Ios UILabel上的instrictContentSize在不同的实例中返回不同的值

我正在swift 3.0中的一个项目中工作，在UIStoryBoard中有三个UILabel，numberOFLines设置为6。在标签下面，我放置了三个UIButton，作为“查看更多”选项。有时我的代码工作正常，如果我截断标签，它会显示“查看更多”按钮，单击后会显示整个内容，而有时即使UILabel内容被截断，它仍然不会显示“查看更多”按钮，因此我无法看到整个内容。我在代码中遗漏了什么，请帮忙

   import UIKit

class MP3ViewController: UIViewController,UITableViewDataSource,UITableViewDelegate {

    @IBOutlet var descriptionSeeMoreBtn: UIButton!

    @IBOutlet var howToUseSeeMoreBtn: UIButton!

    @IBOutlet var cautionsSeeMreBtn: UIButton!
    var seeMoreIsShowing =  false
    @IBOutlet var cautionsContentLbl: UILabel!
    @IBOutlet var howToUseContentLbl: UILabel!
    @IBOutlet var descriptionContentLbl: UILabel!

   override func viewDidLoad() {
        self.descriptionContentLbl.sizeToFit()
        self.howToUseContentLbl.sizeToFit()
        self.cautionsContentLbl.sizeToFit()
        getItButton.layer.cornerRadius = 5
        activityIndicator.startAnimating()
        let mediaID = mediaDetails?["entity_key"] as! String
        let url = URL(string: Config.MP3_LIST + "?mediaId=\(mediaID)")
        let task = URLSession.shared.dataTask(with: url!, completionHandler: { (data, response, error) in

            if(error != nil){
                print(error!);
                DispatchQueue.main.sync(execute: {
                    self.activityIndicator.stopAnimating()
                })
            }
            else{
                do{
                    if let urlContent = data {
                        let  serverResponseData = try (JSONSerialization.jsonObject(with: urlContent, options: JSONSerialization.ReadingOptions.mutableContainers)) as! NSDictionary
                        if(serverResponseData["error"] == nil){
                            self.mediaDetails = serverResponseData
                            print("Media :",self.mediaDetails!)
                            self.mediaList = (self.mediaDetails?["trackList"]as? NSArray)!

                            DispatchQueue.main.sync(execute: {

                                self.descriptionContentLbl.text =  self.mediaDetails?["description"] as? String ?? "description...."
                                self.howToUseContentLbl.text =  self.mediaDetails?["howToUse"] as? String ?? "How to use......."
                                self.cautionsContentLbl.text =  self.mediaDetails?["cautions"] as? String ?? "cautions...."
                                let track = ((self.mediaDetails?["trackList"] as! NSArray)[0]) as! NSDictionary
                                self.activityIndicator.stopAnimating()
                            })
                        }
                    }
                }
                catch {
                    print("Error In Json De-serialization")
                }
                DispatchQueue.main.sync(execute: {
                    self.activityIndicator.stopAnimating()
                })
            }
        })
        task.resume();

    }

    override func viewDidAppear(_ animated: Bool) {
        loadTheInitialLabelText()
        self.tableView.tableFooterView = UIView(frame: .zero)
    }

    @IBAction func descriptionSeeMoreButtonPressed(_ sender: Any) {
        if (seeMoreIsShowing) {
            self.descriptionContentLbl.numberOfLines = 6
            self.descriptionSeeMoreBtn.setTitle("see more", for: .normal)
        }else {
            self.descriptionContentLbl.numberOfLines = 0
            self.descriptionSeeMoreBtn.setTitle("show less", for: .normal)
        }
        seeMoreIsShowing = !seeMoreIsShowing
    }
    @IBAction func howToUSeSeeMoreButtonPressed(_ sender: Any) {
        if (seeMoreIsShowing) {
            self.howToUseContentLbl.numberOfLines = 6
            self.howToUseSeeMoreBtn.setTitle("see more", for: .normal)
        }else {
            self.howToUseContentLbl.numberOfLines = 0
            self.howToUseSeeMoreBtn.setTitle("show less", for: .normal)
        }
        seeMoreIsShowing = !seeMoreIsShowing
    }


    @IBAction func cautionsSeeMoreButtonPressed(_ sender: Any) {
        if (seeMoreIsShowing) {
            self.cautionsContentLbl.numberOfLines = 6
            self.cautionsSeeMreBtn.setTitle("see more", for: .normal)
        }else {
            self.cautionsContentLbl.numberOfLines = 0
            self.cautionsSeeMreBtn.setTitle("show less", for: .normal)
        }
        seeMoreIsShowing = !seeMoreIsShowing
    }

func loadTheInitialLabelText() {
        let DescriptionTextheight = self.descriptionContentLbl.text?.height(withConstrainedWidth: self.descriptionContentLbl.frame.width, font: self.descriptionContentLbl.font)
        if self.descriptionContentLbl.intrinsicContentSize.height < DescriptionTextheight! {
            self.descriptionSeeMoreBtn.isHidden = false
        }else{
            self.descriptionSeeMoreBtn.isHidden = true
        }

        let howToUseTextheight = self.howToUseContentLbl.text?.height(withConstrainedWidth: self.howToUseContentLbl.frame.width, font: self.howToUseContentLbl.font)
        if self.howToUseContentLbl.intrinsicContentSize.height < howToUseTextheight! {
            self.howToUseSeeMoreBtn.isHidden = false
        }else{
            self.howToUseSeeMoreBtn.isHidden = true
        }

        let cautionsTextheight = self.cautionsContentLbl.text?.height(withConstrainedWidth: self.cautionsContentLbl.frame.width, font: self.cautionsContentLbl.font)
        if self.cautionsContentLbl.intrinsicContentSize.height < cautionsTextheight! {
            self.cautionsSeeMreBtn.isHidden = false
        }else{
            self.cautionsSeeMreBtn.isHidden = true
        }

    }

}
extension String {

    func height(withConstrainedWidth width: CGFloat, font: UIFont) -> CGFloat {
        let constraintRect = CGSize(width: width, height: .greatestFiniteMagnitude)
        let boundingBox = self.boundingRect(with: constraintRect, options: .usesLineFragmentOrigin, attributes: [NSFontAttributeName: font], context: nil)

        return boundingBox.height
    }
}

导入UIKit
类MP3ViewController:UIViewController、UITableViewDataSource、UITableViewDelegate{
@IBOutlet var描述查看更多BTN:UIButton！
@IBOUTLE var HOWTUSESEEMOREBTN:UIButton！
@IBOUTLE var警告重新发布：UIButton！
var seeMoreIsShowing=false
@IBOUTLE var警戒内容BL:UILabel！
@IBOUTLE var HOWTUSECONTENTLBL:UILabel！
@IBOutlet var descriptionContentBL:UILabel！
重写func viewDidLoad（）{
self.descriptionContentBl.sizeToFit（）的名称
self.howtuseContentlbl.sizeToFit（）文件
self.cautionsContentBl.sizeToFit（）的
getItButton.layer.cornerRadius=5
activityIndicator.startAnimating（）
让mediaID=mediaDetails？[“实体_键”]作为！字符串
让url=url（字符串：Config.MP3\u LIST+“？mediaId=\（mediaId）”）
让task=URLSession.shared.dataTask（带：url！，completionHandler:{（数据，响应，错误）在
如果（错误！=nil）{
打印（错误！）；
DispatchQueue.main.sync（执行：{
self.activityIndicator.stopAnimating（）
})
}
否则{
做{
如果让urlContent=data{
让serverResponseData=try（JSONSerialization.jsonObject（with:urlContent，options:JSONSerialization.ReadingOptions.mutableContainers））作为！NSDictionary
if（serverResponseData[“error”]==nil）{
self.mediaDetails=serverResponseData
打印（“媒体：，self.mediaDetails！”）
self.mediaList=（self.mediaDetails？[“trackList”]as？NSArray）！
DispatchQueue.main.sync（执行：{
self.descriptionContentBL.text=self.mediaDetails？[“描述”]作为？字符串？？？“描述…”
self.howToUseContentLbl.text=self.mediaDetails？[“howToUse”]作为？字符串？？“如何使用……”
self.cautionscontetlbl.text=self.mediaDetails？[“注意事项”]作为？字符串？？“注意事项…”
让track=（（self.mediaDetails？[“trackList”]as！NSArray）[0]）as！NSDictionary
self.activityIndicator.stopAnimating（）
})
}
}
}
抓住{
打印（“Json反序列化错误”）
}
DispatchQueue.main.sync（执行：{
self.activityIndicator.stopAnimating（）
})
}
})
task.resume（）；
}
覆盖函数视图显示（u动画：Bool）{
加载初始标签文本（）
self.tableView.tableFooterView=UIView（帧：.0）
}
@iAction func description查看更多按钮已按下（\发送方：任何）{
如果（请参见更多信息显示）{
self.descriptionContentLbl.numberOfLines=6
self.descriptionSeeMoreBtn.setTitle（“查看更多”，用于：。正常）
}否则{
self.descriptionContentBL.numberOfLines=0
self.descriptionSeeMoreBtn.setTitle（“显示较少”，表示：。正常）
}
seeMoreIsShowing=！seeMoreIsShowing
}
@iAction func HowtouseSemoRebuttonPressed（\发送方：任何）{
如果（请参见更多信息显示）{
self.howtusecontentlbl.numberOfLines=6
self.howtuseseemorebtn.setTitle（“查看更多”，用于：。正常）
}否则{
self.howtusecontentlbl.numberOfLines=0
self.howtuseseemorebtn.setTitle（“显示较少”，表示：。正常）
}
seeMoreIsShowing=！seeMoreIsShowing
}
@iAction func告诫删除拒绝已发布（uu发件人：任何）{
如果（请参见更多信息显示）{
self.cautionsContentBL.numberOfLines=6
self.cautionsSeeMreBtn.setTitle（“请参阅更多”，用于：。正常）
}否则{
self.cautionsContentBL.numberOfLines=0
self.cautionsSeeMreBtn.setTitle（“显示较少”，用于：。正常）
}
seeMoreIsShowing=！seeMoreIsShowing
}
func加载初始标签文本（）{
让DescriptionTextheight=self.DescriptionContentBl.text？.height（带约束宽度：self.DescriptionContentBl.frame.width，字体：self.DescriptionContentBl.font）
如果self.descriptionContentBl.intrinsicContentSize.height