CRITICAL BUG FIX: today's date and iOS 4.0 multitasking.

Root cause: If an application using Kal is suspended in the background for an extended period of time (specifically, crossing the midnight threshold), when the app is resumed, Kal will still think that "today" has not changed. In my original implementation, I had naively assumed that the app would never be used for such an extended period of time, but iOS 4.0 multitasking makes my assumption invalid.

Solution: Listen for the UIApplicationSignificantTimeChangeNotification from the OS and respond appropriately by recaching today's date and refreshing the UI.

src/KalDate.m

@@ -8,12 +8,24 @@
 
 static KalDate *today;
 
+
+@interface KalDate ()
++ (void)cacheTodaysDate;
+@end
+
+
 @implementation KalDate
 
 + (void)initialize
 {
+  [[NSNotificationCenter defaultCenter] addObserver:self selector:@selector(cacheTodaysDate) name:UIApplicationSignificantTimeChangeNotification object:nil];
+  [self cacheTodaysDate];
+}
+
++ (void)cacheTodaysDate
+{
+  [today release];
   today = [[KalDate dateFromNSDate:[NSDate date]] retain];
-  // TODO set a timer for midnight to recache this value
 }
 
 + (KalDate *)dateForDay:(unsigned int)day month:(unsigned int)month year:(unsigned int)year

src/KalViewController.m

@@ -43,6 +43,7 @@ - (id)initWithSelectedDate:(NSDate *)selectedDate
   if ((self = [super init])) {
     logic = [[KalLogic alloc] initForDate:selectedDate];
     initialSelectedDate = [selectedDate retain];
+    [[NSNotificationCenter defaultCenter] addObserver:self selector:@selector(reloadData) name:UIApplicationSignificantTimeChangeNotification object:nil];
     [[NSNotificationCenter defaultCenter] addObserver:self selector:@selector(reloadData) name:KalDataSourceChangedNotification object:nil];
   }
   return self;
@@ -191,6 +192,7 @@ - (void)viewDidAppear:(BOOL)animated
 
 - (void)dealloc
 {
+  [[NSNotificationCenter defaultCenter] removeObserver:self name:UIApplicationSignificantTimeChangeNotification object:nil];
   [[NSNotificationCenter defaultCenter] removeObserver:self name:KalDataSourceChangedNotification object:nil];
   [initialSelectedDate release];
   [logic release];