如何设置下拉菜单的动画显示？

Question

我需要帮助创建一个带有子控制器表的下拉菜单。

示例代码：

class ParentViewController: UIViewController {


  func displayShowCountries() {

   if let textField = self.activeTextField, let superview = textField.superview {
       let convert = superview.convert(textField.frame, to: self.view)

       let row = viewModel.count - 1
       let indexPath = IndexPath(row: row, section: 0)
       guard let cell = tableView.cellForRow(at: indexPath) else { return }
       let cellConvert = tableView.convert(cell.frame, to: self.view)


       addChild(selectCountry)
       view.addSubview(selectCountry.view)
       selectCountry.didMove(toParent: self)

       // start frame
       selectCountry.view.frame = CGRect(x: convert.origin.x, y: convert.maxY, width: convert.width, height: 0)

       let height = (cellConvert.origin.y - convert.origin.y) + 8

       UIView.animate(
          withDuration: 0.3, 
          delay: 0, 
          usingSpringWithDamping: 1, 
          initialSpringVelocity: 1, 
          options: .curveEaseOut, 
          animations: {
               self.selectCountry.view.frame = CGRect(x: convert.origin.x, y: convert.maxY, width: convert.width, height: height)
          },
          completion: nil)
    }

  }
}

对于SelectCountry（）

class SelectCountry: UIViewController {

   override func viewDidLayoutSubviews() {
        super.viewDidLayoutSubviews()

        tableView.frame = view.bounds
    }

}

动画仅适用于selectCountry.view，但它位于selectCountry.view的所有内容都不会显示动画。

Answer 1

尝试在动画块中添加self.view.layoutIfNeeded()，如下所示

 UIView.animate(
          withDuration: 0.3, 
          delay: 0, 
          usingSpringWithDamping: 1, 
          initialSpringVelocity: 1, 
          options: .curveEaseOut, 
          animations: {
               self.selectCountry.view.frame = CGRect(x: convert.origin.x, y: convert.maxY, width: convert.width, height: height)
    self.view.layoutIfNeeded()
          },
          completion: nil)

Answer 2

动画不会对你的selectCountry.view的子视图起作用，因为你只为selectCountry.view的框架设置动画，并且因为它的子视图的框架不是“相对”它的框架它们不会动画，这就是为什么你应该使用autoLayout，甚至是编程，至少要设置相对于selectCountry.view的子视图的约束，这样当它的帧改变时，它们将相应地改变