Access Denied error with basic XML file operations

Question

Hi,
I'm trying to set up a basic read, write and delete code for XML files which I can build upon in the future. The three methods are bound to three buttons on the page and all three calls are awaited. Here's my code:
Write:
XElement uservarnodes = new XElement("uservars",
new XElement("uservar1", "1"),
new XElement("uservar2", "2"),
new XElement("uservar3", "3"),
new XElement("uservar4", "4"),
new XElement("uservar5", "5"),
new XElement("uservar6", "6"),
new XElement("uservar7", "7"),
new XElement("uservar8", "8"));
StorageFolder local = Windows.Storage.ApplicationData.Current.LocalFolder;
var file = await local.CreateFileAsync("uservarfile.xml", CreationCollisionOption.ReplaceExisting);
var stream = await file.OpenAsync(Windows.Storage.FileAccessMode.ReadWrite);
using (var outputStream = stream.GetOutputStreamAt(0))
DataWriter mydataWriter = new DataWriter(outputStream);
mydataWriter.WriteString(uservarnodes.ToString());
await mydataWriter.StoreAsync();
await outputStream.FlushAsync();
Read (outputs the data to a textblock):
StorageFolder local = Windows.Storage.ApplicationData.Current.LocalFolder;
var file = await local.GetFileAsync("uservarfile.xml");
string readtext = await Windows.Storage.FileIO.ReadTextAsync(file);
XElement uservarnodes = XElement.Parse(readtext);
txtTarget.Text = uservarnodes.ToString();
Delete:
StorageFolder local = Windows.Storage.ApplicationData.Current.LocalFolder;
var file = await local.GetFileAsync("uservarfile.xml");
await file.DeleteAsync(StorageDeleteOption.PermanentDelete);
When I tap each of the buttons once it all seems to work. But when I tap any of the buttons again within the same debug session I get an Access denied exception (E_ACCESSDENIED). Other people with this error had to await when calling their method, but I'm
already doing that: private async void btnWrite_Click(object sender, RoutedEventArgs e) { await WriteToXMLFile(); }, etc.
And the intervals between my taps isn't that short that you'd expect that the previously called method still had not finished completing. I don't understand why I'm getting the access denied error.
Related to my question: I have added XML to the File Type Associations, File Open Picker and File Save Picker in the appxmanifest, but somewhere I read that you do not need to do this if you're working with local app data only. Is this true?

Answer 1

var stream = await file.OpenAsync(Windows.Storage.FileAccessMode.ReadWrite);
I think because of your file stream hasn't been closed.
by the way, it can be easier  by using System.IO.OpenStreamForWriteAsync extension method
async public static Task<bool> SaveTextFileAsync(string filename, string data)
byte[] fileBytes = System.Text.Encoding.UTF8.GetBytes(data);
StorageFolder local = Windows.Storage.ApplicationData.Current.LocalFolder;
var file = await local.CreateFileAsync(filename, CreationCollisionOption.ReplaceExisting);
try
using (var s = await file.OpenStreamForWriteAsync())
s.Write(fileBytes, 0, fileBytes.Length);
return true;
catch
return false;
(need using System.IO namespace)
在現實生活中，你和誰在一起的確很重要，甚至能改變你的成長軌跡，決定你的人生成敗。 和什麼樣的人在一起，就會有什麼樣的人生。 和勤奮的人在一起，你不會懶惰； 和積極的人在一起，你不會消沈； 與智者同行，你會不同凡響； 與高人為伍，你能登上巔峰。