ios - 尝试以编程方式实现约束时约束被忽略

Question

我试图通过设置约束使 logoImage 水平和垂直居中，但在测试时，它显示在 (x:0, y:0) 上。知道如何解决这个问题吗？谢谢

var movieView : UIView?
let logoImage = UIImageView(image: #imageLiteral(resourceName: "my_logo"))

// This function runs in viewWillAppear
internal func setupIntroMovie() {
    movieView = UIView(frame: view.frame)
    view.addSubview(movieView!)
    view.addSubview(logoImage)

    let horizontalConstraint = NSLayoutConstraint(item: logoImage,
                                                  attribute: .centerX,
                                                  relatedBy: .equal,
                                                  toItem: view,
                                                  attribute: .centerX,
                                                  multiplier: 1,
                                                  constant: 0)
    let verticalConstraint = NSLayoutConstraint(item: logoImage,
                                                attribute: .centerY,
                                                relatedBy: .equal,
                                                toItem: view,
                                                attribute: .centerY,
                                                multiplier: 1,
                                                constant: 0)
    view.addConstraints([horizontalConstraint,
                              verticalConstraint])
    updateViewConstraints()
}

Answer 1

您需要设置 logoImage.translatesAutoresizingMaskIntoConstraints = false，因为它确定 View 的自动调整掩码是否转换为自动布局约束。

internal func setupIntroMovie() {
        movieView = UIView(frame: view.frame)
        view.addSubview(movieView!)
        view.addSubview(logoImage)

        let horizontalConstraint = NSLayoutConstraint(item: logoImage,
                                                      attribute: .centerX,
                                                      relatedBy: .equal,
                                                      toItem: view,
                                                      attribute: .centerX,
                                                      multiplier: 1,
                                                      constant: 0)
        let verticalConstraint = NSLayoutConstraint(item: logoImage,
                                                    attribute: .centerY,
                                                    relatedBy: .equal,
                                                    toItem: view,
                                                    attribute: .centerY,
                                                    multiplier: 1,
                                                    constant: 0)
        // Update 
        logoImage.translatesAutoresizingMaskIntoConstraints = false

        view.addConstraints([horizontalConstraint,
                             verticalConstraint])
        updateViewConstraints()
    }

If this property’s value is true, the system creates a set of constraints that duplicate the behavior specified by the view’s autoresizing mask. This also lets you modify the view’s size and location using the view’s frame , bounds , or center properties, allowing you to create a static, frame-based layout within Auto Layout.