Question Trouble writing to file on HoloLens 2

Hi,

I've been trying to get my program to write to a file for two weeks now, and none of the solutions I've tried have worked. Yes, I have tried to enable every single capability, but that has not made any difference. Writing to a file shouldn't be this hard, and I need this to work in order to quantify test results for my master's thesis

In the following code, filename is a string and spectrogram is an array of bytes. The writes are triggered by a button press event from a MRTK button.

My first attempt was the usual System.IO stuff:

Code (CSharp):

1. var path = Path.Combine(Application.persistentDataPath, filename);
2. File.WriteAllText($"{path}.png", spectrogram);

This resulted in an error about the path not exisiting.

After some googling I tried the UWP way:

Code (CSharp):

1. #if WINDOWS_UWP
2.         private async Task SaveState(string filename, string probeData, byte[] spectrogram)
3.         {
4.             try
5.             {
6.                 // Either this
7.                 var storageFolder = ApplicationData.Current.LocalFolder;
8.                 // Or this
9.                 var storageFolder = KnownFolders.CameraRoll;
10.                 // But neither folder made any difference
11.                 var pngFile =
12.                     await storageFolder.CreateFileAsync($"{filename}.png", CreationCollisionOption.ReplaceExisting);
13.                 await FileIO.WriteBytesAsync(pngFile, spectrogram);
14.             }
15.             catch (Exception e)
16.             {
17.                 Debug.LogWarning(e);
18.             }
19.         }
20. #endif
21.  
22. // then called from a non-async method

which gave absolutely no error messages until I added the try-catch, which printed the error you see in the attached image. Might this just be async shenanigans?

My last attempt was using Unity's own UWP classes:

Code (CSharp):

1. #if WINDOWS_UWP
2.     var path = Path.Combine(UnityEngine.Windows.Directory.localFolder, filename);
3.     UnityEngine.Windows.File.WriteAllBytes($"{path}.png", spectrogram);
4. #else
5. // normal Unity file write

to which it complained that it "failed to open C:\Data\Users\<user>\AppData\Local\Packages\<packagename>\LocalState\2023-04-19T11:47:32.png for writing", which... at least is getting somewhere

 

Found the issue eventually. The timestamp I tried to use as filename had : in it, which is invalid on Windows filesystems