System Alerts

System Alerts Calling Methods

System alerts, such as “Low battery, 20% of battery remaining” will call the following methods:

applicationWillResignActive called before the alert comes up

applicationDidBecomeActive called after the alert is dismissed

A typical problem is if you use applicationDidBecomeActive to detect your app starting up from a suspended state (from multitasking).  To solve this use applicationWillEnterForeground (which isn’t called after a system alert), or if you need a ‘did’ rather than a ‘will’ method then you can use this approach:

- (BOOL)application:(UIApplication *)application didFinishLaunchingWithOptions:(NSDictionary *)launchOptions
{
	...
	ThisIsAppStartup = YES;
}
- (void)applicationWillEnterForeground:(UIApplication *)application
{
	ThisIsAppStartup = YES;
}
- (void)applicationDidBecomeActive:(UIApplication *)application
{
	if (ThisIsAppStartup)		//Don't do if we're just returning from a system alert like low battery
	{
		//We are here after didFinishLaunchingWithOptions and applicationWillEnterForeground
		ThisIsAppStartup = NO;
		...
	}
}