如何在 Xcode 游乐场中使用自动布局约束显示视图?

问题描述

我试图在 XCode playground 中显示配置有 autolayout 约束的视图，但它似乎不起作用.就像游乐场完全忽略了约束，我在任何地方都找不到有关此问题的信息.

I am trying to display views configured with autolayout constraints in XCode playground, but it doesn't seem to work. It's like playground ignores the constraints completely, and I can't find information about this issue anywhere.

这是我尝试过的代码:

let view = UIView()
view.frame = CGRectMake(0, 0, 400, 200)
view.backgroundColor = UIColor.lightGrayColor()

let label = UILabel() // I can only see the label if I set a frame
         // UILabel(frame: CGRectMake(0, 0, 200, 50))
label.backgroundColor = UIColor.greenColor()
label.text = "I am a label"
label.setTranslatesAutoresizingMaskIntoConstraints(false)
view.addSubview(label)

let views = ["label":label]
let options = NSLayoutFormatOptions(0)

let cs1 = NSLayoutConstraint.constraintsWithVisualFormat(
    "H:|-[label]-|", options: options, metrics: nil, views:views )

let cs2 = NSLayoutConstraint.constraintsWithVisualFormat(
    "V:|-[label]-|", options: options, metrics: nil, views:views )

view.addConstraints(cs1)
view.addConstraints(cs2)

提前致谢

推荐答案

也就是说你可以使用 PlaygroundPage 的 liveView 属性来预览你的 UI.

That being said you can use the liveView property of PlaygroundPage to preview your UI.

import PlaygroundSupport

PlaygroundPage.current.needsIndefiniteExecution = true
PlaygroundPage.current.liveView = myLiveView

这是一个进一步扩展的 链接.

Here's a link that expands on this further.

如果它不起作用，您可能需要触发 layoutIfNeeded 但这不应该真正解决问题，因为 Swift 4

If its not working you may need to trigger a layoutIfNeeded but that shouldn't really solve the issue since Swift 4

另外，在您的视图中包含 translatesAutoresizingMaskIntoConstraints = false.喜欢:

Also, include translatesAutoresizingMaskIntoConstraints = false on your view. Like:

import PlaygroundSupport

myLiveView.translatesAutoresizingMaskIntoConstraints = false
PlaygroundPage.current.needsIndefiniteExecution = true
PlaygroundPage.current.liveView = myLiveView

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