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POWhat is the correct way to reload data in a UICollectionView?
 

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  1. POWhat is the correct way to reload data in a UICollectionView?
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    <p>If I am getting information from an album in the users assetslibrary and they add a picture or remove on from it while my app is in the background. Whats the best way to reload them.</p> <p>Currently I have:</p> <pre><code>[[NSNotificationCenter defaultCenter] addObserver:self selector:@selector(assetsLibraryDidChange:) name:ALAssetsLibraryChangedNotification object:_photoListArray]; </code></pre> <p>To get the initial notification and then it calls my assetLibraryDidChange method:</p> <p>Which looked like this:</p> <pre><code>- (void)assetsLibraryDidChange:(NSNotification *)note { //dict nil reload if(note.userInfo==nil) { [self.CoverView reloadData]; return; } //dict empty no reload if(note.userInfo.count == 0) { NSLog(@"empty"); return; } else { [self.CoverView reloadData]; } } </code></pre> <p>Although I am considering removing all the if's and else and just having it reload every time. </p> <hr> <p>What I'm getting to:</p> <p>There seems to be a gap between when my app receives the notification and it actually updates. Apple's default photos app seems to be able to do it in around 3-4 seconds while it takes mine almost 10!. Is there a more efficient way to do this?</p> <hr> <p>I went ahead and put a nslog before all the if's to see how many times the method was being called as well.</p> <pre><code>//Library Updated - (void)assetsLibraryDidChange:(NSNotification *)note { NSLog(@"photos updated"); //dict nil reload if(note.userInfo==nil) { dispatch_async(dispatch_get_main_queue(), ^{ [self.CoverView reloadData]; NSLog(@"note: %@", note.userInfo); NSLog(@"array: %@", _photoListArray); return; }); } //dict empty no reload if(note.userInfo.count == 0) { NSLog(@"empty"); return; } else { dispatch_async(dispatch_get_main_queue(), ^{ [self.CoverView reloadData]; NSLog(@"note2: %@", note.userInfo); NSLog(@"array2: %@", _photoListArray); }); } } </code></pre> <p>And they resulted in the following:</p> <pre><code>2013-08-16 10:41:51.622 app[180:1803] photos updated 2013-08-16 10:41:51.635 app[180:60b] note2: { ALAssetLibraryUpdatedAssetsKey = "{(\n assets-library://asset/asset.JPG?id=CCA17BE2-5633-4FFE-A113-F21E37B9882C&amp;ext=JPG,\n assets-library://asset/asset.JPG?id=7B05283E-87A5-4CFE-BDBE-7703E311E0DF&amp;ext=JPG,\n assets-library://asset/asset.JPG?id=5B1E736F-E21E-4400-9679-5DE8215AC09D&amp;ext=JPG\n)}"; } 2013-08-16 10:41:51.638 app[180:60b] array2: ( "&lt;Media: 0x176b3410&gt;", "&lt;Media: 0x176b5b00&gt;", "&lt;Media: 0x176b5c90&gt;", "&lt;Media: 0x176b7590&gt;", "&lt;Media: 0x176b47c0&gt;", "&lt;Media: 0x176b7e10&gt;", "&lt;Media: 0x176b83b0&gt;", "&lt;Media: 0x176b8990&gt;", "&lt;Media: 0x176b8f40&gt;", "&lt;Media: 0x176b9530&gt;", "&lt;Media: 0x176ba160&gt;", "&lt;Media: 0x176ba960&gt;", "&lt;Media: 0x175794d0&gt;", "&lt;Media: 0x175503c0&gt;", "&lt;Media: 0x17571f80&gt;", "&lt;Media: 0x1756dc20&gt;", "&lt;Media: 0x17571060&gt;", "&lt;Media: 0x1757b0d0&gt;", "&lt;Media: 0x1757b8f0&gt;", "&lt;Media: 0x1757bee0&gt;", "&lt;Media: 0x1757bcf0&gt;", "&lt;Media: 0x1757ca80&gt;", "&lt;Media: 0x1757cbd0&gt;" ) 2013-08-16 10:41:51.827 app[180:3e07] photos updated 2013-08-16 10:41:51.831 app[180:3e07] empty 2013-08-16 10:41:51.893 app[180:3e07] photos updated 2013-08-16 10:41:51.897 app[180:3e07] empty 2013-08-16 10:41:52.059 app[180:3e07] photos updated 2013-08-16 10:41:52.074 app[180:3e07] empty 2013-08-16 10:41:52.092 app[180:5117] photos updated 2013-08-16 10:41:52.095 app[180:5117] empty </code></pre> <p>The Media objects are a class which I am just using to add data and have it stored along with them. Name, ext. Nothing that changes the actual image.</p> <p>Without the dispatch:</p> <pre><code>2013-08-16 11:37:53.246 app[296:3d07] photos updated 2013-08-16 11:37:53.255 app[296:3d07] note2: { ALAssetLibraryUpdatedAssetsKey = "{(\n assets-library://asset/asset.JPG?id=CCA17BE2-5633-4FFE-A113-F21E37B9882C&amp;ext=JPG,\n assets-library://asset/asset.PNG?id=D72A00CE-4198-45BE-BCC5-8DEB8419A5C8&amp;ext=PNG,\n assets-library://asset/asset.JPG?id=5B1E736F-E21E-4400-9679-5DE8215AC09D&amp;ext=JPG\n)}"; } 2013-08-16 11:37:53.260 app[296:3d07] array2: ( "&lt;Media: 0x176271b0&gt;", "&lt;Media: 0x17577920&gt;", "&lt;Media: 0x17579c50&gt;", "&lt;Media: 0x17579eb0&gt;", "&lt;Media: 0x17579e00&gt;", "&lt;Media: 0x1757a9b0&gt;", "&lt;Media: 0x1757af50&gt;", "&lt;Media: 0x1757b540&gt;", "&lt;Media: 0x1757baf0&gt;", "&lt;Media: 0x1757c0e0&gt;", "&lt;Media: 0x17656510&gt;", "&lt;Media: 0x176570f0&gt;", "&lt;Media: 0x176572b0&gt;", "&lt;Media: 0x17657840&gt;", "&lt;Media: 0x17657e20&gt;", "&lt;Media: 0x17658400&gt;", "&lt;Media: 0x176589e0&gt;", "&lt;Media: 0x17659270&gt;", "&lt;Media: 0x17650470&gt;", "&lt;Media: 0x17659380&gt;", "&lt;Media: 0x176507a0&gt;", "&lt;Media: 0x17650ab0&gt;", "&lt;Media: 0x17659cb0&gt;", "&lt;Media: 0x1765a340&gt;" ) 2013-08-16 11:37:53.404 app[296:4e17] photos updated 2013-08-16 11:37:53.408 app[296:4e17] empty 2013-08-16 11:37:53.450 app[296:3d07] photos updated 2013-08-16 11:37:53.458 app[296:3d07] empty 2013-08-16 11:37:53.466 app[296:4e17] photos updated 2013-08-16 11:37:53.470 app[296:4e17] empty </code></pre>
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    1. COIs the notification sent on a non-main thread? In that case you have to dispatch `reloadData` to the main thread.
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