Swift Snippet: NSTimer Block Extension

November 19, 2015

Schedule a block on a timer using a method similar to the standard SDK. I think it looks cleaner, and more obvious, when used in the code than the original target-action invocation.

The scheduled block is retained by the TimerBlock instance wrapping it, which is in its place retained by the NSTimer scheduler until the timer is fired.

import Foundation


extension NSTimer {
    
    class func scheduledTimerWithTimeInterval(
        timeInterval: NSTimeInterval, userInfo: AnyObject?, repeats: Bool, block: (timer: NSTimer) -> Void) -> NSTimer
    {
        let minion = TimerBlock(block: block)
        // The `minion` will be retained by the `NSTimer` as its `target`, until the timer is invalidated.
        return NSTimer.scheduledTimerWithTimeInterval(
            timeInterval, target: minion, selector: Selector("timerDidFire:"), userInfo: userInfo, repeats: repeats)
    }
}


final class TimerBlock: NSObject {
    
    private let block: (timer: NSTimer) -> Void
    
    init(block: (timer: NSTimer) -> Void) {
        self.block = block
    }
    
    func timerDidFire(timer: NSTimer) {
        block(timer: timer)
    }
}

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