ios - 设置约束后 subview 无法显示

Question

我想在 ImageView 顶部添加一个带有文本“Original”的小覆盖 View ，该 View 仅在用户查看原始图像时才可见。

这是我的toggleImage函数，当用户按下它时， ImageView 将显示原始图像(并且将弹出带有文本“原始”的 View )，然后当用户抬起手时返回到过滤后的图像。

    func toggleImage(sender: UILongPressGestureRecognizer) {
    sender.minimumPressDuration = 0.3
    if sender.state == .Began{
        imageView.image = self.rawImage!

        view.addSubview(originalText)


    }else if sender.state == .Ended{
        imageView.image = self.newImage
    }

现在我想用文本对 View 设置约束。

    func toggleImage(sender: UILongPressGestureRecognizer) {
    sender.minimumPressDuration = 0.3
    if sender.state == .Began{
        imageView.image = self.rawImage!

        view.addSubview(originalText)

        originalText.translatesAutoresizingMaskIntoConstraints = false

        let bottomConstraint = originalText.bottomAnchor.constraintEqualToAnchor(view.topAnchor)
        let leftConstriant = originalText.leftAnchor.constraintEqualToAnchor(view.leftAnchor)
        let rightConstraint = originalText.rightAnchor.constraintEqualToAnchor(view.rightAnchor)
        let heightConstraint = originalText.heightAnchor.constraintEqualToConstant(44)

        NSLayoutConstraint.activateConstraints([bottomConstraint,leftConstriant,rightConstraint,heightConstraint])
        view.layoutIfNeeded()



    }else if sender.state == .Ended{
        imageView.image = self.newImage
    }

subview 现在无法显示，如何解决这个问题？

这是未设置约束时模拟器的屏幕截图。 screenshot

Answer 1

底部等于顶部:

let bottomConstraint = originalText.bottomAnchor.constraintEqualToAnchor(view.topAnchor)

您的 View 很可能在屏幕外/ View 边界之外渲染。

将其更改为:

let topConstraint = originalText.topAnchor.constraintEqualToAnchor(view.topAnchor)