iOS 计算文本的高度

- (double)calculateTextHeight:(NSString*)strTitle width:(CGFloat)textWidth withFont:(UIFont *)textfont{
    // 计算出每个Cell的高度
    NSMutableAttributedString *attributeString = [[NSMutableAttributedString alloc]initWithString:strTitle];
    NSMutableParagraphStyle *style = [[NSMutableParagraphStyle alloc] init];
    // TODO: 行间距可以设置成动态的
    style.lineSpacing = 2;
    [attributeString addAttribute:NSParagraphStyleAttributeName value:style range:NSMakeRange(0, strTitle.length)];
    [attributeString addAttribute:NSFontAttributeName value:textfont range:NSMakeRange(0, strTitle.length)];
    NSStringDrawingOptions options = NSStringDrawingUsesLineFragmentOrigin | NSStringDrawingUsesFontLeading;
    CGFloat boundingRectHeight = [attributeString boundingRectWithSize:CGSizeMake(textWidth, MAXFLOAT) options:options context:nil].size.height;
    if ([attributeString.string isEqualToString:@""] || [attributeString.string isEqualToString:@"(null)"]) {
        boundingRectHeight = 0;
    }
    return boundingRectHeight;
}