如何检测 UISearchBar/UITextField 输入中的暂停？

我有以下 UISearchbar 代码：

- (void)searchBar:(UISearchBar *)searchBar textDidChange:(NSString *)searchText
{
    [UIApplication sharedApplication].networkActivityIndicatorVisible = YES;
    NSString* endpoint =[NSString stringWithFormat:@"http://www.someurl/",
                         [searchText stringByReplacingOccurrencesOfString:@" " withString:@"+"]];
    NSURL* url = [NSURL URLWithString:endpoint];
    NSURLRequest* request = [NSURLRequest requestWithURL:url];
    GTMHTTPFetcher* myFetcher = [GTMHTTPFetcher fetcherWithRequest:request];
    [myFetcher beginFetchWithDelegate:self didFinishSelector:@selector(searchResultsFetcher:finishedWithData:error:)];
}

我想在输入暂停后发送此请求，并在每次击中角色时重置计时器。我怎样才能做到这一点？

它不必使用 NSTimer。

- (void)searchBar:(UISearchBar *)searchBar textDidChange:(NSString *)searchText
        {
           [NSObject cancelPreviousPerformRequestsWithTarget:self selector:@selector(request) object:nil];

          //.....

           [self performSelector:@selector(request) withObject:nil afterDelay:yourpausetime];

        }