在Swift4中，替换navigationItem.leftBarButtonItem大小是不必要的。

Question

当返回到具有不同帧和图像值的VC时，UIBarButtonItem大小有问题。

var selectedR = 1
var leftFrame = CGRect()
var leftImage = UIImage()

override func viewDidLoad() {
    super.viewDidLoad()

    if selectedR == 0
    {
        leftFrame = CGRect(x: 0, y: 0, width: 33, height: 33)
        leftImage = UIImage(named: “pic-0”)!
    }
    else if selectedR == 1
    {
        leftFrame = CGRect(x: 0, y: 0, width: 79, height: 33)
        leftImage = UIImage(named: "pic-1")!
    }
    else if selectedR == 2
    {
        leftFrame =  CGRect(x: 0, y: 0, width: 34, height: 33)
        leftImage = UIImage(named: "pic-2”)!
    }

    let cButton = UIButton(frame: leftFrame)
    cButton.setImage(leftImage, for: UIControlState())
    cButton.addTarget(self.revealViewController(), action: #selector(SWRevealViewController.revealToggle(_:)), for: .touchUpInside)
    cButton.contentMode = UIViewContentMode.scaleAspectFit
    let leftItem = UIBarButtonItem(customView: cButton)
    self.navigationItem.leftBarButtonItem = leftItem
}

selectedR =1的第一次完美大小

返回到具有不同selectedR值和图像的selectedR，扭曲和设置leftFrame大小是不受尊重的。

这一切都很完美，在斯威夫特3，但斯威夫特4它到处都是。如有任何帮助或建议，将不胜感激。

Answer 1

iOS 10和11之间的一个主要变化是现在条形按钮由自动布局引擎进行布局。通常，这应该是向后兼容的。但是，如果您在布局条形按钮项目方面有问题，您应该尝试设置约束，看看它是否解决了您的问题。

在你的情况下，你会说：

var selectedR = 1
var leftFrame = CGRect()
var leftImage = UIImage()

override func viewDidLoad() {
    super.viewDidLoad()

    if selectedR == 0
    {
        leftFrame = CGRect(x: 0, y: 0, width: 33, height: 33)
        leftImage = UIImage(named: “pic-0”)!
    }
    else if selectedR == 1
    {
        leftFrame = CGRect(x: 0, y: 0, width: 79, height: 33)
        leftImage = UIImage(named: "pic-1")!
    }
    else if selectedR == 2
    {
        leftFrame =  CGRect(x: 0, y: 0, width: 34, height: 33)
        leftImage = UIImage(named: "pic-2”)!
    }

    let cButton = UIButton(frame: leftFrame)
    cButton.widthAnchor.constraint(equalToConstant: leftFrame.width).isActive = true
    cButton.heightAnchor.constraint(equalToConstant: leftFrame.height).isActive = true
    cButton.setImage(leftImage, for: UIControlState())
    cButton.addTarget(self.revealViewController(), action: #selector(SWRevealViewController.revealToggle(_:)), for: .touchUpInside)
    cButton.contentMode = UIViewContentMode.scaleAspectFit
    let leftItem = UIBarButtonItem(customView: cButton)
    self.navigationItem.leftBarButtonItem = leftItem
}

这在苹果2017年的会议https://developer.apple.com/videos/play/wwdc2017/204中有报道。