空数组的作用是什么？

[jj89757hhb]

CustomCollectionView demo中 [_sections addObject:[NSMutableArray array]]; 是什么作用 _sections = [NSMutableArray array]; [sections addObject:[NSMutableArray array]]; for (NSUInteger idx = 0, section = 0; idx < kNumberOfImages; idx++) { NSString *name = [NSString stringWithFormat:@"image%lu.jpg", (unsigned long)idx]; [_sections[section] addObject:[UIImage imageNamed:name]]; if ((idx + 1) % 5 == 0 && idx < kNumberOfImages - 1) { section++; [_sections addObject:[NSMutableArray array]]; } }