Swift基础 Dictionary字典

字典

字典和数组都是集合类型，字典元素可以是值类型也可以是引用类型。
键名不允许重复。

字典的声明方式（三种）

显式：

    var studentList : Dictionary<String,Float> = ["xiaoMing":172.5,"xiaoHong":168.5]
    //以键值对的形式遍历
    for (name,height) in studentList {
    
    
        print("\(name):\(height)");
    }

运行结果:

xiaoMing:172.5
xiaoHong:168.5

隐式：

    var studentList : [String:Float] = ["xiaoMing":172.5,"xiaoHong":168.5]
    for (name) in studentList.keys {
    
    
        print("key:\(name)");
    }

运行结果：

key:xiaoHong
key:xiaoMing

简略：

    var studentList = ["xiaoMing":172.5,"xiaoHong":168.5]
    for (height) in studentList.values {
    
    
        print("value:\(height)");
    }

运行结果：

value:172.5
value:168.5

快捷声明：

var occupations = [:]

取值：

var studentList = ["xiaoMing":172.5,"xiaoHong":168.5]
print(studentList["xiaoMing"] ?? "unknown")

更新：

var studentList = ["xiaoMing":172.5,"xiaoHong":168.5]
studentList.updateValue("xiaoHua", forKey:155.0)
//如果studentList里面有xiaoHua则会更新上，
//如果没有xiaoHua则会加上去

删除：

var studentList = ["xiaoMing":172.5,"xiaoHong":168.5]
studentList.removeValue(forKey: "xiaoMing")

合并

错误写法：dic1+dic2
由于两个字典里面可能会有相同的键名，所以在加的时候，无法对相同键名的值进行取舍，所以不能简单粗暴地使用+语法。

对于这样的合并需求，只能乖乖进行遍历合并。

let studentHeightList = ["xiaoMingHeight":172.5,"xiaoHongHeight":168.5]
let studentAchievementList = ["xiaoMingAchievement":355.0,"xiaoHongAchievement":384.0]

//错误示范：let studentInfo = studentHeightList + studentAchievementList

var studentInfo = studentHeightList
for (key,value) in studentAchievementList {
    
    
    studentInfo[key] = value
}

print(studentInfo)

运行结果:

["xiaoMingAchievement": 355.0, "xiaoHongHeight": 168.5, "xiaoMingHeight": 172.5, "xiaoHongAchievement": 384.0]