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ios - 如何使用约束从下到上为 UIView 设置动画？

问题描述

我正在以编程方式创建 UIView，之后我将使用约束从下到上为该视图设置动画。但是动画不会显示在这个视图对象上。

        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()
            }
        }
    }

标签： iosswiftuiviewnslayoutanchor

解决方案

我通过评论指出了一些事情，阅读评论，你就会明白你的代码有什么问题，检查下面的代码。

=> 你的代码：overlay!.addSubview(contentView)

   @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
                }
            }
        }

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