iOS reloadSections 页面跳动解决办法

@property (nonatomic, strong) NSMutableDictionary *cellHeightsDictionary;
self.cellHeightsDictionary = @{}.mutableCopy;
// save height
- (void)tableView:(UITableView *)tableView willDisplayCell:(UITableViewCell *)cell forRowAtIndexPath:(NSIndexPath *)indexPath {
    [self.cellHeightsDictionary setObject:@(cell.frame.size.height) forKey:indexPath];
}
// give exact height value
- (CGFloat)tableView:(UITableView *)tableView estimatedHeightForRowAtIndexPath:(NSIndexPath *)indexPath {
    NSNumber *height = [self.cellHeightsDictionary objectForKey:indexPath];
    if (height) return height.doubleValue;
    return UITableViewAutomaticDimension;
}