How can I debounce a method call?

Question

I\'m trying to use a UISearchView to query google places. In doing so, on text change calls for my UISearchBar, I\'m making a request to google pla

Answer 1

Swift 3 version

1. Basic debounce function

func debounce(interval: Int, queue: DispatchQueue, action: @escaping (() -> Void)) -> () -> Void {
    var lastFireTime = DispatchTime.now()
    let dispatchDelay = DispatchTimeInterval.milliseconds(interval)

    return {
        lastFireTime = DispatchTime.now()
        let dispatchTime: DispatchTime = DispatchTime.now() + dispatchDelay

        queue.asyncAfter(deadline: dispatchTime) {
            let when: DispatchTime = lastFireTime + dispatchDelay
            let now = DispatchTime.now()
            if now.rawValue >= when.rawValue {
                action()
            }
        }
    }
}

2. Parameterized debounce function

Sometimes it's useful to be have the debounce function take a parameter.

typealias Debounce = (_ : T) -> Void

func debounce(interval: Int, queue: DispatchQueue, action: @escaping Debounce) -> Debounce {
    var lastFireTime = DispatchTime.now()
    let dispatchDelay = DispatchTimeInterval.milliseconds(interval)

    return { param in
        lastFireTime = DispatchTime.now()
        let dispatchTime: DispatchTime = DispatchTime.now() + dispatchDelay

        queue.asyncAfter(deadline: dispatchTime) {
            let when: DispatchTime = lastFireTime + dispatchDelay
            let now = DispatchTime.now()

            if now.rawValue >= when.rawValue {
                action(param)
            }
        }
    }
}

3. Example

In the following example you can see, how the debouncing works, using a string parameter to identify the calls.

let debouncedFunction = debounce(interval: 200, queue: DispatchQueue.main, action: { (identifier: String) in
    print("called: \(identifier)")
})

DispatchQueue.global(qos: .background).async {
    debouncedFunction("1")
    usleep(100 * 1000)
    debouncedFunction("2")
    usleep(100 * 1000)
    debouncedFunction("3")
    usleep(100 * 1000)
    debouncedFunction("4")
    usleep(300 * 1000) // waiting a bit longer than the interval
    debouncedFunction("5")
    usleep(100 * 1000)
    debouncedFunction("6")
    usleep(100 * 1000)
    debouncedFunction("7")
    usleep(300 * 1000) // waiting a bit longer than the interval
    debouncedFunction("8")
    usleep(100 * 1000)
    debouncedFunction("9")
    usleep(100 * 1000)
    debouncedFunction("10")
    usleep(100 * 1000)
    debouncedFunction("11")
    usleep(100 * 1000)
    debouncedFunction("12")
}

Note: The usleep() function is only used for demo purposes and may not be the most elegant solution for a real app.

Result

You always get a callback, when there is an interval of at least 200ms since the last call.

called: 4
called: 7
called: 12