Calculating cell heights from auto layout prototype cells, each type of which will always be the same height

gistfile1.m

//  http://stackoverflow.com/a/16881312/2199136
- (CGFloat)tableView:(UITableView *)tableView heightForRowAtIndexPath:(NSIndexPath *)indexPath {
    NSString *cellIdentifier = [self cellIdentifierForIndexPath:indexPath];
    static NSMutableDictionary *heightCache;
    if (!heightCache)
        heightCache = [[NSMutableDictionary alloc] init];
    NSNumber *cachedHeight = heightCache[cellIdentifier];
    if (cachedHeight)
        return cachedHeight.floatValue;
    
    UITableViewCell *cell = [tableView dequeueReusableCellWithIdentifier:cellIdentifier];
    CGFloat height = cell.bounds.size.height;
    heightCache[cellIdentifier] = @(height);
    return height;
}