I would like a for in loop to send off a bunch of network requests to firebase, then pass the data to a new view controller once the the method finishes executing. Here is my code:
var datesArray = [String: AnyObject]()
for key in locationsArray {
let ref = Firebase(url: "http://myfirebase.com/" + "\(key.0)")
ref.observeSingleEventOfType(.Value, withBlock: { snapshot in
datesArray["\(key.0)"] = snapshot.value
})
}
// Segue to new view controller here and pass datesArray once it is complete
I have a couple concerns. First, how do I wait until the for loop is finished and all the network requests are complete? I can't modify the observeSingleEventOfType function, it is part of the firebase SDK. Also, will I create some sort of race condition by trying to access the datesArray from different iterations of the for loop (hope that makes sense)? I've been reading about GCD and NSOperation but I'm a bit lost as this is the first app I've built.
Note: Locations array is an array containing the keys I need to access in firebase. Also, it's important that the network requests are fired off asynchronously. I just want to wait until ALL the asynchronous requests complete before I pass the datesArray to the next view controller.
You can use Swift Concurrency to achieve this. For example:
Task {
let responses = try await withThrowingTaskGroup(of: Data.self) { group in
for i in 0..<5 {
group.addTask {
let url = URL(string: "https://httpbin.org/get?foo=\(i)")!
let (data, _) = try await URLSession.shared.data(from: url)
print("Finished request \(i)")
return data
}
}
var responses = [Data]()
for try await response in group {
responses.append(response)
}
return responses
}
print("Finished all requests.")
}
Finished request 1
Finished request 0
Finished request 2
Finished request 4
Finished request 3
Finished all requests.
You can use dispatch groups to fire an asynchronous callback when all your requests finish.
Here's an example using dispatch groups to execute a callback asynchronously when multiple networking requests have all finished.
override func viewDidLoad() {
super.viewDidLoad()
let myGroup = DispatchGroup()
for i in 0 ..< 5 {
myGroup.enter()
Alamofire.request("https://httpbin.org/get", parameters: ["foo": "bar"]).responseJSON { response in
print("Finished request \(i)")
myGroup.leave()
}
}
myGroup.notify(queue: .main) {
print("Finished all requests.")
}
}
Output
Finished request 1
Finished request 0
Finished request 2
Finished request 3
Finished request 4
Finished all requests.