【Swift学习】Swift编程之旅---集合类型之字典（八）

　　字典是一种存储相同类型多重数据的存储器。每个值（value）都关联独特的键（key），键作为字典中的这个值数据的标识符。和数组中的数据项不同，字典中的数据项并没有具体顺序。

　　字典写作Dictionary<Key, Value>。也可以写作[Key: Value]

　　创建空字典

var namesOfIntegers = [Int: String]()
// namesOfIntegers is an empty [Int: String] dictionary

　　类型推断写作[:]

namesOfIntegers[16] = "sixteen"
// namesOfIntegers now contains 1 key-value pair
namesOfIntegers = [:]
// namesOfIntegers is once again an empty dictionary of type [Int: String]

　　创建字典字面量

[key 1: value 1, key 2: value 2, key 3: value 3]

var airports: [String: String] = ["YYZ": "Toronto Pearson", "DUB": "Dublin"]

　　类型推断写作

var airports = ["YYZ": "Toronto Pearson", "DUB": "Dublin"]

　　访问和修改

　　count返回字典的键值对数

　　isEmpty判断字典是否为空

　　

airports["LHR"] = "London Heathrow

if let oldValue = airports.updateValue("Dublin Airport", forKey: "DUB") {
    print("The old value for DUB was (oldValue).")
}
// Prints "The old value for DUB was Dublin.

　　removeValueForKey(_:)删除键值对  

if let removedValue = airports.removeValueForKey("DUB") {
    print("The removed airport's name is (removedValue).")
} else {
    print("The airports dictionary does not contain a value for DUB.")
}
// Prints "The removed airport's name is Dublin Airport.

 遍历

for (airportCode, airportName) in airports {
    print("(airportCode): (airportName)")
}
// YYZ: Toronto Pearson
// LHR: London Heathrow

for airportCode in airports.keys {
    print("Airport code: (airportCode)")
}
// Airport code: YYZ
// Airport code: LHR
 
for airportName in airports.values {
    print("Airport name: (airportName)")
}
// Airport name: Toronto Pearson
// Airport name: London Heathrow