nslayout 约束不使对象出现

Question

我下面的代码使用没有故事板的代码来显示对象。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。我试图不使用故事板。

 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

您需要将 translatesAutoresizingMaskIntoConstraints 设置为 false:

enterWeight.translatesAutoresizingMaskIntoConstraints = false

Answer 2

您有相互冲突的约束，它们永远不会以这种方式工作。

首先，如iFlames所述，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，会引起冲突。

nslayout 约束不使对象出现

nslayout constraint not making object appear

ios

swift4

nslayoutconstraint

subview