以编程方式添加约束不起作用
Adding Constraint Programmatically Does Not Work
我正在以编程方式设置对图像视图的约束,如下所示:
imgScrollView = UIScrollView(frame: CGRect(x: 0, y: 0, width: 100, height: 100))
imgScrollView.showsHorizontalScrollIndicator = false
imgScrollView.showsVerticalScrollIndicator = false
imgScrollView.bouncesZoom = false
imgScrollView.bounces = false
view.addSubview(imgScrollView)
imgScrollView.translatesAutoresizingMaskIntoConstraints = false
imgScrollView.topAnchor.constraint(equalTo: view.safeAreaLayoutGuide.topAnchor, constant: 0).isActive = true
imgScrollView.bottomAnchor.constraint(equalTo: toolBar.topAnchor, constant: -100).isActive = true
imgScrollView.leftAnchor.constraint(equalTo: view.safeAreaLayoutGuide.leftAnchor, constant: 0).isActive = true
imgScrollView.rightAnchor.constraint(equalTo: view.safeAreaLayoutGuide.rightAnchor, constant: 0).isActive = true
// add image view to scrollview
imgView = UIImageView(frame: CGRect(x: 0, y: 0,width: 100, height: 100))
imgScrollView.addSubview(imgView)
imgView.translatesAutoresizingMaskIntoConstraints = false
imgView.topAnchor.constraint(equalTo: imgScrollView.contentLayoutGuide.topAnchor, constant: 0).isActive = true
imgView.bottomAnchor.constraint(equalTo: imgScrollView.contentLayoutGuide.bottomAnchor, constant: 0).isActive = true
imgView.leftAnchor.constraint(equalTo: imgScrollView.contentLayoutGuide.leftAnchor, constant: 0).isActive = true
imgView.rightAnchor.constraint(equalTo: imgScrollView.contentLayoutGuide.rightAnchor, constant: 0).isActive = true
imgView.widthAnchor.constraint(equalTo: imgScrollView.widthAnchor, multiplier: 1).isActive = true
现在稍后通过点击按钮添加额外的约束
imgView.heightAnchor.constraint(equalTo: imgScrollView.heightAnchor, multiplier: 1).isActive = true
但是没有添加约束。为什么会这样?
你的实现逻辑对我有用。
- 左图显示了没有高度限制的实现。
- 右图显示按下高度限制的按钮。
在函数 viewDidLoad 中
override func viewDidLoad() {
super.viewDidLoad()
view.backgroundColor = .white
scrollView.isScrollEnabled = true
scrollView.bounces = false
scrollView.alwaysBounceVertical = true
imageView.image = UIImage(color: .lightGray)
navigationItem.rightBarButtonItem = barButtonItem
view.addSubview(scrollView)
scrollView.addSubview(imageView)
scrollView.translatesAutoresizingMaskIntoConstraints = false
imageView.translatesAutoresizingMaskIntoConstraints = false
NSLayoutConstraint.activate([
scrollView.topAnchor.constraint(equalTo: view.safeAreaLayoutGuide.topAnchor),
scrollView.leftAnchor.constraint(equalTo: view.leftAnchor),
scrollView.bottomAnchor.constraint(equalTo: view.safeAreaLayoutGuide.bottomAnchor),
scrollView.rightAnchor.constraint(equalTo: view.rightAnchor)
])
NSLayoutConstraint.activate([
imageView.topAnchor.constraint(equalTo: scrollView.contentLayoutGuide.topAnchor),
imageView.leftAnchor.constraint(equalTo: scrollView.contentLayoutGuide.leftAnchor),
imageView.bottomAnchor.constraint(equalTo: scrollView.contentLayoutGuide.bottomAnchor),
imageView.rightAnchor.constraint(equalTo: scrollView.contentLayoutGuide.rightAnchor),
imageView.widthAnchor.constraint(equalTo: scrollView.widthAnchor)
])
}
在函数 buttonPressed 中
@objc func buttonPressed() {
navigationItem.rightBarButtonItem = nil
UIView.animate(withDuration: 1) {
NSLayoutConstraint.activate([
self.imageView.heightAnchor.constraint(equalTo: self.scrollView.heightAnchor)
])
self.view.setNeedsLayout()
self.view.layoutIfNeeded()
}
}
UIImage 实用程序 Create UIImage with solid color in Swift
fileprivate extension UIImage {
convenience init?(color: UIColor, size: CGSize = CGSize(width: 1, height: 1)) {
let rect = CGRect(origin: .zero, size: size)
UIGraphicsBeginImageContextWithOptions(rect.size, false, 0.0)
color.setFill()
UIRectFill(rect)
let image = UIGraphicsGetImageFromCurrentImageContext()
UIGraphicsEndImageContext()
guard let cgImage = image?.cgImage else { return nil }
self.init(cgImage: cgImage)
}
}
我正在以编程方式设置对图像视图的约束,如下所示:
imgScrollView = UIScrollView(frame: CGRect(x: 0, y: 0, width: 100, height: 100))
imgScrollView.showsHorizontalScrollIndicator = false
imgScrollView.showsVerticalScrollIndicator = false
imgScrollView.bouncesZoom = false
imgScrollView.bounces = false
view.addSubview(imgScrollView)
imgScrollView.translatesAutoresizingMaskIntoConstraints = false
imgScrollView.topAnchor.constraint(equalTo: view.safeAreaLayoutGuide.topAnchor, constant: 0).isActive = true
imgScrollView.bottomAnchor.constraint(equalTo: toolBar.topAnchor, constant: -100).isActive = true
imgScrollView.leftAnchor.constraint(equalTo: view.safeAreaLayoutGuide.leftAnchor, constant: 0).isActive = true
imgScrollView.rightAnchor.constraint(equalTo: view.safeAreaLayoutGuide.rightAnchor, constant: 0).isActive = true
// add image view to scrollview
imgView = UIImageView(frame: CGRect(x: 0, y: 0,width: 100, height: 100))
imgScrollView.addSubview(imgView)
imgView.translatesAutoresizingMaskIntoConstraints = false
imgView.topAnchor.constraint(equalTo: imgScrollView.contentLayoutGuide.topAnchor, constant: 0).isActive = true
imgView.bottomAnchor.constraint(equalTo: imgScrollView.contentLayoutGuide.bottomAnchor, constant: 0).isActive = true
imgView.leftAnchor.constraint(equalTo: imgScrollView.contentLayoutGuide.leftAnchor, constant: 0).isActive = true
imgView.rightAnchor.constraint(equalTo: imgScrollView.contentLayoutGuide.rightAnchor, constant: 0).isActive = true
imgView.widthAnchor.constraint(equalTo: imgScrollView.widthAnchor, multiplier: 1).isActive = true
现在稍后通过点击按钮添加额外的约束
imgView.heightAnchor.constraint(equalTo: imgScrollView.heightAnchor, multiplier: 1).isActive = true
但是没有添加约束。为什么会这样?
你的实现逻辑对我有用。
- 左图显示了没有高度限制的实现。
- 右图显示按下高度限制的按钮。
在函数 viewDidLoad 中
override func viewDidLoad() {
super.viewDidLoad()
view.backgroundColor = .white
scrollView.isScrollEnabled = true
scrollView.bounces = false
scrollView.alwaysBounceVertical = true
imageView.image = UIImage(color: .lightGray)
navigationItem.rightBarButtonItem = barButtonItem
view.addSubview(scrollView)
scrollView.addSubview(imageView)
scrollView.translatesAutoresizingMaskIntoConstraints = false
imageView.translatesAutoresizingMaskIntoConstraints = false
NSLayoutConstraint.activate([
scrollView.topAnchor.constraint(equalTo: view.safeAreaLayoutGuide.topAnchor),
scrollView.leftAnchor.constraint(equalTo: view.leftAnchor),
scrollView.bottomAnchor.constraint(equalTo: view.safeAreaLayoutGuide.bottomAnchor),
scrollView.rightAnchor.constraint(equalTo: view.rightAnchor)
])
NSLayoutConstraint.activate([
imageView.topAnchor.constraint(equalTo: scrollView.contentLayoutGuide.topAnchor),
imageView.leftAnchor.constraint(equalTo: scrollView.contentLayoutGuide.leftAnchor),
imageView.bottomAnchor.constraint(equalTo: scrollView.contentLayoutGuide.bottomAnchor),
imageView.rightAnchor.constraint(equalTo: scrollView.contentLayoutGuide.rightAnchor),
imageView.widthAnchor.constraint(equalTo: scrollView.widthAnchor)
])
}
在函数 buttonPressed 中
@objc func buttonPressed() {
navigationItem.rightBarButtonItem = nil
UIView.animate(withDuration: 1) {
NSLayoutConstraint.activate([
self.imageView.heightAnchor.constraint(equalTo: self.scrollView.heightAnchor)
])
self.view.setNeedsLayout()
self.view.layoutIfNeeded()
}
}
UIImage 实用程序 Create UIImage with solid color in Swift
fileprivate extension UIImage {
convenience init?(color: UIColor, size: CGSize = CGSize(width: 1, height: 1)) {
let rect = CGRect(origin: .zero, size: size)
UIGraphicsBeginImageContextWithOptions(rect.size, false, 0.0)
color.setFill()
UIRectFill(rect)
let image = UIGraphicsGetImageFromCurrentImageContext()
UIGraphicsEndImageContext()
guard let cgImage = image?.cgImage else { return nil }
self.init(cgImage: cgImage)
}
}