ios - Collection view is crashing for some reason -

    //collection view     uicollectionviewflowlayout *layout=[[uicollectionviewflowlayout alloc] init];     self.collectionview=[[uicollectionview alloc] initwithframe:self.view.frame collectionviewlayout:layout];     [self.collectionview setdatasource:self];     [self.collectionview setdelegate:self];      [self.collectionview registerclass:[uicollectionviewcell class] forcellwithreuseidentifier:@"cellidentifier"];     [self.collectionview setbackgroundcolor:[uicolor redcolor]];      [self.view addsubview:self.collectionview];   }    - (nsinteger)collectionview:(uicollectionview *)tcollectionview numberofitemsinsection:(nsinteger)section {     return 15; }   // cell returned must retrieved call -dequeuereusablecellwithreuseidentifier:forindexpath: - (uicollectionviewcell *)collectionview:(uicollectionview *)collectionview cellforitematindexpath:(nsindexpath *)indexpath {     uicollectionviewcell *cell=[collectionview dequeuereusablecellwithreuseidentifier:@"cellidentifier" forindexpath:indexpath];      cell.backgroundcolor=[uicolor greencolor];     return cell; }  - (cgsize)collectionview:(uicollectionview *)collectionview layout:(uicollectionviewlayout*)collectionviewlayout sizeforitematindexpath:(nsindexpath *)indexpath {     return cgsizemake(50, 50); } 

crash on :

 -[nsisunrestrictedvariable collectionview:numberofitemsinsection:]: unrecognized selector sent instance 0x7fce804111b0 

what ? (the collection view inside view controller,tand inside scrollview)

it looks uicollectionview has been deallocated memory still trying access it.

enable nszombies , you'll see make call deallocated memory , fix code accordingly.