如何将JSON加载到TableView中？

Question

我想将一个练习JSON加载到表视图中，我有一个服务函数从一个源代码获取数据作为JSON，并有一个视图控制器和一个表，我想要加载信息到。代码中没有错误，但表格加载空白行，调试部分通过打印命令显示JSON数据。我是一个初学者，所以我很确定我错过了一个核心元素，但无法解决它！

API服务

class ApiService { 

static var swiftyJsonVar:JSON? 

class func getExerciseData() { 

    Alamofire.request("https://wger.de/api/v2/exercise/?format=json").responseJSON { (responseData) -> Void in 
     if((responseData.result.value) != nil) { 
      swiftyJsonVar = JSON(responseData.result.value!) 
      print(swiftyJsonVar ?? nil) 
     } 

    } 
} 

视图控制器

class ExerciseDatabaseController: UIViewController, UITableViewDataSource, UITableViewDelegate { 

@IBOutlet weak var ExerciseSearchField: UISearchBar! 
@IBOutlet weak var ExercisesTableView: UITableView! 

var arrRes = [[String:AnyObject]]() // Array of dictionary 

override func viewDidLoad() { 
    super.viewDidLoad() 

    let arrRes = ApiService.getExerciseData() 

    if let resData = ApiService.swiftyJsonVar?["exercise"].arrayObject { 
     self.arrRes = resData as! [[String:AnyObject]] 
    } 
    if self.arrRes.count > 0 { 
     self.ExercisesTableView.reloadData() 
    } 

    print(arrRes) 
    // Do any additional setup after loading the view. 
} 

func tableView(_ tableView: UITableView, numberOfRowsInSection section: Int) -> Int { 
    return arrRes.count 
} 

func tableView(_ tableView: UITableView, cellForRowAt indexPath: IndexPath) -> UITableViewCell { 
    let cell = tableView.dequeueReusableCell(withIdentifier: "Cell", for: indexPath) 
    var dict = arrRes[indexPath.row] 
    cell.textLabel?.text = dict["name"] as? String 
    cell.detailTextLabel?.text = dict["description"] as? String 
    return cell 
} 

Answer 1

你应该异步加载你的JSON，这意味着你应该在，让您的alamofire调用方法关闭。

class ApiService { 

class func getExerciseData(completion: @escaping ([[String: AnyObject]]) ->()) { 

    Alamofire.request("https://wger.de/api/v2/exercise/?format=json").responseJSON { (responseData) -> Void in 
     guard let jsonResponse = responseData.result.value else { 
     //possibly put some sort of protection, or what you want to do if there is not a response here 
     return 
     } 
     //instead of creating a variable for swiftyJsonVar in this class, 
     //you want to use a completion to send the array of dictionaries to the tableview asynchronously, 
     //that way it doesn't load blank 
     //I'm not super familiar with swifty json(sorry). What I normally do is below. 
     let swiftyJsonVar = JSON(jsonResponse) 
     guard let dictArray = swiftyJsonVar["exercise"].arrayObject as? [[String: AnyObject]] else { 
     //some sort of protection here if this fails 
     return 
     } 
     completion(dictArray) 
    } 
} 

所以，现在我们已经取得了我们的异步调用（通常要做到这一点，只要你在视觉上，这不是已经预装了互联网电话/应用程序中保存的地方显示信息）。

接下来，我们希望在tableview加载时在tableview中显示这些信息。

class ExerciseDatabaseController: UIViewController, UITableViewDataSource, UITableViewDelegate { 
    //these should start with lower cases(exerciseSearchField), never uppercased 
    @IBOutlet weak var ExerciseSearchField: UISearchBar! 
    @IBOutlet weak var ExercisesTableView: UITableView! 

    var arrRes = [[String:AnyObject]]() // Array of dictionary 

    override func viewDidLoad() { 
     super.viewDidLoad() 
     //you said you would use these delegates up top when you created the class, so you have to set them 
     ExercisesTableView.delegate = self 
     ExercisesTableView.dataSource = self 
     fetchData() 
     // Do any additional setup after loading the view. 
    } 

    //this method will make the api call 
    //you'll notice that if you set breakpoints, it will reach the end of the method before hitting self?.arrRes = dictArray 
    //this is normal and how asynchronous calls work, look into tableview threading for a deeper explanation of why that is. It is super important to understand threading in iOS 
    //once it gets data back from the API call, it will go to the main thread and tell the tableview to reload with that data 

    func fetchData() { 
     ApiService.getExerciseData { [weak self] (dictArray) in 
     self?.arrRes = dictArray 
     print(self?.arrRes) 
     if self?.arrRes.count > 0 { 
      DispatchQueue.main.async { 
      self?.ExercisesTableView.reloadData() 
      } 
     } 
     } 
    } 

    func tableView(_ tableView: UITableView, numberOfRowsInSection section: Int) -> Int { 
     return arrRes.count 
    } 

    func tableView(_ tableView: UITableView, cellForRowAt indexPath: IndexPath) -> UITableViewCell { 
     let cell = tableView.dequeueReusableCell(withIdentifier: "Cell", for: indexPath) 
     var dict = arrRes[indexPath.row] 
     cell.textLabel?.text = dict["name"] as? String 
     cell.detailTextLabel?.text = dict["description"] as? String 
     return cell 
    } 

你会看到我在上面使用[weak self]。欲了解更多的为什么是必要的异步网络电话的解释/无论何时使用闭包，你可以在这里阅读： http://krakendev.io/blog/weak-and-unowned-references-in-swift

有很多其他资源的阅读弱和强引用/父子东西在iOS版用快速的谷歌搜索。并且，在iOS中追求异步/同步的研究。这两个主题在开始学习时非常重要。

Answer 2

刷新您的tableView一旦收到来自异步请求的JSON数据。所以，你的

self.ExercisesTableView.reloadData() 

将里面去

Alamofire.request("https://wger.de/api/v2/exercise/?format=json").responseJSON { (responseData) -> Void in 
    if((responseData.result.value) != nil) { 
     swiftyJsonVar = JSON(responseData.result.value!) 
     print(swiftyJsonVar ?? nil) 
    } 
}