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POCollection View Error : request for number of items before section 7 when there are only 1 sections in the collection view
 

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  1. POCollection View Error : request for number of items before section 7 when there are only 1 sections in the collection view
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    <p>I'm using a Collection View and I'm trying to switch from one Collection View Layout to another using:</p> <pre><code>[self.collectionView setCollectionViewLayout:newLayout animated:animated]; </code></pre> <p>Which all seems to work fine and I get a new layout with all my items in.</p> <p>However, when I switch to the new layout, I want to only show the items in a particular section. I suppose my first question is, does anyone have any pointers as to correct way to achieve this?</p> <p>The way I'm doing it is to remove items from the array that is used for the collection view. To do this, I'm using</p> <pre><code>- (void)removeObjectsInArray:(NSArray *)otherArray </code></pre> <p>to remove the items from my model, and then</p> <pre><code>- (void)deleteSections:(NSIndexSet *)sections </code></pre> <p>to remove sections from the collection view.</p> <p>On doing this, I get the following error</p> <pre><code>*** Assertion failure in -[UICollectionViewData numberOfItemsBeforeSection:], /SourceCache/UIKit_Sim/UIKit-2380.17/UICollectionViewData.m:415 2013-05-03 07:35:18.543 Clients[69375:c07] *** Terminating app due to uncaught exception 'NSInternalInconsistencyException', reason: 'request for number of items before section 7 when there are only 1 sections in the collection view' </code></pre> <p>Does anyone have any thoughts on why I would get this specific error. Any searching I've done seems to point to similar errors, but not this exact one. Any thoughts anyone has greatly appreciated.</p> <p>Thanks.</p> <p>--- UPDATE</p> <p>I should have mentioned that I'm doing this inside a gesture recogniser, as that now seems to be important. I've extracted the code and added a button to run it too. Running it with the button seems to work (except the animations are off), but doing the gesture still gives me the error.</p> <p>The code is as follows:</p> <pre><code>[self.collectionView performBatchUpdates:^{ NSString *selectedMarketSector = [[[[_allMarketSectors objectAtIndex:stacksLayout.pinchedStackIndex] clients] objectAtIndex:0] clientMarketSector]; NSMutableArray* removeObjects = [[NSMutableArray alloc] init]; NSMutableIndexSet *removeSections = [[NSMutableIndexSet alloc] init]; for (TBMarketSector* sector in _marketSectors) { if (![[[[sector clients] objectAtIndex:0] clientMarketSector ] isEqualToString:selectedMarketSector]) { [removeObjects addObject:sector]; [removeSections addIndex:[_marketSectors indexOfObject:sector]]; } } [_marketSectors removeObjectsInArray:removeObjects]; [self.collectionView deleteSections:removeSections]; } completion:^(BOOL finished) { [self setLayoutStyle:TBLayoutGrid animated:YES]; }]; </code></pre> <p>--- UPDATE 2</p> <p>I finally discovered that my first custom layout was still trying to layout items after I'd removed them from the collection view and the model. I first had to stop the layout by setting the pinched stack index back to -1:</p> <pre><code>[stacksLayout setPinchedStackIndex:-1]; </code></pre> <p>So that the code in the stacks layout would stop trying to layout the items:</p> <pre><code>- (void)setPinchedStackIndex:(NSInteger)pinchedStackIndex { _pinchedStackIndex = pinchedStackIndex; BOOL wasPinching = self.isPinching; [self setPinching:pinchedStackIndex &gt;= 0]; if (self.isPinching != wasPinching) { if (self.isPinching) self.gridLayout = [[GridLayout alloc] init]; else self.gridLayout = nil; } [self invalidateLayout]; } </code></pre> <p>This was from the sample code <a href="http://markpospesel.wordpress.com/2012/12/11/decorationviews/" rel="nofollow">from Mark Pospesel</a></p> <p>So my code now looks as follows:</p> <pre><code>[self.collectionView performBatchUpdates:^{ NSString *selectedMarketSector = [[[[_marketSectors objectAtIndex:stacksLayout.pinchedStackIndex] clients] objectAtIndex:0] clientMarketSector]; [stacksLayout setPinchedStackIndex:-1]; NSMutableArray* removeObjects = [[NSMutableArray alloc] init]; NSMutableIndexSet *removeSections = [[NSMutableIndexSet alloc] init]; for (TBMarketSector* sector in _marketSectors) { if (![[[[sector clients] objectAtIndex:0] clientMarketSector ] isEqualToString:selectedMarketSector]) { [removeObjects addObject:sector]; [removeSections addIndex:[_marketSectors indexOfObject:sector]]; } } [_marketSectors removeObjectsInArray:removeObjects]; [self.collectionView deleteSections:removeSections]; } completion:^(BOOL finished) { [self setLayoutStyle:TBLayoutGrid animated:YES]; }]; </code></pre> <p>That now gives me a separate problem which I guess I should log separately, but essentially, when I pinch a stack out, the stack layout lines all the items up nicely in a temporary grid, but then when it switches layouts to the grid layout they momentarily bounce back into a stack and back out as a grid again.</p> <p>I suppose that goes back to my original question which is, what is the correct way to switch from one layout to the next -- the photos app on the iPad seems to switch out the view completely, but doesn't seem to 'jump' from one layout to the next, even though there is a pinch gesture going on for example.</p> <p>Thanks for any additional information anyone can provide.</p>
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    1. COshow ur removeObjectsInArray: and deleteSections:(NSIndexSet *)sections methods?
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      1. USAnil Varghese
    2. COJust updated with a bit more information... thanks.
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      1. USDarren
 

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