Trouble using child snapshot inside for loop - swift

Question

I have a Firebase DB with "post/(randID)" structure, and Post class that inherits from an Item class. I already wrote a snapshot function that properly takes the value of all child nodes, but am now trying to only take a snapshot of post/ children that match elements of a name array I already have.
I'm properly getting values but not correctly appending temp values to my Item array at the breakpoint. Any help would be much appreciated
----------- CODE -----------
func getWavePosts() {
self.tempPosts = []
for name in self.tempNames {
var postRef = Database.database().reference().child("posts/\(name)")
postRef.observe(.value, with: {snapshot in
var test = snapshot.value as? [String:Any]
var author = test!["author"] as? [String:Any]
var uid = author!["uid"] as? String
var username = author!["username"] as? String
var photoURL = author!["photoURL"] as? String
var url = URL(string: photoURL!)
var imageURL = test!["imageURL"] as? String
var text = test!["text"] as? String
var timestamp = test!["timestamp"] as? Double
var userProfile = UserProfile(uid: uid!, username: username!, photoURL: url!)
var post = Post(id: name, author: userProfile, text: text!, timestamp: timestamp!, imageURL: imageURL!)
self.tempPosts.append(post)
//print(self.tempPosts)
//self.items = self.tempPosts
})
//self.items = self.tempPosts
}
print(self.tempPosts.count)
print(self.items.count)
}

Answer 1

First, your function should have completion with array of Post as parameter
func getWavePosts(_ completion: #escaping ([Post]) -> () )
...now let's meet with DispatchGroup.
First declare new DispatchGroup before foreach loop. Then before you observe postRef enter to dispatchGroup and after you append received Post to an array (define this array within function, don't use global variable) leave dispatchGroup. When every Post is added to an array, call completion in closure of dispatchGroup.notify(queue:)
func getWavePosts(_ completion: #escaping ([Post]) -> () ) {
var tempPosts = []
let dispatchGroup = DispatchGroup()
for name in self.tempNames {
dispatchGroup.enter()
var postRef = Database.database().reference().child("posts/\(name)")
postRef.observe(.value, with: { snapshot in
...
tempPosts.append(post)
dispatchGroup.leave()
})
}
dispatchGroup.notify(queue: .main) {
completion(tempPosts)
}
}
Then you have access to your received posts in closure of this method when you call it
getWavePosts { posts in
... // do whatever you want to
}