如何在数据类中初始化GeoPoint的默认值 [英] How to initialize default values for GeoPoint in a data class

问题描述

我正在尝试将文档从Firestore转换为对象，但是当我创建数据类时，我不知道如何使用默认值初始化GeoPoint，因为它需要为空的构造函数声明

I'm trying to convert documents to objects from Firestore, but when I create my data class , I dont know how to initialize the GeoPoint with default values as it needs to be declared for an empty constructor

data class MapObj(val geopoint:Geopoint) //--> how to initialize it to get an empty constructor

问题取决于此行

val obj = snapshot.toObject(MapObj::class.java)

谢谢

推荐答案

问题是Firestore SDK找不到MapObj的默认，无参数构造函数.如果Kotlin数据类的所有属性都用val声明，则没有.对于声明为val的属性，Kotlin要求在构造函数中指定它们的值，因为它们以后可能无法更改.

The problem is that the Firestore SDK isn't finding a default, no argument constructor for MapObj. Kotlin data classes don't have one if all of their properties are declared with val. For properties declared val, Kotlin requires that their values be specified in the constructor, since they can't possibly change afterward.

如果必须从Firestore取回数据类，则必须将其所有属性设置为具有默认值的可选var，以便Kotlin为其生成一个无参数的构造函数.

If you must get a data class back from Firestore, you will have to make all of its properties optional var with a default value, so that Kotlin will generate a no-arg constructor for it.

data class MapObj(var geopoint: Geopoint? = null)

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