How can I fix the Firebase Storage platform thread error on Windows Desktop in my Flutter app?

Below is some background on what’s happening and potential next steps to work around it.

What’s Happening

Firebase’s support on desktop (Windows, macOS, Linux) is provided through the Firebase C++ SDK desktop workflow. This support is currently in beta and some Firebase plugins (in your case, it’s the Firebase Storage channel) aren’t fully thread‐safe out of the box on desktop. The error

  "The 'plugins.flutter.io/firebase_storage/taskEvent/{{id}}' channel sent a message from native to Flutter on a non‑platform thread"

indicates that the native code is dispatching messages from a thread other than the main or platform thread. Flutter requires that all platform channel communication occurs on the platform thread to prevent data loss or crashes.

Why It Only Happens on Windows Desktop

When you previously built your app for mobile or web, the underlying Firebase libraries properly marshal callbacks on the correct thread. On Windows desktop the Firebase C++ SDK and its integration via FlutterFire (or a custom plugin layer) is still in beta. As a result, some implementations (like the Firebase Storage/Firestore use case) may lack the proper thread switching logic.

Even though you haven’t explicitly used compute or isolates, the beta Firebase desktop support has its own internal threading behavior that you may need to work around.

What You Can Try

1. Check for Plugin Updates:

   • Ensure you’re on the very latest versions of FlutterFire plugins. The desktop support is actively being developed, so there may be improvements or fixes that address this thread issue.

2. Use a Platform-Thread Wrapper (Temporary Workaround):

   • If you’re comfortable modifying native code, you could wrap the callback in code that posts the message back onto the platform thread. This is generally done by replacing a direct channel invocation with one that uses the platform dispatcher.
   • For example, in the Firebase C++ SDK code (or the Windows plugin integration layer), one would need to ensure that the callback (e.g. task events) is dispatched via the main message loop of the application.

3. Review CMake and SDK Setup:

   • Although you haven’t yet modified your CMake settings, desktop apps using Firebase do require the Firebase C++ SDK libraries to be linked. Verify that your project’s CMake configuration correctly references the official Firebase libraries (such as firebase_storage and others you use). Follow the documentation for setting up desktop builds with Firebase to make sure no steps are missed.
   • If Visual Studio is asking for adjustments to CMake, it may be because the expected libraries or CMake targets aren’t fully configured. Sometimes manually adjusting the CMake configuration helps the project use the right native binaries (which might have bug fixes).

4. Monitor the Issues/Repo:

   • Since you’ve noted several GitHub or Stack Overflow posts, keep an eye on the official Firebase or FlutterFire repositories. There are ongoing discussions about desktop support issues, and official guidance or fixes may be released soon.

Summary

The error is due to the current beta status of Firebase’s desktop support where some native messages (here from Firebase Storage) are dispatched on a non‑platform thread. This is not a problem in your application logic but in the underlying plugin/SDK. Your options include checking for plugin updates, potentially modifying native code to ensure messages are sent on the platform thread, and verifying your CMake configuration to ensure proper linking with Firebase C++ SDK desktop libraries.

Given the beta nature of desktop support, if these workarounds do not resolve the issue, consider filing an issue with the FlutterFire team (including details on your configuration and error logs) so the community and maintainers can address this threading issue.

Let me know if you need further details on any of these steps.