添加观察者UITableViewController的条形按钮？

Question

I have a ViewController that starts a number of NSTimers . I add each of these NSTimers as an observer to UIApplicationDidEnterBackgroundNotification so that I can stop them if the application goes into the background. Works well.

[[NSNotificationCenter defaultCenter]
addObserver:anotherTimer
selector:@selector(goBackground)
name:UIApplicationDidEnterBackgroundNotification
object:nil];

....

- (void) goBackground {
    [[NSNotificationCenter defaultCenter] removeObserver:self];
    [self invalidate];
}

Here's the problem: I also have subclassed UITableViewController to add a Bar Button ("I" for information) to each of my ViewControllers. The Bar Button opens another ViewController which shows information about the app. Just like when the app goes into the background, I want all the NSTimers to stop when the user taps the Bar Button.

Is there a way to make the NSTimers observers of when the user taps the Bar Button or when the ViewController exits?

Answer 1

The answer was much easier than I thought. The correct way to do this is to create a new notification with an arbitrary name (eg, "infoButtonTapped") and add all NSTimers as an observer to that notification. The notification calls the same method as the notification sent when the application goes into the background ("goBackground"):

[[NSNotificationCenter defaultCenter]
addObserver:aTimer
selector:@selector(goBackground)
name:@"infoButtonTapped"
object:nil];

The method called when the user taps the info Bar Button posts the notification with the same name:

[[NSNotificationCenter defaultCenter] postNotificationName:@"infoButtonTapped" object:self];

Then all the NSTimers' goBackground methods will be called when the info Bar Button is pressed.

Note that I created a Category for NSTimer which includes setObservers, removeObservers, and goBackground methods which handle the notifications work very nicely.

I should also note that whenever one of the NSTimers is invalidated (whether in goBackground or elsewhere), it must first be removed as an observer to all notifications:

[aTimer removeObservers];
[aTimer invalidate];

Otherwise, the app will crash when one of these notifications is sent...