从上周开始,我就一直在想办法解决这个问题。好的,所以我需要在Swift中使用以下代码应用一些约束到UIView:

var new_view:UIView! = UIView(frame: CGRectMake(0, 0, 100, 100));
new_view.backgroundColor = UIColor.redColor();
view.addSubview(new_view);

var constX:NSLayoutConstraint = NSLayoutConstraint(item: new_view, attribute: NSLayoutAttribute.CenterX, relatedBy: NSLayoutRelation.Equal, toItem: self.view, attribute: NSLayoutAttribute.CenterX, multiplier: 1, constant: 0);
self.view.addConstraint(constX);

var constY:NSLayoutConstraint = NSLayoutConstraint(item: new_view, attribute: NSLayoutAttribute.CenterY, relatedBy: NSLayoutRelation.Equal, toItem: self.view, attribute: NSLayoutAttribute.CenterY, multiplier: 1, constant: 0);
self.view.addConstraint(constY);

var constW:NSLayoutConstraint = NSLayoutConstraint(item: new_view, attribute: NSLayoutAttribute.Width, relatedBy: NSLayoutRelation.Equal, toItem: new_view, attribute: NSLayoutAttribute.Width, multiplier: 1, constant: 0);
self.view.addConstraint(constW);

var constH:NSLayoutConstraint = NSLayoutConstraint(item: new_view, attribute: NSLayoutAttribute.Height, relatedBy: NSLayoutRelation.Equal, toItem: new_view, attribute: NSLayoutAttribute.Height, multiplier: 1, constant: 0);
self.view.addConstraint(constH);

但是Xcode返回了这个奇怪的输出:

2014-10-03 09:48:12.657 Test[35088:2454916] Unable to simultaneously satisfy constraints.  Probably at least one of the constraints in the following list is one you don't want. Try this: (1) look at each constraint and try to figure out which you don't expect; (2) find the code that added the unwanted constraint or constraints and fix it. (Note: If you're seeing NSAutoresizingMaskLayoutConstraints that you don't understand, refer to the documentation for the UIView property translatesAutoresizingMaskIntoConstraints) 
(
"<NSLayoutConstraint:0x7fa4ea446830 UIView:0x7fa4ea429290.centerX == UIView:0x7fa4ea4470f0.centerX>",
"<NSAutoresizingMaskLayoutConstraint:0x7fa4ea4516c0 h=--& v=--& UIView:0x7fa4ea429290.midX == + 50>",
"<NSLayoutConstraint:0x7fa4ea452830 'UIView-Encapsulated-Layout-Width' H:[UIView:0x7fa4ea4470f0(375)]>",
"<NSAutoresizingMaskLayoutConstraint:0x7fa4ea446db0 h=-&- v=-&- 'UIView-Encapsulated-Layout-Left' H:|-(0)-[UIView:0x7fa4ea4470f0]   (Names: '|':UIWindow:0x7fa4ea444b20 )>"
)

Will attempt to recover by breaking constraint <NSLayoutConstraint:0x7fa4ea446830 UIView:0x7fa4ea429290.centerX == UIView:0x7fa4ea4470f0.centerX>

Make a symbolic breakpoint at UIViewAlertForUnsatisfiableConstraints to catch this in the debugger. The methods in the UIConstraintBasedLayoutDebugging category on UIView listed in
<UIKit/UIView.h> may also be helpful.

2014-10-03 09:48:12.658 Test[35088:2454916] Unable to simultaneously satisfy constraints.  Probably at least one of the constraints in the following list is one you don't want. Try this: (1) look at each constraint and try to figure out which you don't expect; (2) find the code that added the unwanted constraint or constraints and fix it. (Note: If you're seeing NSAutoresizingMaskLayoutConstraints that you don't understand, refer to the documentation for the UIView property translatesAutoresizingMaskIntoConstraints)
(
"<NSLayoutConstraint:0x7fa4ea44d160 UIView:0x7fa4ea429290.centerY == UIView:0x7fa4ea4470f0.centerY>",
"<NSAutoresizingMaskLayoutConstraint:0x7fa4ea451b30 h=--& v=--& UIView:0x7fa4ea429290.midY == + 50>",
"<NSLayoutConstraint:0x7fa4ea44cf00 'UIView-Encapsulated-Layout-Height' V:[UIView:0x7fa4ea4470f0(667)]>",
"<NSAutoresizingMaskLayoutConstraint:0x7fa4ea452700 h=-&- v=-&- 'UIView-Encapsulated-Layout-Top' V:|-(0)-[UIView:0x7fa4ea4470f0]  (Names: '|':UIWindow:0x7fa4ea444b20 )>"
)

Will attempt to recover by breaking constraint <NSLayoutConstraint:0x7fa4ea44d160 UIView:0x7fa4ea429290.centerY == UIView:0x7fa4ea4470f0.centerY>

Make a symbolic breakpoint at UIViewAlertForUnsatisfiableConstraints to catch this in the debugger. The methods in the UIConstraintBasedLayoutDebugging category on UIView listed in <UIKit/UIView.h> may also be helpful.

你能帮我吗? 非常感谢


当前回答

它帮助我直观地学习,所以这是一个补充答案。

样板代码

override func viewDidLoad() {
    super.viewDidLoad()

    let myView = UIView()
    myView.backgroundColor = UIColor.blue
    myView.translatesAutoresizingMaskIntoConstraints = false
    view.addSubview(myView)

    // Add constraints code here
    // ...
}

下面的每个例子都是相互独立的。

引脚左边缘

myView。leading = leadingMargin + 20

方法1:锚式

let margins = view.layoutMarginsGuide
myView.leadingAnchor.constraint(equalTo: margins.leadingAnchor, constant: 20).isActive = true

除了leadingAnchor,还有trailingAnchor, topAnchor和bottomAnchor。

方法2:NSLayoutConstraint样式

NSLayoutConstraint(item: myView, attribute: NSLayoutAttribute.leading, relatedBy: NSLayoutRelation.equal, toItem: view, attribute: NSLayoutAttribute.leadingMargin, multiplier: 1.0, constant: 20.0).isActive = true

除了。leading,还有。tailed,。top,和。bottom。 除了。leadingmargin,还有。trailingmargin, . topmargin和.bottom margin。

设置宽度和高度

宽度= 200 高度= 100

方法1:锚式

myView.widthAnchor.constraint(equalToConstant: 200).isActive = true
myView.heightAnchor.constraint(equalToConstant: 100).isActive = true

方法2:NSLayoutConstraint样式

NSLayoutConstraint(item: myView, attribute: NSLayoutAttribute.width, relatedBy: NSLayoutRelation.equal, toItem: nil, attribute: NSLayoutAttribute.notAnAttribute, multiplier: 1, constant: 200).isActive = true
NSLayoutConstraint(item: myView, attribute: NSLayoutAttribute.height, relatedBy: NSLayoutRelation.equal, toItem: nil, attribute: NSLayoutAttribute.notAnAttribute, multiplier: 1, constant: 100).isActive = true

集装箱中心

myView。centerX = centerX myView。世纪=世纪

方法1:锚式

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

方法2:NSLayoutConstraint样式

NSLayoutConstraint(item: myView, attribute: NSLayoutAttribute.centerX, relatedBy: NSLayoutRelation.equal, toItem: view, attribute: NSLayoutAttribute.centerX, multiplier: 1, constant: 0).isActive = true
NSLayoutConstraint(item: myView, attribute: NSLayoutAttribute.centerY, relatedBy: NSLayoutRelation.equal, toItem: view, attribute: NSLayoutAttribute.centerY, multiplier: 1, constant: 0).isActive = true

笔记

锚的风格是首选的方法超过NSLayoutConstraint风格,但它只适用于iOS 9,所以如果你是支持iOS 8,那么你仍然应该使用NSLayoutConstraint风格。 上面的例子只显示了我们所关注的一两个约束条件。然而,为了在我的测试项目中正确地放置myView,我需要有四个约束。

进一步的阅读

以编程方式创建约束文档

其他回答

想在Imanou Petit的回答中添加一些理论概念,这样人们就可以了解自动布局是如何工作的。

要理解自动布局,请将您的视图视为橡胶的对象,最初是收缩的。

要在屏幕上放置一个对象,我们需要4件强制性的事情:

物体的X坐标(水平位置)。 物体的Y坐标(垂直位置) 对象的宽度 物体的高度。

X坐标:有多种方式给视图X坐标。

如前向约束,后向约束,水平中心 等。

2 Y坐标:给视图Y坐标有多种方式:

如顶部约束,底部约束,垂直中心等。

有两种方法来限制一个视图的宽度:

a.添加固定宽度约束(将此约束视为固定宽度的铁棒,并与橡胶对象水平挂钩,使橡胶对象不会收缩或膨胀)

b.不要添加任何宽度约束,而是在视图的前端和前端添加x坐标约束,这两个约束将通过从前端和前端拉动橡胶对象来扩展/收缩。

对象的高度:类似于宽度,有两种方法来限制视图的高度:

a.添加固定高度约束(将此约束视为固定高度的铁棒,并与橡胶物体垂直挂钩,使橡胶物体不会收缩或膨胀)

b.不要添加任何高度约束,但在视图的顶部和底部两端添加x坐标约束,这两个约束将从两端、顶部和底部拉伸/推动橡胶对象。

它帮助我直观地学习,所以这是一个补充答案。

样板代码

override func viewDidLoad() {
    super.viewDidLoad()

    let myView = UIView()
    myView.backgroundColor = UIColor.blue
    myView.translatesAutoresizingMaskIntoConstraints = false
    view.addSubview(myView)

    // Add constraints code here
    // ...
}

下面的每个例子都是相互独立的。

引脚左边缘

myView。leading = leadingMargin + 20

方法1:锚式

let margins = view.layoutMarginsGuide
myView.leadingAnchor.constraint(equalTo: margins.leadingAnchor, constant: 20).isActive = true

除了leadingAnchor,还有trailingAnchor, topAnchor和bottomAnchor。

方法2:NSLayoutConstraint样式

NSLayoutConstraint(item: myView, attribute: NSLayoutAttribute.leading, relatedBy: NSLayoutRelation.equal, toItem: view, attribute: NSLayoutAttribute.leadingMargin, multiplier: 1.0, constant: 20.0).isActive = true

除了。leading,还有。tailed,。top,和。bottom。 除了。leadingmargin,还有。trailingmargin, . topmargin和.bottom margin。

设置宽度和高度

宽度= 200 高度= 100

方法1:锚式

myView.widthAnchor.constraint(equalToConstant: 200).isActive = true
myView.heightAnchor.constraint(equalToConstant: 100).isActive = true

方法2:NSLayoutConstraint样式

NSLayoutConstraint(item: myView, attribute: NSLayoutAttribute.width, relatedBy: NSLayoutRelation.equal, toItem: nil, attribute: NSLayoutAttribute.notAnAttribute, multiplier: 1, constant: 200).isActive = true
NSLayoutConstraint(item: myView, attribute: NSLayoutAttribute.height, relatedBy: NSLayoutRelation.equal, toItem: nil, attribute: NSLayoutAttribute.notAnAttribute, multiplier: 1, constant: 100).isActive = true

集装箱中心

myView。centerX = centerX myView。世纪=世纪

方法1:锚式

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

方法2:NSLayoutConstraint样式

NSLayoutConstraint(item: myView, attribute: NSLayoutAttribute.centerX, relatedBy: NSLayoutRelation.equal, toItem: view, attribute: NSLayoutAttribute.centerX, multiplier: 1, constant: 0).isActive = true
NSLayoutConstraint(item: myView, attribute: NSLayoutAttribute.centerY, relatedBy: NSLayoutRelation.equal, toItem: view, attribute: NSLayoutAttribute.centerY, multiplier: 1, constant: 0).isActive = true

笔记

锚的风格是首选的方法超过NSLayoutConstraint风格,但它只适用于iOS 9,所以如果你是支持iOS 8,那么你仍然应该使用NSLayoutConstraint风格。 上面的例子只显示了我们所关注的一两个约束条件。然而,为了在我的测试项目中正确地放置myView,我需要有四个约束。

进一步的阅读

以编程方式创建约束文档

通过对图像施加约束来实现自动布局。使用NSLayoutConstraint。我们可以在所有设备上实现理想而漂亮的设计。请尝试下面的代码。

import UIKit

class ViewController: UIViewController {

override func viewDidLoad() {
super.viewDidLoad()

let myImageView:UIImageView = UIImageView()
myImageView.backgroundColor = UIColor.red
myImageView.image = UIImage(named:"sample_dog")!
myImageView.translatesAutoresizingMaskIntoConstraints = false
myImageView.layer.borderColor = UIColor.red.cgColor
myImageView.layer.borderWidth = 10
self.view.addSubview(myImageView)
        
view.removeConstraints(view.constraints)


view.addConstraint(NSLayoutConstraint(
item: myImageView,
attribute: .top,
relatedBy: .equal,
toItem: view,
attribute: .top,
multiplier: 1,
constant:100)
    
)

view.addConstraint(NSLayoutConstraint(
item: myImageView,
attribute: .centerX,
relatedBy: .equal,
toItem: view,
attribute: .centerX,
multiplier: 1,
constant:0)
)
    
view.addConstraint(NSLayoutConstraint(
item: myImageView,
attribute: .height,
relatedBy: .equal,
toItem: view,
attribute: .width,
multiplier: 0.5,
constant:40))
    
view.addConstraint(NSLayoutConstraint(
item: myImageView,
attribute: .width,
relatedBy: .equal,
toItem: view,
attribute: .width,
multiplier: 0.5,
constant:40))
    
}

override func didReceiveMemoryWarning() {
    super.didReceiveMemoryWarning()
}
}

这个问题,正如错误消息所暗示的,是你的NSAutoresizingMaskLayoutConstraints类型的约束与你的显式约束冲突,因为new_view。translatesAutoresizingMaskIntoConstraints设置为true。

这是在代码中创建的视图的默认设置。你可以像这样关闭它:

var new_view:UIView! = UIView(frame: CGRectMake(0, 0, 100, 100))
new_view.translatesAutoresizingMaskIntoConstraints = false

此外,宽度和高度的限制也很奇怪。如果你想让视图有一个恒定的宽度,这是正确的方法:

new_view.addConstraint(NSLayoutConstraint(
    item:new_view, attribute:NSLayoutAttribute.Width,
    relatedBy:NSLayoutRelation.Equal,
    toItem:nil, attribute:NSLayoutAttribute.NotAnAttribute,
    multiplier:0, constant:100))

(将100替换为您想要的宽度。)

如果你的部署目标是iOS 9.0或更高版本,你可以使用这个简短的代码:

new_view.widthAnchor.constraintEqualToConstant(100).active = true

不管怎样,对于这样的布局(固定大小,在父视图居中),使用自动调整蒙版并让系统将蒙版转换为约束会更简单:

var new_view:UIView! = UIView(frame: CGRectMake(0, 0, 100, 100))
new_view.backgroundColor = UIColor.redColor();
view.addSubview(new_view);

// This is the default setting but be explicit anyway...
new_view.translatesAutoresizingMaskIntoConstraints = true

new_view.autoresizingMask = [ .FlexibleTopMargin, .FlexibleBottomMargin,
    .FlexibleLeftMargin, .FlexibleRightMargin ]

new_view.center = CGPointMake(view.bounds.midX, view.bounds.midY)

请注意,使用自动调整大小是完全合法的,即使你也使用自动布局。(UIKit仍然在内部的很多地方使用自动调整大小。)问题是很难对使用自动调整大小的视图应用额外的约束。

基本上有3个步骤

fileprivate func setupName() { 

    lblName.text = "Hello world"

    // Step 1
    lblName.translatesAutoresizingMaskIntoConstraints = false

    //Step 2
    self.view.addSubview(lblName)

    //Step 3
    NSLayoutConstraint.activate([
        lblName.centerXAnchor.constraint(equalTo: self.view.centerXAnchor),
        lblName.centerYAnchor.constraint(equalTo: self.view.centerYAnchor)
    ])
}

这将把标签“hello world”置于屏幕中心。

请参考链接自动布局约束编程