Friday, September 22, 2017

UWP Tip #6 - UWP Community Toolkit - Part 4, Leveraging the StorageFiles and Storage Code Helpers

Welcome back to the UWP Community Toolkit series. You'll have to excuse the delay between posts as TechBash 2017 has been monopolizing my free time this month.

Previous Tips in the UWP Community Toolkit series:


This tip will continue exploring the Code Helpers that we started looking at in Part 3. There are five types of helpers remaining, and today we'll look at the StorageFileHelper and Storage helpers.


The StorageFileHelper utility class has helper methods for reading from and writing to disk. There are method overloads to read and write both text and binary data to a file either directly to the local storage folder or to given folderId and/or folderName. Some overloads for writing take a CreationCollisionOptions parameter to decide how to handle conflicts during file or folder creation. All StorageFile operations are async.

Here is a simple example of simple read and write service methods that wrap calls to the StorageFileHelper methods that use the user's local storage.

 public async Task WriteUserData(string data, string fileName)
    await StorageFileHelper.WriteTextToLocalFileAsync(data, fileName);

public async Task<string> ReadUserData(string fileName)
    return await StorageFileHelper.ReadTextFromLocalFileAsync(fileName);


The StorageService, not to be confused with the previous StorageFileHelper, is for reading and writing objects within your application. The objects can be read and written locally or you can choose to roam the data across all the user's devices. This selection is made by using either a LocalObjectStorageHelper or a RoamingObjectStorageHelper. Makes sense.

Let's say you had a health care application of some kind and you wanted to save an object containing the currently selected clinic's information.

 public class Clinic : IClinic
    public string Name { get; set; }
    public string Location { get; set; }
    public int NumberOfBeds { get; set; }
    public ClinicType Type { get; set; }

We want to take this and persist it for the current device. So, we'll create some service methods to read and write the object local to the current device.

    public class StorageService
        private LocalObjectStorageHelper _localStorageHelper = new LocalObjectStorageHelper();

        public async Task SaveClinic(IClinic clinic, string key)
            await _localStorageHelper.SaveFileAsync(key, clinic);

        public async Task<IClinic> ReadClinic(string key)
            return await _localStorageHelper.ReadFileAsync<IClinic>(key);

That's it. We've wrapped the methods to read and write and only need to deal with our own interfaces in and out. If you wrap this service class in an interface and inject the helper itself, it will be nicely abstracted for testability. You can use these service methods from any of the existing ViewModels in your UWP app.


Next time we will continue with the Code Helpers in the UWP Community Toolkit. The Streams helper is up next.

Happy coding!

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