How to append elements into a dictionary in Swift?

swift nsdictionary
Dharmesh Kheni picture Dharmesh Kheni · Dec 5, 2014 · Viewed 304.5k times · Source

I have a simple Dictionary which is defined like:

var dict : NSDictionary = [ 1 : "abc", 2 : "cde"]

Now I want to add an element into this dictionary: 3 : "efg"

How can I append 3 : "efg" into this existing dictionary?

Answer

Antonio picture Antonio · Dec 5, 2014

You're using NSDictionary. Unless you explicitly need it to be that type for some reason, I recommend using a Swift dictionary.

You can pass a Swift dictionary to any function expecting NSDictionary without any extra work, because Dictionary<> and NSDictionary seamlessly bridge to each other. The advantage of the native Swift way is that the dictionary uses generic types, so if you define it with Int as the key and String as the value, you cannot mistakenly use keys and values of different types. (The compiler checks the types on your behalf.)

Based on what I see in your code, your dictionary uses Int as the key and String as the value. To create an instance and add an item at a later time you can use this code:

var dict = [1: "abc", 2: "cde"] // dict is of type Dictionary<Int, String>
dict[3] = "efg"

If you later need to assign it to a variable of NSDictionary type, just do an explicit cast:

let nsDict = dict as! NSDictionary

And, as mentioned earlier, if you want to pass it to a function expecting NSDictionary, pass it as-is without any cast or conversion.

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