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  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

Restrictions, Capabilities, Prompting for Access

4  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

 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 5

Adding capabilities, using the storage API

7  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

 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 8

Live Demo

Winows.Storage.Pickers

11  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

Introduction to pickers, picking a folder

13  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 FileTypeFilter to 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

Live Demo

Opening existing files

16  File Open pickers open existing files  Result is received asynchronously  PickSingleFileAsync()/PickMultipleFilesAsync() return an awaitable IAsyncOperation  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

Live Demo

Using Winows.Storage.FileIO

19  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)

Live Demo

Creating files from Apps

22  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 var textFileTypes = new List (new string[]{".txt"}); picker.FileTypeChoices.Insert("Plain Text", textFileTypes);

Live Demo

Creating files from Apps

25  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)

 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) 26 var accessCache = Windows.Storage.AccessCache; var futureAccessList = accessCache. StorageApplicationPermissions.FutureAccessList; StorageApplicationPermissions.FutureAccessList; futureAccessList.Add(file); var file = await futureAccessList.GetFileAsync(token); //use file here

Live Demo

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1. 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 Gestures and Responding to InteractionsGestures and Responding to Interactions  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.)