Question

我正在使用greenDAO进行Android项目，我不得不说我对它非常满意。

可悲的是，我目前遇到了一个非常奇怪的问题：使用新创建的 LocationCoords 对象的 LocationCoordsDao 进行插入时出现NullPointerException。它只发生在这个特定的实体上，因为例如 Meal 实体中的插入效果很好。

这是我的描述：

public class MealsDiaryGenerator {

    public static void main(String[] args) {
        Schema schema = new Schema(2, "ch.cidzoo.journalibs.db");

        addMeal(schema);

        try {
            new DaoGenerator().generateAll(schema, "../JournalIBS/src");
        } catch (Exception e) {
            e.printStackTrace();
        }
    }

    private static void addMeal(Schema schema) {
        Entity loc = schema.addEntity("LocationCoords");
        loc.addIdProperty().autoincrement();
        loc.addDoubleProperty("latitude").notNull();
        loc.addDoubleProperty("longitude").notNull();

        Entity meal = schema.addEntity("Meal");
        meal.addIdProperty();
        meal.addDateProperty("date");
        Property locId = meal.addLongProperty("locationCoordsId").getProperty();
        meal.addToOne(loc, locId);
    }

}

现在它失败了：

@Override
public void onLocationChanged(Location location) {
    double lat = location.getLatitude();
    double lon = location.getLongitude();

    Log.i("onLocationChanged", "got a location update: lat=" + lat + " / lon=" + lon);

    LocationCoords loc = new LocationCoords(null, lat, lon);
    locationCoordsDao.insert(loc); //NullPointerException
    Log.d("DaoExample", "Inserted new coord, ID: " + loc.getId());

    Meal meal = new Meal(null, new Date(), null);
    mealDao.insert(meal);
    Log.d("DaoExample", "Inserted new meal, ID: " + meal.getId());
    ((MealAdapter)getListAdapter()).updateMeals(mealDao.loadAll());
}

我试图交换插入（之前用餐）没有效果。我也尝试过没有更多运气的LocationCoords实体的所有构造函数。

非常感谢任何帮助！

Answer 1

在开始使用之前，您必须首先启动DAO。就像这样

 DevOpenHelper helper = new DaoMaster.DevOpenHelper(this.getActivity(),
            "DB name", null);
    db = helper.getWritableDatabase();
    mDaoMaster = new DaoMaster(db);
    mDaoSession = mDaoMaster.newSession();
    LocationCoordsDao mLocationCoordsDao = mDaoSession.getLocationCoordsDao();

然后你可以

    LocationCoords loc = new LocationCoords(null, lat, lon);
    mLocationCoordsDao.insert(loc); // init before use

greenDAO：插入时出现NullPointerException

1 个答案: