Swift 如何把元素追加到字典中

Swift有各种方法可以将元素追加到字典中。

我们将使用下面的方法来追加Swift语言中字典中的元素-

使用 updateValue() 方法追加元素
使用下标语法追加元素。
使用merging()方法追加元素。

使用updateValue()方法

swift中的updateValue(:forKey:)方法用于更新一个现有键的值或向现有字典中添加一个新的键值组合。如果该键以前不在字典中，该方法将返回 nil 而不是该键以前的值，这里有一个例子

例子

import Foundation
var userInfo: [String: Any] = ["firstName": "Alex",
   "school": "St. Primary School",
   "score": 8.8,
   "age": 16]
print("Original User Info: \(userInfo)")

// Adding new key-value pairs
userInfo.updateValue("USA", forKey: "country")
userInfo.updateValue("Murphy", forKey: "lastName")
userInfo.updateValue("Martin Murphy", forKey: "fatherName")
print("Updated User Info: \(userInfo)")

输出

Original User Info: ["firstName": "Alex", "age": 16, "school": "St. Primary School", "score": 8.8]
Updated User Info: ["fatherName": "Martin Murphy", "age": 16, "score": 8.8, "lastName": "Murphy", "firstName": "Alex", "school": "St. Primary School", "country": "USA"]

使用下标语法

另外，你也可以使用下标语法来为一个新的或现有的键赋值。下面是一个例子。

例子

import Foundation
var userInfo: [String: Any] = ["firstName": "Alex",
   "school": "St. Primary School",
   "score": 8.8,
   "age": 16]
print("Original User Info: \(userInfo)")

// Adding new key-value pairs
userInfo["country"] = "USA"
userInfo["lastName"] = "Murphy"
userInfo["fatherName"] = "Martin Murphy"
print("Updated User Info: \(userInfo)")

输出

Original User Info: ["age": 16, "school": "St. Primary School", "firstName": "Alex", "score": 8.8]
Updated User Info: ["firstName": "Alex", "fatherName": "Martin Murphy", "country": "USA", "score": 8.8, "age": 16, "school": "St. Primary School", "lastName": "Murphy"]

使用 merging() 方法

你也可以使用 Dictionary 的 .merging(_:uniquingKeysWith:) 方法来追加元素到一个 dictionary 中。

merging(_:uniquingKeysWith:) 是 Swift 中 Dictionary 类型上的一个方法，它允许你把一个 dictionary 的内容合并到另一个 dictionary 中，并指定如何处理重复的键。

这个方法需要两个参数

第一个参数是你想合并到当前 dictionary 中的那个 dictionary。
第二个参数是一个闭包，它接收相同键的两个值并返回你想保留的值。

例子

下面是一个演示如何使用merging(_:uniquingKeysWith:)方法的例子-

import Foundation
var userInfo: [String: Any] = ["firstName": "Alex",
   "school": "St. Primary School",
   "score": 8.8,
   "age": 16]
print("Original User Info: \(userInfo)")
// creating a new dictionary with other info
let otherInfo: [String: Any] = ["country": "USA",
   "lastName": "Murphy",
   "fatherName": "Martin Murphy",
   "pincode": 6783456]
userInfo = userInfo.merging(otherInfo, uniquingKeysWith: { current, _ in
   return current
})
print("Updated User Info: \(userInfo)")

输出

Original User Info: ["school": "St. Primary School", "score": 8.8, "age": 16, "firstName": "Alex"]
Updated User Info: ["firstName": "Alex", "pincode": 6783456, "country": "USA", "lastName": "Murphy", "school": "St. Primary School", "age": 16, "fatherName": "Martin Murphy", "score": 8.8]