xcode - Swift:如何声明 View 后代

Question

我正在尝试添加以下约束来对齐表格单元格内的图像。 self 指的是 ImageView 将驻留在其中的 UITableViewCell 对象:

    var imageViewTest = UIImageView();

    self.rowImageView = imageViewTest;

    var xAlignmentConstraint = NSLayoutConstraint(
        item: imageViewTest,
        attribute: NSLayoutAttribute.CenterX,
        relatedBy: NSLayoutRelation.Equal,
        toItem: self,
        attribute: NSLayoutAttribute.CenterX,
        multiplier: 1,
        constant: 137
    );


NSLayoutConstraint.activateConstraints([xAlignmentConstraint]);

self.addConstraint(xAlignmentConstraint);

运行代码时，出现以下错误:

Unable to activate constraint with items because they have no common ancestor. Does the constraint reference items in different view hierarchies? That's illegal.

如何声明 imageViewTest 是 self 的后代？

Answer 1

您需要添加rowImageView作为self的 subview 。

var imageViewTest = UIImageView()
self.rowImageView = imageViewTest
self.addSubview(self.rowImageView)