Question

我无法将Retrofit与MVVM体系结构链接。确实，在阅读了文档之后，他们只讨论了用于SQLite本地数据库的Room，我进行了相同的搜索，但搜索了来自Rest Server的数据。所以，我试图做类似的事情，但没有成功： https://proandroiddev.com/mvvm-architecture-viewmodel-and-livedata-part-1-604f50cda1

我有一个观察ViewModel的活动：

活动代码：

mFlightPlanViewModel = ViewModelProviders.of(this).get(FlightPlanViewModel.class);
        mFlightPlanViewModel.getFlightPlans().observe(this, (flightPlans) -> {
            Log.d(TAG, "ON_CHANGED");

            mFlightPlanAdapter.setFlightPlans(flightPlans);
        });

ViewModel：

public class FlightPlanViewModel extends AndroidViewModel {
    private static final String TAG = "FlightPlanViewModel";

    private LiveData<List<FlightPlan>> mFlightPlans;
    private FlightPlanRepository mFlightPlanRepository;

    public FlightPlanViewModel(@NonNull Application application) {
        super(application);
        Log.d(TAG, "CONSTRUCTOR");

        mFlightPlanRepository = FlightPlanRepository.getInstance();
        mFlightPlans = mFlightPlanRepository.getFlightPlans();
    }

    public LiveData<List<FlightPlan>> getFlightPlans() {
        Log.d(TAG, "GET_FLIGHT_PLANS");

        return mFlightPlans;
    }
}

ViewModel回答使用单例模式的存储库：

public class FlightPlanRepository {
    private static final String TAG = "FlightPlanRepository";

    private static FlightPlanRepository instance;
    private RestApi mRestApi;

    private FlightPlanRepository() {
        Log.d(TAG, "CONSTRUCTOR");

        mRestApi = RestDao.getRestDao();
    }

    public static FlightPlanRepository getInstance() {
        Log.d(TAG, "GET_INSTANCE");

        if (instance == null) {
            instance = new FlightPlanRepository();
        }
        return instance;
    }

    public MutableLiveData<List<FlightPlan>> getFlightPlans() {
        Log.d(TAG, "GET_FLIGHT_PLANS");

        final MutableLiveData<List<FlightPlan>> data = new MutableLiveData<>();

        mRestApi.getFlightPlanList().enqueue(new Callback<List<FlightPlan>>() {
            @Override
            public void onResponse(Call<List<FlightPlan>> call, Response<List<FlightPlan>> response) {
                if (response.code() == 200) {
                    List<FlightPlan> temp = response.body();
                    for (FlightPlan flightPlan : temp) {
                        Log.d(TAG + "res", flightPlan.toString());
                    }
                    data.setValue(response.body());
                    Log.d(TAG + "res", response.toString());
                }
            }

            @Override
            public void onFailure(Call<List<FlightPlan>> call, Throwable t) {
                List<FlightPlan> flightPlans = new ArrayList<>();
                flightPlans.add(new FlightPlan(0, "Test", 3.551, 50.52, 3.55122, 50.52625));
                data.setValue(flightPlans);
                Log.d(TAG, t.getMessage());
            }
        });

        return data;
    }
}

存储库使用Retrofit实例：

public class RestDao {
    private static final String BASE_URL = "http://192.168.1.78:8080";
    private static Retrofit instance;

    private static Retrofit getInstance() {
        if (instance == null) {
            instance = new Retrofit.Builder()
                    .baseUrl(BASE_URL)
                    .addConverterFactory(GsonConverterFactory.create())
                    .build();
        }
        return instance;
    }

    public static RestApi getRestDao() {
        return getInstance().create(RestApi.class);
    }
}

它使用此界面：

public interface RestApi {
    @GET("/plan/list")
    Call<List<FlightPlan>> getFlightPlanList();
}

部分无效的代码是：

public MutableLiveData<List<FlightPlan>> getFlightPlans() {
    Log.d(TAG, "GET_FLIGHT_PLANS");

    final MutableLiveData<List<FlightPlan>> data = new MutableLiveData<>();

    mRestApi.getFlightPlanList().enqueue(new Callback<List<FlightPlan>>() {
        @Override
        public void onResponse(Call<List<FlightPlan>> call, Response<List<FlightPlan>> response) {
            if (response.code() == 200) {
                List<FlightPlan> temp = response.body();
                for (FlightPlan flightPlan : temp) {
                    Log.d(TAG + "res", flightPlan.toString());
                }
                data.setValue(response.body());
                Log.d(TAG + "res", response.toString());
            }
        }

        @Override
        public void onFailure(Call<List<FlightPlan>> call, Throwable t) {
            List<FlightPlan> flightPlans = new ArrayList<>();
            flightPlans.add(new FlightPlan(0, "Test", 3.551, 50.52, 3.55122, 50.52625));
            data.setValue(flightPlans);
            Log.d(TAG, t.getMessage());
        }
    });

    return data;
}

这将返回一个空列表。我想我明白为什么：调用enqueue（）方法发出的请求在另一个线程中，因此在这里我们返回数据而无需等待结果。

所以我的问题是如何链接Retrofit和ViewModel？

Answer 1

凯文（Kevin）只是对您的代码进行了微小的更改。而不是MutableLiveData从存储库返回LiveData：

library(seqinr)
library(shiny)
# User interface
ui <- fluidPage(
  titlePanel("Welcome to DotMatcher Plot App"),
  sidebarLayout(
    sidebarPanel (
      fileInput("protein1",
                label = "Choose a file",
                multiple = FALSE,
                accept =c("text", "fasta")),
      fileInput( "protein2",
                 label = NULL,
                 multiple=FALSE,
                 accept =c("text", "fasta"))
    ),
    # Outputs
    mainPanel(
      plotOutput(outputId = "plot")
    )
  )
)

# Server Function
server <- function(input, output) {
  seq1 <- reactive({
    req(s2c(paste(input$protein1, collapse = "")})
  seq2 <- reactive({
    req(s2c(paste(input$protein2, collapse = "")
  })

  output$plot <- renderPlot({



    dotPlot(seq1(), seq2(), wsize = 100, wstep = 100, nmatch = 100)

  })

}
# App 
shinyApp(ui = ui, server = server)

Answer 2

如果我这样做：

public LiveData<List<FlightPlan>> getFlightPlans() {
    Log.d(TAG, "GET_FLIGHT_PLANS");

    final MutableLiveData<List<FlightPlan>> data = new MutableLiveData<>();


    List<FlightPlan> flightPlans = new ArrayList<>();
    flightPlans.add(new FlightPlan(5, "Test5", 3.551, 50.52, 3.55122, 50.52625));
    data.setValue(flightPlans);
    Log.d(TAG, data.getValue().toString());


    mRestApi.getFlightPlanList().enqueue(new Callback<List<FlightPlan>>() {
        @Override
        public void onResponse(Call<List<FlightPlan>> call, Response<List<FlightPlan>> response) {
            if (response.code() == 200) {
                List<FlightPlan> temp = response.body();
                for (FlightPlan flightPlan : temp) {
                    Log.d(TAG + "res", flightPlan.toString());
                }
                data.setValue(response.body());
                Log.d(TAG + "res", response.toString());
            }
        }

        @Override
        public void onFailure(Call<List<FlightPlan>> call, Throwable t) {
            List<FlightPlan> flightPlans = new ArrayList<>();
            flightPlans.add(new FlightPlan(0, "Test", 3.551, 50.52, 3.55122, 50.52625));
            data.setValue(flightPlans);
            Log.d(TAG, t.getMessage());
        }
    });

    return data;
}

我可以在Logcat中看到默认值，两个值来自我的rest服务器，但是字符串是空值，并且int / doubles为0，并且不会将这两个rest条目添加到回收器视图中。 / p>

这是我的活动代码：

public class FlightPlanActivity extends AppCompatActivity implements View.OnClickListener, SwipeRefreshLayout.OnRefreshListener, LifecycleOwner {
    private static final String TAG = "FlightPlanActivity";

    private FlightPlanAdapter mFlightPlanAdapter;
    private FlightPlanViewModel mFlightPlanViewModel;

    /**
     * UI
     */
    private FloatingActionButton mAddPlanButton;
    private RecyclerView mRecyclerView;
    private SwipeRefreshLayout mSwipeRefreshLayout;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        this.setContentView(R.layout.activity_flight_plan);

        Log.d(TAG, "onCreate called");

        initUI();
    }

    private void initUI() {
        this.setTitle("Flight Plans");

        mRecyclerView = findViewById(R.id.flight_plan_list);
        mAddPlanButton = findViewById(R.id.add_flight_plan);
        mSwipeRefreshLayout = findViewById(R.id.refresh_flight_plan_list);

        mAddPlanButton.setOnClickListener(this);
        mSwipeRefreshLayout.setOnRefreshListener(this);

        mFlightPlanAdapter = new FlightPlanAdapter();

        mRecyclerView.setHasFixedSize(true);
        mRecyclerView.setLayoutManager(new LinearLayoutManager(this));
        mRecyclerView.setAdapter(mFlightPlanAdapter);

        mFlightPlanViewModel = ViewModelProviders.of(this).get(FlightPlanViewModel.class);
        mFlightPlanViewModel.getFlightPlans().observe(this, (flightPlans) -> {
            Log.d(TAG, "ON_CHANGED");

            mFlightPlanAdapter.setFlightPlans(flightPlans);
        });
    }

    @Override
    public void onClick(View v) {
        if (v.getId() == mAddPlanButton.getId()) {
            // TODO: A implémenter
        }
    }

    @Override
    public void onRefresh() {
        mFlightPlanAdapter.setFlightPlans(mFlightPlanViewModel.getFlightPlans().getValue());

        mSwipeRefreshLayout.setRefreshing(false);
    }
}

Answer 3

那么，如果我做出回应，会发生什么？

public LiveData<List<FlightPlan>> getFlightPlans() {
    Log.d(TAG, "GET_FLIGHT_PLANS");

    MutableLiveData<List<FlightPlan>> data = new MutableLiveData<>();

    mRestApi.getFlightPlanList().enqueue(new Callback<List<FlightPlan>>() {
        @Override
        public void onResponse(Call<List<FlightPlan>> call, Response<List<FlightPlan>> response) {
            if (response.code() == 200) {
                data.setValue(response.body());
            }
        }

        @Override
        public void onFailure(Call<List<FlightPlan>> call, Throwable t) {
            // Do something
        }
    });

    return data;
}

我运行该命令，首先有一个空对象返回，但是如果有响应，它将返回一些东西吗？

我尝试过：

public LiveData<List<FlightPlan>> getFlightPlans() {
    Log.d(TAG, "GET_FLIGHT_PLANS");

    MutableLiveData<List<FlightPlan>> data = new MutableLiveData<>();
    List<FlightPlan> flightPlans;

    try {
        Response<List<FlightPlan>> response = mRestApi.getFlightPlanList().execute();
        if (response.isSuccessful()) {
            flightPlans = response.body();
        } else {
            Log.d(TAG, "Can't get data !");
            throw new Exception("Can't get data !");
        }
    } catch (Exception e) {
        e.printStackTrace();

        flightPlans = new ArrayList<>();
        flightPlans.add(new FlightPlan(5, "Test5", 3.551, 50.52, 3.55122, 50.52625));
    }

    data.setValue(flightPlans);
    Log.d(TAG, data.getValue().toString());

    return data;
}

现在它在执行行上崩溃，因为我在主线程中启动了它。所以我必须做一个异步任务，但是在哪里？

其他选项：首先像执行异步任务一样，将setter放置到模型视图对象中，当有响应时，我将其称为setter。这样做很好吗？

感谢您给我的请求！这很有帮助。

编辑：为什么在Google文档中有此代码：

public class UserRepository {
    private Webservice webservice;
    // ...
    public LiveData<User> getUser(int userId) {
        // This isn't an optimal implementation. We'll fix it later.
        final MutableLiveData<User> data = new MutableLiveData<>();
        webservice.getUser(userId).enqueue(new Callback<User>() {
            @Override
            public void onResponse(Call<User> call, Response<User> response) {
                data.setValue(response.body());
            }

            // Error case is left out for brevity.
        });
        return data;
    }
}

这意味着可以这样做吗？

解决方案！

编辑：

How to connect ViewModel with Repository so that data is propagated to the View (MVVM, Livedata)

这对我有很大帮助！

我找到了解决方案！我很愚蠢：我在gradle文件中插入了旧的依赖项！

如何为MVVM模式链接Retrofit和Repository / ViewModel？

3 个答案: