Question

在下面的自动布局挑战6中，来自Ray W，我无法理解代码中的位置，在多次点击后宽度和高度发生变化。

在IB中设置为50，并且在tappedImage方法中的第一次运行中，在最后一个条件中，width.constant = 100，但是什么时候重新定义为50（width.constant = 50 ）？！？

AND，在第一次点击后（即此图像的宽度和高度= 100），然后点击另一个图像，第一个图像的宽度和高度返回到50，而第二个图像增长到100。最后一个条件是否告诉第一张图片调整为50？

   import UIKit

   class ViewController: UIViewController {

  @IBOutlet weak var rayWidth: NSLayoutConstraint!
  @IBOutlet weak var rayHeight: NSLayoutConstraint!
  @IBOutlet weak var ray: UIImageView!

  @IBOutlet weak var vickiWidth: NSLayoutConstraint!
  @IBOutlet weak var vickiHeight: NSLayoutConstraint!
  @IBOutlet weak var vicki: UIImageView!

  @IBOutlet weak var gregWidth: NSLayoutConstraint!
  @IBOutlet weak var gregHeight: NSLayoutConstraint!
  @IBOutlet weak var greg: UIImageView!

  @IBOutlet weak var micWidth: NSLayoutConstraint!
  @IBOutlet weak var micHeight: NSLayoutConstraint!
  @IBOutlet weak var mic: UIImageView!

  @IBOutlet weak var christineWidth: NSLayoutConstraint!
  @IBOutlet weak var christineHeight: NSLayoutConstraint!
  @IBOutlet weak var christine: UIImageView!

  @IBOutlet weak var name: UILabel!
  @IBOutlet weak var bio: UITextView!

  var heights:[NSLayoutConstraint]!
  var widths:[NSLayoutConstraint]!
  var bios: [String]!
  var names: [String]!


  @IBOutlet weak var emailButton: UIButton!
  var previousHeight: NSLayoutConstraint?
  var previousWidth: NSLayoutConstraint?

  override func viewWillAppear(animated: Bool) {

    bios = ["Ray is an indie software developer currently focusing on iPhone and iPad development, and the administrator of this site. He’s the founder of a small iPhone development studio called Razeware, and is passionate both about making apps and teaching others the techniques to make them.", "Vicki Wenderlich discovered a love of digital art in 2009, and has been making app art and digital illustrations ever since. She is passionate about helping people pursue their dreams, and makes free app art for developers available on her website, http://www.vickiwenderlich.com.", "Greg is an iOS developer and trainer, and has been on the raywenderlich.com editorial team since 2012. He has been nerding out with computers since the Commodore 64 era in the 80s and continues to this day on the web and on iOS. He likes caffeine, codes with two-space tabs, and writes with semicolons.", "Mic Pringle is a developer, editor, podcaster, and video tutorial maker. He's also Razeware's third full-time employee. When not knee-deep in Swift or stood in-front of his green screen, he enjoys spending time with his wife Lucy and their daughter Evie, as-well as attending the football matches of his beloved Fulham FC. You can find Mic on Twitter, GitHub, and Stack Overflow.", "Christine is Ray's administrative assistant. She tries to keep order in the ever expanding world of raywenderlich.com so that Ray and the team can stay focused on making more tutorials, books, and apps!"]
    names = ["Ray Wenderlich", "Vicki Wenderlich", "Greg Heo", "Mic Pringle", "Christine Sweigart"]
    name.text = ""
    emailButton.hidden = true

  }

  override func viewDidLoad() {
    super.viewDidLoad()

    var razeware = [ray, vicki, greg, mic, christine]
    heights = [rayHeight, vickiHeight, gregHeight,micHeight,christineHeight]
    widths = [rayWidth, vickiWidth, gregWidth,micWidth,christineWidth]


    for image in razeware {
      var tapGesture = UITapGestureRecognizer(target: self, action: "tappedImage:")
      image.userInteractionEnabled = true
      image.addGestureRecognizer(tapGesture)
    }
  }

  func tappedImage(sender:UITapGestureRecognizer!) {

    var tag = 0
    // index /  tag who's been tapped
    if let senderTag = sender.view?.tag {
      tag = senderTag
    }

    let width = widths[tag]             // get the width  constraint from the array
    let height = heights[tag]

    print(width)

    view.setNeedsUpdateConstraints()

    if previousHeight == height {
      if previousHeight?.constant == 100 {
        previousHeight?.constant = 50
        previousWidth?.constant = 50
        print("through here")
        //UIView.animateWithDuration(3.0, animations: { () -> Void in
            self.name.text = ""
            self.bio.text = ""
            self.emailButton.hidden = true
          //  self.view.layoutIfNeeded()
     //   })
      } else {
        previousHeight?.constant = 100
        previousWidth?.constant = 100
        print("Going here")
        name.text = names[tag]
        bio.text = bios[tag]
        bio.font = UIFont.systemFontOfSize(15.0)
        bio.textColor = UIColor.whiteColor()
        emailButton.hidden = false
      }
    } else {
      previousHeight?.constant = 50
      previousWidth?.constant = 50
            UIView.animateWithDuration(5.0, animations: { () -> Void in
            width.constant = 100
            height.constant = 100
            self.name.text = self.names[tag]
            self.bio.text = self.bios[tag]
            self.bio.font = UIFont.systemFontOfSize(15.0)
            self.bio.textColor = UIColor.whiteColor()
            self.emailButton.hidden = false
            self.view.layoutIfNeeded()
        })
    }
    print(width)

    previousHeight = height
    previousWidth = width

    print("Previous: \(previousHeight)")
    print("Height: \(height)")
  }

  override func didReceiveMemoryWarning() {
    super.didReceiveMemoryWarning()
    // Dispose of any resources that can be recreated.
  }


  }

Answer 1

即使先前在其他地方的代码中重新定义了约束，layoutIfNeeded（）也将恢复为原始IB定义的约束值 - 除非在setNeedsUpdateContraints（）之后再次重新定义约束（以维持其新值）。 / p>

这是基于大量试验的更多错误。也许还有机会找到更好的答案......

了解设置自动约束的位置

1 个答案: