Question

我正在尝试使用已编程的约束来创建按钮。我试图不使用情节提要。我在拆开按钮时遇到麻烦。我该怎么做？

import UIKit

var aa: [NSLayoutConstraint] = []

class ViewController: UIViewController {

    var btn: UITextField!

    override func viewDidLoad() {
        super.viewDidLoad()

        self.view.addSubview(btn)
        let leadingc2 = btn.widthAnchor.constraint(equalToConstant: 80)
        let trailingC2 = btn.heightAnchor.constraint(equalToConstant: 50)
        let topc2 = btn.centerXAnchor.constraint(equalTo: self.view.centerXAnchor, constant: -50)
        let bottomc2 = btn.centerYAnchor.constraint(equalTo: self.view.centerYAnchor, constant: -250)

        aa = [leadingc2,trailingC2,topc2,bottomc2]

        NSLayoutConstraint.activate(aa)
    }
}

Answer 1

您不需要打开包装。您需要先实例化它，然后再使用它。

override func viewDidLoad() {
    super.viewDidLoad()

    btn = UITextField() // Create the button like this before using it.
    self.view.addSubview(btn)

    btn.translatesAutoresizingMaskIntoConstraints = false
    let leadingc2 = btn.widthAnchor.constraint(equalToConstant: 80)
    let trailingC2 = btn.heightAnchor.constraint(equalToConstant: 50)
    let topc2 = btn.centerXAnchor.constraint(equalTo: self.view.centerXAnchor, constant: -50)
    let bottomc2 = btn.centerYAnchor.constraint(equalTo: self.view.centerYAnchor, constant: -250)

    aa = [leadingc2,trailingC2,topc2,bottomc2]

    NSLayoutConstraint.activate(aa)

}

用!声明的任何变量都将被强制解包，这意味着如果您忘记创建实例并使用该变量，它将抛出错误并使应用程序崩溃。

Answer 2

使用此代码：

@Entity(name = "my_entit_name")

如何解包已编程的UIButton（swift4）

2 个答案: