I'm actually trying to parse a Json object with Swift3 on Xcode8.1.
This is my code:
if let objData = objJson["DATA"] as! NSDictionary? {
var msg: String = ""
if let tmp = objData.object(forKey: "Message") {
msg = tmp as! String
} else {
print("NIIILLLLL")
}
}
I'm getting this error message: Could not cast value of type 'NSNull' (0x4587b68) to 'NSString' (0x366d5f4) at this line msg = tmp as! String.
I'm not understanding why I'm getting this error because the type of tmp is Any and it should display the print instead of convert tmp as! String
Thank you for the help,
You can add casting in let.
if let tmp = objData.object(forKey: "Message") as? String {
msg = tmp
}
With Swift 3, for example:
fileprivate var rawNull: NSNull = NSNull()
public var object: Any {
get {
return self.rawNull
}
}
You can check field object as:
if self.object is NSNull {
// nil
}
So to answer your question in why you are getting that error, in your code "tmp" is not nil its something of type NSNull (if you want to know more about NSNull check the docs) but its basically "A singleton object used to represent null values in collection objects that don’t allow nil values."
The rest is just you are force casting which I recommend avoiding this is a safer way to do what you are doing.
guard let objData = objJson["DATA"] as? [String: Any], let msg = objData["Message"] else { return }
// now you can use msg only if exists and also important keeping its unmutable state
Related
I'm new to Swift and ObjC and can't get this simple bit of code to work. I get the error 'String?' is not convertible to 'String'; did you mean to use 'as!' to force downcast?
guard let data = context as? Dictionary<String,String> else {return}
var str : String
str = data["Score"] as String //<<<I get the error here
When I change it to as! I know get this warning: Forced cast from 'String?' to 'String' only unwraps optionals; did you mean to use '!'?
Any ideas how to extract the string from the dictionary so I can use it?
It might be possible, that the key "Score" is not set in your dictionary and may return nil. Use this code to unwrap the optional:
if let score = data["Score"] {
str = score
}
Since you already unwrapped context to Dictionary<String, String>, Swift will automatically infer the type of score as String.
You don't need to cast because data dictionary would always return optional String type and you can use guard statement
guard let str = data[Score] else { return }
// Your code here
The type returned by subscripting a Dictionary is an optional, since it is valid to subscript it with non-existinent keys. So, as per the error message, in a dictionary with String values, the return type is String?.
If you know for sure that the key always exist in the dictionary, you can force-unwrap it as data["Score"]! to make the type String (without casting, but crashing if it doesn't exist). Otherwise handle the nil in some way, e.g., if let str = data["Score"] or str = data["Score"] ?? "0".
Use like this:
if let dataDictionary = context as? [String: Any] {
if let someString = dataDictionary["score"] as? String {
print(someString)
}
}
We don't know what kind of data you're working with but you're likely either getting back a dictionary actually of type [String: String], in which case you would:
func getData(context: [String: String]) {
guard let str = context["Score"] else {
return
}
print(str)
}
...or you're really getting back a dictionary of type [String: Any] (more common with database dictionaries), in which case you would:
func getData(context: [String: Any]) {
guard let str = context["Score"] as? String else {
return
}
print(str)
}
I am trying to access the values of a dictionary which I passed into UserDefaults, however I get this error:
Type 'Any' has no subscript members.
I have looked around on StackOverflow for answers but everything I tried is failing.
This is the Dictionary object that I stored in UserDefaults and I am trying to access Authorities.levelAcess:
{
accountEnabled = 0;
accountLocked = 0;
Authorities = {
levelAccess = "tier2";
accessType = "3rd party";
};
message = "Logged in Successfully";
profile = "trust";
roles = (
{
authority = "admin";
}
);
status = 1;
}
This the code for UserDefaults:
let keyDict: Dictionary<String, AnyObject> = json
UserDefaults.standard.set(json, forKey: "dict")
This is how I am trying to access the dictionary:
The reason of showing this error in your code is: the compiler cannot recognize result as dictionary, if you tried to option and click on result you would see that its type is Any. You have to cast it first as [String: AnyObject] and then get "Authorities" form it.
It should be like this:
if let result = UserDefaults.standard.dictionary(forKey: "dict") {
print(result)
}
That's how you should "optional binding" the dictionary, thus (assumeing that "Authorities" is a [String: String]):
if let addresses = result["Authorities"] as? [String: String] {
print(addresses)
}
You could also do it as one step:
if let result = UserDefaults.standard.dictionary(forKey: "dict"),
let addresses = result["Authorities"] as? [String: String] {
print(result)
print(addresses)
let levelAccess = addresses["levelAccess"]
print(levelAccess) // optional
}
Finally, you could get the levelAcess from addresses as:
let levelAccess = addresses["levelAccess"]
Again, note that levelAccess would be an optional string (String?), which means you should also handle it.
For fetching a dictionary from UserDefaults, use
dictionary(forKey: key)
In your case:
var result = UserDefaults.standard.dictionary(forKey: "dict")
I have a class in my app, where the user inputs values and i set them to an instance of the class, then i upload this data to Database, but i have to convert the class to something the database accepts and i'm converting to dictionary using Mirror Reflection. Some properties in my class can be nil, because by design not all properties are required. But i can't pass nil values to the database.
I have recreated my example is very simplified playground. i didn't set a value for the name property of the class
I tried to check for nil before adding the key, value pair to the dictionary
Below is my code
import UIKit
class Color: NSObject {
var name: String?
var code: Int?
var shade: String?
}
let cl = Color()
cl.code = 3456
cl.shade = "DARK"
var colorDict = [String: Any]()
for x in Mirror(reflecting: cl).children.makeIterator() {
if let val = x.value as Any? {
print(type(of: val))
colorDict[x.label!] = val
}
}
print (colorDict)
the output in console is as below
Optional<String>
Optional<Int>
Optional<String>
["name": nil, "code": Optional(3456), "shade": Optional("DARK")]
how can i check for nil values and skip adding that property to the Dictionary
i have tried to loop through the dictionary after i add all values including nils and check for values too but i get the below warning
Comparing non-optional value of type 'Any' to nil always returns false
declaring the dictionary as below
var colorDict = [String: Any?]()
for x in colorDict {
if x.value == nil {
colorDict.removeValue(forKey: x.key)
}
}
removes the warning but it doesn't remove anything.
I would really appreciate your help.
The way of unwrapping objects of type Any that contain optionals is kind of weird but you can check that the values aren't nil in your mirror like this:
for x in Mirror(reflecting: cl).children {
if case Optional<Any>.some(let val) = x.value {
print(type(of: val))
colorDict[x.label!] = val
}
}
You can do this really easily in a one-liner, using filter:
let dict: [String : Any?] = ["Foo" : 3, "Bar" : nil, "Baz" : "Qux"]
let noNils = dict.filter { $0.value != nil }
print(noNils) // prints ["Foo": Optional(3), "Baz": Optional("Qux")]
As i have suggested, initialise all values.
If you decide not to store the nil values you will end up with children that some of them will have 1, some 2 and some 3 nodes, nothing wrong with that, BUT what happens when you go to read them?
You havent shared any info as to how these values will be used by the app, but assuming you have one function to read the properties/nodes of stored colors, it will go to read all 3 :
ref.child("colors").child("someSpecificColor").observeSingleEvent(of: .value, with: { (snapshot) in
// Get color values
let value = snapshot.value as? NSDictionary
let name = value?["name"] as? String ?? ""
let code = value?["code"] as? String ?? ""
let shade = value?["shade"] as? String ?? ""
// ...
}) { (error) in
print(error.localizedDescription)
}
See the issue?
Here is a simple solution :
var colorDict = [String: Any?]()
for x in Mirror(reflecting: cl).children.makeIterator() {
if let val = x.value, val != nil {
print(type(of: val))
colorDict[x.label!] = val
}
}
Here before to print and add you val, you check if the val is different than nil. As your output suggests in your console log you print :
Optional<String>
Optional<Int>
Optional<String>
val is an optional. So, if it's nil it won't be added. If not, you enter into the if statement and that's it.
So here I have a basic setup
var preferenceSpecification = [String : String?]()
preferenceSpecification["Key"] = "Some Key"
preferenceSpecification["Some Key"] = nil
preferenceSpecification["DefaultValue"] = "Some DefaultValue"
print(preferenceSpecification)
var defaultsToRegister = [String : String]()
if let key = preferenceSpecification["Key"], let defaultValueKey = preferenceSpecification["DefaultValue"] {
defaultsToRegister[key] = preferenceSpecification[defaultValueKey]!
}
But the error points out where it demands that I force unwrap this, to be like this:
defaultsToRegister[key!] = preferenceSpecification[defaultValueKey!]!
Which doesn't make sense, because keyValue and defaultValue already are unwrapped
When you extract a value from a dictionary like this using subscript
[String: String?]
you need to manage 2 levels of optional. The first one because the subscript returns an optional. The second one because the value of you dictionary is an optional String.
So when you write
if let value = preferenceSpecification["someKey"] {
}
you get value defined as an optional String.
Here's the code to fix that
if let
optionalKey = preferenceSpecification["Key"],
key = optionalKey,
optionalDefaultValueKey = preferenceSpecification["DefaultValue"],
defaultValueKey = optionalDefaultValueKey,
value = preferenceSpecification[defaultValueKey] {
defaultsToRegister[key] = value
}
Suggestions
You should avoid force unwrapping as much as possible. Instead you managed to put 3 ! on a single line!
You should also try to use better name for your constants and variables.
You could also define an extension which helps get rid of the double optional situation.
extension Dictionary where Value == Optional<String> {
func flattened(_ key: Key) -> Value {
if let value = self[key] {
return value
}
return nil
}
}
Usage: preferenceSpecification.flattened("someKey")
If I have a Dictionary returned from a NSNotification containing the following
print(notificationObj.object)
Optional({
age = "<null>";
names = (
David
);
})
Then the guard else is called when trying to assign this to a variable:
guard let categories = notificationObj.object as? [String:[String]] else {
// Gets to here
return
}
How can I handle the case where a Dictionary key is null.
Your dictionary does contain ...
Optional({
age = "<null>";
names = (
David
);
})
... and ...
age = ... is String = String (value is single String),
names = ( ... ) is String = [String] (value is array of Strings).
You can't cast it to [String:[String]] because the first pair doesn't fit this type. This is the reason why your guard statement hits else.
Hard to answer your question. Dictionary contains names, you want categories, names key does contain David, which doesn't look like category, ... At least you know why guard hits else.
Your questions is not very clear.
However IF
You have a dictionary declared as follow [String:[String]]
And you want manage the scenario where a given key is not present
Like this
let devices : [String:[String]] = [
"Computers": ["iMac", "MacBook"],
"Phones": ["iPhone 6S", "iPhone 6S Plus"]
]
Then you can at least 2 solutions
1. conditional unwrapping
if let cars = devices["Car"] {
// you have an array of String containing cars here
} else {
print("Ops... no car found")
}
2. guard let
func foo() {
guard let cars = devices["Car"] else {
print("Ops... no car found")
return
}
// you have an array of String containing cars here...
cars.forEach { print($0) }
}
It appears that your printed notificationObject.object is constructed from a JSON string that looks like this:
"{ \"age\": null, \"names\":[\"David\"] }"
The reason that you are hitting your else clause is because age is actually a nil, and not a valid String array. I tried using [String: [String]?] and [String: NSArray?] neither of which seem to work. The type is actually an NSNull (which inherits from NSObject).
So you can cast to [String: AnyObject] and check for NSArray like this:
if let categories = j as? [String: AnyObject] where (categories["age"] is NSArray) {
print("age was array")
} else {
print("age is probably null")
}
You might be better off if your notification object simply omitted the "age" property when the value is null. Then you would be able to cast to [String: [String]].