如果你想修改或更新NSDictionary那么 首先，将它类型转换为NSMutableDictionary

let newdictionary = NSDictionary as NSMutableDictionary

然后简单地使用

 newdictionary.setValue(value: AnyObject?, forKey: String)

给出以下两本词典:

var dic1 = ["a": 1, "c": 2]
var dic2 = ["e": 3, "f": 4]

下面是如何添加从dic2到dic1的所有项:

dic2.forEach {
   dic1[$0.key] = $0.value
}

(字符串:任何)

对于使用[String:Any]而不是Dictionary下面是扩展名

extension Dictionary where Key == String, Value == Any {
    
    mutating func append(anotherDict:[String:Any]) {
        for (key, value) in anotherDict {
            self.updateValue(value, forKey: key)
        }
    }
}

字典updateValue更新字典中现有键的值，如果键不存在，则添加新的键-值对。

的例子,

var caseStatusParams: [String: AnyObject] = ["userId" : UserDefault.userID ]
caseStatusParams.updateValue("Hello" as AnyObject, forKey: "otherNotes")

结果- - - - - -

▿  : 2 elements
    - key : "userId"
    - value : 866
▿  : 2 elements
    - key : "otherNotes"
    - value : "Hello"

如果你的字典是Int到String，你可以简单地做:

dict[3] = "efg"

如果你的意思是向字典的值中添加元素，一个可能的解决方案是:

var dict = Dictionary<String, Array<Int>>()

dict["key"]! += [1]
dict["key"]!.append(1)
dict["key"]?.append(1)

For whoever reading this for swift 5.1+

  // 1. Using updateValue to update the given key or add new if doesn't exist


    var dictionary = [Int:String]()    
    dictionary.updateValue("egf", forKey: 3)



 // 2. Using a dictionary[key]

    var dictionary = [Int:String]()    
    dictionary[key] = "value"



 // 3. Using subscript and mutating append for the value

    var dictionary = [Int:[String]]()

    dictionary[key, default: ["val"]].append("value")