Selfish pad - generally speaking selfishly

I had written programs using other languages to read and write from txt file on windows, but it was the first time to do it in a system targeted to mobile like UWP. It was so different from what I knew, so I spent a lot of time in looking for information in the internet.

Summarizing what Selfish pad does, the main functions are:
(the code (C#) below for each one, including the file accessing)

//1.Read from a txt file.
Windows.Storage.Pickers.FileOpenPicker open = new Windows.Storage.Pickers.FileOpenPicker();
Windows.Storage.StorageFile file = await open.PickSingleFileAsync();
using (Stream st = (await file.OpenReadAsync()).AsStream())
using (TextReader reader = new StreamReader(st, System.Text.Encoding.GetEncoding("utf-8")))
            { string text = await reader.ReadToEndAsync(); }

//2.Write to a txt file.
FileSavePicker savePicker = new FileSavePicker();
savePicker.SuggestedStartLocation = PickerLocationId.DocumentsLibrary;
savePicker.FileTypeChoices.Add("Plain Text", new List<string>() { ".txt" });
StorageFile file = await savePicker.PickSaveFileAsync();
string[] lines = {"line1","line2","line3" };
await FileIO.WriteLinesAsync(file, lines, Windows.Storage.Streams.UnicodeEncoding.Utf8);


Selfish pad は上記の二つの機能(Read, Write)がメインです。それぞれのコード(C#)をその下に書いてます。(ファイルにアクセスする部分も入ってます)