How to add nil value to Swift Dictionary?
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??
.
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"}
You can use the updateValue
method:
postDict.updateValue(nil, forKey: surname)
postDict[surname] = Optional<AnyObject>(nil)