我希望在iOS上创建一个类似于Android的菜单。我正在使用布局约束来设置约束条件。当我尝试在按钮点击时更新图像的左侧约束时(它应该动画到单击的按钮位置),我遇到了问题。有人能帮我吗?它应该支持横向和纵向。 我不想使用第三方代码,也不想使用NSLayoutconstraint。
这是我的代码。
class MenuViewController: UIViewController {
var buttons: [UIButton] = []
var imageView : UIImageView!
override func viewDidLoad() {
super.viewDidLoad()
}
override func viewDidAppear(_ animated: Bool) {
super.viewDidAppear(animated)
addMenuItems()
}
func addMenuItems() {
for _ in 0...4 {
let button : UIButton = UIButton()
self.view.addSubview(button)
button.backgroundColor = UIColor.darkGray
button.addTarget(self, action: #selector(didSelectedButton(_:)), for: .touchUpInside)
self.buttons.append(button)
}
for (index, button) in buttons.enumerated() {
button.setTitle(" \(index)", for: .normal)
if index == 0 {
button.translatesAutoresizingMaskIntoConstraints = false
button.leftAnchor.constraint(equalTo: self.view.safeAreaLayoutGuide.leftAnchor, constant: 0).isActive = true
button.widthAnchor.constraint(greaterThanOrEqualToConstant: 1).isActive = true
button.heightAnchor.constraint(equalToConstant: 50).isActive = true
button.topAnchor.constraint(equalTo: self.view.topAnchor, constant:200).isActive = true
self.imageView = UIImageView()
self.view.addSubview(self.imageView)
self.imageView.backgroundColor = UIColor.red
self.imageView.translatesAutoresizingMaskIntoConstraints = false
self.imageView.leftAnchor.constraint(equalTo: button.leftAnchor, constant: 0).isActive = true
self.imageView.widthAnchor.constraint(equalTo: button.widthAnchor, multiplier: 1).isActive = true
self.imageView.heightAnchor.constraint(equalToConstant: 4).isActive = true
self.imageView.topAnchor.constraint(equalTo: self.view.topAnchor, constant:250).isActive = true
}
else {
let preButton = buttons\[index - 1\]
button.translatesAutoresizingMaskIntoConstraints = false
button.leftAnchor.constraint(equalTo: preButton.rightAnchor, constant: 0).isActive = true
button.widthAnchor.constraint(equalTo: preButton.widthAnchor, multiplier: 1).isActive = true
button.heightAnchor.constraint(equalToConstant: 50).isActive = true
button.topAnchor.constraint(equalTo: self.view.topAnchor, constant:200).isActive = true
if index == self.buttons.count - 1 {
button.rightAnchor.constraint(equalTo: self.view.safeAreaLayoutGuide.rightAnchor, constant: 0).isActive = true
}
}
}
}
@objc func didSelectedButton(_ button:UIButton) {
UIView.animate(withDuration: 1, animations: {
self.imageView.leftAnchor.constraint(equalTo: button.leftAnchor).isActive = true
self.imageView.layoutIfNeeded()
}, completion: nil)
}
}
.isActive = false
” 实际上是做什么的?它会将其保留在长列表中还是移动到忽略的队列末尾(就像 UNIX 中的调度程序一样)?因为随着时间的推移,这些已停用的约束可能会累积并减慢速度,如果不进行垃圾回收(而且我不知道为什么它们会被垃圾回收,因为它们可以重新激活)。我想在每次有人编辑文本字段时更改约束。这可能不是一个频繁发生的问题,所以不会有问题,而且我想如果您想调整约束,NSConstraint 类允许修改.constant
。 - clearlightfalse
会将其从视图层次结构中移除(意味着减少一个保留它的对象)。如果您没有另一个强指针指向该约束条件,那么它将被释放。在这个例子中,约束条件由var imageLeftConstraint: NSLayoutConstraint?
属性持有,但当它的指针被新创建的约束条件重写时,它将没有强引用,并被释放。 - vacawama