if anyone wants to refresh the data, you can't put mutableLiveData into a method

[Fxy4ever]

public LiveData<List<Project>> getProjectList(String userId) {
        final MutableLiveData<List<Project>> data = new MutableLiveData<>();
      
like this, if you use the method to refresh data, you can only get a new mutableLiveData which can't be observed the change ,you should put mutableLiveData out of the method.

        //something...

        return data;
    }