java.lang.RuntimeException:无法创建 ViewModel 类的实例

Question

我正在尝试在我的活动中实例化UserViewModel，但它一直给我一个java.lang.RuntimeException: Cannot create an instance of viewmodel class kindly assist.

这就是我的视图模型的样子

public class UserViewModel extends AndroidViewModel {
private NodeAuthService api;
private SharedPreferences pref;
private static MutableLiveData<List<User>> userDetails = new MutableLiveData<>();
public UserViewModel(@NonNull Application application) {
super(application);
api = AuthRetrofitClient.getInstance().create(NodeAuthService.class);
}

private String email = pref.getString("email", "");
public void loadUser(){
Call<List<User>> call;
call = api.getUser(email);
call.enqueue(new Callback<List<User>>() {
@Override
public void onResponse(Call<List<User>> call, Response<List<User>> response) {
userDetails.postValue(response.body());
}
@Override
public void onFailure(Call<List<User>> call, Throwable t) {
Log.d("USER",t.getMessage());
}
});
}
public MutableLiveData<List<User>>getUserDetails(){
return userDetails;
}
}

这就是我的活动的设置方式

@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.navigation_drawer);
String nameVm;
userViewModel = ViewModelProviders.of(this).get(UserViewModel.class);
userViewModel.loadUser();
userViewModel.getUserDetails().observe(this, new Observer<List<User>>() {
@Override
public void onChanged(List<User> users) {
if (users != null){
for (int i = 0; i<users.size(); i++){
nameVm = String.valueOf(users.get(0));
}
}
}
});
}

Answer 1

Create ViewModelFactory class

public class MyViewModelFactory implements ViewModelProvider.Factory {
private Application mApplication;
public MyViewModelFactory(Application application) {
mApplication = application;           
}
@Override
public <T extends ViewModel> T create(Class<T> modelClass) {
// Replace UserViewModel →  with whatever or however you create your ViewModel
return (T) new UserViewModel(mApplication);
}
}

并初始化ViewModel喜欢

UserViewModel myViewModel = ViewModelProviders.of(this, new MyViewModelFactory(this.getApplication())).get(UserViewModel.class);