我正在创建一个自定义类以使 View 可扩展;该类与 UIPanGestureRecognizer 一起使用,修改 View 的高度约束。在调试代码时,我使用以下代码来显示与 View 关联的高度约束。
print(self.constraints.filter({ $0.firstAttribute == .height}).map{print("costraints \($0)")})
奇怪的是,除了通过扩展 View 的方法创建的余弦之外,还有一个不知从何而来的余弦。以下是控制台中打印的内容:
constraint <NSAutoresizingMaskLayoutConstraint:0x6140002828f0 h=--& v=--& UIStackView:0x7ff1c871d0e0.height == 190 (active)>
constraint <NSLayoutConstraint:0x60800009c160 PhotoMapping.ExpandableView:0x7ff1c8416fa0.height == 100 (active)>
这是该类的完整代码。
import Foundation
import UIKit
class ExpandableView: UIView {
let panGestureRecognizer = UIPanGestureRecognizer()
var minHeight: CGFloat = 0 {
didSet {
initialHeight = minHeight
}
}
var maxHeight: CGFloat = 0
var initialHeight: CGFloat = 0
var initialPoint: CGPoint? = nil
var heightConstraintConstant: CGFloat {
get {
if !self.constraints.filter({ $0.firstAttribute == .height}).isEmpty {
return self.constraints.filter({$0.firstAttribute == .height && $0.secondItem == nil}).first!.constant
} else {
let constrain = NSLayoutConstraint(item: self, attribute: .height, relatedBy: .equal, toItem: nil, attribute: .height, multiplier: 1.0, constant: initialHeight)
self.addConstraint(constrain)
return constrain.constant
}
}
set(newConstant){
if !self.constraints.filter({ $0.firstAttribute == .height}).isEmpty {
self.constraints.filter({$0.firstAttribute == .height && $0.secondItem == nil}).first?.constant = newConstant
self.constraints.filter({$0.firstAttribute == .height && $0.secondItem == nil}).map{print("constant \($0.constant)")}
} else {
let constrain = NSLayoutConstraint(item: self, attribute: .height, relatedBy: .equal, toItem: nil, attribute: .height, multiplier: 1.0, constant: newConstant)
self.addConstraint(constrain)
}
self.layoutIfNeeded()
}
}
func initialize(minHeight: CGFloat, maxHeight: CGFloat) {
panGestureRecognizer.addTarget(self, action: #selector(handlePan(_:)))
panGestureRecognizer.minimumNumberOfTouches = 1
panGestureRecognizer.maximumNumberOfTouches = 1
self.addGestureRecognizer(panGestureRecognizer)
self.minHeight = minHeight
self.maxHeight = maxHeight
}
@objc func handlePan(_ sender: Any) {
let translation = panGestureRecognizer.translation(in: self)
if initialPoint == nil {
initialPoint = translation
}
let translationHeight = CGFloat(translation.y - initialPoint!.y)
print("translationHeight: \(translationHeight)")
if panGestureRecognizer.state == .changed {
let finalHeight = translationHeight + initialHeight
print("finalHeight: \(finalHeight)")
if finalHeight <= maxHeight && finalHeight >= minHeight {
heightConstraintConstant = finalHeight
}
} else if panGestureRecognizer.state == .ended {
let mediumY = maxHeight / 2 + minHeight / 2
if translation.y <= 0 {
heightConstraintConstant = minHeight
} else if translationHeight >= maxHeight {
heightConstraintConstant = minHeight
} else if heightConstraintConstant >= mediumY {
UIView.animate(withDuration: 0.4) {
self.heightConstraintConstant = self.maxHeight
self.layoutIfNeeded()
}
} else if heightConstraintConstant <= mediumY {
UIView.animate(withDuration: 0.2) {
self.heightConstraintConstant = self.minHeight
self.layoutIfNeeded()
}
}
initialPoint = nil
initialHeight = heightConstraintConstant
}
layoutIfNeeded()
}
}
我在 StoryBoard 中将 View 的类设置为“ExpandableView”,并在父类(super class) viewController 中初始化它,如下所示: 这是 ViewController 内的代码,我在其中初始化名为 profileView 的 View 。
profileView.isUserInteractionEnabled = true
profileView.initialize(minHeight: 100, maxHeight: 190)
最佳答案
将 View 上的 translatesAutoresizingMaskIntoConstraints
设置为 false
。
当它为true
时,它将创建一些定义其位置和大小的约束。
关于ios - View 内发现未知约束,我们在Stack Overflow上找到一个类似的问题: https://stackoverflow.com/questions/52265746/