以编程方式添加带有自动布局的uibutton

Question

我想像这样添加UIButton：

 let switchTheme: UIButton = {
    let button = UIButton.init()
    button.backgroundColor = .red
    button.setTitleColor(.blue, for: .normal)
    button.setTitle(Settings.isLightTheme() ? Strings.Various.switchToDark.value : Strings.Various.switchToLight.value, for: .normal)
    button.translatesAutoresizingMaskIntoConstraints = false
    return button
}()

然后设置约束如：

switchTheme.bottomAnchor.constraint(equalTo: view.bottomAnchor)
switchTheme.leftAnchor.constraint(equalTo: view.leftAnchor)
switchTheme.rightAnchor.constraint(equalTo: view.rightAnchor)
switchTheme.heightAnchor.constraint(equalToConstant: 40.0)

但它不是在底部显示，而是在顶部并且没有应用约束。

Answer 1

您需要设置约束activate state = true。你可以做到这一点，

NSLayoutConstraint.activate([
    //Move your existing code HERE with comma separated
])

如有任何问题，您可以检查以下功能：

func setConstraints() {
    NSLayoutConstraint.activate([
        switchTheme.bottomAnchor.constraint(equalTo: self.view.safeAreaLayoutGuide.bottomAnchor), // bottomAnchor to set bottom target.
        switchTheme.leftAnchor.constraint(equalTo: self.view.leftAnchor), // leftAnchor to set X left
        switchTheme.rightAnchor.constraint(equalTo: self.view.rightAnchor), // rightAnchor to set X right
        switchTheme.heightAnchor.constraint(equalToConstant: 40.0) //heightAnchor to set appropriate height.
    ])
}

Answer 2

你需要像这样简单地激活这些约束：

 switchTheme.bottomAnchor.constraint(equalTo: view.bottomAnchor).isActive = true
 switchTheme.leftAnchor.constraint(equalTo: view.leftAnchor).isActive = true
 switchTheme.rightAnchor.constraint(equalTo: view.rightAnchor).isActive = true
 switchTheme.heightAnchor.constraint(equalToConstant: 40.0).isActive = true

Answer 3

您的约束必须激活：

switchTheme.bottomAnchor.constraint(equalTo: view.bottomAnchor).isActive = true