In Swift, how do you check if an object (AnyObject) is a String?

Question

Tried using:

obj.isKindOfClass(String)

But it says Type 'String' does not conform to protocol 'AnyObject'

So how can you tell if an object is a string or not?

The context of this question is the UIActivity method, prepareWithActivityItems, in which I need to save the activity item, but if there are multiple activity items, how do you figure out which is which?

Answer 1

Check:

obj is String // true or false

Convert:

obj as? String // nil if failed to convert

Optional binding:

if let str = obj as? String {
    // success
} else {
    // fail
}

Answer 2

I'm going to go off on a bit of a tangent so you understand what is going on.

Strings are not objects in swift. !!!

Kinda. ???

Because of the way toll-free bridging works... if you import the Objective-C runtime then you can treat strings as an object... check this out:

This code will not compile at all:

// Playground - noun: a place where people can play

// import Foundation

var foo: AnyObject = "hello"
                     ^ Type 'String' does not conform to protocol 'AnyObject'

But if I uncomment the Foundation framework, then it compiles perfectly fine, because we're activating bridging between String and NSString:

// Playground - noun: a place where people can play

import Foundation

var foo: AnyObject = "hello" // We're all good here!

And if you want to check if foo is a string... you can do this:

import Foundation

var foo: AnyObject = "hello"

foo.isKindOfClass(NSString) // this returns true

So... string is not an object but if you treat it as one it will be converted into an NSString and now it is an object. But you can't check if an object belongs to the String class, because there is no such thing as a String object. You have to use NSString.

Of course, you should still be doing what Scott said in his answer, by using the is or as? keywords.