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

if getting information album in users assetslibrary , add picture or remove on while app in background. whats best way reload them.

currently have:

[[nsnotificationcenter defaultcenter] addobserver:self selector:@selector(assetslibrarydidchange:) name:alassetslibrarychangednotification object:_photolistarray]; 

to initial notification , calls assetlibrarydidchange method:

which looked 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 considering removing if's , else , having reload every time.

---

what i'm getting to:

there seems gap between when app receives notification , updates. apple's default photos app seems able in around 3-4 seconds while takes mine 10!. there more efficient way this?

---

i went ahead , put nslog before if's see how many times method being called 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 resulted in 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 class using add data , have stored along them. name, ext. nothing changes actual image.

without 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 

any ui changing stuff should done on 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];         }     } }