ios - 为什么在 subview 中添加 UILabel 会使其像素化

Question

我正在制作一条消息，当 tableView 为空并且我在我的 subView 中添加了一个标签并且它看起来是像素化时显示。但是当我在我的 tableView 中添加一些东西并将其删除时，显示的消息 (UILabel) 就完全没问题了。不知道为什么。

在我的 self.tableView.backgroundView = emptyLabel 中添加标签解决了这个问题，但我想添加两个标签，所以我在 subView 中添加一个标签，使其像素化。

这是我的代码:

class ReminderTableViewController: UITableViewController
{

@IBOutlet var myTableView: UITableView!
@IBOutlet weak var dateLabel: UIView!
@IBAction func back(_ sender: Any) {
    dismiss(animated: true, completion: nil)
}


override func viewDidLoad() {
    super.viewDidLoad()

    self.tableView.separatorColor = UIColor.clear
    tableView.separatorStyle = .none
    }

override func tableView(_ tableView: UITableView, didSelectRowAt indexPath: IndexPath) {
   performSegue(withIdentifier: "details", sender: self)

}
 public func buttonImageForEmptyStateView() -> UIImage? {
    return UIImage.init(named: "Exclamation Mark Filled-100-2")
}



override func viewDidAppear(_ animated: Bool) {
    tableView.reloadData()
     self.reloadEmptyState(forTableView: self.tableView)

}


override func didReceiveMemoryWarning() {
    super.didReceiveMemoryWarning()
    // Dispose of any resources that can be recreated.
}


override func numberOfSections(in tableView: UITableView) -> Int {

    return 1
}

override func tableView(_ tableView: UITableView, numberOfRowsInSection section: Int) -> Int {


    if list.count==0{
        let emptyLabel=UILabel(frame: CGRect(x: 0,y: 0, width: self.view.bounds.width, height: self.view.bounds.height))
        let emptyLabel2=UILabel(frame: CGRect(x: 0.0,y: 20.0, width: self.view.bounds.width, height: self.view.bounds.height))


        self.view.addSubview(emptyLabel2)
        self.view.addSubview(emptyLabel)

        let emptyImage = UIImageView(image: UIImage(named: "Quote Right Filled-100 (3)"))
        emptyImage.translatesAutoresizingMaskIntoConstraints = false 
        self.view.addSubview(emptyImage)
        emptyImage.alpha=0.1
        NSLayoutConstraint.activate([
            emptyImage.centerXAnchor.constraint(equalTo: self.view.centerXAnchor),
            emptyImage.centerYAnchor.constraint(equalTo: self.view.centerYAnchor),
            emptyImage.heightAnchor.constraint(equalToConstant: 90),
            emptyImage.widthAnchor.constraint(equalToConstant: 90)
            ])


        emptyLabel.text = "no present reminders"
        emptyLabel.textColor=UIColor.darkGray
        emptyLabel.font=UIFont(name: "HelveticaNeue-Light", size: 18)
        emptyLabel.textAlignment = NSTextAlignment.center

        emptyLabel2.text = "you add by going back to the homescreen"
        emptyLabel2.textColor=UIColor.gray
        emptyLabel2.font=UIFont(name: "HelveticaNeue-Light", size: 11)
        emptyLabel2.textAlignment = NSTextAlignment.center


        self.tableView.separatorStyle = UITableViewCellSeparatorStyle.none

        return 0
    }
    else{
         return (list.count)
    }

}

override func tableView(_ tableView: UITableView, cellForRowAt indexPath: IndexPath) -> UITableViewCell {

    let cell=UITableViewCell(style: UITableViewCellStyle.default, reuseIdentifier: "cell")
    cell.textLabel?.text=list[indexPath.row]
    cell.contentView.backgroundColor = UIColor(red:0.89, green:0.89, blue:0.89, alpha:0.7)
    cell.textLabel?.textColor=UIColor.black
    cell.textLabel?.font=UIFont(name: "HelveticaNeue-Light", size: 16)
    return (cell)
}





override func tableView(_ tableView: UITableView, commit editingStyle: UITableViewCellEditingStyle, forRowAt indexPath: IndexPath) {
    if editingStyle==UITableViewCellEditingStyle.delete{
        list.remove(at: indexPath.row)
        tableView.reloadData()
    }
}
}

Answer 1

numberOfRowsInSection 被多次调用，所以没有添加 subview 的好地方，因为每次调用此函数时另一个 UILabel 的实例添加到 View 层次结构。

删除 numberOfRowsInSection 中的添加标签。添加类变量:

var emptyLabel: UILabel!
var emptyLabel2: UILabel!
var emptyImage: UIImageView!

然后添加函数

 func createEmptyLabels() {
    emptyLabel=UILabel(frame: CGRect(x: 0,y: 0, width: self.view.bounds.width, height: self.view.bounds.height))
    emptyLabel2=UILabel(frame: CGRect(x: 0.0,y: 20.0, width: self.view.bounds.width, height: self.view.bounds.height))


    self.view.addSubview(emptyLabel2)
    self.view.addSubview(emptyLabel)

    emptyImage = UIImageView(image: UIImage(named: "Quote Right Filled-100 (3)"))
    emptyImage.translatesAutoresizingMaskIntoConstraints = false
    self.view.addSubview(emptyImage)
    emptyImage.alpha=0.1
    NSLayoutConstraint.activate([
        emptyImage.centerXAnchor.constraint(equalTo: self.view.centerXAnchor),
        emptyImage.centerYAnchor.constraint(equalTo: self.view.centerYAnchor),
        emptyImage.heightAnchor.constraint(equalToConstant: 90),
        emptyImage.widthAnchor.constraint(equalToConstant: 90)
        ])


    emptyLabel.text = "no present reminders"
    emptyLabel.textColor=UIColor.darkGray
    emptyLabel.font=UIFont(name: "HelveticaNeue-Light", size: 18)
    emptyLabel.textAlignment = NSTextAlignment.center

    emptyLabel2.text = "you add by going back to the homescreen"
    emptyLabel2.textColor=UIColor.gray
    emptyLabel2.font=UIFont(name: "HelveticaNeue-Light", size: 11)
    emptyLabel2.textAlignment = NSTextAlignment.center

    emptyLabel.isHidden = true
    emptyLabel2.isHidden = true
    emptyImage.isHidden = true
}

在viewDidLoad中调用这个函数

在 numberOfRowsInSection 中:

let hideEmptyViews = (list.count != 0)
emptyLabel.isHidden = hideEmptyViews
emptyLabel2.isHidden = hideEmptyViews
emptyImage.isHidden = hideEmptyViews