Kotlin如何从包含特定ID的列表中返回单个对象?

问题描述

美好的一天，我一直在努力弄清楚如何从列表中获取单个对象，我做了google，但是所有主题都展示了如何返回带有已排序对象或类似对象的List.

Good day, i'm stuck figuring out how to get a single object from a list, i did google but all the topics show how to return a List with sorted objects or something similar.

我有一个User Class

class User() {

    var email: String = ""
    var firstname:  String = ""
    var lastname: String  = ""
    var password: String  = ""
    var image: String  = ""
    var userId: String  = ""

    constructor(email:String,
                firstname: String,
                lastname: String,
                password: String,
                image: String, userId : String) : this() {
        this.email = email
        this.firstname = firstname
        this.lastname = lastname
        this.password = password
        this.image = image
        this.userId = userId
    }
}

在Java中，我会写类似的东西

In java i would write something like

 User getUserById(String id) {
        User user = null;
        for(int i = 0; i < myList.size;i++;) {
            if(id == myList.get(i).getUserId())
            user = myList.get(i)
        }
        return user;
    }

我如何在Kotlin中获得相同的结果?

How can i achieve the same result in kotlin?

推荐答案

您可以使用 find ，它为您提供了与给定谓词(或null，如果没有匹配)匹配的列表的第一个元素:

You can do this with find, which gives you the first element of a list that matches a given predicate (or null, if none matched):

val user: User? = myList.find { it.userId == id }

或者，如果您确实确实需要与谓词匹配的最后一个元素(如Java示例代码一样)，则可以使用 last :

Or if you really do need the last element that matches the predicate, as your Java example code does, you can use last:

val user: User? = myList.last { it.userId == id }

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