How to first read and the write to a file - windows-runtime

Question

I am trying to read tags, change tags,, and then and write back data to the same file. Reading tags is no problem but write are not working. Data seems not to be saved to disk.
My test case.
var file = await KnownFolders.MusicLibrary.GetFileAsync("sampleUnderTest.wav");
var content = await ReadFileAsynch(file);
content.Add("newTag","newValue")
await SubmittFileAsynch(file, content)
var newContent = await ReadFileAsynch(file);
Assert.NotEqual(content,newContent)
The Assert throws a Exception because content and newContent are identical.
This is part my code:
public async Task SubmittFileAsynch(StorageFile file, Content content)
{
var accessStream = await file.OpenAsync(FileAccessMode.ReadWrite);
using (accessStream)
await CommitAsynch(accessStream, content);
}
internal async Task CommitAsynch(IRandomAccessStream accessStream, Content content)
{
List<byte[]> tbw = new List<byte[]>();
using (var InStream = accessStream.AsStreamForRead())
{
using (var br = new BinaryReader(InStream))
{
//Reads file until it reaches the part of the containing tags and
//that are going to be modified by content.
//tbw is created from data in content and from the read process.
await BuildAsync(br, content, tbw);
using (var outstream = (accessStream.GetOutputStreamAt(0)))
using (var bw = new DataWriter(outstream))
{
await CommitAsync(tbw, bw);
await bw.FlushAsync();
}
}
}
}
private async Task CommitAsync(List<byte[]> tbw, DataWriter bw)
{
await Task.Run(() =>
{
foreach (byte[] buf in tbw)
bw.WriteBytes(buf);
});
}
I can't see what I am doing wrong ,, and are hoping for some help.
//lg

Answer 1

I am back smile
Finally I solved my problem. There where some threading issues in my code. I changed the write part to:
using (var bw = new DataWriter(outstream))
{
//await CommitAsync(tbw, bw);
foreach (byte[] buf in tbw)
bw.WriteBytes(buf);
await bw.StoreAsync();
bw.DetachStream();
}
await outstream.FlushAsync();
Now it works nicely. I am not sure if there are som part of the code that are redundant,, with respect to the "using" clause.
If anyone can tip me about some good reading regarding fileIO, streams etc,,, I would be greatful. All that I found on internet,, was very basic,,
Hope this will help someone else.