Live search throttle in Swift 3

Question

I'm trying to live search at my PHP API with Swift. Until now i've done this thing.

 var filteredData = [Products]()


 func getSearch(completed: @escaping DownloadComplete, searchString: String) {

        let parameters: Parameters = [
            "action" : "search",
            "subaction" : "get",
            "product_name"  : searchString,
            "limit" : "0,30"
        ]
        Alamofire.request(baseurl, method: .get, parameters: parameters).responseJSON { (responseData) -> Void in
            if((responseData.result.value) != nil) {
                let result = responseData.result

                if let dict = result.value as? Dictionary<String, AnyObject>{
                    if let list = dict["products_in_category"] as? [Dictionary<String, AnyObject>] {
                        if self.filteredData.isEmpty == false {
                            self.filteredData.removeAll()
                        }
                        for obj in list {
                            let manPerfumes = Products(productDict: obj)
                            self.filteredData.append(manPerfumes)
                        }
                    }
                }
                completed()
            }
        }
    }


extension SearchViewController: UISearchResultsUpdating {

    func updateSearchResults(for searchController: UISearchController) {

        if (searchController.searchBar.text?.characters.count)! >= 3 {
                    self.getSearch(completed: {
                    self.searchResultTable.reloadData()

                    self.searchResultTable.setContentOffset(CGPoint.zero, animated: true)
                }, searchString: searchController.searchBar.text!)


        } else {
            self.searchResultTable.reloadData()
        }


    }
}

And the table view is being updated with the filteredData. How can i throttle the search so lets say when the user writes

"example" -> shows the results with example
then he erase the "le" -> 
"examp" -> if the previous request is not completed, cancel it -> make request for "examp" and show the data in table view!

P.S. from another answer i found

func searchBar(searchBar: UISearchBar, textDidChange searchText: String) {
    // to limit network activity, reload half a second after last key press.
    NSObject.cancelPreviousPerformRequests(withTarget: self, selector: #selector(self.reload), object: nil)
    self.perform(#selector(self.reload), with: nil, afterDelay: 0.5)
}
func reload() {
    print("Doing things")
}

Although if I try to replace "self.reload" with my function, I get an error cannot convert value of type () to expected argument type selector

Association

how did you replace the self.reload function into the cancelPreviousPerformRequests selector parameter? It seems like you forgot to put that function in #selector? – Gormandize

Because if I try doing it like this, I get the same error as you did: NSObject.cancelPreviousPerformRequests(withTarget: self, selector: self.fetchFriends(user:completion:), object: nil). Notice how I didn't add the #selector into my function? – Gormandize

@rockyraccoon still the same error! – Association

well, I tried replicating what you're trying to accomplish and I get no errors: func searchBar() { NSObject.cancelPreviousPerformRequests(withTarget: self, selector: #selector(self.getSearch(completed:searchString:)), object: nil) perform(#selector(self.getSearch(completed:searchString:)), with: nil, afterDelay: 0.5) } – Gormandize

@rockyraccoon ok this is error free! you where right. Although in perform, how can i pass string to the function? – Association

that's what worried me lol. But I just found a function for that. Try to use this function: func perform(_ aSelector: Selector!, with object1: Any!, with object2: Any!). This is in the docs, or you can auto complete it to see it. – Gormandize

Answer 1

Your error was because you probably forgot the #selector() part.

Here's how it should look:

func searchBar() { 
    NSObject.cancelPreviousPerformRequests(withTarget: self,    
                                           selector: #selector(self.getSearch(completed:searchString:)), 
                                           object: nil) 

    perform(#selector(self.getSearch(completed:searchString:)), 
            with: nil, afterDelay: 0.5) }

You get the error because you didn't enclose your function in #selector

Now, as for the arguments, here's a function for that:

perform(#selector(getSearch:completion:searchString), with: <some completion>, with: "search string")

Gormandize

And if i would like to add timeinterval is not possible :( – Association

You can do that. BUT, if you notice on autocomplete, there's a function that has timeInterval, except it only has one parameter to put it in your argument. My idea was, you can extend the class to add more arguments, but I feel that's a bit too much. Perhaps you should ask another question pertaining to this certain issue:) – Gormandize

your answer is correct for this issue! I open another one! – Association

#42446368 – Association

Answer 2

Use DispatchWorkItem with Swift 4 !

// Add a searchTask property to your controller
var searchTask: DispatchWorkItem?


// then in your search bar update method

// Cancel previous task if any
self.searchTask?.cancel()

// Replace previous task with a new one
let task = DispatchWorkItem { [weak self] in
    self?.sendSearchRequest() 
}
self.searchTask = task

// Execute task in 0.75 seconds (if not cancelled !)
DispatchQueue.main.asyncAfter(deadline: DispatchTime.now() + 0.75, execute: task)

Hope it helps !

Clew

FYI, Cancellation does not affect the execution of a work item that has already begun. according to developer.apple.com/documentation/dispatch/dispatchworkitem/… – Malfeasance

Answer 3

• disclaimer: I am a writer.

Throttler could be the right tool to get it done.

You can do debounce and throttle without going reactive programming using Throttler like,

import Throttler

// advanced debounce, running a first task immediately before initiating debounce.

for i in 1...1000 {
    Throttler.debounce {
        print("debounce! > \(i)")
    }
}

// debounce! > 1
// debounce! > 1000


// equivalent to debounce of Combine, RxSwift.

for i in 1...1000 {
    Throttler.debounce(shouldRunImmediately: false) {
        print("debounce! > \(i)")
    }
}

// debounce! > 1000

Throttler also can do advanced debounce, running a first event immediately before initiating debounce that Combine and RxSwift don't have by default.

You could, but you may need a complex implementation yourself for that.

Outlandish