设备方向后的 UIView 位置 [英] UIView Position After Device Orientation

问题描述

考虑将一个视图作为子视图添加到主视图中，如下所示:

Consider that a view is added as subview to the main view as follows:

override func viewDidLoad()
{
    super.viewDidLoad()
    let subview = UIView(frame: CGRect(x: 150, y: 350, width: 20, height: 20))
    subview.backgroundColor = UIColor.blue
    self.view.addSubview(subview)
}

当设备从纵向变为横向时，默认行为是子视图以一种方式移动，它与设备左上角的水平和垂直距离保持不变.我怎样才能改变它，使其与设备中心的水平和垂直距离保持不变?谢谢

When the device goes from portrait to landscape, the default behaviour is that the subview is moved in a way that its horizontal and vertical distance from the upper left corner of the device, remain unchanged. How can i change this so that its horizontal and vertical distance from the center of the device, remain unchanged? Thank you

推荐答案

最简单的方法是为视图使用约束而不是固定框架.代码看起来像这样:

The easiest way is to use constraints instead of a fixed frame for your view. The code would look something like this:

override func viewDidLoad()
{
    super.viewDidLoad()
    let subview = UIView()

    /// You do not need to refer to self and UIColor, Swift does that for you.
    subview.backgroundColor = .blue
    view.addSubview(subview)

    /// Do not forget the following line
    subview.translatesAutoresizingMaskIntoConstraints = false

    /// Create and activate your constraints in one step.
    NSLayoutConstraint.activate([
        /// Set the height and width of your subview
        subview.heightAnchor.constraint(equalToConstant: 20),
        subview.widthAnchor.constraint(equalToConstant: 20),

        /// This centers the subview vertically and horizontally in the parent view
        subview.centerXAnchor.constraint(equalTo: view.centerXAnchor),
        subview.centerYAnchor.constraint(equalTo: view.centerYAnchor)
    ])
}

你也应该重构上面的代码，例如设置所有内容并在 viewDidLoad 中调用它的 create 方法.

Also you should refactor the code above, e.g. create method that sets up everything and call it inside of viewDidLoad.

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