从Kotlin的乐趣中返回null [英] Return null from fun in kotlin

问题描述

我编写了一个函数来执行数据库查询.如果它无法获取任何结果，我希望它返回null.

I've written a function to perform a database query. I want it to return null if it cannot fetch any result.

fun getServiceCharge(model: String): ServiceChargeMasterList {
    val unique = VideoconApplication.daoSession.serviceChargeMasterListDao.queryBuilder().where(ServiceChargeMasterListDao.Properties.ModelCategory.eq(model)).unique()
    if (unique != null)
        return unique
    else
        return null!!
}

它给了我 kotlin.KotlinNullPointerException .

It gives me kotlin.KotlinNullPointerException.

谁能告诉我该怎么解决?

Can anyone tell me how can I solve this?

推荐答案

只需将您的返回类型指定为ServiceChargeMasterList?并返回null. !!运算符非常难看.

Just specify your return type as ServiceChargeMasterList? and return null. The !! operator is very ugly to use.

如果您的unique()方法返回并且是可选的(或Java对象)，则甚至不必使用该if语句.在这种情况下，您的方法可能如下所示:

You don't even have to use that if statement if your unique() method return and optional (or Java object). In that case, you method could look like this:

fun getServiceCharge(model: String): ServiceChargeMasterList? {
    return VideoconApplication.daoSession.serviceChargeMasterListDao.queryBuilder().where(ServiceChargeMasterListDao.Properties.ModelCategory.eq(model)).unique()
}

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