Getting a crash after sending a message - ios

Question

Everything was working fine, then I deleted some old messages and conversations from My Firebase Database. Now every time I send a message I get a crash. I deleted all old users and created new users and tried to send messages and I still keep getting a crash. I am not sure what can be causing this. Any suggestions will be helpful. It first happened after I tested out this function to delete the table cell...
func deleteConversation(_ conversation:Conversation) {
guard let user = Auth.auth().currentUser else { return }
let ref = Database.database().reference()
let obj = [
"conversations/users/\(user.uid)/\(conversation.partner_uid)/muted": true
] as [String:Any]
print("OBBJ: \(obj)")
ref.updateChildValues(obj, withCompletionBlock: { error, ref in
if error != nil {
let alert = UIAlertController(title: "Error deleting conversation!", message: nil, preferredStyle: .alert)
alert.addAction(UIAlertAction(title: "Okay", style: .default, handler: nil))
} else {
let alert = UIAlertController(title: "Conversation deleted!", message: nil, preferredStyle: .alert)
alert.addAction(UIAlertAction(title: "Okay", style: .default, handler: nil))
}
})
}
func downloadMessages() {
self.messages = []
downloadRef?.observe(.childAdded, with: { snapshot in
let dict = snapshot.value as! [String:AnyObject]
if let sender = dict["sender"] as! String!, let recipient = dict["recipient"] as! String!, let text = dict["text"] as! String!, text.characters.count > 0 {
let timestamp = dict["timestamp"] as! Double
let date = NSDate(timeIntervalSince1970: timestamp/1000)
let message = JSQMessage(senderId: sender, senderDisplayName: "", date: date as Date!, text: text)
self.messages.append(message!)
self.reloadMessagesView()
self.finishReceivingMessage(animated: true)
}
else if let id = dict["sender"] as! String!,
let photoURL = dict["imageUrl"] as! String!, photoURL.characters.count > 0 { // 1
// 2
if let mediaItem = JSQPhotoMediaItem(maskAsOutgoing: id == self.senderId) {
// 3
let timestamp = dict["timestamp"] as! Double
let date = NSDate(timeIntervalSince1970: timestamp/1000)
if let message = JSQMessage(senderId: id, senderDisplayName: "", date: date as Date!, media: mediaItem) {
self.messages.append(message)
if (mediaItem.image == nil) {
self.photoMessageMap[snapshot.key] = mediaItem
}
self.collectionView.reloadData()
}
if photoURL.hasPrefix("gs://") {
self.fetchImageDataAtURL(photoURL, forMediaItem: mediaItem, clearsPhotoMessageMapOnSuccessForKey: nil)
}
}
}
else {
print("Error! Could not decode message data")
}
})
// We can also use the observer method to listen for
// changes to existing messages.
// We use this to be notified when a photo has been stored
// to the Firebase Storage, so we can update the message data
updatedMessageRefHandle = downloadRef?.observe(.childChanged, with: { (snapshot) in
let key = snapshot.key
let messageData = snapshot.value as! Dictionary<String, String> // 1
if let photoURL = messageData["imageUrl"] as String! { // 2
// The photo has been updated.
if let mediaItem = self.photoMessageMap[key] { // 3
self.fetchImageDataAtURL(photoURL, forMediaItem: mediaItem, clearsPhotoMessageMapOnSuccessForKey: key) // 4
}
}
})
}

Answer 1

It's very likely the error is a result of force casting - as!
Instead of
let messageData = snapshot.value as! Dictionary<String, String>
do
guard let messageData = snapshot.value as? Dictionary<String, String> else { return }
Your snapshot.value is either nil, or is not an instance of Dictionary<String, String>, and force casting it to such will result in crash.
You should also read more about optionals and type casting in Swift, because you use ! a lot, and not once in your program is it used correctly.