Creating threads in swift?

Question

I am trying to spawn a thread in swift. So I have this line:

. . .

let thread = NSThread(target: self, selector: doSomething(), object: nil)

. . .

doSomething is a function within the scope of the class.

That line gives this error: "could not find an overload for init() that accepts the supplied arguments"

What am I missing here? Ho can I create a new thread in swift?

Gardia

Answer 1

As of Xcode 7.3 and Swift 2.2, you can use the special form #selector(...) where Objective-C would use @selector(...):

let thread = NSThread(target:self, selector:#selector(doSomething), object:nil)

Leekgreen

How would you do it if doSomething required an argument (say of type NSString)? – Pictorial

That is what the object argument is for. – Leekgreen

I tried that, but I keep getting an NSInvalidArgumentException: [NSThread initWithTarget:selector:object:]: target does not implement selector. It apparently doesn't recognize my function name. (Should I post this as a new question?) – Pictorial

If the selector takes an argument then it must end with a colon. Example: NSThread(target:self, selector:"doSomethingWithObject:", object:someObject) – Leekgreen

@Pictorial Make sure that your target class inherits from NSObject. – Irrespective

@Irrespective doesn't every class automatically inherit from NSObject? – Pictorial

@Pictorial Possibly not. I had the same problem that you mentioned above. I could only solve it by letting my class inherit from NSObject. To my excuse I should mention that this was my first try with Swift though... – Irrespective

No, classes don't inherit from NSObject by default. If you make a subclass of anything in the Cocoa Touch frameworks, it will inherit NSObject indirectly. Otherwise, in Swift, you need to explicitly inherit from NSObject, or declare your class @objc, in order to use it with NSThread. – Leekgreen

In Swift 2.2, you now use #selector(doSomething). – Centrist

Answer 2

NSThread takes a selector as it's second parameter. You can describe Objective-C selectors as Strings in Swift like this:

let thread = NSThread(target: myObj, selector: "mySelector", object: nil)

Swift functions aren't equivalent objective-c methods though. If you have a method in a swift class, you can use it as a selector if you use the @objc attribute on the class:

@objc class myClass{
    func myFunc(){
    }
}

var myObj = myClass()
let thread = NSThread(target: myObj, selector: "myFunc", object: nil)

Torrez

Answer 3

1. When we call a selector on a target, we should check if the target exists and it responds to the selector. Only class that extend from NSObject or it's subclasses can use respondsToSelector:

2. You can use a NSDictionary to store parameters if you have more than 2 parameters.

   Ex:

   //this code is in Objective-C but the same code should exist in Swift
   
   NSDictionary *params = [NSDictionary dictionaryWithObjectsAndKeys:object1, @"key1", object2, @"key2",nil]; 
   

then pass 'params' to parameter of selector:

Extract