File System AccessAccess to known folders, using pickers, writing to and
reading from files, caching files for future access
George Georgiev
Telerik Software Academyacademy.telerik.com
Technical Traineritgeorge.net
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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
Store Apps File AccessRestrictions, Capabilities, Prompting for Access
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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
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
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Accessing Known FoldersAdding capabilities, using the storage
API
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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
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
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Accessing Known Folders
Live Demo
PickersWinows.Storage.Pickers
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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
Folder PickerIntroduction to pickers, picking a
folder
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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 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
Folder PickerLive Demo
File Open PickerOpening existing files
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File Open Picker 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
File Open PickerLive Demo
Reading and Writing Files
Using Winows.Storage.FileIO
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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)
Reading and Writing Files
Live Demo
File Save PickerCreating files from Apps
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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
var textFileTypes = new List<string>(new string[]{".txt"});picker.FileTypeChoices.Insert("Plain Text", textFileTypes);
File Save PickerLive Demo
Storing Files in the Access CacheCreating files from Apps
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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)
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) 26
var accessCache = Windows.Storage.AccessCache;var futureAccessList = accessCache. StorageApplicationPermissions.FutureAccessList;
futureAccessList.Add(file);
var file = await futureAccessList.GetFileAsync(token);//use file here
Storing Files in Access Cache
Live Demo
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Questions?
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File System Access
http://academy.telerik.com
Exercises1. 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.)