doesn't require any capability declarations • Except if using Known Folders for suggestedStartLocation

14. Folder Picker Live Demo

15. File Open Picker Opening existing files

16. File Open Picker • File Open pickers open existing files • Result is received asynchronously • pickSingleFileAsync()/pickMultipleFilesAsync() return a promise • Result value is a StorageFile • Read, write, rename, delete, copy, move, properties, thumbnail, etc. • Requires FileTypeFilter(same as in FolderPicker) • Doesn't require any capability declarations • Except if using Known Folders for suggestedStartLocation

17. File Open Picker Live Demo

18. Reading and Writing Files Using Winows.Storage.FileIO

19. Reading an Writing files • Access to file contents happens through Windows.Storage.FileIO • Provides several read and write methods • Reading, writing & appending strings, bytes, etc. • Operations are asynchronous (return promises) • Read operation get content in success handler • Write operations could skip handling • Except for success/error notification Windows.Storage.FileIO.writeTextAsync(file, text) .done(writeSuccessMessage, writeErrorMessage); Windows.Storage.FileIO.readTextAsync(file) .done(function (text) {/*use text here*/})

20. Reading and Writing Files Live Demo

21. Transacted File Write Using transaction stream to ensure write integrity

22. Transacted File Write • Some apps need stream operations over files • Streams are supported by FileIO • Stream writing can be interrupted by an error • Losing part of the data, corrupting files • For writes that need to be atomic use transactStream from WinRT • Works asynchronously • Ensures a full write or no write at all

23. Transacted File Write Live Demo

24. File Save Picker Creating files from Apps

25. File Save Picker • File Save pickers create or overwrite files • Created file is received asynchronously • pickSaveFileAsync() returns a promise • Result value is a StorageFile • Requires FileTypeChoices(key-value pairs) • Key: the user-friendly file type (e.g. "Web Page") • Value: list of strings, possible filename extensions (e.g. [".htm", ".html"]) • Doesn't require any capability declarations • Except if using Known Folders for suggestedStartLocation picker.fileTypeChoices.insert("Plain Text", [".txt"])

26. File Save Picker Live Demo

27. Storing Files in the Access Cache Creating files from Apps

28. Storing Files in Access Cache • Apps access files through StorageFile objects • Folders through StorageFolder objects • Apps can't create such objects on their own • E.g. need a file picker to do it • Can't save the URI of a file and access it • Unless file is in AppData • WinRT supports an API which saves StorageFiles and persists them • Called futureAccessList • Key-value pairs (string token – StorageFile pairs)

29. Storing Files in Access Cache • Using futureAccessList • Insert the StorageFile the app will need later • The file needs a unique string token (e.g. filename + timestamp) • The file can be accessed at any time (even after app has restarted) varaccessCache = Windows.Storage.AccessCache; varfutureAccessList = accessCache. StorageApplicationPermissions.futureAccessList; futureAccessList.addOrReplace(token, file); futureAccessList.getFileAsync(token) .then(function(file){/*use file here*/});

30. Storing Files in Access Cache Live Demo

31. File System Access http://academy.telerik.com

32. Exercises • Implement a simple Video Player app • The app should be able to open video files through file pickers • The opened files should be stored into an in-app playlist • The app should be able to play any file from the playlist • * after a file has finished playing, the next one should start • The app should be able to remove songs from the playlist • The app should be able to save the playlist through a file save picker • Save the file in any format you like (e.g. your own or a one of the built into Windows) • The app should be able to load a any playlist it saved through a file open picker and be able to play its files • * buttons for adding/removing songs should be in AppBar