将所有值注入数组后，如何从数组中提取值？

Question

The solution help me avoid the empty array but can't let me extract values beside array[0].
I'd like to extract 2 values after appending all values to the array.
array[0] is printed out successfully but the error message appeared as "Index out of range" while I tried to print out array 1 .

below is the code:

    var followingList = [User]()

    func fetchfollowingList(callback: @escaping ([User]) -> Void) {

        API.User.fetchFollowingList { followingUser in

            self.followingList.append(followingUser)
            callback(self.followingList)
          print(self.followingList)
        }
          print(self.followingList[0].displayName)
          print(self.followingList[1].displayName)
    }

the "print(self.followingList)" result in console:

[APP01.User]  
[APP01.User, APP01.User]   
[APP01.User, APP01.User, APP01.User]

I inferred that the array 1 is being extracted from the 1st array appended with only one value instead of the 3rd array appended with all values and not knowing how to fix it.

thanks

Answer 1

The function that fills the array is an async one, so when the compiler reaches the print state, it may not be filled yet . So you should check for that asynchronously too. Something like:

func fetchfollowingList(callback: @escaping ([User]) -> Void) {

    API.User.fetchFollowingList { followingUser in

        self.followingList.append(followingUser)
        callback(self.followingList)
        print(self.followingList)

        self.printIfNeeded() // <- Check everytime something appended
    }
}

func printIfNeeded() {
    guard followingList.count > 1 else { return } // Check the condition you need.

    print(self.followingList[0].displayName)
    print(self.followingList[1].displayName)
}