i have the following data structure in my cloud firestore db:
In my data parsing method i'm trying the following:
if document.get("decisions") == nil{
object.decisions = document.get("decisions") as! [String: String]
}
The result is that the app is crashing, because my if clause allows to get the data, even if "decisions" is null
I would say that you would better like to make a safe check, alltogether with casting the type like so:
if let decisions = document.get("decisions") as? [String: String] {
object.decisions = decisions
}
try like this
if document.get("decisions") != nil{
object.decisions = document.get("decisions") as! [String: String]
}
You can do this way which will convert null value to nil and won't cause crash in your app.
func nullToNil(value : AnyObject?) -> AnyObject? {
if value is NSNull {
return nil
} else {
return value
}
}
object.decisions = nullToNil(dict["decisions"])
or you can use
object.decisions = document.get("decisions") as? [String: String]
Related
I'm trying to compare my responses with other people's responses in the firebase database. My script currently has 2 if statements saying if it's my response, record my answers and then use that to compare against other responses, but it doesn't register my second if statement.
let responsesReference = Database.database().reference().child("responses")
responsesReference.observeSingleEvent(of: .value) { (snapshot: DataSnapshot) in
guard let json = snapshot.value as? [String: Any] else { return }
do {
var similarities = [Similarity]()
for answerElement in json {
if self.currentUser.uid == answerElement.key,
let myanswer = answerElement.value as? [String: Any] {
if self.currentUser.uid != answerElement.key, //DOES NOT REGISTER
let otheranswer = answerElement.value as? [String: Any] {
let percentage = myanswer.similarity(with: otheranswer)
similarities.append(
Similarity(name: answerElement.key, percentage: percentage, answer: otheranswer)
)
}
}
}
self.similarities = similarities.sorted(by: { (a, b) -> Bool in
return a.percentage > b.percentage
})
self.tableView.reloadData()
}
Here's your code properly formatted (I copy and pasted it with no changes other than formatting it)
do {
var similarities = [Similarity]()
for answerElement in json {
if self.currentUser.uid == answerElement.key, let myanswer = answerElement.value as? [String: Any] {
if self.currentUser.uid != answerElement.key, let otheranswer = answerElement.value as? [String: Any] {
let percentage = myanswer.similarity(with: otheranswer)
similarities.append( Similarity(name: answerElement.key, percentage: percentage, answer: otheranswer) )
}
}
Take a look here
if self.currentUser.uid == answerElement.key
and note the next if is nested inside that one
if self.currentUser.uid == answerElement.key
if self.currentUser.uid != answerElement.key
If those two vars are equal in the outside if, they will be equal with the inside if as well so the second check will always fail.
The generic solution is to use and else with your if
if self.currentUser.uid == answerElement.key {
let myanswer = answerElement.value as? [String: Any] <- OPTIONAL!
//do something because they are equal
} else {
let otheranswer = answerElement.value as? [String: Any] <- OPTIONAL!
// do something else because they are NOT equal
}
also note that you've got some optionals in that code and if those go to nil your app will either crash or silently fail with no indication as to why.
The logic isn't exactly clear in this code
let percentage = myanswer.similarity(with: otheranswer)
as each time through the loop
for answerElement in json {
}
there will only be one answer in an answerElement. e.g. there won't be a myAnswer and otherAnswer, there will only be theAnswer. Perhaps there should be a comparison to the prior answer from the loop; I'll expand on that
Here's an example based on reading in all users, getting the answer for this user, removing the user from the results and then comparing that to other users answers. Assume users uid's are used at the key to each user node (which also contains an answer they provides) and we know the auth'd users uid.
let thisUsersUid = "uid_1"
let usersRef = self.ref.child("users") //self.ref points to MY firebase
usersRef.observeSingleEvent(of: .value, with: { snapshot in
var allUsersSnap = snapshot.children.allObjects as! [DataSnapshot]
guard let index = allUsersSnap.firstIndex { $0.key == thisUsersUid } else {
print("no user: \(thisUsersUid) found")
return
}
let thisUserSnap = allUsersSnap[index] //keep this so it can be compared later
allUsersSnap.remove(at: index)
let thisUsersAnswer = thisUserSnap.childSnapshot("answer").value as? String ?? "No Answer"
for otherUserSnap in allUsersSnap {
let otherUsersAnswer = otherUserSnap.childSnapshot("answer").value as? String ?? "No Answer"
if orherUsersAnswer == thisUsersAnswer {
//do something because the answers match
}
}
})
I have this code
let jsonData = try JSONSerialization.jsonObject(with: data, options: []) as! [Any?]
if var first = jsonData[0] as! String?{
if(first=="Error"){
DispatchQueue.main.async(execute: {
self.postNotFoundLabel.isHidden = false
});
}else if(first=="Empty"){
print("Empty")
}
}
What i want to do is to cast jsonData[0] to String if it's possible and if it's not then move on.But instead when it's not possible application stops and gives me an error
Could not cast value of type '__NSDictionaryI' (0x1092054d8) to 'NSString' (0x108644508).
How can i cast only when it's possible?
You are trying to force-cast to an optional String. That's not what you want.
Change:
if var first = jsonData[0] as! String? {
to:
if var first = jsonData[0] as? String {
This tries to cast to String. If jsonData[0] isn't actually a String, you get nil and the if var fails.
And you probably want if let, not if var since you don't seem to be making any change to first.
First of all JSON objects will never return optional values so [Any?] is nonsense.
Second of all the error message says the type cast to string is inappropriate because the type of the result is actually a dictionary.
Solution: Check the type for both String and Dictionary
if let jsonData = try JSONSerialization.jsonObject(with: data) as? [Any],
let first = jsonData.first {
if let firstIsDictionary = first as? [String:Any] {
// handle case dictionary
} else if let firstIsString = first as? String {
// handle case string
}
}
PS: A type cast forced unwrap optional to optional (as! String?) is nonsense, too.
Here's the Swifty way to do what you're doing :)
guard let jsonData = try JSONSerialization.jsonObject(with: data, options: []) as? [Any?], let first = jsonData[0] as? String else {
DispatchQueue.main.async(execute: {
self.postNotFoundLabel.isHidden = false
});
return
}
if(first == "Empty") {
print(first)
}
Don't use as! if you are not sure that casting will succeed. The exclamation mark after the as keyword forces the casting, which throws an error if the casting does not succeed.
Use as? instead, which returns an optional variable of the type you were trying to casting to. If the casting fails, instead of throwing an error, it just returns nil.
let jsonData = try JSONSerialization.jsonObject(with: data) as? [Any]
if var first = jsonData.first as? String{
if(first=="Error"){
DispatchQueue.main.async(execute: {
self.postNotFoundLabel.isHidden = false
});
}else if(first=="Empty"){
print("Empty")
}
}
I am fairly new to the Swift syntax and am receiving this error with my code "Cannot assign through subscript: subscript is get only"
This is from the line: friendDictionary[(friendUID as? String)!] = ["name": friendsData!["name"]]
Any advice on the correct way of doing it would be very helpful.
func getFriendsUIDs() {
if FBSDKAccessToken.currentAccessToken() == nil {
print("failed to start graph request")
return
}else{
}
if FBSDKAccessToken.currentAccessToken() != nil {
}
let parameters = ["fields": "name, id, picture"]
FBSDKGraphRequest(graphPath: "/me/friends", parameters: parameters).startWithCompletionHandler {
(NSURLConnection, result, requestError) in
let friendIds = result["id"] as? NSDictionary
let friendsData = friendIds!["data"] as? [NSDictionary]
var ref: FIRDatabaseReference!
ref = FIRDatabase.database().reference()
ref.child("users").child((FIRAuth.auth()?.currentUser?.uid)!).child("friendUIDs").observeEventType(.Value, withBlock: { (snapshot) in
self.FriendUIDs = NSArray()
self.FriendUIDs = (snapshot.value as? NSArray)!
print(self.FriendUIDs)
var friendDictionary = NSDictionary()
for friendUID in self.FriendUIDs {
friendDictionary[(friendUID as? String)!] = ["name": friendsData!["name"]]
}
self.fetchFriendFeed(friendDictionary)
}) { (error) in
print(error.localizedDescription)
}
}
}
func fetchFriendFeed(friendDictionary: NSDictionary) {
var ref: FIRDatabaseReference!
ref = FIRDatabase.database().reference()
for friendUID in FriendUIDs {
ref.child("users").child(friendUID as! String).child("Agenda").observeEventType(.ChildAdded, withBlock: { (snapshot) in
print(snapshot)
if let dictionary = snapshot.value as? [String: AnyObject] {
let friendPost = FriendPost()
friendPost.picture = friendDictionary[friendUID as! String]? ["picture"] as? String
friendPost.activity = dictionary["activity"] as? String
friendPost.date = dictionary["date"] as? String
friendPost.time = dictionary["time"] as? String
friendPost.friendname = friendDictionary[friendUID as! String]? ["name"] as? String
self.friendPosts.append(friendPost)
dispatch_async(dispatch_get_main_queue(), {
self.collectionView?.reloadData()
Nothing to do with Swift. You've elected to use Objective-C, in effect, by making friendDictionary an NSDictionary. NSDictionary is immutable; you can't assign into it or alter it in any way. That is simply a fact about Objective-C. The Swift var declaration makes no difference to this fact.
A better choice, since you are writing in Swift, would be to use a Swift dictionary, which is [AnyHashable:Any]() (in Swift 3). This will interchange with NSDictionary when you are talking to Objective-C, but it will give you a mutable dictionary because you (rightly) declared it with var.
Have you tried using NSMutableDictionary? That solved the issue for me.
For those who get stuck here, another reason for this happens when you try to assign something that does not conform the actual dictionary, in my example i was doing something like this:
var dict = [Date : UUID]()
let randomUUID = UUID()
dict[randomUUID] = Date.now
whereas I meant to write UUID : Date but I was sleepy so i made a mistake, and Swift gave me a misleading error saying subscript is get-only. So this error also appears with type mismatch for Swift 5.7.
I've been working on a recursive function to extract String values out of JSON data represented as an NSDictionary. The function allows you to do this:
if let value = extractFromNestedDictionary(["fee" : ["fi" : ["fo" : "fum"]]], withKeys: ["fee", "fi", "fo"]) {
println("\(value) is the value after traversing fee-fi-fo");
}
And the function implementation looks like this:
// Recursively retrieves the nested dictionaries for each key in `keys`,
// until the value for the last key is retrieved, which is returned as a String?
func extractFromNestedDictionary(dictionary: NSDictionary, withKeys keys: [String]) -> String? {
if keys.isEmpty { return nil }
let head = keys[0]
if let result: AnyObject = dictionary[head] {
if keys.count == 1 {
return result as? String
} else {
let tail: [String] = Array(keys[1..<keys.count])
if let result = result as? NSDictionary {
return extractFromNestedDictionary(result, withKeys: tail)
} else {
return nil
}
}
} else {
return nil
}
}
Are there some syntactical features related to optional binding in Swift 1.2/2.x that can:
make this function more succinct
use less if nesting
Instead of recursion, you can use reduce on the keys array
to traverse through the dictionary:
func extractFromNestedDictionary(dictionary: NSDictionary, withKeys keys: [String]) -> String? {
return reduce(keys, dictionary as AnyObject?) {
($0 as? NSDictionary)?[$1]
} as? String
}
Inside the closure, $0 is the (optional) object on the current level and $1
the current key. The closure returns the object on the next level
if $0 is a dictionary and has a value for the current key,
and nil otherwise. The return value from reduce() is then
the object on the last level or nil.
I originally didn't want to just make it without you trying first, but I did it anyways because I love Swift and had fun doing it:
func extractFromNestedDictionary(dictionary: [NSObject : AnyObject], var withKeys keys: [String]) -> String? {
if let head = keys.first, result = dictionary[head] {
if keys.count == 1 {
return result as? String
} else if let result = result as? [NSObject : AnyObject] {
keys.removeAtIndex(0)
return extractFromNestedDictionary(result, withKeys: keys)
}
}
return nil
}
extractFromNestedDictionary(["A" : ["B" : ["C" : "D"]]], withKeys: ["A", "B", "C"])
A few notes:
Try to avoid NSDictionary and use [NSObject : AnyObject] instead, which can be bridged to NSDictionary anyways and is much more Swifty
When asking a question, try to make a better example than you did there, from your example I wasn't able to know what exactly you want to do.
I know this isn't strictly answering the question. But you could just use valueForKeypath:
let fum = dict.valueForKeyPath("fee.fi.fo")
Here's the best I came up with...
func extractFromNestedDictionary(dictionary: [NSObject : AnyObject], withKeys keys: [String]) -> String? {
if let head = keys.first,
result = dictionary[head] as? String
where keys.count == 1 {
return result
} else if let head = keys.first,
result = dictionary[head] as? [NSObject : AnyObject] {
return extractFromNestedDictionary(result, withKeys: Array(keys[1..<keys.count]))
}
return nil
}
I want to safely search through values in a swift Dictionary using if lets and making sure it is type safe as I get deeper and deeper into the dictionary. The dictionary contains dictionaries that contains NSArray that contains more dictionary.
At first attempt my code looks like this:
if let kkbox = ticket["KKBOX"] as? Dictionary<String, AnyObject> {
if let kkboxDlUrlDict = kkbox["kkbox_dl_url_list"] as? Dictionary<String, AnyObject> {
if let kkboxDlUrlArray = kkboxDlUrlDict["kkbox_dl_url"] as? NSArray {
for dict in kkboxDlUrlArray {
if let name = dict["name"] as? String {
if name == mediaType.rawValue {
urlStr = dict["url"] as String
}
}
}
} else { return nil }
} else { return nil }
} else { return nil }
How do I shorten it to perhaps one or 2 line?
I realised I can chain it if it is 2 layers. This works:
if let kkboxDlUrlArray = ticket["KKBOX"]?["kkbox_dl_url_list"] as? NSArray {
}
But any chain longer than that, will not compile.
Is there a way to chain through a dictionary more than once?
Thank you
You can chain, but with proper downcast at each step:
if let kkboxDlUrlArray = ((((ticket["KKBOX"] as? Dictionary<String, AnyObject>)?["kkbox_dl_url_list"]) as? Dictionary<String, AnyObject>)?["kkbox_dl_url"]) as? NSArray {
for dict in kkboxDlUrlArray {
println(dict)
}
}
That doesn't look good though - it's one line, but not readable.
Personally, without using any fancy functional way to do it, I would make the chain more explicit with just one optional binding:
let kkbox = ticket["KKBOX"] as? Dictionary<String, AnyObject>
let kkboxDlUrlDict = kkbox?["kkbox_dl_url_list"] as? Dictionary<String, AnyObject>
if let kkboxDlUrlArray = kkboxDlUrlDict?["kkbox_dl_url"] as? NSArray {
for dict in kkboxDlUrlArray {
println(dict)
}
}
In my opinion much easier to read, and with no unneeded indentation
Alternatively, you could use this extension, which mimics the original valueForKeyPath method that used to exist in NSDictionary but got axed for whatever reason:
Swift 4.1
extension Dictionary where Key: ExpressibleByStringLiteral {
func valueFor(keyPath: String) -> Any? {
var keys = keyPath.components(separatedBy: ".")
var val : Any = self
while keys.count > 0 {
if let key = keys[0] as? Key {
keys.remove(at: 0)
if let dic = val as? Dictionary<Key, Value> {
if let leaf = dic[key] {
val = leaf
} else {
return nil
}
} else {
return nil
}
} else {
return nil
}
}
return val
}
Your code would then read:
if let array = ticket.valueFor("KKBOX.kkbox_dl_url_list.kkbox_dl_url") as? [] {
// do something with array
}
Seems like swift 1.2 has added this feature.
"More powerful optional unwrapping with if let — The if let construct can now unwrap multiple optionals at once, as well as include intervening boolean conditions. This lets you express conditional control flow without unnecessary nesting."
https://developer.apple.com/swift/blog/