xcode - What is the correct way to see if the current group has been removed with ALAssetsLibraryChangedNotification? -

when group has been removed –groupforurl:resultblock:failureblock: not able find group anymore. might must compare nsurl received notification nsurl when using alassetsgrouppropertyurl on current group. when current group has filter on it, nsurl appended &filter= , nsurls won't match.

so if have current group of type alassetsgroup , receive notification alassetslibrarychangednotification. how check if current group 1 got removed?

my code far:

- (void)viewdidload {     [super viewdidload];      self.collectionview.alwaysbouncevertical    = yes;     self.collectionview.backgroundcolor         = [uicolor whitecolor];     self.collectionview.opaque                  = yes;     self.collectionview.contentinset            = uiedgeinsetsmake(9, 0, 0, 0);      [self.collectionview registerclass:[cmphotocollectionviewcell class] forcellwithreuseidentifier:@"photocell"]; }  - (void)viewwillappear:(bool)animated {     [super viewwillappear:animated];     [[nsnotificationcenter defaultcenter] addobserver:self selector:@selector(assetslibrarydidchange:) name:alassetslibrarychangednotification object:nil];      self.title = [self.album.group valueforproperty:alassetsgrouppropertyname];      if (!self.assets)         _assets = [nsmutablearray new];     else         [self.assets removeallobjects];      alassetsgroupenumerationresultsblock assetsenumerationblock = ^(alasset *result, nsuinteger index, bool *stop)     {         if (result) [self.assets addobject:result];     };      [self.album.group enumerateassetsusingblock:assetsenumerationblock]; }  - (void)viewwilldisappear:(bool)animated {     [super viewwilldisappear:animated];     [[nsnotificationcenter defaultcenter] removeobserver:self]; }  - (void)viewdidappear:(bool)animated {     [super viewdidappear:animated];     [self.collectionview reloaddata]; }  #pragma mark - #pragma mark assets library  - (void)assetslibrarydidchange:(nsnotification *)notification {     if (notification.userinfo[alassetlibrarydeletedassetgroupskey])     {         nslog (@"album removed: %@", notification.userinfo[alassetlibrarydeletedassetgroupskey]);         nslog (@"this album: %@", self.album.group);         nslog (@"%@", [self.album.group valueforproperty:alassetsgrouppropertyurl]);          // nsset nsurls of groups have been removed.         // nsurl seems without filter, if current item         // has filter on it, urls don't match.     } }  #pragma mark - uicollectionviewdelegate  - (nsinteger)collectionview:(uicollectionview *)view numberofitemsinsection:(nsinteger)section {     return self.assets.count; }  - (uicollectionviewcell *)collectionview:(uicollectionview *)collectionview cellforitematindexpath:(nsindexpath *)indexpath {     cmphotocollectionviewcell    *cell      = [collectionview dequeuereusablecellwithreuseidentifier:@"photocell" forindexpath:indexpath];     alasset                     *asset      = self.assets[indexpath.row];     uiimage                     *thumbnail  = [uiimage imagewithcgimage:asset.thumbnail];      cell.imageview.image = thumbnail;      return cell; }