从Json API获取数据

Question

我想从urlString获取JSON数据，但我不知道要放在jsonObj!.value(forKey: "") as?中的值。如果你看一下JSON结构，它就没有主要名称来进入数据。

final let urlString = "https://api.coinmarketcap.com/v1/ticker/" 

func downloadJsonWithURL() {
    let url = NSURL(string: urlString)
    URLSession.shared.dataTask(with: (url as? URL)!, completionHandler: {(data, response, error) -> Void in

        if let jsonObj = try? JSONSerialization.jsonObject(with: data!, options: .allowFragments) as? NSDictionary {
            print(jsonObj!.value(forKey: ""))

            if let actorArray = jsonObj!.value(forKey: "") as? NSArray {
                for actor in actorArray{
                    if let actorDict = actor as? NSDictionary {
                        if let name = actorDict.value(forKey: "name") {
                            self.nameArray.append(name as! String)
                        }
                        if let name = actorDict.value(forKey: "rank") {
                            self.rankArray.append(name as! String)
                        }   
                    }
                }
            }

            OperationQueue.main.addOperation({
                self.tableView.reloadData()
            })
        }
    }).resume()
}

JSON结构

[
    {
    id: "bitcoin",
    name: "Bitcoin",
    symbol: "BTC",
    rank: "1",
    price_usd: "9361.68",
    price_btc: "1.0",
    24h_volume_usd: "9720310000.0",
    market_cap_usd: "156442678736",
    available_supply: "16710962.0",
    total_supply: "16710962.0",
    max_supply: "21000000.0",
    percent_change_1h: "-1.11",
    percent_change_24h: "-15.97",
    percent_change_7d: "14.51",
    last_updated: "1512057553"
    }
   ]