In my Flutter application I need to allow admin users to download a CSV file with all the data entered into Firebase.

To do this, admins must press a button. If they do it from the web, the file is downloaded via the browser, while if they are on another device, a dialog opens asking if they want to download or share the file.

Creating the file takes some time, so I would like to show a CircularProgressIndicator while waiting for the AlertDialog to open.
I don’t know how to do this though, because I typically show the CircularProgressIndicator when calling a Future function via FutureBuilder, but showDialog doesn’t return a Widget.

So how can I show a CircularProgressIndicator before opening AlertDialog?

Here is my code, thanks in advance!

FilledButton.icon(
  onPressed: () async {
    // This function creates a CSV file by retrieving data from Firebase,
    // and takes some time to run
    final String fileData = await getCsv();

    if (kIsWeb) {
      // running on the web
      downloadFileOnWeb(fileData);
    } else {
      // NOT running on the web
      if (!context.mounted) return;
      return showDialog<void>(
        context: context,
        builder: (context) => AlertDialog(
          content: const Text("Get report"),
          actions: [
            IconButton(
              icon: const Icon(Icons.download),
              onPressed: () => downloadFile(fileData),
            ),
            IconButton(
              icon: const Icon(Icons.share),
              onPressed: () => shareFile(fileData),
            ),
          ],
        ),
      );
    }
  },
  icon: const Icon(Icons.file_open),
  label: const Text("Report"),
),