File IO in Windows 8

Question

I have been trying to read a file, and calculate the hash of the contents to find duplicates. The problem is that in Windows 8 (or WinRT or windows store application or however it is called, I'm completely confused), System.IO has been replaced with Windows.Storage, which behaves differently, and is very confusing. The official documentation is not useful at all.

First I need to get a StorageFile object, which in my case, I get from browsing a folder from a file picker:

var picker = new Windows.Storage.Pickers.FolderPicker();
picker.SuggestedStartLocation = Windows.Storage.Pickers.PickerLocationId.MusicLibrary;
picker.FileTypeFilter.Add("*");
var folder = await picker.PickSingleFolderAsync();
var files = await folder.GetFilesAsync(Windows.Storage.Search.CommonFileQuery.OrderByName);

Now in files I have the list of files I need to index. Next, I need to open that file:

foreach (StorageFile file in files)
{
    var filestream = file.OpenAsync(Windows.Storage.FileAccessMode.Read);

Now is the most confusing part: getting the data from the file. The documentation was useless, and I couldn't find any code example. Apparently, Microsoft thought getting pictures from the camera is more important than opening a file.

The file stream has a member ReadAsync which I think reads the data. This method needs a buffer as a parameter and returns another buffer (???). So I create a buffer:

    var buffer = new Windows.Storage.Streams.Buffer(1024 * 1024 * 10); // 10 mb should be enough for an mp3
    var resultbuffer = await filestream.ReadAsync(buffer, 1024 * 1024 * 10, Windows.Storage.Streams.InputStreamOptions.ReadAhead);

I am wondering... what happens if the file doesn't have enough bytes? I haven't seen any info in the documentation.

Now I need to calculate the hash for this file. To do that, I need to create an algorithm object...

    var alg = Windows.Security.Criptography.Core.HashAlgorithmProvider.OpenAlgorithm("md5");
    var hashbuff = alg.HashData(resultbuffer);

    // Cleanup
    filestream.Dispose();

I also considered reading the file in chunks, but how can I calculate the hash like that? I looked everywhere in the documentation and found nothing about this. Could it be the CryptographicHash class type with it's 'append' method?

Now I have another issue. How can I get the data from that weird buffer thing to a byte array? The IBuffer class doesn't have any 'GetData' member, and the documentation, again, is useless.

So all I could do now is wonder about the mysteries of the universe...

    // ???
}

So the question is... how can I do this? I am completely confused, and I wonder why did Microsoft choose to make reading a file so... so... so... impossible! Even in Assembly I could figure it out easier than.... this thing.

See this similar question: http://stackoverflow.com/questions/12703816/how-to-read-file-metro-winrt/12704209#12704209 — Matthew Watson, Nov 16 '12 at 13:58
Check out the [Windows 8 special edition of MSDN Magazine](http://msdn.microsoft.com/en-us/magazine/ee310108.aspx). There are a lot of useful examples. — Joseph Yaduvanshi, Nov 16 '12 at 14:00

score 2 · Accepted Answer · answered Nov 16 '12 at 14:03

WinRT or Windows Runtime should not be confused with .NET as it is not .NET. WinRT has access to only a subset of the Win32 API but not to everything like the .NET is. Here is a pretty good article on what are the rules and restrictions in WinRT.

The WinRT in general does not have access to the file system. It works with capabilities and you can allow file access capability but this would restrict your app's access only to certain areas. Here is a good example of how do to file access via WinRT.

File IO in Windows 8

1 Answers1