Swift：类型的值没有成员“ peformSelector”

Question

I'm trying to implement protocol/delegate using performSelector but I'm getting this error:

Value of type 'DoingSomething' has no member 'peformSelector'

Here is my implementation:

import UIKit
protocol DoingSomethingDelegate {
    // delegate function
}

class DoingSomething {
    func goDoSomething()  
        self.performSelector(onMainThread: #selector(self.processSomething()), with: nil, waitUntilDone: true)
    }
    func processSomething() {

        print("I'm done")
    }
}

But if I move the functions to the viewController I have no errors. Any of you knows why of the error or how can I fix this error?

I'll really appreciate your help.

Answer 1

Per @dan comment I made the changes:

class DoingSomething:NSObject {

    func goDoSomething()  {

        self.performSelector(onMainThread: #selector(self.processSomething), with: nil, waitUntilDone: true)
    }

    func processSomething() {

        print("I'm done")
    }
}

Now is working!

Answer 2

As @vandian suggests in his comment, you should think about using GCD instead. The equivalent code would be:

DispatchQueue.main.async {
  self.processSomething()
}

There are a couple of advantages to using async(). You can provide the code in-line without having to write a separate function, which makes it easier to read and maintain; The closure you execute has access to the enclosing scope, so you can use variables from your function inside that code, eg:

func localScopeFunc {
  var x: Int = 6
  DispatchQueue.main.async {
    //This block of code has access to the local variables from localScopeFunc
    print("x = \(x)")
  }
}

With performSelector() and it's variants you can only invoke functions with zero, one, or 2 arguments, and those arguments must be NSObjects .

Forcing an object to be a subclass of NSObject also has some minor down-sides to it. That forces the compiler to use dynamic dispatching, which is slightly slower than the static dispatching that Swift uses.