- Open the POSSCRE model and add an attribute of type 'platform file' called 'selected file' to represent a user-selected file.
- Add a method called 'setSelectedFile' which takes a 'platform file' type parameter named 'data' and assigns the value of 'data' to 'selectedFile'.
- Implement notification to listeners and modify the 'reset' method to set 'selectedFile' to null.
- Define a file upload method with a return type of 'Future<bool>' called 'uploadFile', which requires a parameter 'poseID' of type 'int'.
- Use the async keyword for the method, create a 'response' variable that awaits the result from an 'app service' - 'API HTTP client' 'upload image' method, which takes 'poseID' and 'selectedFile' as arguments.
- Check if the 'response.statusCode' equals 201, and return true if it does; otherwise, throw an 'HTTPException' with a message that indicates file upload failure.