Coalesce or otherwise fire methods "every so often"? - ios

Question

The server that provides data to my app recently added a feature that allows you do to basic logging like "user selected logo" or "user is quitting".
The only place I'd like to use this is in a page with several sliders that does a calculation on the input values. This is continuous, it re-calculates the output as you move the sliders around.
Which leaves me the problem of when to call this logging method. I don't want to call it every time the numbers change, or I'll murder the server. I could put a "Calculate now" button, but that kills the entire mode-less UI I like.
Is there a way that I can coalesce calls so all the calls made within, say, 5 seconds, results in only one call to the work method? I'd also have to force the method to fire if the user does something else, like navigates away or quits the app.

Answer 1

You can easily add an NSTimer to the IBAction method you have for your slider. Every time that method is called, invalidate the timer and start it again. Put the analytics call in the timer's action method, which will only be called when the timer can actually complete.
For example:
#interface ViewController ()
#property (nonatomic) NSTimer *actionTimer;
#end
#implementation ViewController
- (IBAction)sliderChanged:(UISlider *)sender
{
[self.actionTimer invalidate];
NSLog(#"Slider value: %f", sender.value);
self.actionTimer = [NSTimer scheduledTimerWithTimeInterval:2
target:self
selector:#selector(timerCompleted)
userInfo:nil
repeats:NO];
}
- (void)timerCompleted
{
NSLog(#"Timer completed.");
}
#end

Answer 2

How about a background thread that observes the calculated value and fires an update by scheduling a block on a background thread when the output value is stable, like
[[NSNotificationCenter defaultCenter] addObserver:self
selector:#selector(showValue:)
name:#"showValue"
object:nil];
You can also schedule the block in viewWillDisappear for the leaving the view and (I think) quit events.