ios - How to stop cellForItemAtIndexPath running if its datasource changed -


i collect photos alassetlibrary , present them in uicollectionview. add notification called alassetslibrarychangednotification handle photo changes , call showlatestphotos whenever notification posted. photo-collection function like:

- (void)showlatestphotos {     _latestphotos = [nsmutablearray array];     // photo asset , inset _latestphotos     [_latestphotos insertobject:...];     [_collectionview reloaddata]; }

the problem if perform screenshot(click home , power @ same time), alassetslibrarychangednotification posted more twice, is, showlatestphtots executed twice, , second time when _latestphotos set empty using _latestphotos = [nsmutablearray array], cellforitematindexpath of collectionview's datasource triggered [_collectionview reloaddata] in first call still being called , when call [_latestphotos objectatindex:], application crashes. know how solve bug?

use work

if ([_latestphotos containsobject:yourobject] == no)  {    //    _latestphotos = [nsmutablearray array];    // photo asset , inset _latestphotos    [_latestphotos insertobject:...];    [_collectionview reloaddata]; }

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