gistfile1.m

//------------------------------------------------------------------------------
// 
// kLineCount is number of line in truncated mode

-(NSString *)thumbnailString:(NSString*)string {

    NSInteger lenght = [string length];
    NSString *showMoreString = @"see more";
    UIFont* displayFont = <your font>;
    
    CGFloat hOf4Line = (font.lineHeight * kLineCount);
    for (NSInteger i = lenght;i >= 0; --i)
    {
        NSString *resultString = [string substringWithRange:NSMakeRange(0, i)];
        resultString = [resultString stringByAppendingFormat:@".....%@",showMoreString];
        CGFloat textW = [self targetTextW];
        textW = textW - self.descriptionLeftMargin.constant - self.descriptionRighttMargin.constant;
        NSLog(@"Width: %@", @(self.tvDescription.frame.size.width));
        CGSize size = [resultString sizeForFont:font constraintSize:(CGSize){textW, 99999}];

        if (size.height <= hOf4Line) {
            return resultString;
        }
    }
    return nil;
}



/// .......
/// In NSString category

- (CGSize) sizeForFont: (UIFont*) font constraintSize: (CGSize) size
{
    CGSize reSize;
    NSStringDrawingContext *context = [NSStringDrawingContext new];
    context.minimumScaleFactor = 0.5;
    NSDictionary *stringAttributes = [NSDictionary dictionaryWithObject: font forKey: NSFontAttributeName];
    CGRect bound = [self boundingRectWithSize:size
                                      options:NSStringDrawingUsesLineFragmentOrigin | NSStringDrawingUsesFontLeading
                                   attributes:stringAttributes context:nil];
    reSize = bound.size;

    return reSize;
}