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 an awaitableIAsyncOperation • 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 (awaitable) • Read operation get content in success handler • Write operations could skip handling • Except for success/error notification await Windows.Storage.FileIO.WriteTextAsync(file, text); //here you can notify of success/error (wrap in try-catch) var text = await Windows.Storage.FileIO.ReadTextAsync(file); //use text here or notify of error (wrap in try-catch)

20. Reading and Writing Files Live Demo

21. File Save Picker Creating files from Apps

22. File Save Picker • File Save pickers create or overwrite files • Created file is received asynchronously • PickSaveFileAsync() returns an awaitable • 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 vartextFileTypes = new List<string>(new string[]{".txt"}); picker.FileTypeChoices.Insert("Plain Text", textFileTypes);

23. File Save Picker Live Demo

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

25. 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)

26. Storing Files in Access Cache • Using futureAccessList • Insert the StorageFile the app will need later • Can place a unique string token (e.g. filename + timestamp, if not, the system randomizes one) • The file can be accessed at any time (even after app has restarted) varaccessCache = Windows.Storage.AccessCache; varfutureAccessList = accessCache. StorageApplicationPermissions.FutureAccessList; futureAccessList.Add(file); var file = await futureAccessList.GetFileAsync(token); //use file here

27. Storing Files in Access Cache Live Demo

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

29. Exercises • Take the PaintRT app you wrote for the Gestures and Responding to Interactions homework and implement a Save file feature and an Open File feature • Save the file in your own format, so that all generated objects are loadable • Open files your app created, enabling the user to continue working on them, as if the app wasn't closed – e.g. users should still be able to change the color of an object by double-tapping it • * Bonus (not obligatory): add a feature for exporting drawings as image files (e.g. Bitmap, PNG, etc.)