I believe it has something to do with optionals, but I'm safely unwrapping sourceURL so I'm still not sure where the error is! I'm trying to access a JSON object's array's dictionary value.
However, I'm still getting the "could not find overload for 'subscript' that accepts the supplied arguments.
It seems simple, but I just can't seem to figure it out!
var dictTemp: NSDictionary! = NSJSONSerialization.JSONObjectWithData(data!, options: NSJSONReadingOptions.MutableContainers, error: &localError) as? NSDictionary
var finalURL: String
// error line below
if let sourceURL = dictTemp[0]["source"]["sourceUrl"] as? NSString {
finalURL = sourceURL as String
}
NSDictionary accessed from Swift is an interesting beast.
As long as Swift only knows something is an NSDictionary (not a more specific [Key: Value] Swift-style dictionary), you can only retrieve AnyObject?s out of it.
let dictTemp: NSDictionary = // from somewhere...
let step1 = dictTemp[0] // step1 is an AnyObject?
But then, since you've imported Foundation, you can keep going with a magical subscript operator that works on AnyObject, and checks whether the thing is a dictionary:
let step2 = step1?["source"] // step2 is any AnyObject??
Here's where it gets interesting, because
if step1 was a dictionary with a "source" key inside it, step2 will be the corresponding value.
if step1 was a dictionary without a "source" key, step2 will be nil — in particular, it's AnyObject??.Some(AnyObject?.None).
if step1 was nil (the original dictionary didn't have 0 as a key), or not a dictionary (it had a 0 key with some other kind of value), then step2 will be nil — in particular, AnyObject??.None.
(The distinction between the last 2 cases is mostly unimportant and you shouldn't worry about it, but if you're interested you can see it by using dump).
And of course, we can apply the same principle again:
let step3 = step2??["sourceUrl"] // step3 is AnyObject?? again
Now, binding them all in one if:
if let url = dictTemp[0]?["source"]??["sourceUrl"] as? String {
// do something with url...
}
Caveat
This type of syntax can be dangerous, since it works with arrays and dictionaries at the same time. What would you expect in these situations?
let dict: NSDictionary = [0: ["source": [3: "result"]]]
dict[0]?["source"]??[3] // returns nil (surprise!)
dict[0]?["source"]??[3 as NSNumber] // returns "result"
let dict2: NSDictionary = [0: ["source": [8, 7, 6, 5, 4]]]
dict2[0]?["source"]??[3] // returns 5
dict2[0]?["source"]??[3 as NSNumber] // returns nil (surprise!)
Related
I'm new to Swift, very experienced in Objective-C.
In my app, I am receiving data from a server and mapping it to an NSMutableDictionary. The reason I am using an NSMutableDictionary is that the values are not consistent coming from the server, it's a mix of strings and numbers. And that appears to break a Swift Dictionary that expects only one type of value.
Sometimes the server is not sending a value that the NSMutableDictionary is expecting and it crashes the app.
In my research, it appears that I have to check every object to see if the value exists in Swift before setting it into the NSMutableDictionary.
This is my current code:
let userDictionary:NSMutableDictionary = [
"name": data.objectForKey("name") as! String,
... // many more values
This crashes if there is no "name" value in the response from the server.
It appears the solution would be:
if let nameValue = data.objectForKey("name") as! String {
//not sure what to do in here since the var is assigned as I need
}
// ... check many more values
let userDictionary:NSMutableDictionary = [
"name": nameValue,
// ... assign many more values that I checked above
This seems like a lot of extra code to check every single value from the server. Is there a simpler solution?
Thank you for your time.
#Matt below. Here is the code in detail (took out some of the values in the userDictionary for brevity). I'm taking data from Facebook, adding additional info and saving it to Firebase:
//check all of the values
var birthdayValue:String? = "";
if let value:String? = data.objectForKey("birthday") as? String {
birthdayValue = value;
}
let userDictionary:NSMutableDictionary = [
"name": data.objectForKey("name") as! String,
"birthday": birthdayValue!,
"email": data.objectForKey("email") as! String,
"firstName": data.objectForKey("first_name") as! String,
"lastName": data.objectForKey("last_name") as! String,
"description": "",
"distance": 50,
"facebookID": data.objectForKey("id") as! String,
"location":[ 37.12314, -122.49182 ], //TODO: Get location
"points" : 0,
"rating" : 1,
"school" : "",
]
//we need to convert the FB profile pic to a base 64 string and add it here
let imagePath:String = "https://graph.facebook.com/\(data.objectForKey("id") as! String)/picture?width=375&height=667"
self.getDataFromUrl(NSURL(string: imagePath)!) { (imageData, response, error) -> Void in
//convert the data to base 64
let imgString:String = self.convertDataToBase64(imageData);
let images:Array<String> = [imgString];
userDictionary.setValue(images, forKey: "profilePics")
//save the user to Firebase
userRef.childByAppendingPath(data.objectForKey("id") as! String).setValue(userDictionary)
self.currentUserID = (data.objectForKey("id")) as! String
}
Swift actually support multiple types in a dictionary. The following is legal.
let arr: [NSObject: AnyObject] = [1: "hello", "a": 19, 2: "Swift"]
And you can store optional object in the dictionary:
let arr: [NSObject: AnyObject?] = [1: "hello", "a": 19, 2: nil]
And yes, you might need to check the existence of the value if you do care about it. Instead of if, I would use guard to make sure you can use the variable later.
guard let nameValue = data.objectForKey("name") as? String else {
return
}
// Now you can safely use nameValue.
In my app, I am receiving data from a server and mapping it to an NSMutableDictionary
There is no need for this at all. The data is coming to you as a dictionary (at least I presume it is; if it weren't, you could hardly be calling objectForKey, it seems to me). So now just proceed to use it. There is nothing to "map".
For example, suppose that data is the result of calling NSJSONSerialization's JSONObjectWithData:options: on an original NSData d. And suppose what you expect this to serialize to is a dictionary. So after you've said
var data = try! NSJSONSerialization.JSONObjectWithData(
d, options:[]) as! [NSObject:AnyObject]
...you are finished: that's a mutable dictionary and you are off to the races.
If your data is a mix of strings and numbers you could perhaps try to store it as AnyObject in the dictionary, e.g. [String: AnyObject]
Then you could just try to save your data like this:
var userDictionary: [String: AnyObject] = [:]
userDictionary["name"] = data.objectForKey("name")
And when you need to access it:
if let name = userDictionary["name"] as? String {
// Do something with name
}
If you don't want to save it as AnyObject I'd suggest you create a struct instead.
as! is a force downcast, which causes an exception if this downcast isn't possible (which obviously is the case if the value is nil). as?, on the other hand, only downcasts where possible, and results in nil otherwise (which sounds like what you want).
let userDictionary:NSMutableDictionary = [
"name": data.objectForKey("name") as? String,
... // many more values
]
This should work.
Edit: Never mind, this would only work if you'd use a native Swift dictionary. It's still useful to know about the difference between as? and as!, though.
This is what I am trying to do with the dictionary:
if let deliveries = dictionary["deliveries"] as? NSDictionary {
var castedDeliveries = [Double: Double]()
for delivery in deliveries {
if let value = delivery.value as? Double {
castedDeliveries[Double(delivery.key as! NSNumber)] = value //Could not cast value of type 'NSTaggedPointerString' (0x1a1e3af20) to 'NSNumber' (0x1a1e458b0).
}
}
settings!.deliveries = castedDeliveries
}
And this is what I try to cast, as a part of JSON response from server:
deliveries = {
2 = 0;
5 = "2.59";
7 = "3.59";
};
It doesnt work, because there is an error at commented line:
Could not cast value of type 'NSTaggedPointerString' (0x1a1e3af20) to 'NSNumber' (0x1a1e458b0).
You are trying to cast dictionary directly but instead you need to cast each key - value pair. If you want generic solution to this problem take a look at SwiftyJSON library which address JSON parsing problem for you.
Casting doens't mean data transformation from a type to another.
Your dictionary seems to be composed by Integer keys and String values.
If you want to transform in something else you ca use the map function.
let converted = deliveries.map{[Double($0) : Double($1)]}
But pay attention.
Here we are saying, iterate over the dictionary (in the $0 there is the dictionary key in the $1 there is the value) and create a new dictionary that has as a key a Double initialized at the key value and as a new value a Double initialized as the old dictionary value. The last conversion can fail, so the returned data is an optional.
As I noted in the comments, this isn't casting. You want a data conversion. You need to do that explicitly, especially in this case since it might fail.
Looking at the error, I think you really have a dictionary of [String:String] here (in NSDictionary form). That suggests the JSON is badly encoded, but such is life. Assuming that dictionary looks something like this:
let dictionary: NSDictionary = ["deliveries": ["2":"0", "5": "2.59", "7": "3.59"]]
You would convert it to [Double:Double] like this:
if let jsonDeliveries = dictionary["deliveries"] as? [String:String] {
var deliveries: [Double: Double] = [:]
for (key, value) in jsonDeliveries {
if let keyDouble = Double(key),
valueDouble = Double(value) {
deliveries[keyDouble] = valueDouble
}
}
// Use deliveries
}
This silently ignores any values that can't be converted to Double. If you would rather generate errors, use a guard let rather than an if let.
I'm creating an app that should retrieve some JSON from a database.
This is how my JSON looks:
[{"id":"1","longitude":"10","latitude":"10","visibility":"5","timestampAdded":"2015-10-01 15:01:39"},{"id":"2","longitude":"15","latitude":"15","visibility":"5","timestampAdded":"2015-10-01 15:06:25"}]
And this is the code i use:
if let jsonResult = JSON as? Array<Dictionary<String,String>> {
let longitudeValue = jsonResult[0]["longitude"]
let latitudeValue = jsonResult[0]["latitude"]
let visibilityValue = jsonResult[0]["visibility"]
print(longitudeValue!)
print(latitudeValue!)
print(visibilityValue!)
}
As you can see it only gets the first chunk from the JSON and if there are no JSON at all it will crash, but if i want it to count the amount and make an array out of it like this:
var longitudeArray = [10, 15]
var latitudeArray = [10, 15]
And so on...
I also need this to be apple watch compatible so i can't use SwiftyJSON.
What do i do? I really hope you can help me!
Thanks.
SOLVED!
Problems was solved by "Eric D."
This is the code:
do {
if let url = NSURL(string: "YOU URL HERE"),
let data = NSData(contentsOfURL: url),
let jsonResult = try NSJSONSerialization.JSONObjectWithData(data, options: []) as? [[String:AnyObject]] {
print(jsonResult)
let longitudeArray = jsonResult.flatMap { $0["longitude"] as? String }
let latitudeArray = jsonResult.flatMap { $0["latitude"] as? String }
print(longitudeArray)
print(latitudeArray)
}
} catch let error as NSError {
print(error.description)
}
Thank you soo much Eric!! :-)
You could use flatMap to get an array of your elements:
let longitudeArray = jsonResult.flatMap { $0["longitude"] as? String }
let latitudeArray = jsonResult.flatMap { $0["latitude"] as? String }
etc.
flatMap is like map but unwraps optionals, which is adequate because we need to safely cast the type of the object we get from each dictionary in the json array.
$0 represents the object in the current iteration of flatMap of the array it's applied to.
If you're currently using SwiftyJSON, then that would be:
let longitudeArray = jsonResult.flatMap { $1["longitude"].string }
let latitudeArray = jsonResult.flatMap { $1["latitude"].string }
because .string is SwiftyJSON's optional String value getter.
But as you said, you don't want to use it (anymore), so you need to use NSJSONSerialization to decode your JSON data, there's plenty of examples on the Web and on SO. Then you will be able to use my original answer.
You're already getting an array with all of the elements (not just the first one. you're simply only accessing the first one). jsonResult is an array of dictionaries. Each dictionary (in this case, based on the json you provided) contains these elements: id, longitude, latitude, visibility and timestampAdded. In order to access each of them, you can simply loop over jsonResult and access the i'th element (and not always the 0 element). This will also prevent the crash you're experiencing with the json is blank or invalid (since you'll only be going over the valid elements in jsonResult.
This will give you the flexibility to create the custom arrays you wish to create (in order to create an array of all of the longitudes, for example, you will simply add that element to the new array while looping over jsonResult). However, if you'd like to save yourself the trouble of manually building these arrays and assuming you have control over the json structure, I would recommend changing the received json to the relevant structure (a dictionary or arrays instead of an array of dictionaries), so it would better fit your needs and provide you the results in the relevant format right "out of the box".
I am building a game in Xcode and I'm storing the details for the level in text files e.g. Level1.txt, Level2.txt etc.
I read in the data from a text file and store it in a Dictionary.
When I try to assign the values from the dictionary to the global variables, it doesn't work.
Text File Contents (Level1.txt)
LevelNum:1
weaponPickupRate:10.0
weaponPickupAmount:50.0
monsterMinSpeed:10.0
monsterMaxSpeed:15.0
monsterRate:1.0
totalMonsters:10.0
goldPerMonster:10
Global Variables
var settings = [String: Any]()
var monsterMaxSpeed = 0.0
Function For Obtaining Level Details
func GenerateLevel(levelNumber: Int) {
fileName = "level\(levelNumber).txt"
levelPath = "\(NSBundle.mainBundle().resourcePath!)/\(fileName)"
var err: NSError? = NSError()
let s = String(contentsOfFile: levelPath, encoding: NSUTF8StringEncoding, error: &err)
if let content = s {
var array = content.componentsSeparatedByString("\n")
for a in array {
var v = a.componentsSeparatedByString(":")
settings[v[0]] = v[1]
}
}
println(settings) // A
var e = settings["monsterMaxSpeed"]
println(e) // B
monsterMaxSpeed = settings["monsterMaxSpeed"] // C
}
Println(setting) (A) - prints:
[monsterRate: 1.0, monsterMinSpeed: 10.0, weaponPickupRate: 10.0, weaponPickupAmount: 50.0, goldPerMonster: 10, totalMonsters: 10.0, LevelNum: 1, monsterMaxSpeed: 15.0]
Println(e) (B) prints:
Optional("15.0")
This Line Does not work
it shows up an error and doesn't allow me to build my project. The Error given is:
'(String, Any)' is not convertible to 'Double'
monsterMaxSpeed = settings["monsterMaxSpeed"]
Please can someone help and advise me what I need to do?
Thanks,
Ryann
You have two problems here.
First, fetching from a [String:Any] dictionary by key does not return an Any. It returns an Any? i.e. an optional that may or may not contain an Any. This is because that key may not be present in the dictionary.
You need to test if the value is non-nil and unwrap the value if it is:
if let speed = settings["monsterMaxSpeed"] {
monsterMaxSpeed = speed
}
else {
// handle there being no speed setting in your file
// by reporting an error or similar
}
Or, if you’re happy with just using a default, you can use the nil coalescing operator:
// if the key is present, us the unwrapped value, if not use 0.0
monsterMaxSpeed = settings["monsterMaxSpeed"] ?? 0.0
Second, you’ve declared monsterMaxSpeed as a Double not an Any. So once you resolve your optional unwrapping problem you’ll get a second problem. You need to convert the Any to a Double using as?. The ? in as? is important – if the value is not a double (suppose there was a rogue character in the entry in your file), you will get a nil back. Again, you would need to test for this and handle the error.
Happily, you can do this all in one go:
monsterMaxSpeed = (settings["monsterMaxSpeed"] as? Double) ?? 0.0
(it’s probably the confluence of the two of these issues that’s causing you to get a particularly enigmatic error – the error relates to the other version of Dictionary.subscript which takes an index, not a key, and returns a key/value pair, which isn’t optional, because indices should only address entries that are definitely in the dictionary)
I'm new to Swift. I'll explain what I'm trying to do in Java terms and hopefully someone can help me understand.
I want a class scoped array that is instantiated/set in viewDidLoad of a view controller. It sounds simple enough, but this is what I had to do to get it to work. Could someone explain to me why the _dictionary must be instantiated as an empty array and why I need to use as? when unpacking dictionary even though the componentsSeparatedByString function returns an array? Thanks.
class ViewController: UIViewController, UITextFieldDelegate
{
var _dictionary : [String] = []
override func viewDidLoad()
{
super.viewDidLoad()
let bundle = NSBundle.mainBundle()
let path = bundle.pathForResource(“TextFile”, ofType: "txt")
var err: NSError?
let dico = NSString(contentsOfFile: path!, encoding: NSUTF8StringEncoding, error: &err)
if let dictionary = dico?.componentsSeparatedByString("\n") as? [String]
{
_dictionary = dictionary
}
else
{
println("Error reading dictionary")
}
}
}
_dictionary must be given an initial value because all instance properties must be given an initial value. That is a Swift safety feature to make sure that all instances are well-formed at birth. You could have done this by initializing _dictionary in an actual initializer, but you didn't. You chose to give it its first "real" value in viewDidLoad which is much later. Therefore you have forced yourself to supply a "fake" initial value until such time as viewDidLoad comes along and gives you a "real" initial value.
I don't understand your other question because I don't know what "unpacking dictionary" means. But perhaps you are referring to the rest of the stuff in this code. I'll talk you through it.
dico is an Optional wrapping a String. It is an Optional because the contentsOfFile: initializer of String returns an Optional - it is a failable initializer. That is because there might be no such file, or that file might not have that encoding, in which case the initializer needs to return nil.
So now dico is an Optional wrapping a String that must be unwrapped - or nil. So you do unwrap it as dico? in the next line. dico? is a String at that point, assuming that dico was not nil.
Then you call componentsSeparatedByString. It returns an array of AnyObject. So you have chosen to cast it down to an array of String using as?. I don't know why you chose to use as? since you know it will be an array of String if we get to this point - personally, I would have used as. But in any case, as? always returns an Optional! So you unwrap that, optionally, by using an if let conditional binding.
The irony throughout is that _dictionary is not and never was or will be a dictionary - it is an array. Your name for this (and for dictionary) is very poorly chosen! dico is a String, and dictionary and _dictionary are arrays. There is not a dictionary in sight.
Assuming we keep your rather odd names, though, you could have done all this much more briefly and clearly, like this:
var err : NSError?
if let dico = NSString(contentsOfFile: path!,
encoding: NSUTF8StringEncoding, error: nil) {
_dictionary = dico.componentsSeparatedByString("\n") as [String]
} else {
println(err)
}
Moreover, if you start with the String class instead of the NSString class, then componentsSeparatedByString will be an array of String instead of an untyped NSArray (i.e. an array of AnyObject), and you can skip the cast:
var err : NSError?
if let dico = String(contentsOfFile: path!,
encoding: NSUTF8StringEncoding, error: nil) {
_dictionary = dico.componentsSeparatedByString("\n")
} else {
println(err)
}