试图为 UITextfield 宽度约束设置动画，但它不起作用

Posted 2023-02-23

【中文标题】试图为 UITextfield 宽度约束设置动画，但它不起作用

【英文标题】：Trying to animate UITextfield width constraint, but it won't work

【发布时间】：2019-10-11 20:03:46

【问题描述】：

我正在尝试为 UITextfield 的宽度约束设置动画，我想要实现的是在动画时将 UITextfield 从宽度 0 变为宽度 X。

这是我目前所拥有的：

let MAX_SEARCH_BAR_WIDHT: CGFloat = 285
var searchBarWidth: CGFloat = 0

private func setupSearchBar()  
    addSubview(searchBar)
    NSLayoutConstraint.activate([
        searchBar.topAnchor.constraint(equalTo: self.safeAreaLayoutGuide.topAnchor, constant: 8),
        searchBar.trailingAnchor.constraint(equalTo: searchBtn.leadingAnchor, constant: -8),
        searchBar.heightAnchor.constraint(equalToConstant: 30),
        searchBar.widthAnchor.constraint(equalToConstant: searchBarWidth),
    ])

这是我尝试为 UITextfield 设置动画的地方：

func handleSearch() 
    mView.isSearchingAlready = !mView.isSearchingAlready
    UIView.animate(withDuration: 0.3, delay: 0, options: .curveEaseInOut, animations: 
        self.mView.searchBarWidth += self.mView.MAX_SEARCH_BAR_WIDHT
        self.mView.layoutIfNeeded()
    , completion: nil)

当我点击搜索按钮时会调用handleSearch。 单击按钮时， UITextfield 不会出现。 这是 UITextfield：

let searchBar: UITextField = 
   let field = UITextField(frame: CGRect(x: 0, y: 0, width: 1, height: 0))
    field.backgroundColor = .appWhite
    field.tintColor = UIColor.clear
    field.translatesAutoresizingMaskIntoConstraints = false
    field.layer.cornerRadius = 15
    field.isHidden = false

    let padding = UIView(frame: CGRect(x: 0, y: 0, width: 8, height: 1))
    field.leftView = padding
    field.leftViewMode = .always
    field.rightView = padding
    field.rightViewMode = .always

    field.attributedPlaceholder = NSAttributedString(string: NSLocalizedString("searchbar.placeholder", comment: "find"), attributes: [NSAttributedString.Key.foregroundColor: UIColor.init(hexString: "#080708", alpha: 0.5)])

    return field
()

【问题讨论】：

激活运行后更改 searchBarWidth 不会反映到约束的值

【参考方案1】：

你应该改变约束的常量值，所以创建一个 var

var widthCon:NSLayoutConstraint! 

从激活块中获取宽度约束

widthCon = searchBar.widthAnchor.constraint(equalToConstant: searchBarWidth)
widthCon.isActive = true

然后

func handleSearch() 
    mView.isSearchingAlready = !mView.isSearchingAlready
    self.mView.widthcon.constant = self.mView.MAX_SEARCH_BAR_WIDHT
    UIView.animate(withDuration: 0.3, delay: 0, options: .curveEaseInOut, animations:  
        self.view.layoutIfNeeded()
    , completion: nil)