Unload UICollectionview and reload?

Question

I have a probem when trying to reload a UICollectionview in iOS.

I am using it to display levels in a game.

The collectionview consists of 10 cells. The content of the cells depends if a level is unlocked. If the level is unlocked the cell displays the level (a custom UIView), else it displays an image. I had to create individual cell identifiers for this to work, and everything displays perfectly on load.

My problem is when a user is playing an unlocked level and then unlocks the next level. When the user navigates back from the game view to the level selection view, the cells are not reloaded correctly (just shows up empty where the custom views should be, the images display correctly).

I have tried to unload the array with levels in viewWillAppear and then calling [collectionview reloadData];, then loading the levels and reloading the collectionview again, but that does not help.

How can I empty the entire collectionview and recreate the cell identifiers when the view is displayed?

Thanks

-EDIT! UPDATED WITH CODE -

-(void)viewWillAppear:(BOOL)animated {
[super viewWillAppear:YES];

levelsArray = nil;
puzzlesArray = nil;

levelsArray = [[NSMutableArray alloc]init];
puzzlesArray = [[NSMutableArray alloc]init];

[collectionView reloadData];

NSUserDefaults *defaults = [NSUserDefaults standardUserDefaults];
NSData *data = [defaults objectForKey:@"puzzles"];
puzzlesArray = [NSKeyedUnarchiver unarchiveObjectWithData:data];

if ([puzzlesArray count] == 0) {
    [self.navigationController popViewControllerAnimated:YES];
}
else {
    NSLog(@"%i puzzles loaded", [puzzlesArray count]);

    //Get alle puzzles for the current category
    for (Puzzle *puzzle in puzzlesArray) {

        if ([[[NSUserDefaults standardUserDefaults]objectForKey:@"Category"] isEqualToString:[puzzle categoryName]]) {
            [levelsArray addObject:puzzle];
        }

    }

}

NSLog(@"View will appear");
[collectionView reloadData];

}

And in the cell for item at index path

    - (UICollectionViewCell *)collectionView:(UICollectionView *)cv cellForItemAtIndexPath:(NSIndexPath *)indexPath; {

    BOOL isUnlocked = [self isPuzzleUnlocked:[indexPath row]];

    if ([[NSUserDefaults standardUserDefaults]boolForKey:@"u"] == YES) {
        isUnlocked = YES;
    }

    [self.collectionView registerNib:[UINib nibWithNibName:@"CVCell" bundle:nil] forCellWithReuseIdentifier:[NSString stringWithFormat:@"%@%d", kCellReuseIdentifier, indexPath.row]];

    CVCell *cell = (CVCell *)[collectionView dequeueReusableCellWithReuseIdentifier:[NSString stringWithFormat:@"%@%d", kCellReuseIdentifier, indexPath.row] forIndexPath:indexPath];

[cell setPuzzleInfo:[levelsArray objectAtIndex:[indexPath row]] unlocked:isUnlocked];

        return cell;

}

Answer 1

In line with Rob's suggestion.

-(void)viewWillAppear {
   [super viewWillAppear];
   [self.collectionView reloadData]; 
}

In cellForItemAtIndexPath you should simply check if the item is unlocked or not and display the proper image or custom cell.

That's all. It is definitely not necessary to recreate the collection view.

You might want to honour the MVC (model-view-controller) design pattern by giving both your game controller and the level controller access to the data that models the levels. When what is happening in the game unlocks a new level, it should change this data. The collection view should reload itself based on this data just before it appears.

EDIT:

If you get the same cells/items as before even though you reloadData, this means that your configuration is not set up correctly. The key is to set both states of unlocked explicitly - reloadData will then update the item if it has changed.

EDIT2:

Both your itemForRowAtIndexPath methods are messed up. The call to registerNib does not belong there at all! It is supposed to be called during the initialization process. If you use storyboard, it is not necessary at all.

Here is a simple framework that you should use:

- (UICollectionViewCell *)collectionView:(UICollectionView *)cv 
                  cellForItemAtIndexPath:(NSIndexPath *)indexPath; {

   PuzzleInfo *puzzleObject = [dataArray objectAtIndex:indexPath.row]; 
   // you can use your more complicated data structure here, but 
   // have one object, dictionary, array item, etc. that has the info you need

   NSString *identifier = puzzleObject.unlocked ? kUnlockedCell : kLockedCell;
   CVCell *cell = [collectionView dequeueReusableCellWithReuseIdentifier:identifier
           forIndexPath:indexPath];

   if (puzzleObject.unlocked) {
      // configure the unlocked cell 
   }
   else {
      // configure the locked cell
   }

   return cell;
}

Answer 2

I fixed it!

- (UICollectionViewCell *)collectionView:(UICollectionView *)cv cellForItemAtIndexPath:(NSIndexPath *)indexPath; {
NSLog(@"CALLED");
BOOL isUnlocked = [self isPuzzleUnlocked:[indexPath row]];

if ([[NSUserDefaults standardUserDefaults]boolForKey:@"u"] == YES) {
    isUnlocked = YES;
}
int rand = arc4random() % 99001;
[self.collectionView registerNib:[UINib nibWithNibName:@"CVCell" bundle:nil] forCellWithReuseIdentifier:[NSString stringWithFormat:@"%@%d%i", kCellReuseIdentifier, indexPath.row, rand]];

CVCell *cell = (CVCell *)[collectionView dequeueReusableCellWithReuseIdentifier:[NSString stringWithFormat:@"%@%d%i", kCellReuseIdentifier, indexPath.row, rand] forIndexPath:indexPath];
[cell setPuzzleInfo:[levelsArray objectAtIndex:[indexPath row]] unlocked:isUnlocked];

    return cell;

}

Not a very memory effecient solution (or elegant), but it works. Adding a random number to each cell forces it to be recreated each time. As long as I only have 10 cells in a collectionview I think it will be ok..

Thanks for all your help :]