UWP/C# - How can I wait for a file to appear before reading it?

Question

I am writing to a file, then reading it back right after:

await FileIO.WriteTextAsync(file, command, Windows.Storage.Streams.UnicodeEncoding.Utf8);   
var readFile = await ApplicationData.Current.TemporaryFolder.GetFileAsync(WEB_LOG);

However, GetFileAsync throws a FileNotFoundException because the file hasn't appeared yet. If I use the debugger and wait a little after WriteTextAsync finishes, I can see the file appear in the folder and GetFileAsync does not throw an exception. How can I wait for the file to be fully written to and appear in the folder so that GetFileAsync does not throw an exception?

Answer 1

You could try to use StorageFolder.TryGetItemAsync(String) to check if the file is ready. This method returns null instead of raising a FileNotFoundException if the specified file or folder is not found.

Like this:

 var target=  await ApplicationData.Current.TemporaryFolder.TryGetItemAsync("FileName");

        if (target != null)
        {
            // file is ready
        }
        else 
        {
            //wait and try to get the file again
        }

Answer 2

There is no function, which will allow you to wait on a particular file to be available for reading. You have to check if it is not ready then wait...

 await FileIO.WriteTextAsync(file, command, Windows.Storage.Streams.UnicodeEncoding.Utf8); 

        while (true)
        {
            try
            {
                using (FileStream inputStream = File.Open(filename, FileMode.Open, FileAccess.Read, FileShare.None))
                    if (inputStream.Length > 0)
                        break;
            }
            catch (Exception)
            {
                await Task.Delay(50);
            }
        }

var readFile = await ApplicationData.Current.TemporaryFolder.GetFileAsync(WEB_LOG);