根据方向更新自动布局约束

Question

我有一个 ViewController class 有一个 textField 变量，它被配置在 ViewController.

的 viewDidLoad 方法中设置时

class ViewController: UIViewController {

    weak var textField: UITextField! {
        didSet {
            textField.delegate = self
            textField.placeholder = "Enter Text"
            view.addSubview(textField)
            view.addConstraint(NSLayoutConstraint(item: textField, attribute: .Width, relatedBy: .Equal, toItem: view, attribute: .Width, multiplier: 0.80, constant: 0))
            view.addConstraint(NSLayoutConstraint(item: textField, attribute: .Height, relatedBy: .Equal, toItem: view, attribute: .Height, multiplier: 0.05, constant: 0))
            view.addConstraint(NSLayoutConstraint(item: textField, attribute: .CenterX, relatedBy: .Equal, toItem: view, attribute: .CenterX, multiplier: 1, constant: 0))
            view.addConstraint(NSLayoutConstraint(item: textField, attribute: .CenterY, relatedBy: .Equal, toItem: view, attribute: .CenterY, multiplier: 1, constant: 0))
        }
    }

    override func viewDidLoad() {
        super.viewDidLoad()
        textField = UITextField()
    }
}

视图中添加了一组自动布局约束。我想要这个文本字段居中于中间（.CenterX 和 .CenterY），为宽度（高度）的 80% (5%) ViewController 的 view 在纵向模式下计算。

如果设备的方向 (UIDevice.currentDevice().orientation) 旋转到横向，或者从横向呈现，我想要宽度（高度）保持与纵向相同。

正在为 toItem 中的 attribute 更改：

view.addConstraint(NSLayoutConstraint(item: textField, attribute: .Height, relatedBy: .Equal, toItem: view, attribute: .Height, multiplier: 0.05, constant: 0))

至：

attribute: (UIDeviceOrientationIsPortrait(UIDevice.currentDevice().orientation) ? .Height : .Width)

没有成功，因为我猜 textField 在设备切换方向时没有得到（重新）设置。此外，此检查对于 Swift 似乎有点笨拙。我是不是错过了自动布局的技巧？

Answer 1

一个解决方案是获取屏幕的固定坐标范围 (iOS >= 8) 并适当调整前两个约束：

class ViewController: UIViewController, UITextFieldDelegate {

    override func viewDidLoad() {
        super.viewDidLoad()

        let textField = UITextField()
        textField.translatesAutoresizingMaskIntoConstraints = false
        textField.delegate = self
        textField.placeholder = "Enter Text"
        view.addSubview(textField)

        textField.backgroundColor = UIColor.redColor()
        textField.textAlignment = .Center

        let fixedScreenBounds = UIScreen.mainScreen().fixedCoordinateSpace.bounds

        NSLayoutConstraint.activateConstraints([
            NSLayoutConstraint(item: textField, attribute: .Width, relatedBy: .Equal, toItem: nil, attribute: .NotAnAttribute, multiplier: 0, constant: 0.8*fixedScreenBounds.width),
            NSLayoutConstraint(item: textField, attribute: .Height, relatedBy: .Equal, toItem: nil, attribute: .NotAnAttribute, multiplier: 0, constant: 0.05*fixedScreenBounds.height),
            NSLayoutConstraint(item: textField, attribute: .CenterX, relatedBy: .Equal, toItem: view, attribute: .CenterX, multiplier: 1, constant: 0),
            NSLayoutConstraint(item: textField, attribute: .CenterY, relatedBy: .Equal, toItem: view, attribute: .CenterY, multiplier: 1, constant: 0)
            ])
    }
}

另外，请注意，由于您是在代码中创建文本字段并且想要使用自动布局，因此必须将其 translatesAutoresizingMaskIntoConstraints 设置为 false。

Answer 2

实际上你代码中的问题是你没有将textField的translatesAutoresizingMaskIntoConstraints设置为false，每当你想使用自动布局约束时，你必须将视图的 translatesAutoresizingMaskIntoConstraints 设置为 false.

我已经更新了你的代码看看它工作正常。

class ViewController: UIViewController, UITextFieldDelegate {    
    weak var textField: UITextField! {
        didSet {
            textField.delegate = self
            textField.placeholder = "Enter Text"
            view.addSubview(textField)
            // to see the size of textField
            textField.backgroundColor = UIColor.purpleColor()

            textField.translatesAutoresizingMaskIntoConstraints = false

            view.addConstraint(NSLayoutConstraint(item: textField, attribute: .Width, relatedBy: .Equal, toItem: view, attribute: .Width, multiplier: 0.80, constant: 0))
            view.addConstraint(NSLayoutConstraint(item: textField, attribute: .Height, relatedBy: .Equal, toItem: view, attribute: .Height, multiplier: 0.05, constant: 0))
            view.addConstraint(NSLayoutConstraint(item: textField, attribute: .CenterX, relatedBy: .Equal, toItem: view, attribute: .CenterX, multiplier: 1, constant: 0))
            view.addConstraint(NSLayoutConstraint(item: textField, attribute: .CenterY, relatedBy: .Equal, toItem: view, attribute: .CenterY, multiplier: 1, constant: 0))
        }
    }

    override func viewDidLoad() {
        super.viewDidLoad()
        textField = UITextField()

    }
}

根据方向更新自动布局约束

Updating autolayout constraints depending on orientation

screen-orientation

ios

autolayout

swift