我花了很多时间试图弄清楚为什么在下面的代码(最后)中,ViewModelProvider(this)出现错误。我也尝试了getActivity()而不是'this',同样的问题。我得到的错误是“无法解析构造函数...”
...
import androidx.fragment.app.Fragment;
import androidx.lifecycle.ViewModelProvider;
...
public class ItemSetupFragment extends Fragment {
...
@Override
public View onCreateView(LayoutInflater inflater, ViewGroup container,
Bundle savedInstanceState) {
View view = inflater.inflate(R.layout.fragment_setup, container, false);
return view;
}
@Override
public void onViewCreated(@NonNull View view, Bundle savedInstanceState) {
super.onViewCreated(view, savedInstanceState);
ItemSetupFragmentModel model = new ViewModelProvider(this).get(ItemSetupFragmentModel.class);
model.getKids().observe(this, users -> {
// update UI
});
}
}
您应使用requireActivity()
而不是getActivity()
。这样,您将确保该活动已附加且未获得NullPointerException
。
ItemSetupFragmentModel model = new ViewModelProvider(requireActivity()).get(ItemSetupFragmentModel.class);
您应通过以下方式实例化viewModel:
ItemSetupFragmentModel model = ViewModelProviders.of(this).get(ItemSetupFragmentModel.class);