From Stackoverflow

Question:
In Objective C it was simple: it was sufficient to update the main.m file and change the UIApplicationMain() parameters

return UIApplicationMain(argc, argv, NSStringFromClass([CustomUIApplication class]), NSStringFromClass([AppDelegate class]));

But in swift there is no main.m file, since the guide says

“Code written at global scope is used as the entry point for the program, so you don’t need a main function.”

So, how to subclass UIApplication in swift?? Any suggestion?

Answer:

Ok, I’ve found the solution First, I’ve noticed that, at the top of the AppDelegate.swift file, there is this line

@UIApplicationMain

Since this line is outside any scope (it’s at file level), it’s executed immediately, and I assume that the compiler translate it in a standard main function.

So, I did this, starting from a new Swift-Only application:

– commented out @UIApplicationMain
– added a main.swift file like this (FLApplication is my subclass).

IMPORTANT the file MUST BE NAMED main.swift, since top level statements are not supported on other files! You can’t add the UIApplicationMain() call inside any other file, otherwise you’ll receive this error:
“Expressions are not allowed at the top level”

This is the main.swift file .

import Foundation
import UIKit

UIApplicationMain(C_ARGC, C_ARGV, NSStringFromClass(FLApplication), NSStringFromClass(AppDelegate))

create a swift file for the UIApplication subclass, FLApplication.swift, with this code:

import UIKit
import Foundation

class FLApplication: UIApplication
{
    override func sendEvent(event: UIEvent!)
    {
        println("send event") // this is an example
        // ... dispatch the message...
    }
}

now, UIApplication is correctly subclassed and you’ll see the “send event” messages in the log