swift * 字典/Dictionary初始化以及增、删、改、遍历

学习笔记
1、字典初始化
var
dict = [:]
//初始化无类型空字典
dict = ["1":"aaa","2":"bbb"]
print(dict)
dict = [1:"1","2":2]
//key
和value都是不定类型的
print(dict)

let dict2:Dictionary<String,Int> = ["1":111,"2":222] //限定键值类型
print(dict2)
let
dict3:[String:Int] = ["1":111]
print(dict3)

2、字典操作
var
dict4 = ["apple":"苹果","bag":"包"]

print(dict4["apple"])
dict4["apple"] =
"橘子"
//修改值
print(dict4)
dict4.updateValue("苹果",
forKey: "apple")
//更新键值
如果key存在
更新键值对并且返回key之前的对应的value
print(dict4)
print(dict4.updateValue("苹果",
forKey: "apples"))
//如果key
不存在将增加新的键值对并返回nil
if
let origin = dict4.updateValue("aaaaa",
forKey: "appl") {
print("origin
\(origin)")

}
print(dict4)
dict4["an"] == "一个" //增加/修改键值对
if
let origin = dict4.removeValueForKey("apple")
{
print("删除key\(origin)")
//如果key存在
删除对应的键值对
并返回key对应的值
print(dict4)
}
else {

//不存在key
返回nil
字典不变
}

if let origin = dict4.removeValueForKey("aaaaa") {
print(origin)
}
else {
print(dict4.removeValueForKey("aaaaa"))
//如果key不存在
不作操作并返回nil
}
print(dict4)

3、字典遍历
for
(key,value)
in dict4 {
//使用元组
遍历键值对
print("\(key)
: \(value)")
}
for
key in
dict4.keys
{ //遍历所有key
print(key)
}
for
value in
dict4.values
{ //遍历所有value
print(value)
}