Swift: How to rm Alamofire get request One by One in loop - arrays

Question

I am a beginner in swift and I have come across a case where I need to run AlamoFire GET request in a loop. But As far as i know , the Alamofire Get request is an Asynchronous call and calling it in loop will create a number of threads.
The requirement is :
I have an array of URLs
The array has to be traversed in a loop
URL on each index has to be called through AlamoFire GET request
The received data through the request will be added to an array of
data
After the last data is saved in the array, a
CollectionView.reload call should be called
Pseudo code is as follows:
for bookmarkURL in bookmarks
Alamofire.request(.GET, bookmarkURL ).responseJSON
{ response in switch response.result {
case .Success(let JSON):
x[i] = JSON as! [String : AnyObject] // saving data
case .Failure(let error):
print("the error for \(self.bookmarkURL) is \(error) ")
}
i++
if i == bookmarks.count{
collectionView.reload()
break}
}
can anyone tell me how should I do it in sequence?

Answer 1

Make bookmarks array as class property.
Add a class property index to store index value (Int) while traversing the bookmarks array
Add a function to make API call and call it recursively.
Here is the code:
func getData() {
var x = [[String: AnyObject]]()
Alamofire.request(.GET, bookmarks[index]).responseJSON { response in
switch response.result {
case .Success(let JSON):
x[self.index] = JSON as! [String : AnyObject] // saving data
self.index = self.index + 1
if self.index < self.bookmarks.count {
self.getData()
}else {
self.collectionView.reloadData()
}
case .Failure(let error):
print("the error for \(self.bookmarks[self.index]) is \(error) ")
if self.index < self.bookmarks.count {
self.getData()
}else {
self.collectionView.reloadData()
}
}
}
}
In this way your request will be made only when previous is completed thus making it sequentially instead of parallel and you can also reload the collectionView only after the last request is completed.

Answer 2

If you want to reload your collection view only after receiving whole the data, you can use dispatch_group like,
let group = dispatch_group_create() // create a group.
dispatch_group_enter(group) // enter the group just before create the request
dispatch_group_leave(group)//leave the group on completion closure
dispatch_group_notify(group, group) {
//reload your collection view
}
Full code
for bookmarkURL in bookmarks {
dispatch_group_enter(group)
Alamofire.request(.GET, bookmarkURL ).responseJSON { response in
switch response.result {
case .Success(let JSON):
x[i] = JSON as! [String : AnyObject] // saving data
case .Failure(let error):
print("the error for \(self.bookmarkURL) is \(error) ")
}
dispatch_group_leave(group)
}
}
dispatch_group_notify(group, group) {
collectionView.reload()
}
Note: if your bookmarks array is too large, better not to do it in a loop.
For that you can use following code
func loadBookmarkAtIndex(index: Int) {
if index >= bookmarks.count {
collectionView.reload()
return
}
let bookmarkURL = bookmarks[index]
Alamofire.request(.GET, bookmarkURL ).responseJSON { response in
switch response.result {
case .Success(let JSON):
x[index] = JSON as! [String : AnyObject] // saving data
case .Failure(let error):
print("the error for \(bookmarkURL) is \(error) ")
}
self.loadBookmarkAtIndex(index+1)
}
}
And call self.loadBookmarkAtIndex(0) from where you are initiating the data retrieve.

Answer 3

I think you should reload item of collection view each time you get the response from the sever regarding to the response received.
Here is the solution:
let x : NSMutableArray = NSMutableArray.init(capacity: bookmarks.count)
for var i in 0 ..< x.count {
Alamofire.request(.GET, bookmarkURL ).responseJSON
{ response in switch response.result {
case .Success(let JSON):
x.insertObject(JSON as! [String : AnyObject], atIndex:i)
// x[i] = // saving data
// <reload relative item cell of collectionView>
case .Failure(let error):
print("the error for \(self.bookmarkURL) is \(error) ")
}
i+=1
}
Hope above code will help you.