iOS精確計算label 的高度

CGFloat width = self.view.frame.size.width - 40;

    NSString * string = @"還記得你說家是惟一的城堡隨着稻香河流繼續奔跑微微笑 小時候的夢我知道不要哭讓螢火蟲帶著你逃跑鄉間的歌謠永遠的依靠回家吧 回到最初的sdvsldfjnwefqej;wlednef,sbf.s,bfbkj.fejwfwfkjwjkfwefbwejfbwkjeb美好 還記得你說家是惟一的城堡隨着稻還記得你說家是惟一的城堡隨着稻還記得你說家是惟一的城堡隨着稻還記得你說家是惟一的城堡隨着稻還記得你說家是惟一的城堡隨着稻還你說家是惟一的城堡隨着稻還記得你說家是惟一的城堡隨着稻還記得你說家";


    NSMutableParagraphStyle * paragraph = [[NSMutableParagraphStyle alloc] init];
//    paragraph.lineSpacing = 10;
    
    NSDictionary * dict = @{NSFontAttributeName:[UIFont systemFontOfSize:30],
                            NSParagraphStyleAttributeName:paragraph};
    
    NSAttributedString * attribute = [[NSAttributedString alloc]
                                      initWithString:string attributes:dict];
    //必定要先肯定寬度，再根據寬度和字體計算size
    CGSize size = [string boundingRectWithSize:CGSizeMake(width, MAXFLOAT) options:NSStringDrawingUsesLineFragmentOrigin attributes:dict context:nil].size;
    
    UILabel * label = [[UILabel alloc] init];
    label.bounds = CGRectMake(0, 0, size.width, size.height);
    label.center = self.view.center;
    label.numberOfLines = 0;
    label.attributedText = attribute;
    label.backgroundColor = [UIColor yellowColor];
    [self.view addSubview:label];