UWP: Write file in a generic location using StorageApplicationPermissions.FutureAccessList

Question

I have the following scenario in my UWP App:

1. The user imports a file (e.g. using a FilePicker, or by dragging a file onto the app, etc.) into my application.

2. We save some metadata of this file inside our internal database, and we also save a token retrieved using the following code:

   string token = StorageApplicationPermissions.FutureAccessList.Add(file);
   

3. The user closes the app.

4. The user re-opens the app.

5. Now we want to overwrite the initial file. To do this, we retrieve the StorageFile using this code:

   StorageFile exportTarget = await StorageApplicationPermissions.FutureAccessList.GetFileAsync(token);
   

but when I try to write into the file, e.g. using

using (IRandomAccessStream fs = await exportTarget.OpenAsync(FileAccessMode.ReadWrite))

I get an exception complaining that exportTarget is ReadOnly.

How can I have access to such file in Write mode?

Answer 1

It turned out it was not a strict problem of the StorageApplicationPermissions.FutureAccessList.

The problem happens in fact only if the user imports a file by dragging-and-dropping the file into the app: in this case, the DataPackageView.GetStorageItemsAsync() method returns a list of StorageFile that are ReadOnly.

So, the only way to overwrite those files is by using PathIO methods, as described in this post: https://github.com/microsoft/microsoft-ui-xaml/issues/2421