Async in Windows store application c#

Question

Hello there is something very strange happening here, i have these lines of code working perfectly in another testing solution but when i have them in my main solution i have a problem:

When i run it normally, it doesnt do anything, when i run in Debug and go step by step then it works.

private async void InitializeContents()
    {
        var path = @"Assets\Data\";
        var folder = Windows.ApplicationModel.Package.Current.InstalledLocation;
        try
        {
            var file = await folder.GetFileAsync(path + "test.txt");
            var lines = await FileIO.ReadLinesAsync(file);
            var pref = "";
            foreach (string line in lines)
            {                                       
                if (line.ElementAt(0).Equals('-'))
                {
                    switch (line.ElementAt(1))
                    {
                        case 'c': { pref = @"City\";break; }
                        case 'v': { pref = @"Village\"; break; }
                    }
                    continue;
                }
                file = await folder.GetFileAsync(path + pref + line);
                var sub_lines = await FileIO.ReadLinesAsync(file);
            }

        }
        catch (FileNotFoundException)
        {
        }

What do you mean by "it doesn't do anything"? Have you added any logging to see what's going on? It doesn't help that you're catching an exception and doing nothing with it... — Jon Skeet, Dec 31 '13 at 16:15
I tried adding some Debug.Writeline for checking and 4/5 times i get this "The thread 0x97c has exited with code 0 (0x0)." and it doesnt do the "var sublines.." command and 1/5 works as planed — Stefanos Chrs, Dec 31 '13 at 16:41

score 1 · Accepted Answer · answered Dec 31 '13 at 16:40

1

You are probably not seeing the results because you're not waiting for InitializeContents to complete. Follow the Task-based Asynchronous Pattern (TAP); I also have an async intro on my blog you may find helpful.

If my speculation is correct, then you can fix the code by making InitializeContents return Task instead of void (and also rename it to follow the TAP naming convention: InitializeContentsAsync), and have the calling code await the Task that is returned from InitializeContentsAsync.

answered Dec 31 '13 at 16:40

Stephen Cleary

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Thanks, i changed the return to Task and i used await when calling it and it worked! But can you explain why in the other testing solution i had it worked every time even though i didnt have this additions – Stefanos Chrs Dec 31 '13 at 16:51
1

It would be a race condition whether the method completed or not by the time you read the results. So, sometimes it might work and sometimes not. If your test system was actually using synchronous stubs for the file APIs, then it would always work (because it wouldn't be truly asynchronous). – Stephen Cleary Dec 31 '13 at 17:06

Async in Windows store application c#

1 Answers1