ios - nslayoutconstraint 不使对象出现

Question

我下面的代码使用代码无 Storyboard 来显示对象。该项目已构建，但我看不到我试图以编程方式放置的文本字段。我不知道为什么代码没有出现。我试图不使用 Storyboard。

 var enterWeight = UITextField()




override func viewDidLoad() {
    super.viewDidLoad()

    view.addSubview(enterWeight)

    enterWeight.backgroundColor = UIColor.blue


    NSLayoutConstraint.activate ([

        enterWeight.topAnchor.constraint(equalTo: view.topAnchor, constant : 20),
        enterWeight.bottomAnchor.constraint(equalTo: view.bottomAnchor, constant : 20),
        enterWeight.leadingAnchor.constraint(equalTo: view.leadingAnchor, constant : 20),
        enterWeight.trailingAnchor.constraint(equalTo: view.trailingAnchor, constant : 20),


        enterWeight.widthAnchor.constraint(equalToConstant: 50),
        enterWeight.heightAnchor.constraint(equalToConstant: 30)

        ])

}

Answer 1

你有相互冲突的约束，它们永远不会以这种方式工作。

首先，正如 iFlames 提到的，您需要将 translatesAutoresizingMaskIntoConstraints 设置为 false:

enterWeight.translatesAutoresizingMaskIntoConstraints = false

然后:

NSLayoutConstraint.activate ([
        enterWeight.topAnchor.constraint(equalTo: view.topAnchor, constant : 20),
        enterWeight.leadingAnchor.constraint(equalTo: view.leadingAnchor, constant : 20),
        enterWeight.trailingAnchor.constraint(equalTo: view.trailingAnchor, constant : 20),
        enterWeight.heightAnchor.constraint(equalToConstant: 30)
])

通过给textField一个前导和尾随，你已经隐式地给了它一个宽度约束，它是view的宽度减去常量(20 * 2)，所以你不应该给它一个宽度约束，就会产生冲突。