Question

我有以下活动课程：

public class SplashActivity extends AppCompatActivity {
    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);

        splashViewModel.nameLiveData.observe(this, new Observer<String>() {
            @Override
            public void onChanged(String name) {
                Log.d(TAG, name); //Isn't printing anything
            }
        });
    }
}

这是我的视图模型类：

public class SplashViewModel extends ViewModel {
    private SplashRepository repository;
    MutableLiveData<String> nameLiveData;

    @Inject
    SplashViewModel(SplashRepository repository) {
        this.repository = repository;
        nameLiveData = repository.addNameToLiveData();
    }
}

这是我的存储库类：

class SplashRepository {
    MutableLiveData<String> addNameToLiveData() {
        MutableLiveData<String> nameMutableLiveData = new MutableLiveData<>();
        ref.document(uid).get().addOnCompleteListener(task -> {
            if (task.isSuccessful()) {
                DocumentSnapshot document = task.getResult();
                if(document.exists()) {
                    String name = document.getString("name");
                    Log.d(TAG, name); //Is printed out correctly
                    nameMutableLiveData.postValue(name);
                }
            }
        });
        return nameMutableLiveData;
    }
}

我正在使用postValue()将数据添加到LiveData。在回调中，它可以正确打印名称，但是在观察nameLiveData对象时，甚至不会触发onChanged。该如何解决？

Answer 1

Repos应该具有不可更改的和可变的实时数据对象。Repo应该公开不可更改的实时数据对象，这将在视图模型中使用observeforever方法进行观察。不可更改的对象将使用可更改的对象进行更新。示例应用示例

https://github.com/ashok07m/Pokemon-Sample-App/blob/master/app/src/main/java/com/learning/pokemon/data/repository/MainRepositoryImpl.kt

使用LiveData从Firebase获取数据时，永远不会调用onChanged

1 个答案: