Selecting and Unlocking Levels - Learn SpriteBuilder for iOS Game Development - page 258

objectForKey:KeyForUnlockedLevel];
return (number ? [number intValue] : 1);
}
The setter method defines the maximum number of levels in the game; this game is inten-
ded to have nine levels. The currentLevel property is tested to be in the range 1
through 9 before it is stored in NSUserDefaults . The getter method obtains the stored
NSNumber and either returns its intValue or 1 if there is no entry for the key
KeyForUnlockedLevel yet. It returns 1 because the first level should always be un-
locked.
Unlocking levels is done with the unlockNextLevel method, as you can see in List-
ing 8-7 . Add it just after the highestUnlockedLevel method.
Listing 8-7 . Unlocking the next level
-(BOOL) unlockNextLevel
{
int highest = self.highestUnlockedLevel;
if (_currentLevel >= highest)
{
[self setHighestUnlockedLevel:_currentLevel + 1];
}
return (highest < self.highestUnlockedLevel);
}
The currently highestUnlockedLevel is obtained from the property setter via
self.highestUnlockedLevel and assigned to the highest variable. If cur-
rentLevel is equal to or greater than the highest number, the setHighestUn-
lockedLevel : setter is called so that it unlocks the next level following the current
level. At the end, the method returns a BOOL value that indicates whether the next level
was indeed unlocked or not, by comparing the previous highest number with the current
highestUnlockedLevel .
Highlighting Level Buttons
The level buttons need to be unlocked—that is, their color set to white—if their level is
currently accessible. “Accessible” means that the button's level number is less than or