字典

swift 字典不仅可以存储对象类型的值，还可以存储基本数据类型的值，结构体，枚举值。字典本质上也是结构体。

• 字典声明
  let dic1 = ["key1":1, "key2":2, "key3":3, "key4":4]
  let dic2 = String:Int
  let dic3:[String:Int] = ["key1":1, "key2":2, "key3":3, "key4":4]
  let dic4:Dictionary = ["key1":1,"key2":2];
  // 字典范性定义的方式
  let dic5:Dictionary<String, Int> = ["key1":1, "key2":2, "key3":3]
  let dic6:[String:AnyObject] = ["key1":1 as AnyObject, "key2":2 as AnyObject, "key3":"value3" as AnyObject, "key4":4 as AnyObject]
  let dic7:NSDictionary = NSDictionary(dictionary: ["key1":1, "key2":2, "key3":3, "key4":4])
  //使用init（）构造器
  let dic8:[String:String] = Dictionary<String,String>()
  //使用init(minimumCapacity:Int) 并且指定了字典的最小容量
  let dic9:[String: Int] = Dictionary<String, Int>(minimumCapacity: 5)
• 字典中元素的个数
  print(dic3.count)
  print(dic2.count)
• 字典是否为空
  print(dic1.isEmpty)
• 获取字典中的key／value
  print(dic7.allKeys)
  print(dic7.allValues)
  print(dic4["key1"]!)
  print(dic5["key2"]!)
• 修改字典
  var dic10:Dictionary<String,String>
  dic10 = ["key1":"value1","key2":"value2"]
  dic10["key1"] = "changeString"
  print(dic10)
• 添加字典
  var dic10:Dictionary<String,String>
  dic10 = ["key1":"value1","key2":"value2"]
  dic10["key3"] = "value3"
  dic10.updateValue("value", forKey: "key4")
• 删除
  var dic10:Dictionary<String,String>
  dic10 = ["key1":"value1","key2":"value2"]
  // 删除指定key
  dic10["key1"] = nil
  dic10.removeValue(forKey: "key2")
  // 删除全部
  dic10 = [:]
  dic10.removeAll()
  // 对于 keepCapacity :false /true ,根据需求选择 即可;区别是true的话,会保持数据容量,占据空间?
  dic10.removeAll(keepingCapacity: true)

遍历字典

   for (key, value) in dic3 {
      print(key,value)
  }
  for key in dic3.keys {
      print(key)
  }
  for value in dic3.values {
      print(value)
  }