How to add nil value to Swift Dictionary?

Question

I have made a request to my server in my app. And posted data something like this.Server side is waiting for all parameters even they are nil. But i couldn't add nil values to dictionary.

 var postDict = Dictionary<String,AnyObject>
 postDict[pass]=123
 postDict[name]="ali"
 postDict[surname]=nil // dictionary still has only pass and name variables.

Is there a way to add nil value to dictionary ?

Answer 1

How to add nil value to Swift Dictionary?

Basically the same way you add any other value to a dictionary. You first need a dictionary which has a value type that can hold your value. The type AnyObject cannot have a value nil. So a dictionary of type [String : AnyObject] cannot have a value nil.

If you had a dictionary with a value type that was an optional type, like [String : AnyObject?], then it can hold nil values. For example,

let x : [String : AnyObject?] = ["foo" : nil]

If you want to use the subscript syntax to assign an element, it is a little tricky. Note that a subscript of type [K:V] has type V?. The optional is for, when you get it out, indicating whether there is an entry for that key or not, and if so, the value; and when you put it in, it allows you to either set a value or remove the entry (by assigning nil).

That means for our dictionary of type [String : AnyObject?], the subscript has type AnyObject??. Again, when you put a value into the subscript, the "outer" optional allows you to set a value or remove the entry. If we simply wrote

x["foo"] = nil

the compiler infers that to be nil of type AnyObject??, the outer optional, which would mean remove the entry for key "foo".

In order to set the value for key "foo" to the AnyObject? value nil, we need to pass in a non-nil outer optional, containing an inner optional (of type AnyObject?) of value nil. In order to do this, we can do

let v : AnyObject? = nil
x["foo"] = v

or

x["foo"] = nil as AnyObject?

Anything that indicates that we have a nil of AnyObject?, and not AnyObject??.

Answer 2

You can use the updateValue method:

postDict.updateValue(nil, forKey: surname)

Answer 3

As documented in here, setting nil for a key in dictionary means removing the element itself.

If you want null when converting to JSON for example, you can use NSNull()

var postDict = Dictionary<String,AnyObject>()
postDict["pass"]=123
postDict["name"]="ali"
postDict["surname"]=NSNull()

let jsonData = NSJSONSerialization.dataWithJSONObject(postDict, options: NSJSONWritingOptions.allZeros, error: nil)!
let jsonString = NSString(data: jsonData, encoding: NSUTF8StringEncoding)!
// -> {"pass":123,"surname":null,"name":"ali"}

Answer 4

postDict[surname] = Optional<AnyObject>(nil)

Answer 5

Below dictionary will hold one key with nil value

var dict = [String:Any?]()
dict["someKey"] = nil as Any?

Answer 6

You can use the Optional type

var postDict = ["pass": 123, "name": "ali", "surname": Optional()]

Answer 7

To add a nil value to a dictionary in Swift, your dictionary's values must be of the Optional type.

Consider a Person class:

class Person {
    let name: String
    weak var spouse: Person?

    init(name: String, spouse: Person?) {
        self.name = name
        self.spouse = spouse
    }
}

Instances of the Person type can have a name and an optional spouse. Create two instances, and add the first to a dictionary:

let p1 = Person(name: "John", spouse: nil)
let p2 = Person(name: "Doe", spouse: p1)
p1.spouse = p2
var people = [p1.name: p1.spouse]

This dictionary (called people) maps names to spouses, and is of type [String: Person?]. You now have a dictionary with a value of Optional type: Person?.

To update the value of the key p1.name to be nil, use the updateValue(_: forKey:) method on the Dictionary type.

people.updateValue(nil, forKey: p1.name)
people[p1.name] 

The value for the key p1.name is now nil. Using updateValue(_: forKey:) is a bit more straightforward in this case because it doesn't involve making a throwaway instance, setting it to nil, and assigning that instance to a key in a dictionary.

NB: See rintaro's answer for inserting null into a post's dictionary.

Answer 8

var dict = [Int:Int?]()

dict[0] = (Int?).none // <--- sets to value nil

dict[0] = nil         // <-- removes

dict[0] = .none       // <-- same as previous, but more expressive

switch dict[0] {
case .none:
    Swift.print("Value does not exist")

case .some(let value):
    if let value = value {
        Swift.print("Value exists and is", value)
    } else {
        Swift.print("Value exists and is nil")
    }
}

Answer 9

postDict[surname]=nil

When you use subscript to set nil. It deletes the key if exists. In this case key surname will be removed from dictionary if exists.

To set value as nil, there are certain ways.

postDict.updateValue(nil, forKey: surname)

or

let anyObjectNil : AnyObject? = nil
postDict[surname] = anyObjectNil

or

postDict[surname] = nil as AnyObject?