如何从IOS Swift'Any'类型访问和获取嵌套值？

Question

I am trying to read from Firestore into a Dictionary[Any] type using Struct. I can get the values loaded into variable "data" dictionary with Any type. However I cannot loop thru it to access normal nested Dictionary variable. I cannot get Key, values printed.

Following is my code:

    class PullQuestions {
    //shared instance variable 
    **public var data = [Any]()**
    private var qdb = Firestore.firestore()

    public struct questionid
    {
        let qid : String
        var questions : [basequestion]
        var answers: [baseans]
    }
   public struct basequestion {

        let category : String
        let question : String
    }

   public struct baseans {
        let answer : String
    }

    class var sharedManager: PullQuestions {
        struct Static {
            static let instance = PullQuestions()
        }
        return Static.instance
    }

    static func getData(completion: @escaping (_ result: [Any]) -> Void) {
        let rootCollection = PullQuestions.sharedManager.qdb.collection("questions")
        //var data = [Any]()
        rootCollection.order(by: "upvote", descending: false).getDocuments(completion: {
            (querySnapshot, error) in

            if error != nil {
                print("Error when getting data \(String(describing: error?.localizedDescription))")
            } else {
                guard let topSnapshot = querySnapshot?.documents else { return }
               // var questiondoc = [basequestion]()
                for questioncollection in topSnapshot {
                    rootCollection.document(questioncollection.documentID).collection("answers").getDocuments(completion: {
                        (snapshot, err) in

                        guard let snapshot = snapshot?.documents else { return }

                        var answers = [baseans]()

                        for document in snapshot { //There should be only one Document for each answer collection
                            //Read thru all fields
                            for i in 0..<document.data().count
                            {
                            let newAns = baseans(answer: answer)
                           print("Answer Docs=>", (answer))
                            answers.append(newAns)
                            }
                        }
                        let qid = questioncollection.documentID
                        let category = questioncollection.data()["category"] as! String
                        let question =  questioncollection.data()["question"] as! String

                        let newQuestions = basequestion(category: category ,question: question)

                        let newQuestionDict = questionid(qid: qid, questions: [newQuestions], answers: answers)

                        PullQuestions.sharedManager.data.append(newQuestionDict)
                        //Return data on completion
                        completion(PullQuestions.sharedManager.data)
                    })
                }
            }
        })
  }
}

I can print like this

print("Count =>", (PullQuestions.sharedManager.data.count))
        //  print(PullQuestions.sharedManager.data.first ?? "Nil")
        print(PullQuestions.sharedManager.data[0])

        for  element in PullQuestions.sharedManager.data
        {
            print("Elements in data:=>", (element))
        }

I could access only the key.. how do i go and get the nested values ?

Answer 1

First of all, consider using Swift code conventions (eg your structs are named with small letters, but you should start with capital), this will make your code more readable.

Returning to your question. You use an array instead of dictionary (this piece of code: public var data = [Any]() ). And here you are trying to print values:

for  element in PullQuestions.sharedManager.data
{
    print("Elements in data:=>", (element))
}

In this context element is an Any object, thus you cannot access any underlying properties. In order to do this you have two options:

1. You should specify the type of array's objects in it's declaration like this:

public var data = [questionid]()

or you can user this:

public var data: [questionid] = []

These two are equals, use the one you prefer.

2. If for any reasons you don't want to specify the type in declaration, you can cast it in your loop. Like this:

for  element in PullQuestions.sharedManager.data
{
    if let element = element as? quetionid {
        print("Elements in data:=>", (element))
        // you can also print element.qid, element.questions, element.answers
    } else {
        print("Element is not questionid")
    }
}

You could of course use the force cast:

let element = element as! questionid

and avoid if let syntax (or guard let if you prefer), but I wouldn't recommend this, because it (potentially) can crash your app if element will be nil or any other type.