Delaying, cancelling or replacing a ASIFormDataRequest in a NSOperationQueue (for a searchbox)

I'm successfully making a ASIFormDataRequest using the below code.

    //get groups
    if (![self queue]) {
        [self setQueue:[[[NSOperationQueue alloc] init] autorelease]];
    }

    //make the url by appending the URL from the Constant class to the jsp name 
    NSURL *url = [NSURL URLWithString:[NSString stringWithFormat:@"%@/%@", URL, @"connectors/searchGroupsServlet.jsp"]];

    ASIFormDataRequest *request = [ASIFormDataRequest requestWithURL:url];
    [request addRequestHeader:@"User-Agent" value:USER_AGENT];
    [request addPostValue:[login username] forKey:@"username"];
    [request addPostValue:[login password] forKey:@"password"];
    [request addPostValue:[searchText lowercaseString] forKey:@"query"];
    [request addPostValue:GROUP_FILTER_LIMIT forKey:@"limit"];
    [request setDelegate:self];
    [reques开发者_开发问答t setDidFinishSelector:@selector(requestDone:)];
    [request setDidFailSelector:@selector(requestWentWrong:)];

This request is currently made on every key press a user makes in a searchbox (The text typed is sent off in the request as the search string). However, rather than sending the request on every key press, I want to delay the request by a second to allow users to type further characters into the searchbox before the request is sent.

I've successfully made a thread that waits a second as users continue to type (although admittedly Im not convinced this is the best way to do it yet, but it works for now)...

this

[self performSelectorInBackground:@selector(wait:) withObject:request];

calls this

-(void)wait:(NSString *)request
{
    [NSThread sleepForTimeInterval:1.00];
    [[self queue] addOperation:request]; //queue is an NSOperationQueue
}

but, if a user continues to type, I haven't managed to work out how to cancel the request or not put the request in the queue, or empty the queue and replace it with the new request.

Finally, obviously I could force users to wait until they have pressed the 'search' button on the pop-up keyboard, but I was hoping to provide search results without that.

Thanks

The answer was to create an NSTimer, and invalidate it whenever a new key press had been made. Then start it again.

[timer invalidate];

You can try this to cancel

+ (void)cancelPreviousPerformRequestsWithTarget:(id)aTarget selector:(SEL)aSelector object:(id)anArgument