斯威夫特 3 新更新。为什么我的导航标题是更新前的两倍？答案

【问题标题】：Swift 3 new update. Why is my navigation title double the size it was before the update?斯威夫特 3 新更新。为什么我的导航标题是更新前的两倍？
【发布时间】：2017-10-03 17:57:46
【问题描述】：

我有一个将图像设置为导航栏标题的应用。我拥有完美的尺寸，但自从我更新了我的 iPhone 和 mac/xcode 后，图像是图像的实际尺寸，而不是它设置的尺寸。我该如何解决？谢谢。

var titleView : UIImageView

titleView = UIImageView(frame: CGRect(x: 0, y: 0, width: 32, height: 32))

titleView.contentMode = .scaleAspectFit

titleView.image = UIImage(named: "logo.png")

self.navigationItem.titleView = titleView

【问题讨论】：

标签： ios swift3 uiimage uinavigationbar

【解决方案1】：

请这样使用：

var titleView : UIImageView

titleView = UIImageView(frame: CGRect(x: 0, y: 0, width: 32, height: 32))
let widthConstraint = titleView.widthAnchor.constraint(equalToConstant: 32)
let heightConstraint = titleView.heightAnchor.constraint(equalToConstant: 32)
heightConstraint.isActive = true
widthConstraint.isActive = true

【讨论】：

完美。谢谢你。只需要调整尺寸。

【解决方案2】：

添加一个稍微不同的方法：

使用自动布局时，不值得设置视图的框架，因为它们将在布局过程中被覆盖，所以我会这样做，添加 cmets 以解释我在做什么：

// Unless you are going to recreate the view, just use a let not a var.
// A UIImageView is a reference type, so you can still change the image to be displayed.
// Also, there is no point declaring a variable and then setting it on the next line, just do it all at once.
// Using the non-parameterised initialiser uses a zero frame for the rect.
let titleView = UIImageView()

// Since the view is being created in code and autolayout is going to be applied, you need to add this line to prevent layout conflicts.
titleView.translatesAutoresizingMaskIntoConstraints = false

// Configure the aspect ratio of the displayed image.
titleView.contentMode = .scaleAspectFit

// You don't need to keep a reference to the constraint unless you want to activate and deactivate it.
titleView.widthAnchor.constraint(equalToConstant: 32).isActive = true

// Now, since you want the image to be a square, you can create an layout anchor that specifies this requirement, rather than just duplicating the width value.
titleView.heightAnchor.constraint(equalTo: titleView.widthAnchor, multiplier: 1).isActive = true

【讨论】：