Change return type to 'T' errror

Question

I override this function from ViewModelProvider.Factory but I get an error with the generic return type T. Why?

class NewsViewModelProviderFactory(
    val newsRepository: NewsRepository) : ViewModelProvider.Factory {

    override fun <T : ViewModel?> create(modelClass: Class<T>): T {
        return NewsViewModel(newsRepository) as T
    }
}

Answer 1

It looks like the issue comes from the supertype of your type parameter T—that is, ViewModel?. According to the docs, create is declared in ViewModelProvider.Factory as

open fun <T : ViewModel> create(modelClass: Class<T>): T

Notice that it says <T : ViewModel>, not <T : ViewModel?>. This means that any consumer of a ViewModelProvider.Factory expects the create function to return a non-null ViewModel. However, the create function you've written could return null.

If you changed your function to

override fun <T : ViewModel> create(modelClass: Class<T>): T {
    return NewsViewModel(newsRepository) as T
}

that should alleviate the issue.