how to get latest message from firebase database in ios - ios

Question

I have don't know what the problem please help me. When I get a particular message from firebase database then the value is getting but my app got a crash on one line.So please tell me what I do wrong in my code.below is my function.We also provide the screenshot of the error.
func getLatestMessageFromFirebase(token:String,completionmessage: #escaping (_ message:String) -> Swift.Void)
{
print("getModelFromFirebase")
var message:String=""
ref.child("chatmessage/devicetoken/").child(token).queryLimited(toLast: 1).observeSingleEvent(of: .value, with: { (snapshot) in
// Get user value
let value = snapshot.value as? NSDictionary
if value?["message"] as? String != ""
{
DispatchQueue.main.async
{
message = (value?["message"] as? String)! //My app stop on this line
completionmessage(message)
}
}
})
{ (error) in
print(error.localizedDescription)
}
}
func callAPI()
{
let response = (jsonResult.object(forKey: "chatListArr") as? NSArray)!
if response.count > 0
{
for i in 0..<response.count
{
let dict = response[i] as! NSDictionary
let chatlist = ChatList(dict: dict)
self.arr_list.append(chatlist)
}
for i in 0..<self.arr_list.count
{
let chatlist = self.arr_list[i]
self.getLatestMessageFromFirebase(token: chatlist.token, completionmessage: { (message) in
self.arr_list[i].msg = message
})
}
self.table_view.reloadData()
}
}
Please help me.
Thanks in Advance.

Answer 1

First of all you should clean your code up a bit, you do a couple of things which would be considered anti patterns
func getLatestMessageFromFirebase(token:String,completionmessage: #escaping (_ message:String) -> Swift.Void)
{
ref.child("chatmessage/devicetoken/").child(token).queryLimited(toLast: 1).observeSingleEvent(of: .value, with: { (snapshot) in
// Get user value
for snap in snapshot.children.allObjects as [DataSnapshot] {
let value = snap.value as? [String: Any] ?? [:] // A good way to unwrap optionals in a single line
if let message = value["message"] as? String {
DispatchQueue.main.async {
completionmessage(message)
}
}
}
})
{ (error) in
print(error.localizedDescription)
}
}
With the above code your app shouldnt crash. And if there is a message AND it is a string (which might have been your problem before) then your callback will fire.