'(String, AnyObject)' 不能转换为 '[String : AnyObject]'

Question

// response is of type AnyObject!
let responseDic = response as [String : AnyObject]
let userDic = responseDic["user"] as [String : AnyObject]

但是，在最后一行，我得到了错误：

'(String, AnyObject)' is not convertible to '[String : AnyObject]'

所以我猜测在字典中查找一个键会返回一个可选值，所以我尝试了：

let userDic = responseDic["user"]? as [String : AnyObject]

但我明白了：

'String' is not convertible to 'DictionaryIndex<String, AnyObject>'

什么是让它工作的正确方法？

Answer 1

使用感叹号代替可选项：

var response: AnyObject! = ["user" : [String : AnyObject]()]
let responseDic = response as [String : AnyObject]
let userDic: [String : AnyObject] = responseDic["user"]! as [String : AnyObject]

如果你想确保键 'user' 有一个非 nil 值并且它是一个 [String : AnyObject] 你可以使用 if let:

if let user: AnyObject = responseDic["user"] {
    if let userDic = user as? [String : AnyObject]{
        //do stuff with userDic
    }
}