Selecting and Unlocking Levels - Learn SpriteBuilder for iOS Game Development - page 274

Last but not least, let's return to the Scroll View one more time. When you've played
through the first three levels, you've unlocked the first level of the second world. Yet
when you open the level-selection popover in the MainScene , it will always show the first
page. This ought to be fixed.
Open MainScene.m , and import the GameState header just below the other import, as
shown in Listing 8-22 .
Listing 8-22 . Importing GameState
#import "MainScene.h"
#import "GameState.h"
Then go to the didLoadFromCCB method, and replace it with the version in Listing
8-23 .
Listing 8-23 . Switching to the page with the highest unlocked level
-(void) didLoadFromCCB
{
int numPages
= _levelSelectScrollView.numHorizontalPages;
if (numPages > 0)
{
int highest = [GameState
sharedGameState].highestUnlockedLevel;
int worldPage = (highest - 1) / numPages;
worldPage = MIN(worldPage, numPages - 1);
_levelSelectScrollView.horizontalPage = worldPage;
}
}
The numHorizontalPages returns 3 in this case, because there are three pages
(worlds). By dividing the highestUnlockedLevel minus 1 by the number of pages,
the result is a value in the range of 0 to 3—for instance, (1 - 1) / 3 = 0 , which is
what happens when you first run the app. Consider that (3 - 1) / 3 = 0 , so if you
happen to have unlocked all three levels of the first world, the first page (index 0) would
still be shown. Unlocking another level, such as (4 - 1) / 3 = 1 , will then show the
second page (world).