UIImageView忽略宽度/高度约束

Question

这是我的班级：

class Some: UIView{
override init(frame: CGRect) {
    super.init(frame: frame)
    load()

}

required init?(coder aDecoder: NSCoder) {
    super.init(coder: aDecoder)
    load()
}

private func load(){
    let someImage = UIImageView()
    someImage.translatesAutoresizingMaskIntoConstraints = false
    someImage.image = UIImage(named: "Test")
    self.addSubview(someImage)
    someImage.centerYAnchor.constraint(equalTo: self.centerYAnchor).isActive = true
    someImage.centerXAnchor.constraint(equalTo: self.centerXAnchor).isActive = true
    someImage.widthAnchor.constraint(equalTo: self.widthAnchor, multiplier: 0.5)
    someImage.heightAnchor.constraint(equalTo: self.heightAnchor, multiplier: 0.5)
    }
}

结果如下：

（橙色是我的ViewController的背景）

为什么我的图片会忽略这一行：

someImage.widthAnchor.constraint(equalTo: self.widthAnchor, multiplier: 0.5)
someImage.widthAnchor.constraint(equalTo: self.widthAnchor, multiplier: 0.5)

图像中的乘数明显为1.0。它实际上应该占据屏幕的一半，高度和宽度，如乘数（0.5）所示。我做错了什么？

Answer 1

仅仅是我还是最后两个限制中缺少“.isActive = true”？