从xib加载自定义视图后，IBOutlet属性为零

Question

IBOutlets发生了一些奇怪的事情。

在代码中我尝试访问此属性，但它们是nil。码：

class CustomKeyboard: UIView {

    @IBOutlet var aButt: UIButton!
    @IBOutlet var oButt: UIButton!

    class func keyboard() -> UIView {
        let nib = UINib(nibName: "CustomKeyboard", bundle: nil)
        return nib.instantiateWithOwner(self, options: nil).first as UIView
    }

    override init() {
        super.init()
        commonInit()
    }

    override init(frame: CGRect) {
        super.init(frame: frame)
        commonInit()
    }

    required init(coder aDecoder: NSCoder) {
        super.init(coder: aDecoder)
        commonInit()
    }

    // MARK: - Private
    private func commonInit() {
        println(aButt)
        // aButt is nil

        aButt = self.viewWithTag(1) as UIButton
        println(aButt)
        // aButt is not nil
    }
}

Answer 1

这是预期的，因为在初始化程序被调用时没有分配IBOutlet。您不需要commonInit，只需覆盖awakeFromNib，如下所示：

override func awakeFromNib() {
    super.awakeFromNib()

    print(aButt)
}

Answer 2

假设您尝试了连接IBOutlet的标准故障排除步骤，请尝试以下操作：

显然，您需要在某些运行时情况下禁用nib唤醒。

  override func awakeAfter(using aDecoder: NSCoder) -> Any? {
      guard subviews.isEmpty else { return self }
      return Bundle.main.loadNibNamed("MainNavbar", owner: nil, options: nil)?.first
  }

Answer 3

您的笔尖可能未连接。我的解决方案非常简单。在项目的某个地方（我创建了一个名为UIViewExtension.swift的类），使用这个方便的connectNibUI方法添加UIView的扩展。

extension UIView {
    func connectNibUI() {
        let nib = UINib(nibName: String(describing: type(of: self)), bundle: nil).instantiate(withOwner: self, options: nil)
        let nibView = nib.first as! UIView
        nibView.translatesAutoresizingMaskIntoConstraints = false

        self.addSubview(nibView)
        //I am using SnapKit cocoapod for this method, to update constraints.  You can use NSLayoutConstraints if you prefer.
        nibView.snp.makeConstraints { (make) -> Void in
            make.edges.equalTo(self)
        }
    }
}

现在您可以在任何视图上调用此方法，在init方法中，执行以下操作：

override init(frame: CGRect) {
    super.init(frame: frame)
    connectNibUI()
}

Answer 4

你是如何从控制器发起你的观点的？像这样：

var view = CustomKeyboard.keyboard()
self.view.addSubview(view)

Answer 5

在@ScottyBlades的基础上，我创建了这个子类：

class UIViewXib: UIView {
    // I'm finding this necessary when I name a Xib-based UIView in IB. Otherwise, the IBOutlets are not loaded in awakeFromNib.
    override func awakeAfter(using aDecoder: NSCoder) -> Any? {
        guard subviews.isEmpty else { return self }
        return Bundle.main.loadNibNamed(typeName(self), owner: nil, options: nil)?.first
    }
}

func typeName(_ some: Any) -> String {
    return (some is Any.Type) ? "\(some)" : "\(type(of: some))"
}