Delayed search in swift iOS app

Question

I have UITextField for entering search string and UITableView with results. What i want is to run search function when user entered more than 3 letters and it at least 0,5 sec passed since last symbol added to UITextView.

I found (Detect when user stopped / paused typing in Swift) function and I added it to my ViewController that have class SearchVC and method server_search

func textField(_ textField: UITextField, shouldChangeCharactersIn range: NSRange, replacementString string: String) -> Bool {
    NSObject.cancelPreviousPerformRequests(
        withTarget: self,
        selector: #selector(SearchVC.server_search),
        object: textField)
    self.perform(
        #selector(SearchVC.server_search),
        with: textField,
        afterDelay: 0.5)
    return true
}

But nothing happens.

Answer 1

While using a Timer is still a valid answer, since Swift 3, you can use a DispatchWorkItem…

var workItem: DispatchWorkItem?

func textField(_ textField: UITextField, shouldChangeCharactersIn range: NSRange, replacementString string: String) -> Bool {

    // Cancel any outstanding search
    self.workItem?.cancel() 

    guard let text = textField.text, let textRange = Range(range, in: text) else {
        return true
    }

    let updatedText = text.replacingCharacters(in: textRange, with: string)

    guard updatedText.count >= 3 else { 
        return true
    }

    // Set up a DispatchWorkItem to perform the search
    let workItem = DispatchWorkItem { [weak self] in
        self?.performSearch(updatedText)
    }

    // Run this block after 0.5 seconds
    DispatchQueue.main.asyncAfter(deadline: .now() + 0.5, execute: workItem)

    // Keep a reference to it so it can be cancelled
    self.workItem = workItem 

    return true   
}

func performSearch(_ text: String) {

} 

Answer 2

The use of Timers have some advantages. With your implementation you would cancel all the performs in for your object, which is something that may go out of control.

A Timer, instead, lets you fine grain control it. See the following implementation:

var searchTimer: Timer?
func textField(_ textField: UITextField, shouldChangeCharactersIn range: NSRange, replacementString string: String) -> Bool {
    // Invalidate remove the previous timer, since it's optional if the previous timer is already cancelled or nil, it won't affect execution
    searchTimer?.invalidate()
    searchTimer = Timer.scheduledTimer(withTimeInterval: 0.5, repeats: false, block: { (timer) in
        //do Something crazy
        self.server_search()
    })
    return true
}