如何使用约束自底向上动画UIView？

Question

我正在以编程方式创建UIView，之后我将使用约束从下到上设置该视图的动画。但动画不会显示在此视图对象上。

        overlay!.addSubview(contentView)
        contentView.translatesAutoresizingMaskIntoConstraints = false
        contentView.leadingAnchor.constraint(equalTo: vc.view.leadingAnchor, constant: 20).isActive = true
        contentView.trailingAnchor.constraint(equalTo: vc.view.trailingAnchor, constant: -20).isActive = true

        contentView.addSubview(messageLabel)
        messageLabel.leadingAnchor.constraint(equalTo: contentView.leadingAnchor, constant: 8).isActive = true
        messageLabel.trailingAnchor.constraint(equalTo: contentView.trailingAnchor, constant: -8).isActive = true
        messageLabel.topAnchor.constraint(equalTo: contentView.topAnchor, constant: 8).isActive = true
        messageLabel.bottomAnchor.constraint(equalTo: contentView.bottomAnchor, constant: -8).isActive = true

        let width: CGFloat = vc.view.frame.width - 40 - 16
        stringHeight = calculateEstimatedHeight(width: width, text: text) + 16
        contentView.heightAnchor.constraint(equalToConstant: stringHeight).isActive = true

        bottomConstraint = contentView.bottomAnchor.constraint(equalTo: vc.view.bottomAnchor, constant: stringHeight)
        bottomConstraint.isActive = true

        DispatchQueue.main.asyncAfter(deadline: .now() + 1.5) {
            self.showToastViewWithAnimation(viewController: vc)
        }


@objc func showToastViewWithAnimation(viewController: Any) {
        if let vc = viewController as? ViewController {

            vc.view.layoutIfNeeded()

            UIView.animate(withDuration: 0.8) {
                self.bottomConstraint.constant = -20
                vc.view.layoutIfNeeded()
            }
        }
    }

Answer 1

在代码中添加此行：

self.translatesAutoresizingMaskIntoConstraints = false
contentView.translatesAutoresizingMaskIntoConstraints = false

在你的ShowToastView函数中，首先找到哪个是底部约束，然后尝试这样更新它（记住它是一个提示代码，你可以根据你的要求更新它）：

@objc func showToastViewWithAnimation(viewController: Any) {
    if let vc = viewController as? ViewController {
        if let bottom = self.contentView.superview?.constraints.first(where: { (constraint) -> Bool in
        return constraint.firstAttribute == .bottom}){ 
// in this condition find your bottom constraint and update it, don't save your constraint in a variable.
           bottom.constant = -20 
           UIView.animate(withDuration: 0.8, animations: {               
             vc.view.layoutIfNeeded()
           }) { (complete) in

           }
        }
    }
}

Answer 2

我通过评论指出了一些事情，阅读评论，您将了解代码中的问题，请查看下面的代码。

=

   @objc func showToastViewWithAnimation(viewController: Any) {
            if let vc = viewController as? ViewController {
                //vc.view.layoutIfNeeded() - this is not required before updating constraint value
                self.bottomConstraint.constant = -20 //update contstraint outside of the animation block
                UIView.animate(withDuration: 0.8) {                
                    //vc.view.layoutIfNeeded() 
                    self.overlay?.layoutIfNeeded() //you needs to layout the overlay view, as your other toast views are added in overlay view and not in view of viewcontroller as per your code
                }
            }
        }