NSURLSession，完成块，Swift

Question

我正在使用NSURLSession。 我有一个带有餐厅的数组，我向api中的数组中的每个餐厅索要菜肴。 dataTask工作正常，仅在所有dataTasks完成后才尝试调用方法确实很困难。

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

无论我的完成块如何，self.updateDataSourceAndREloadTableView都不会被调用。 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dataTasks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()
}

就像我之前说过的那样，我需要等到有趣的findAllDishesOfRestaurants完成。 我尝试编写完成块，但不确定执行是否正确。 任何帮助是极大的赞赏。 谢谢

Answer 1

问题是您要在completion任务之前在findAllDishesOfRestaurants中调用completion方法。 实际上，您为列表中的每个餐厅都调用一次，这可能不是您想要的。

我的建议是让您研究NSOperationQueue的原因有两个：

1. 这将使您限制对服务器的并发请求数，因此服务器不会被请求淹没。
2. 它使您可以轻松控制何时完成所有操作。

但是，如果您正在寻找快速解决方案，则需要使用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)
    }
}