How to used the PickerClosingOperation.GetDeferral | getDeferral method

Hi,

How to used the PickerClosingOperation.GetDeferral | getDeferral method?

In my app, I called follow codes,

async void  fileOpenPickerUI_Closing(Windows.Storage.Pickers.Provider.FileOpenPickerUI sender, Windows.Storage.Pickers.Provider.PickerClosingEventArgs args)
        {
            var defer = args.ClosingOperation.GetDeferral();
            storage file =  await SaveToFileAsync("aaaa", filePath);
defer.Complete();
        }

but it doesnot work well, it's not async? how can I do it?

Thank you!

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自强不息，知行合一。