Question

我有一个小部件，每次更新数据库时都想更新，并且即使应用程序未运行，也希望在小部件上显示数据库中的内容。我的db是使用Room实现的，而小部件是使用 IntentService。每次进行更新时，onHandleIntent都会尝试从数据库中获取新条目并更新小部件。

但是对于下面的代码，它总是从数据库中返回空List

是否有实现此目的的替代方法？ AsyncTask在这里不起作用，因为它需要在主线程上执行。

我是Room和RxJava的新手，所以不确定我是否错过任何明显的事情。

@Override
    protected void onHandleIntent(@Nullable Intent intent) {
        if (intent == null || intent.getAction() == null) return;
        if (intent.getAction().equals(UPDATE_WIDGET)) {
            Context context = getApplicationContext();
            AppWidgetManager appWidgetManager = AppWidgetManager.getInstance(this);
            int[] appWidgetIds = appWidgetManager.getAppWidgetIds(new ComponentName(this, ParkWidgetProvider.class));
            Observable.fromCallable(() -> {
                db = FavDatabase.getInstance(context);
                return db;
            })
                    .subscribeOn(Schedulers.io())
                    .observeOn(AndroidSchedulers.mainThread())
                    .subscribe(result -> {
                        List<FavParkEntity> favParkEntityList = result.favDoa().getFavPark().getValue();
                        if (favParkEntityList != null) {
                            if (favParkEntityList.size() == 1) {
                                FavParkEntity favParkEntity = favParkEntityList.get(0);
                                latLong = favParkEntity.getLatLong();
                                parkCode = favParkEntity.getParkCode();
                                imgUrl = favParkEntity.getImage();
                                title = favParkEntity.getPark_name();
                                Log.e(TAG, "onHandleIntent: HERE: " + title);
                                StringToGPSCoordinates stringToGPSCoordinates = new StringToGPSCoordinates();
                                final String gpsCoodinates[] = stringToGPSCoordinates.convertToGPS(latLong);
                                getLastLocation(gpsCoodinates);
                                String weatherDetails[] = getCurrentWeather(context, gpsCoodinates);
                                ParkWidgetProvider.updateAppWidgets(context, appWidgetManager, appWidgetIds, parkCode, imgUrl, title, weatherDetails, distance);
                            } else {
                                Log.e(TAG, "onHandleIntent: HERE SIZE");
                            }
                        } else {
                            Log.e(TAG, "onHandleIntent: HERE NULL");
                        }
                    });
        }
    }

数据库：

@Database(entities = {FavParkEntity.class},version = 1, exportSchema = false)
@TypeConverters({Converters.class})
public abstract class FavDatabase extends RoomDatabase {

    public static final String DATABASE_NAME = "favorites";

    private static final Object LOCK = new Object();
    private static FavDatabase sInstance;

    public static  FavDatabase getInstance(Context context){
        if(sInstance==null){
            synchronized (LOCK){
                sInstance = Room.databaseBuilder(context.getApplicationContext(),FavDatabase.class, FavDatabase.DATABASE_NAME)
                        .build();
            }
        }
        return sInstance;
    }

    public RoomDatabase dbExist(){
        return sInstance;
    }

    public abstract FavDao favDoa();

}

道：

@Dao
public interface FavDao {

    @Insert(onConflict = OnConflictStrategy.REPLACE)
    void save(FavParkEntity park);
    @Query("SELECT * FROM favorites")
    LiveData<List<FavParkEntity>> getFavPark();
    @Query("DELETE FROM favorites")
    void clearTable();
}

型号：

@Entity(tableName = "favorites")
public class FavParkEntity extends ParkEntity {

    public FavParkEntity() {
    }

    public FavParkEntity (ParkEntity parkEntity){
        this.setPark_id(parkEntity.getPark_id());
        this.setPark_name(parkEntity.getPark_name());
        this.setStates(parkEntity.getStates());
        this.setParkCode(parkEntity.getParkCode());
        this.setLatLong(parkEntity.getLatLong());
        this.setDescription(parkEntity.getDescription());
        this.setDesignation(parkEntity.getDesignation());
        this.setAddress(parkEntity.getAddress());
        this.setPhone(parkEntity.getPhone());
        this.setEmail(parkEntity.getEmail());
        this.setImage(parkEntity.getImage());
    }

}

Answer 1

实施中有很多问题。

首先，result.favDoa().getFavPark().getValue()将始终返回null，因为LiveData是异步的。 LiveData是要遵守的。

使用RxJava的方式似乎也不正确。您没有异步完成任何实际工作。可以完全不使用RxJava来编写该实现。

还要注意，没有一种简单的方法可以将LiveData和RxJava一起使用，因为它们不能直接互换。人们喜欢使用“完整LiveData”，“完整RxJava”或“ RxJava”，直到UI组件然后切换到LiveData。

有很多解决方法。一种选择是将您的实现完全更改为RxJava。（房间具有RxJava支持：https://developer.android.com/topic/libraries/architecture/adding-components#room）

道：

@Dao
public interface FavDao {

    @Insert(onConflict = OnConflictStrategy.REPLACE)
    void save(FavParkEntity park);
    @Query("SELECT * FROM favorites")
    Single<List<FavParkEntity>> getFavPark(); // Switch to RxJava
    @Query("DELETE FROM favorites")
    void clearTable();
}

您的主要代码：

@Override
    protected void onHandleIntent(@Nullable Intent intent) {
        if (intent == null || intent.getAction() == null) return;
        if (intent.getAction().equals(UPDATE_WIDGET)) {
            Context context = getApplicationContext();
            AppWidgetManager appWidgetManager = AppWidgetManager.getInstance(this);
            int[] appWidgetIds = appWidgetManager.getAppWidgetIds(new ComponentName(this, ParkWidgetProvider.class));
            FavDatabase.getInstance(context).favDoa().getFavPark()  // Access database here.
                    .subscribeOn(Schedulers.io())
                    .observeOn(AndroidSchedulers.mainThread())
                    .subscribe(favParkEntityList -> {
                        // Put your mainThread works here.
                        if (favParkEntityList != null) {
                            if (favParkEntityList.size() == 1) {
                                FavParkEntity favParkEntity = favParkEntityList.get(0);
                                latLong = favParkEntity.getLatLong();
                                parkCode = favParkEntity.getParkCode();
                                imgUrl = favParkEntity.getImage();
                                title = favParkEntity.getPark_name();
                                Log.e(TAG, "onHandleIntent: HERE: " + title);
                                ...
                            } else {
                                Log.e(TAG, "onHandleIntent: HERE SIZE");
                            }
                        } else {
                            Log.e(TAG, "onHandleIntent: HERE NULL");
                        }
                   });
        }
    }

（可选）如果无法将Dao从LiveData切换到RxJava，则可以创建getFavPark()的同步版本。

道：

@Dao
public interface FavDao {

    @Insert(onConflict = OnConflictStrategy.REPLACE)
    void save(FavParkEntity park);
    @Query("SELECT * FROM favorites")
    LiveData<List<FavParkEntity>> getFavPark();
    @Query("SELECT * FROM favorites")
    List<FavParkEntity> getFavParkSync(); // Synchronous access
    @Query("DELETE FROM favorites")
    void clearTable();
}

您的主要代码：

@Override
    protected void onHandleIntent(@Nullable Intent intent) {
        if (intent == null || intent.getAction() == null) return;
        if (intent.getAction().equals(UPDATE_WIDGET)) {
            Context context = getApplicationContext();
            AppWidgetManager appWidgetManager = AppWidgetManager.getInstance(this);
            int[] appWidgetIds = appWidgetManager.getAppWidgetIds(new ComponentName(this, ParkWidgetProvider.class));
            Observable.fromCallable(() -> {
                // fromCallable and subscribeOn will make
                // below code run in a worker thread asynchronously.
                return FavDatabase.getInstance(context).favDoa().getFavParkSync();
            })
                    .subscribeOn(Schedulers.io())
                    .observeOn(AndroidSchedulers.mainThread())
                    .subscribe(favParkEntityList -> {
                        // Put your mainThread works here.
                        if (favParkEntityList != null) {
                            if (favParkEntityList.size() == 1) {
                                FavParkEntity favParkEntity = favParkEntityList.get(0);
                                latLong = favParkEntity.getLatLong();
                                parkCode = favParkEntity.getParkCode();
                                imgUrl = favParkEntity.getImage();
                                title = favParkEntity.getPark_name();
                                Log.e(TAG, "onHandleIntent: HERE: " + title);
                                ...
                            } else {
                                Log.e(TAG, "onHandleIntent: HERE SIZE");
                            }
                        } else {
                            Log.e(TAG, "onHandleIntent: HERE NULL");
                        }
                   });
        }
    }

访问Room数据库以更新IntentService的onHandleIntent方法中的小部件

1 个答案: