uilable根据内容多少自动改变高度

//将获取的问题内容给quest_str    NSString *quest_str = [NSString stringWithFormat:@""];    lab_quests_content.text = quest_str;        [lab_quests_content setNumberOfLines:0];    [lab_quests_content setLineBreakMode:UILineBreakModeWordWrap];        UIFont *font_lab_quest = [UIFont systemFontOfSize:13.0];    lab_quests_content.font = font_lab_quest;        CGSize size = CGSizeMake(lab_quests_content.frame.size.width, 200);    CGSize labSize = [quest_str sizeWithFont:font_lab_quest constrainedToSize:size lineBreakMode:UILineBreakModeWordWrap];        CGRect frame = lab_quests_content.frame;    frame.size.height = labSize.height;    lab_quests_content.frame = frame;        //answer_view    view_quests_answers.frame = CGRectMake(frame.origin.x, frame.origin.y + labSize.height + 20, view_quests_answers.frame.size.width, view_quests_answers.frame.size.height);