objective c - Table reloadData can cause crashes -

very (once week'ish) crashlytics reporting crashes such

fatal exception: nsrangeexception -[__nsarraym objectatindex:]: index 7 beyond bounds [0 .. 1]  [musiclist tableview:heightforrowatindexpath:] 

i'm wondering if these occurring due data being reloaded before table finishes rendering, when requests piece of data has been removed , not yet been re-inserted?

if case, best remove reloaddata call viewwillappear , place in viewdidappear? displaying potentially old data, refreshing newer content might jarring end user.

this code far controller:

@implementation musiclist  - (void)viewdidload {     [super viewdidload];      [self settitles:[[nsmutablearray alloc] init]];     [self setdata:  [[nsmutablearray alloc] init]]; }  - (void)viewwillappear:(bool)animated {     [super viewwillappear:animated];      dispatch_queue_t loadmusic = dispatch_queue_create("loadmusic", null);     dispatch_async(loadmusic, ^{         nsmutabledictionary * data = [music getmusiclist];          [self settitles:[data objectforkey:@"titles"]];         [self setdata:  [data objectforkey:@"tracks"]];          dispatch_async(dispatch_get_main_queue(), ^{             [tablemusiclist reloaddata];         });     }); }  - (nsinteger)numberofsectionsintableview:(uitableview *)tableview {     return [_titles count]; }  - (nsinteger)tableview:(uitableview *)tableview numberofrowsinsection:(nsinteger)section {     return [_data[section] count]; }  - (cgfloat)tableview:(uitableview *)tableview heightforrowatindexpath:(nsindexpath *)indexpath {     return [_titles[indexpath.section] isequaltostring:@"nowplaying"]         ? 100.0         : 44.0; } 

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update: data returned musiclist:

- (nsmutabledictionary *)getmusiclist {     db                  * db   = [[db alloc] init];     nsmutabledictionary * data = [[nsmutabledictionary alloc] init];      [data setobject:[[nsmutablearray alloc] init] forkey:@"titles"];     [data setobject:[[nsmutablearray alloc] init] forkey:@"tracks"];      if ([db prepare:@"select `date`, `name` `music` order `date` desc limit 25"]) {         nsstring * date;         nsstring * name;          while ([db stepthrough]) {             date = [db get:0];             name = [db get:1];              if (date && name) {                 [[data objectforkey:@"titles"] addobject:date];                 [[data objectforkey:@"tracks"] addobject:name];             }         }     }      return data; } 

the problem inside uitableview delegates, though apple don't have documentation order of calls delegate can check , see nslog(); in every delegate..

in code:

- (cgfloat)tableview:(uitableview *)tableview heightforrowatindexpath:(nsindexpath *)indexpath {      return [_titles[indexpath.section] isequaltostring:@"nowplaying"] ? 100.0: 44.0; } 

is dependent delegate

- (nsinteger)numberofsectionsintableview:(uitableview *)tableview {     return [_titles count]; } 

this delegate tell indexpath how many section there, if heightforrowatindexpath called first before numberofsectionsintableview ??

another, reloading uitableview inside -viewwillappear, dont know reason behind had problem before , did double checking datasource inside uitableviewdelegates like:

- (nsinteger)numberofsectionsintableview:(uitableview *)tableview {      if (!_titles) // double check if _title allocated , avoid `[nsnull length] error`         _titles = [[nsmutablearray alloc] init];      return [_titles count]; }  - (nsinteger)tableview:(uitableview *)tableview numberofrowsinsection:(nsinteger)section {      if (section < _data.count) // prevent out of bounds          return [_data[section] count];      return 0; // 0 number of row in section if out of bounds }  - (cgfloat)tableview:(uitableview *)tableview heightforrowatindexpath:(nsindexpath *)indexpath {      if (indexpath.section < _titles.count) // prevent out of bounds         return [_titles[indexpath.section] isequaltostring:@"nowplaying"] ? 100.0 : 44.0;      return 0;  // 0 height of row in @ indexpath if out of bounds } 

that's i've learn using _titles[indexpath.section] or variable[index] in dynamic kind of way,

always check bounds avoid out of it(bounds).. happy coding, cheers!