Kotlin中的Getters和Setters应该和Android中的Java一样吗

Question

这个 Model class 的 getter 和 setter 实现与 Java 相同，但现在写在 Kotlin

 class HousePost{
private var uid: String = ""
private var postImage: String = ""
private var rent: String = ""
private var description: String = ""
private var publisher: String = ""
private var location: String = ""
private var postId: String? = ""
private var rooms: String = ""
private var caption: String = ""
private var dateTime: String = ""
var expandable: Boolean = false

constructor()
constructor(
   uid: String,
   postImage: String,
   rent: String,
   description: String,
   location: String,
   postId: String,
   publisher: String,
   rooms: String,
   caption: String,
   dateTime : String
) {
   this.uid = uid
   this.postImage = postImage
   this.rent = rent
   this.description = description
   this.location = location
   this.postId = postId
   this.publisher = publisher
   this.rooms = rooms
   this.caption = caption
   this.dateTime = dateTime
   this.expandable = false
}
//Post Details getters
fun getUid() : String {
   return uid
}
fun getPostId (): String? {
   return postId
}
fun getPostImage():String {
   return postImage
}
fun getDescription():String {
   return description
}
fun getLocation():String {
   return location
}
fun getRent():String {
   return rent
}
fun getPublisher(): String {
   return publisher
}

fun getRooms(): String {
   return rooms
}
fun getCaption() : String {
   return caption
}
fun getDateTime() : String {
   return dateTime
}

//Post Details setters
fun setUid (uid: String) {
   this.uid = uid
}
fun setPostId(postId: String) {
   this.postId = postId
}
fun setPostImage(postImage: String) {
   this.postImage = postImage
}
fun setLocation(location: String) {
   this.location = location
}
fun setDescription(description: String) {
   this.description = description
}
fun setRent(rent: String) {
   this.rent = rent
}
fun setPublisher(publisher: String) {
   this.publisher = publisher
}
fun setCaption(caption: String) {
   this.caption = caption
}
fun setDateTime(dateTime: String) {
   this.dateTime = dateTime
}

}

这个 class 应该是我数据库中的 model 数据。 这是 Kotlin 中的正确方法吗？ 我遇到了一个No setter/field for class found错误。 我的 recyclerview 根本不显示数据，我认为是由于错误造成的。

Answer 1

在 Kotlin 中，属性不需要显式的 getter 或 setter 方法。

Kotlin 类中的属性既可以使用var关键字声明为可变的，也可以使用val关键字声明为只读的。

一个 class 其主要目的是在 Kotlin 中保存数据这些称为数据类并用data标记。 例如，在您的情况下， class 可以定义如下：

data class HousePost(
    val uid: String = ""
    val postImage: String = ""
    val rent: String = ""
    val description: String = ""
    val publisher: String = ""
    val location: String = ""
    val postId: String? = ""
    val rooms: String = ""
    val caption: String = ""
    val dateTime: String = ""
    val expandable: Boolean = false
)

val关键字使此数据 class 的属性不可变。 这意味着您无法在初始化后更改其属性。

要使属性可变，您可以使用var 。

例如：

val housePost = HousePost() // This will use all the default value
housePost.expandable = true // Val cannot be reassigned

要使可扩展可变使用var ，如下所示：

data class HousePost(
    .
    .
    .
    var expandable: Boolean = false
)

val housePost = HousePost()
housePost.expandable = true // Can be reassigned

编辑

您收到错误（找不到 class 的设置器/字段错误），因为您将 class 属性标记为私有。 您可以通过删除当前 class 中的 private、构造函数、getter 和 setter 来简单地修复它。

在 class 中还有其他方法可以定义属性。您将在学习过程中了解如何使用它们。

class HousePost {
    var uid: String = ""
    var postImage: String = ""
    var rent: String = ""
    var description: String = ""
    var publisher: String = ""
    var location: String = ""
    var postId: String? = ""
    var rooms: String = ""
    var caption: String = ""
    var dateTime: String = ""
    var expandable: Boolean = false
}

或这个：

class HousePost (
    var uid: String = ""
    var postImage: String = ""
    var rent: String = ""
    var description: String = ""
    var publisher: String = ""
    var location: String = ""
    var postId: String? = ""
    var rooms: String = ""
    var caption: String = ""
    var dateTime: String = ""
    var expandable: Boolean = false
)

Answer 2

你只是简单地做到这一点。 删除功能，不能用

class HousePost {
    private var uid: String = ""
    private var postImage: String = ""
    private var rent: String = ""
    private var description: String = ""
    private var publisher: String = ""
    private var location: String = ""
    private var postId: String? = ""
    private var rooms: String = ""
    private var caption: String = ""
    private var dateTime: String = ""
    var expandable: Boolean = false

    constructor()
    constructor(uid: String,
                postImage: String,
                rent: String,
                description: String,
                location: String,
                postId: String,
                publisher: String,
                rooms: String,
                caption: String,
                dateTime: String) {
        this.uid = uid
        this.postImage = postImage
        this.rent = rent
        this.description = description
        this.location = location
        this.postId = postId
        this.publisher = publisher
        this.rooms = rooms
        this.caption = caption
        this.dateTime = dateTime
        this.expandable = false
    }
}

Answer 3

Kotlin 为properties提供了默认的getters和setters ，您不必手动定义它们。

Kotlin

var data: String = ""

相当于

var data: String = ""
    get() = field
    set(value) {
        field = value
    }

因为 Kotlin 编译器会为您生成它。 但是如果你只想让你的getter public而不是setter ，那么你可以覆盖setter

var data: String = ""
    private set
    

你也可以为getter做同样的事情。

---

这个 class 应该是我数据库中的 model 数据。 这是 Kotlin 中的正确方法吗？

不，那不是在Kotlin中定义一个model class的正确方法。Kotlin提供data类，其主要function是保存数据的。 Data class主构造函数至少需要一个参数。

所以，你的 model class 可以这样重构

data class HousePost(
    var uid: String = "",
    var postImage: String = "",
    var rent: String = "",
    var description: String = "",
    var publisher: String = "",
    var location: String = "",
    var postId: String? = "",
    var rooms: String = "",
    var caption: String = "",
    var dateTime: String = "",
    var expandable: Boolean = false
)

在任何情况下，如果您只需要任何字段的私有设置器，您可以将该constructor属性设为private ，然后创建一个委托给该私有字段的公共属性。

data class HousePost(
    private var _uid: String = "",
    var postImage: String = "",
    var rent: String = "",
    var description: String = "",
    var publisher: String = "",
    var location: String = "",
    var postId: String? = "",
    var rooms: String = "",
    var caption: String = "",
    var dateTime: String = "",
    var expandable: Boolean = false
) {
    val uid: String get() = _uid
}