Why is my function to download avatars being called thousands of times? - ios

Question

My print statement shows that the function is called 4771 times in about 15 seconds, obviously resulting in a crash.
This is the function:
override func collectionView(_ collectionView: JSQMessagesCollectionView!, avatarImageDataForItemAt indexPath: IndexPath!) -> JSQMessageAvatarImageDataSource! {
count += 1
print("\n\nAvatar func called \(count)\n")
let databaseRef = FIRDatabase.database().reference()
let message = messages[indexPath.item]
let placeHolderImage = UIImage(named: "Logo")
let avatarImage = JSQMessagesAvatarImage(avatarImage: nil, highlightedImage: nil, placeholderImage: placeHolderImage)
if let messageID = message.senderId {
// Check cache for avatar
if imageCache.object(forKey: messageID as NSString) != nil {
DispatchQueue.main.async {
avatarImage!.avatarImage = imageCache.object(forKey: messageID as NSString)
avatarImage!.avatarHighlightedImage = imageCache.object(forKey: messageID as NSString)
self.collectionView.reloadData()
}
} else {
// If avatar isn't cached, fire off a new download
databaseRef.child("users").child(messageID).observe(.value, with: { (snapshot) in
if let profilePic = (snapshot.value as AnyObject!)!["profilePicture"] as! String! {
let profilePicURL: URL = URL(string: profilePic)!
Alamofire.request(profilePicURL)
.responseImage { response in
if let downloadedImage = response.result.value {
imageCache.setObject(downloadedImage, forKey: message.senderId as NSString)
DispatchQueue.main.async {
avatarImage!.avatarImage = imageCache.object(forKey: message.senderId as NSString)
avatarImage!.avatarHighlightedImage = imageCache.object(forKey: message.senderId as NSString)
self.collectionView.reloadData()
}
}
}
}
})
}
}
return avatarImage
}
What's causing the loop? There's only one user (me) to get an avatar for anyway. I'm somewhat new to programming and am trying to figure out how to work with a cache... my intention with this function is to check if the user's avatar is cached, and if so, use it. If not, fire off a new download from Firebase. But I am messing up badly apparently - How can I write this so it efficiently checks the cache and/or downloads the image, and doesn't get stuck in a loop?

Answer 1

You are calling reloadData in your function, which will cause this function to be called again, which calls reloadData and so on; you have created an infinite loop.
You only need to reload anything in the case where you initially return a placeholder and then subsequently retrieve the avatar from the network. In this case it is very wasteful to reload the whole collection view; you simply need to reload the affected item:
override func collectionView(_ collectionView: JSQMessagesCollectionView!, avatarImageDataForItemAt indexPath: IndexPath!) -> JSQMessageAvatarImageDataSource! {
count += 1
print("\n\nAvatar func called \(count)\n")
let databaseRef = FIRDatabase.database().reference()
let message = messages[indexPath.item]
let placeHolderImage = UIImage(named: "Logo")
let avatarImage = JSQMessagesAvatarImage(avatarImage: nil, highlightedImage: nil, placeholderImage: placeHolderImage)
if let messageID = message.senderId {
// Check cache for avatar
if let cacheObject = imageCache.object(forKey: messageID as NSString) {
avatarImage!.avatarImage = cacheObject
avatarImage!.avatarHighlightedImage = cacheObject
} else {
// If avatar isn't cached, fire off a new download
databaseRef.child("users").child(messageID).observe(.value, with: { (snapshot) in
if let profilePic = (snapshot.value as AnyObject!)!["profilePicture"] as! String! {
let profilePicURL: URL = URL(string: profilePic)!
Alamofire.request(profilePicURL)
.responseImage { response in
if let downloadedImage = response.result.value {
imageCache.setObject(downloadedImage, forKey: message.senderId as NSString)
DispatchQueue.main.async {
self.collectionView.reloadItems(at:[indexPath])
}
}
}
}
})
}
}
return avatarImage
}