如何使用實時數據進行多個網絡呼叫？

Question

我正在一個項目中嘗試通過數據綁定實現Android體系結構組件。 我有一個活動，viewmodel和存儲庫，並且現在正在創建一個登錄頁面。 我必須創建兩個存儲庫函數以使用戶登錄，第一個函數將返回uid，並通過傳遞此uid，第二個函數將返回詳細信息。 一旦一切都完成了，那么只有我想將用戶重定向到內頁。 我已經嘗試過Transformations.switchMap，但無法正常工作。 請幫忙...

public class LoginViewModel extends ViewModel {
private final VendorRepository vendorRepository;
private final ResourceProvider resourceProvider;
public MutableLiveData<String> error = new MutableLiveData<>();
public MutableLiveData<Boolean> loading = new MutableLiveData<>();
private MutableLiveData<Resource<String>> vendorId = new MutableLiveData<>();
public LiveData<Resource<Vendor>> vendor;

public LoginViewModel() {
    this.vendorRepository = VendorRepository.getInstance();
    this.resourceProvider = ResourceProvider.getInstance();
    /*vendor = Transformations.switchMap(vendorId, new Function<Resource<String>, LiveData<Resource<Vendor>>>() {
        @Override
        public LiveData<Resource<Vendor>> apply(Resource<String> input) {
            if (input!=null&&input.status.equals(Status.SUCCESS))
            return vendorRepository.getVendor(vendorId.getValue().data);
            else return null;
        }
    });*/
}

/**
 * called when a user clicks on the login button
 * if the inputs are valid, will call the login function
 *
 * @param email    entered email
 * @param password entered password
 */
public void onClickLogin(String email, String password) {
    //loading.setValue(true);
    if (validInputs(email, password)) {
        vendorId = vendorRepository.login(
                email, password
        );
    } else loading.setValue(false);
}}

這是我的視圖模型

public class VendorRepository {
private static VendorRepository INSTANCE;
private FirebaseAuth firebaseAuth;
private FirebaseFirestore firebaseFirestore;

public static VendorRepository getInstance() {
    if (INSTANCE == null)
        INSTANCE = new VendorRepository();
    return INSTANCE;
}

private VendorRepository() {
    this.firebaseAuth = FirebaseAuth.getInstance();
    this.firebaseFirestore = FirebaseFirestore.getInstance();
}

public MutableLiveData<Resource<String>> login(String email, String password) {
    final MutableLiveData<Resource<String>> data = new MutableLiveData<>();
    data.setValue(Resource.<String>loading(null));
    firebaseAuth
            .signInWithEmailAndPassword(email, password)
            .addOnCompleteListener(new OnCompleteListener<AuthResult>() {
                @Override
                public void onComplete(@NonNull Task<AuthResult> task) {
                    if (task.isSuccessful()) {
                        data.postValue(Resource.success(task.getResult().getUser().getUid()));
                    } else {
                        data.postValue(Resource.<String>error(task.getException().getMessage(), null));
                    }
                }
            });
    return data;
}

public LiveData<Resource<Vendor>> getVendor(String id) {
    final MutableLiveData<Resource<Vendor>> data = new MutableLiveData<>();
    data.postValue(Resource.<Vendor>loading(null));
    firebaseFirestore
            .collection(DB_VENDOR)
            .document(id)
            .get()
            .addOnCompleteListener(new OnCompleteListener<DocumentSnapshot>() {
                @Override
                public void onComplete(@NonNull Task<DocumentSnapshot> task) {
                    if (task.isSuccessful()) {
                        Vendor vendor = task.getResult().toObject(Vendor.class);
                        data.postValue(Resource.success(vendor));
                    } else {
                        data.postValue(Resource.<Vendor>error(task.getException().getMessage(), null));
                    }
                }
            });
    return data;
} }

這是我的回購

Answer 1

您需要在activity某個地方添加vendorId livedata的observer ，可能是在初始化viewModel之后添加到onCreate(Bundle) 。

您的代碼將如下所示。

public final class MyActivity extends AppCompatActivity {
    ...
    LoginViewModel mViewModel;

    @Override protected final void onCreate(Bundle savedInstanceState) {

        super.onCreate(savedInstanceState);
        setContentView(R.layout.my_activity);
        mViewModel = ViewModelProviders.of(this)
            .get(LoginViewModel.class);

        //make vendorId public in the viewModel

        mViewModel.vendorId.observe ( this, new Observer<String> (){

            @Override public void onChanged(@Nullable final String vendorId) {
                VendorRepository.getInstance().getVendor(vendorId);
            }
        });

        //Similarly, add observer for the vendor live data
    }

}