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

Question

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.

Currently I have:

[[NSNotificationCenter defaultCenter] addObserver:self selector:@selector(assetsLibraryDidChange:) name:ALAssetsLibraryChangedNotification object:_photoListArray];

To get the initial notification and then it calls my assetLibraryDidChange method:

Which looked like this:

- (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];
    }
}

Although I am considering removing all the if's and else and just having it reload every time.

---

What I'm getting to:

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?

---

I went ahead and put a nslog before all the if's to see how many times the method was being called as well.

//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);
        });
    }

}

And they resulted in the following:

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&ext=JPG,\n    assets-library://asset/asset.JPG?id=7B05283E-87A5-4CFE-BDBE-7703E311E0DF&ext=JPG,\n    assets-library://asset/asset.JPG?id=5B1E736F-E21E-4400-9679-5DE8215AC09D&ext=JPG\n)}";
}
2013-08-16 10:41:51.638 app[180:60b] array2: (
    "<Media: 0x176b3410>",
    "<Media: 0x176b5b00>",
    "<Media: 0x176b5c90>",
    "<Media: 0x176b7590>",
    "<Media: 0x176b47c0>",
    "<Media: 0x176b7e10>",
    "<Media: 0x176b83b0>",
    "<Media: 0x176b8990>",
    "<Media: 0x176b8f40>",
    "<Media: 0x176b9530>",
    "<Media: 0x176ba160>",
    "<Media: 0x176ba960>",
    "<Media: 0x175794d0>",
    "<Media: 0x175503c0>",
    "<Media: 0x17571f80>",
    "<Media: 0x1756dc20>",
    "<Media: 0x17571060>",
    "<Media: 0x1757b0d0>",
    "<Media: 0x1757b8f0>",
    "<Media: 0x1757bee0>",
    "<Media: 0x1757bcf0>",
    "<Media: 0x1757ca80>",
    "<Media: 0x1757cbd0>"
)
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

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.

Without the dispatch:

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&ext=JPG,\n    assets-library://asset/asset.PNG?id=D72A00CE-4198-45BE-BCC5-8DEB8419A5C8&ext=PNG,\n    assets-library://asset/asset.JPG?id=5B1E736F-E21E-4400-9679-5DE8215AC09D&ext=JPG\n)}";
}
2013-08-16 11:37:53.260 app[296:3d07] array2: (
    "<Media: 0x176271b0>",
    "<Media: 0x17577920>",
    "<Media: 0x17579c50>",
    "<Media: 0x17579eb0>",
    "<Media: 0x17579e00>",
    "<Media: 0x1757a9b0>",
    "<Media: 0x1757af50>",
    "<Media: 0x1757b540>",
    "<Media: 0x1757baf0>",
    "<Media: 0x1757c0e0>",
    "<Media: 0x17656510>",
    "<Media: 0x176570f0>",
    "<Media: 0x176572b0>",
    "<Media: 0x17657840>",
    "<Media: 0x17657e20>",
    "<Media: 0x17658400>",
    "<Media: 0x176589e0>",
    "<Media: 0x17659270>",
    "<Media: 0x17650470>",
    "<Media: 0x17659380>",
    "<Media: 0x176507a0>",
    "<Media: 0x17650ab0>",
    "<Media: 0x17659cb0>",
    "<Media: 0x1765a340>"
)
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

Answer 1

any UI changing stuff should be done on the main thread.. try:

- (void)assetsLibraryDidChange:(NSNotification *)note
{

    //dict nil reload
    if(note.userInfo==nil) {
        dispatch_async(dispatch_get_main_queue(), ^{
            [self.CoverView reloadData];
            return;
        }
    }

    //dict empty no reload
    if(note.userInfo.count == 0) {
        NSLog(@"empty");
        return;
    }

    else {
        dispatch_async(dispatch_get_main_queue(), ^{            
            [self.CoverView reloadData];
        }
    }
}