我無法使用 mvvm 在兩個存儲庫之間共享變量

Question

我需要在兩個存儲庫之間共享兩個變量。 我已經嘗試了許多不同的解決方案，但都沒有奏效。 簡而言之：第一個存儲庫包含用戶最后已知的位置（地理緯度和經度）第二個存儲庫調用 api 並具有指定的端點，例如地理緯度和經度。 問題是我不斷收到等於 0,0 的值。 你能給我一些提示我應該怎么做嗎？ 我觀察到的一件事是，整個程序立即運行，而位置存儲庫需要幾秒鍾才能實際獲得緯度和經度。 所以程序只是不斷地調用 api 端點等於 0,0，正如我上面的意思。

位置存儲庫

    public class LocationRepository {

    private double mLatitude, mLongitude;
    
    public void test(Application application) {
        FusedLocationProviderClient client = LocationServices.getFusedLocationProviderClient(application.getApplicationContext());
        {
            if (ContextCompat.checkSelfPermission(
                    application.getApplicationContext(), Manifest.permission.INTERNET) == PackageManager.PERMISSION_GRANTED &&
                    ContextCompat.checkSelfPermission(application.getApplicationContext(), Manifest.permission.ACCESS_FINE_LOCATION) == PackageManager.PERMISSION_GRANTED &&
                    ContextCompat.checkSelfPermission(application.getApplicationContext(), Manifest.permission.ACCESS_COARSE_LOCATION) == PackageManager.PERMISSION_GRANTED) {

                client.getLastLocation().addOnSuccessListener(new OnSuccessListener<Location>() {
                    @Override
                    public void onSuccess(Location location) {
                        mLongitude = location.getLongitude();
                        mLatitude = location.getLatitude();
                    }
                });
            }
        }
    }
}

預測存儲庫

public MutableLiveData<ForecastModel> testCall() {
MutableLiveData<ForecastModel> data = new MutableLiveData<>();

mApi.test(mLatitude, mLongitude, "metric", API_KEY).enqueue(new Callback<ForecastModel>() {
    @Override
    public void onResponse(Call<ForecastModel> call, Response<ForecastModel> response) {
        if (!response.isSuccessful()) {
            Log.i(TAG, "onResponse: " + response.code());
        }
        data.setValue(response.body());
    }
    @Override
    public void onFailure(Call<ForecastModel> call, Throwable t) {
        Log.i(TAG, "onFailure: " + t.getMessage());
    }
});
return data;
}

視圖模型

private ForecastRepository mForecastRepository;
private LocationRepository mLocationRepository;

private MutableLiveData<ForecastModel> mForecastData;

public ForecastViewModel(@NonNull Application application) {
    super(application);
    mLocationRepository = new LocationRepository();
    mLocationRepository.test(application);

    mForecastRepository = new ForecastRepository();
    mForecastData = mForecastRepository.testCall();
}

Answer 1

您可以在 ViewModel 和 Transformation.switchMap() 中使用兩個 livadata 來跟蹤更改。 每次 mLocationData 更改時，mForcastData 也會更新。 如果你不知道 switchMap 是如何工作的，你可以檢查一下如何以及在哪里使用 Transformations.switchMap？ .

像這樣更改您的 ViewModel 和 LocationRepository。

視圖模型

public class ForecastViewModel extends AndroidViewModel {

    private ForcastRepository mForecastRepository;
    private LocationRepostiory mLocationRepository;

    private LiveData<ForecastModel> mForecastData;
    private LiveData<LocationModel> mLocationData;

    public ForecastViewModel(@NonNull Application application) {
        super(application);
        mLocationRepository = new LocationRepostiory();
        mLocationRepository.test(application);
        mLocationData = mLocationRepository.getMutableLiveData();
        mForecastRepository = new ForcastRepository();

        mForecastData = Transformations.switchMap(mLocationData, location->
                mForecastRepository.testCall(location.getLatitude(), location.getLongitude()));
    }

    public LiveData<ForecastModel> getmForecastData() {
        return mForecastData;
    }
}

位置存儲庫

class LocationRepostiory {

private LocationModel mLocation;
private MutableLiveData<LocationModel> mutableLiveData = new MutableLiveData();

public void test(Application application) {
    FusedLocationProviderClient client = LocationServices.getFusedLocationProviderClient(application.getApplicationContext());
    {
        if (ContextCompat.checkSelfPermission(
                application.getApplicationContext(), Manifest.permission.INTERNET) == PackageManager.PERMISSION_GRANTED &&
                ContextCompat.checkSelfPermission(application.getApplicationContext(), Manifest.permission.ACCESS_FINE_LOCATION) == PackageManager.PERMISSION_GRANTED &&
                ContextCompat.checkSelfPermission(application.getApplicationContext(), Manifest.permission.ACCESS_COARSE_LOCATION) == PackageManager.PERMISSION_GRANTED) {

            client.getLastLocation().addOnSuccessListener(location -> {
                mLocation = new LocationModel(location.getLongitude(),location.getLatitude());
                mutableLiveData.setValue(mLocation);
            });
        }
    }
}

public MutableLiveData<LocationModel> getMutableLiveData() {
    return mutableLiveData;
}
}

預測庫

public MutableLiveData<ForecastModel> testCall(double mLatitude, double mLongitude ) {
MutableLiveData<ForecastModel> data = new MutableLiveData<>();

mApi.test(mLatitude, mLongitude, "metric", API_KEY).enqueue(new Callback<ForecastModel>() {
    @Override
    public void onResponse(Call<ForecastModel> call, Response<ForecastModel> response) {
        if (!response.isSuccessful()) {
            Log.i(TAG, "onResponse: " + response.code());
        }
        data.setValue(response.body());
    }
    @Override
    public void onFailure(Call<ForecastModel> call, Throwable t) {
        Log.i(TAG, "onFailure: " + t.getMessage());
    }
});
return data;
}

位置模型

class LocationModel {
    private Double longitude, latitude;

    public LocationModel(Double longitude, Double latitude) {
        this.longitude = longitude;
        this.latitude = latitude;
    }

    public Double getLongitude() {
        return longitude;
    }

    public Double getLatitude() {
        return latitude;
    }
}

如果您不想制作額外的 LocationModel class ，那么您也可以將您的位置數據作為 List 或 Arraylist 發送。 只是我更喜歡這個。

編輯：我已經糾正了一些錯誤。 現在代碼正在運行。 Logcat from testCall() Method in ForcastRepository D/TAG: testCall: 90.3993212,23.7793183