【Swift學習】Swift編程之旅---集合類型之Dictionaries（八）

　　字典是一種存儲相同類型多重數據的存儲器。每個值（value）都關聯獨特的鍵（key），鍵作為字典中的這個值數據的標識符。和數組中的數據項不同，字典中的數據項並沒有具體順序。

　　字典寫作Dictionary<Key, Value>。也可以寫作[Key: Value]

　　創建空字典

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

　　類型推斷寫作[:]

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

　　創建字典字面量

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

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

　　類型推斷寫作

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

　　訪問和修改

　　count返回字典的鍵值對數

　　isEmpty判斷字典是否為空

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(_:)刪除鍵值對  

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.

 遍歷

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