NSURLSession，完成块，Swift

Posted 2023-03-12

【中文标题】NSURLSession，完成块，Swift

【英文标题】：NSURLSession, Completion Block, Swift

【发布时间】：2015-10-16 03:44:06

【问题描述】：

我正在使用 NSURLSession。我有一个包含餐厅的数组，我正在请求数组中每个餐厅的菜肴到 api。 dataTask 有效，我只是在所有 dataTask 都完成后才尝试调用方法。

 self.findAllDishesOfRestaurants(self.restaurantsNearMe)  (result) -> Void in
        if result.count != 0 
              self.updateDataSourceAndReloadTableView(result, term: "protein")
         else 
            print("not ready yet")
         
    

self.updateDataSourceAndREloadTableView 永远不会被调用，无论我的完成块如何。这是我的 findAllDishesOfRestaurants 函数

func findAllDishesOfRestaurants(restaurants:NSArray, completion:(result: NSArray) -> Void) 
    let allDishesArray:NSMutableArray = NSMutableArray()
    for restaurant in restaurants as! [Resturant] 
        let currentRestaurant:Resturant? = restaurant
        if currentRestaurant == nil 
            print("restaurant is nil")
         else 
            self.getDishesByRestaurantName(restaurant, completion:  (result) -> Void in
                                            if let dishesArray:NSArray = result 
                                                restaurant.dishes =  dishesArray
                                                print(restaurant.dishes?.count)
                                                allDishesArray.addObjectsFromArray(dishesArray as [AnyObject])
                                                self.allDishes.addObjectsFromArray(dishesArray as [AnyObject])
                                                print(self.allDishes.count)
                                            
                                            else 
                                                print("not dishes found")
                                        
                                          // completion(result:allDishesArray)
                                    )
             completion(result:allDishesArray)
        
    

这是我执行数据任务的函数。

 func getDishesByRestaurantName(restaurant:Resturant, completion:(result:NSArray) ->Void) 

    var restaurantNameFormatted = String()
    if let name = restaurant.name 
    for charachter in name.characters 
        var newString = String()
        var sameCharacter:Character!
        if charachter == " " 
           newString = "%20"
            restaurantNameFormatted = restaurantNameFormatted + newString
         else 
            sameCharacter = charachter
            restaurantNameFormatted.append(sameCharacter)
        
       // print(restaurantNameFormatted)
    

    var urlString:String!
        //not to myself, when using string with format, we need to igone all  the % marks arent ours to replace with a string, otherwise they will be expecting to be replaced by a value
         urlString = String(format:"https://api.nutritionix.com/v1_1/search/%@?results=0%%3A20&cal_min=0&cal_max=50000&fields=*&appId=XXXXXXXXXappKey=XXXXXXXXXXXXXXXXXXXXXXXXXXXX",restaurantNameFormatted)
    let URL = NSURL(string:urlString)
    let restaurantDishesArray = NSMutableArray()
  let session = NSURLSession.sharedSession()
                let dataTask = session.dataTaskWithURL(URL!)  (data:NSData?, response:NSURLResponse?, error:NSError?) -> Void in
                do 
                let anyObjectFromResponse:AnyObject = try NSJSONSerialization.JSONObjectWithData(data!, options: NSJSONReadingOptions.AllowFragments)
                    if let asNSDictionary = anyObjectFromResponse as? NSDictionary 
                        let hitsArray = asNSDictionary.valueForKey("hits") as? [AnyObject]
                                                for newDictionary in hitsArray! as! [NSDictionary]
                                                    let fieldsDictionary = newDictionary.valueForKey("fields") as? NSDictionary
                                                    let newDish = Dish.init(dictionary:fieldsDictionary!, restaurant: restaurant)
                                                    restaurantDishesArray.addObject(newDish)
                        
                    
                    completion(result:restaurantDishesArray)
                 catch let error as NSError 
                    print("failed to connec to api")
                    print(error.localizedDescription)
                
            
            dataTask.resume()

就像我之前说的，我需要等到有趣的 findAllDishesOfRestaurants 完成。我试着写我的完成块，但我不确定我做得对。任何帮助是极大的赞赏。谢谢

【参考方案1】：

问题是您在所有任务完成之前调用findAllDishesOfRestaurants 中的completion 方法。实际上，您为列表中的每家餐厅调用一次，这可能不是您想要的。

我的建议是让您查看NSOperationQueue，原因有两个：

它可以让您限制对服务器的并发请求数，这样您的服务器就不会被请求淹没。 它可以让您轻松控制所有操作何时完成。

但是，如果您正在寻找快速解决方案，您需要使用 GCD 组 dispatch_group_create、dispatch_group_enter、dispatch_group_leave 和 dispatch_group_notify，如下所示。

func findAllDishesOfRestaurants(restaurants:NSArray, completion:(result: NSArray) -> Void) 
    let group = dispatch_group_create() // Create GCD group

    let allDishesArray:NSMutableArray = NSMutableArray()
    for restaurant in restaurants as! [Resturant] 
        let currentRestaurant:Resturant? = restaurant
        if currentRestaurant == nil 
            print("restaurant is nil")
         else 
            dispatch_group_enter(group) // Enter group for this restaurant
            self.getDishesByRestaurantName(restaurant, completion:  (result) -> Void in
                if let dishesArray:NSArray = result 
                    restaurant.dishes =  dishesArray
                    print(restaurant.dishes?.count)
                    allDishesArray.addObjectsFromArray(dishesArray as [AnyObject])
                    // self.allDishes.addObjectsFromArray(dishesArray as [AnyObject])  <-- do not do this
                    // print(self.allDishes.count)
                
                else 
                    print("not dishes found")
                
                // completion(result:allDishesArray)  <-- No need for this, remove
                dispatch_group_leave(group) // Leave group, marking this restaurant as complete
            )
            // completion(result:allDishesArray) <-- Do not call here either
        
    

    // Wait for all groups to complete
    dispatch_group_notify(group, dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_HIGH, 0)) 
        completion(result:allDishesArray)
    

【讨论】：

是的，我只是将完成部分留在那里，否则它不会被调用，直到为时已晚。您的建议听起来很棒，我什至从未听说过。非常感谢您，我会告诉您进展如何并接受您的回答。

老兄！非常感谢您的建议，“快速修复”工作，但我更关注 NSPertationQueue。