Swift 5.5：如何在更新 TableView 之前将多个闭包的并发 API 结果合并到一个结构中？

Question

我正在尝试将来自三个并发调用的三个 API JSON 结果组合成一个数据结构（例如 CombinedDataStructure ），该数据结构将通过委托协议传递给我的 TableView。 我知道如何通过自己的协议 function 独立地从这些 API 发送结果，但我只想在收到的数据全部可用而不是一一提供时更新 TableView。 我坚持将 API 闭包的结果组合成一个数据结构。 无论我尝试什么，我都无法从闭包中提取值并将其合并为单一数据类型

API1（其他两个类似）：

func getPrice (completion: @escaping (String) -> ()) {

        let urlString = "https://myApi.com/api/ticker/price?symbol=xxxx"
        var testReturnString = "No value" //

        //Make API call
        if let url = URL(string: urlString){
            let session = URLSession(configuration: .default)
            let task = session.dataTask(with: url) { data, response, error in
                if error != nil {
                    print(error as Any)
                }
                if let safeData = data {
                    let decoder = JSONDecoder()
                    do {
                        let decodedData = try decoder.decode(PriceData.self, from: safeData)

                        testReturnString = decodedData.price
                        print("Inside getPrice Closure:\(testReturnString)")  //-> Here we see correct data from server
                        
                        //testStructStr = decodedData.price -> Struct variable assignment - Forces the API to becomes mutating and throws "Cannot use mutating member on immutable value: 'self' is immutable"
                        
                        completion(testReturnString)
                        
                    } catch {
                        print(error)
                    }
                }
            }
            task.resume()
            print("Outside Closure:\(testReturnString)")  //-> Here we see "No Value"
        }
    }

并发部分在viewDidLoad中调用的updateBalanceTable中完成：

func updateBalanceTable(){
        let radQueue = OperationQueue()
        var testStrUpdate = "No Value 2"
        
        let operation1 = BlockOperation {
            let group = DispatchGroup()
            
            //API1
            group.enter()
            getCoinPrice { myStr in
                print("Inside updateBalanceTable closure:\(myStr)")
                testStrUpdate = myStr
            }
            group.leave()
            
            //API2
            group.enter()
            //getExchangeInfo() - not expanded with closures yet
            group.leave()
            
            //API3
            group.enter() 
            //getAllBalances() - not expanded with closures yet
            group.leave()
            
            group.wait()
            //this operation won't return until we have all data
            print("Test StrUpdate inside Wait OP1:\(testStrUpdate)")
            
        }
        let operation2 = BlockOperation {
            print("Test StrUpdate inside OP2:\(testStrUpdate)")
            // Now, operation2 will fire off once operation1 has completed, with results wanted
        }
        operation2.addDependency(operation1)
        radQueue.addOperation(operation1)
        radQueue.addOperation(operation2)
    }

所有这些函数都定义在一个名为 BalanceManager 的结构中：

struct BalanceManager{
    
    var delegate: BalanceProtocol?
    var testStructStr = "" //I have tried updating a string from Struct directly but I get other errors doing so

    func getPrice (completion: @escaping (String) -> ()) { ... }
    func getExchangeInfo(completion: @escaping ([Pairs]) -> ()) { ... }
    func getAllBalances(completion: @escaping ([Assets]) -> ()) { ... }
    func updateBalanceTable() { ... }
}

控制台结果：

Outside Closure: No value
Test StrUpdate inside Wait OP1: No Value 2
Test StrUpdate inside OP2: No Value 2
Inside getPrice Closure: 1234.45
Inside updateBalanceTable closure: 1234.45