Swift解决UITableView空数据视图问题的简单方法

private let EmptyViewTag = 12345;

protocol EmptyViewProtocol: NSObjectProtocol {
 
 ///用以判断是会否显示空视图
 var showEmtpy: Bool {get}
 
 ///配置空数据提示图用于展示
 func configEmptyView() -> UIView?
}

extension EmptyViewProtocol {
 
 func configEmptyView() -> UIView? {
  return nil
 }
}

 func setEmtpyViewDelegate(target: EmptyViewProtocol) {
  self.emptyDelegate = target
  DispatchQueue.once(#function) {
   BQTool.exchangeMethod(cls: self.classForCoder, targetSel: #selector(self.layoutSubviews), newSel: #selector(self.re_layoutSubviews))
  }
 }

 @objc func re_layoutSubviews() {
  self.re_layoutSubviews()
  
  if self.emptyDelegate!.showEmtpy {
   
   guard let view = self.emptyDelegate?.configEmptyView() else {
    return;
   }
   
   view.tag = EmptyViewTag;
   self.addSubview(view)
   
  } else {
   
   guard let view = self.viewWithTag(EmptyViewTag) else {
    return;
   }
   view .removeFromSuperview()
  }
 }
 
//MARK:- ***** Associated Object *****
 private struct AssociatedKeys {
  static var emptyViewDelegate = "tableView_emptyViewDelegate"
 }
 
 private var emptyDelegate: EmptyViewProtocol? {
  get {
   return (objc_getAssociatedObject(self, &AssociatedKeys.emptyViewDelegate) as! EmptyViewProtocol)
  }
  set (newValue){
   objc_setAssociatedObject(self, &AssociatedKeys.emptyViewDelegate, newValue!, .OBJC_ASSOCIATION_RETAIN)
  }
 }

//关键部分代码
class ViewController: UIViewController , EmptyViewProtocol {

 private var datas: Array<Dictionary<String, String>>?
 /// 空数据提示图
 private var label: UILabel? 
 
 var showEmtpy: Bool {
  get {
   if let data = self.datas {
    return data.count == 0
   }
   return true
  }
 }
 
 override func viewDidLoad() {
  super.viewDidLoad()

  let tableView: UITableView = ...
  tableView.setEmtpyViewDelegate(target: self)
  self.view.addSubview(tableView)
 }
 
 func configEmptyView() -> UIView? {
 
  if let view = self.label {
   return view
  }
  
  let lab = UILabel(frame: CGRect(x: 100, y: 300, width: 200, height: 30))
  lab.text = "this is a test"
  lab.textAlignment = .center
  self.label = lab
  
  return lab
 }
}