Question

The title says multiple button presses, but actually I’m looking to stack multiple events. I have a chat application that can receive many chat messages at once. In my messageReceived function, I would like to scroll to the bottom of the most recent chats. The problem I’m having is that sometimes many messages (50+) can come in at the same time. I’ve determined that scrolling to the bottom is a huge performance bottle neck if performed 50 times, but works great if only performed after messages are received.

I’d like scroll to the bottom after a delay, say 0.1 seconds, in my messageReceived function. But I’d like all new chat messages that occur within this 0.1 seconds to “stack”, and only issue a single scroll to bottom request.

I think that a system of setting and canceling timers would work for this, however I can’t get it right. Is there a better way to make this happen! thanks!

Answer 1

If you are setting your delayed “scroll to the bottom” request with something like

[[self myObject] performSelector:@selector(scrollToBottom:) 
                      withObject:nil 
                      afterDelay:0.1];  

then you can use a cancel command like

[NSObject cancelPreviousPerformRequestsWithTarget:[self myObject]
                                        selector:@selector(scrollToBottom:)
                                      object:nil];  

then the only time your scrollToBottom: gets called is when it doesn’t get cancelled (so, the last time in the bunch). Now you don’t need a timer.