How to throttle search (based on typing speed) in iOS UISearchBar?

Try this magic:

- (void)searchBar:(UISearchBar *)searchBar textDidChange:(NSString *)searchText{
    // to limit network activity, reload half a second after last key press.
    [NSObject cancelPreviousPerformRequestsWithTarget:self selector:@selector(reload) object:nil];
    [self performSelector:@selector(reload) withObject:nil afterDelay:0.5];
}

Swift version:

 func searchBar(searchBar: UISearchBar, textDidChange searchText: String) {
    // to limit network activity, reload half a second after last key press.
      NSObject.cancelPreviousPerformRequestsWithTarget(self, selector: "reload", object: nil)
      self.performSelector("reload", withObject: nil, afterDelay: 0.5)
 }

Note this example calls a method called reload but you can make it call whatever method you like!

Thanks to this link, I found a very quick and clean approach. Compared to Nirmit's answer it lacks the "loading indicator", however it wins in terms of number of lines of code and does not require additional controls. I first added the dispatch_cancelable_block.h file to my project (from this repo), then defined the following class variable: __block dispatch_cancelable_block_t searchBlock;.

My search code now looks like this:

- (void)searchBar:(UISearchBar *)searchBar textDidChange:(NSString *)searchText
{
    if (searchBlock != nil) {
        //We cancel the currently scheduled block
        cancel_block(searchBlock);
    }
    searchBlock = dispatch_after_delay(searchBlockDelay, ^{
        //We "enqueue" this block with a certain delay. It will be canceled if the user types faster than the delay, otherwise it will be executed after the specified delay
        [self loadPlacesAutocompleteForInput:searchText]; 
    });
}

Notes:

• The loadPlacesAutocompleteForInput is part of the LPGoogleFunctions library

• searchBlockDelay is defined as follows outside of the @implementation:

  static CGFloat searchBlockDelay = 0.2;

Improved Swift 4+:

Assuming that you are already conforming to UISearchBarDelegate, this is an improved Swift 4 version of VivienG's answer:

func searchBar(_ searchBar: UISearchBar, textDidChange searchText: String) {
    NSObject.cancelPreviousPerformRequests(withTarget: self, selector: #selector(self.reload(_:)), object: searchBar)
    perform(#selector(self.reload(_:)), with: searchBar, afterDelay: 0.75)
}

@objc func reload(_ searchBar: UISearchBar) {
    guard let query = searchBar.text, query.trimmingCharacters(in: .whitespaces) != "" else {
        print("nothing to search")
        return
    }
    
    print(query)
}

The purpose of implementing cancelPreviousPerformRequests(withTarget:) is to prevent the continuous calling to the reload() for each change to the search bar (without adding it, if you typed "abc", reload() will be called three times based on the number of the added characters).

The improvement is: in reload() method has the sender parameter which is the search bar; Thus accessing its text -or any of its method/properties- would be accessible with declaring it as a global property in the class.

For people who need this in Swift 4 onwards:

Keep it simple with a DispatchWorkItem like here.

---

or use the old Obj-C way:

func searchBar(searchBar: UISearchBar, textDidChange searchText: String) {
    // to limit network activity, reload half a second after last key press.
    NSObject.cancelPreviousPerformRequestsWithTarget(self, selector: "reload", object: nil)
    self.performSelector("reload", withObject: nil, afterDelay: 0.5)
}

EDIT: SWIFT 3 Version

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)
}
@objc func reload() {
    print("Doing things")
}