如何在Xcode Playground中使用自动布局约束显示视图？

Question

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.

Here's the code I tried:

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)

Thanks in advance

Answer 1

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

Here's a link that expands on this further.

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

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

import PlaygroundSupport

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

Answer 2

It seems that now you need to do something like this:

import UIKit
import XCPlayground

let main = UIView(frame: CGRect(x: 0, y: 0, width: 320, height: 700))
main.backgroundColor = .blackColor()
XCPlaygroundPage.currentPage.liveView = main

// now add views and constraints to main

main // display view

Answer 3

My final code;

If you only see the yellow outer UIView then definitely need:

XCPlaygroundPage.currentPage.needsIndefiniteExecution = true

And to make sure view is updating change the text of the label

label.text = "I am a label3 "

FULL CODE

import UIKit
import XCPlayground

//http://stackoverflow.com/questions/30333323/how-can-i-display-views-using-autolayout-constraints-in-xcode-playground/30336502#30336502




let view = UIView()
view.frame = CGRectMake(0, 0, 300, 200)
view.backgroundColor = UIColor.yellowColor()

//-------------------------------------------------------------

XCPlaygroundPage.currentPage.liveView = view
//needed else label may not appear
XCPlaygroundPage.currentPage.needsIndefiniteExecution = true


//-------------------------------------------------------------
//LABEL
//-------------------------------------------------------------
let label = UILabel(frame: CGRectMake(0, 0,200, 50))
label.backgroundColor = UIColor.greenColor()
label.textColor = UIColor.redColor()

//TO FORCE REFRESH change text of label
label.text = "I am a label3 "

//add constraints
label.translatesAutoresizingMaskIntoConstraints = false

//COULDNT GET TO WORK
view.addSubview(label)


//--------------------------------------------------------------
//COMMENT OUT TO SEE LABEL with out constraints
//--------------------------------------------------------------
let views = ["label":label]
let options = NSLayoutFormatOptions(arrayLiteral:[])

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)

//XCPlaygroundPage.currentPage.liveView = view

Answer 4

The provided solutions were not useful for me. I wanted a view in which I could work with constraints. To achieve that I had to create a containerView with a CGRect base and adding constraints to it as well. Everything else was not successful. So I got a viewable base and was able to add views just with constraints.

Setup ContainerView:

let containerView = UIView(frame: CGRect(x: 0.0, y: 0.0, width: 600, height: 400))
containerView.backgroundColor = UIColor.lightGray
containerView.translatesAutoresizingMaskIntoConstraints = false

PlaygroundPage.current.needsIndefiniteExecution = true
PlaygroundPage.current.liveView = containerView

containerView.widthAnchor.constraint(equalToConstant: 600).isActive = true
containerView.heightAnchor.constraint(equalToConstant: 400).isActive = true

Place View in ContainerView with constraints:

let myView = UIView(frame: .zero)
myView.backgroundColor = .green
myView.translatesAutoresizingMaskIntoConstraints = false

containerView.addSubview(myView)

myView.widthAnchor.constraint(equalToConstant: 200).isActive = true
myView.heightAnchor.constraint(equalToConstant: 200).isActive = true

myView.centerXAnchor.constraint(equalTo: containerView.centerXAnchor).isActive = true
myView.centerYAnchor.constraint(equalTo: containerView.centerYAnchor).isActive = true

This creates this view: