无法使用swift从json访问嵌套字典/数组

Question

I am trying to access ["upper category"]["first category"][0][0] of local json file

{
    "upper category": {
        "first category": [
            [
                "this is a question", 
                "this is an answer", 
                "this is the rank"
            ], 
            [
                "this is a question2", 
                "this is an answer2", 
                "this is the rank2"
            ]
        ], 
        "second category": [
            [
                "this is a question3", 
                "this is an answer3", 
                "this is the rank3"
            ]
        ]
    }
}

with

let path = Bundle.main.path(forResource: "data", ofType: "json")
do {let data:NSData = try NSData(contentsOfFile: path!)
    let json = try? JSONSerialization.jsonObject(with: data as Data, options: JSONSerialization.ReadingOptions.mutableContainers) as AnyObject

I am not able to access anything beyond the first dictionary.

I tried several times with options like (I tried multiple older solutions but they don't seem to work for me, maybe swift 3)

    if let description = ((((json?["upper category"] as? AnyObject)?["first category"] as? AnyObject)?[0] as? AnyObject)?[0] as? String) {

It is likely a noob question, I am new to ios. While any answer extremely appreciated explaining how to write code for other number of nested types would be best

(xcode 8, swift 3)

Answer 1

It's a bit overkill but you can cast the json to [String:[String:[[String]]]]

let json = try? JSONSerialization.jsonObject(...) as? [String:[String:[[String]]]]

Otherwise, if for example, the dictionary contains elements other than a nested dictionary, you will just have to cast the top level dictionary to [String:Any] and cast the nested elements individually.

if let json = try? JSONSerialization.jsonObject(...) as? [String:Any] {

    let foo = json["foo"] as? Int
    let bar = json["bar"] as? [String:Any]

    ...
}