使用 NSLayoutConstraint 在主视图中定位两个 UIButton 元素

Posted 2023-03-21

【中文标题】使用 NSLayoutConstraint 在主视图中定位两个 UIButton 元素

【英文标题】：Positioning two UIButton elements in the main view using NSLayoutConstraint

【发布时间】：2014-07-27 08:44:36

【问题描述】：

我确定我在这里遗漏了一些非常简单的东西。我正在阅读有关使用 Auto Layout 以编程方式工作的文档，并且我正在尝试按照说明将两个按钮放在一起。

这是我的代码：

override func viewDidLoad() 
    super.viewDidLoad()
    view.backgroundColor = UIColor.grayColor()

    var button1 = UIButton()
    button1.titleLabel.text = "foo"
    button1.backgroundColor = UIColor.redColor()

    var button2 = UIButton()
    button2.titleLabel.text = "bar"
    button2.backgroundColor = UIColor.purpleColor()

    view.addSubview(button1)
    view.addSubview(button2)

    var bindings = [ "button1" : button1, "button2" : button2 ]
    // picked this arbitrarily ...
    var opt = NSLayoutFormatOptions.AlignAllTop

    var formatString = "[button1]-12-[button2]"
    var c = NSLayoutConstraint.constraintsWithVisualFormat(formatString, options: opt, metrics: nil, views: bindings)

    view.addConstraints(c)

当我运行它时，我得到了错误：

2014-07-27 01:41:43.597 dynamiclayout[2366:53275] 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:0x7be6fda0 H:[UIButton:0x7be69a00]-(12)-[UIButton:0x7be6d200]>",
"<NSAutoresizingMaskLayoutConstraint:0x7be74c20 h=--& v=--& UIButton:0x7be69a00.midX ==>",
"<NSAutoresizingMaskLayoutConstraint:0x7be74d40 h=--& v=--& H:[UIButton:0x7be69a00(0)]>",
"<NSAutoresizingMaskLayoutConstraint:0x7be723f0 h=--& v=--& UIButton:0x7be6d200.midX ==>"
)

如果我知道更多信息，我相信这条错误消息会很有帮助，但我不确定从哪里开始解析它。我在这里做错了什么？

【参考方案1】：

如果您以编程方式添加约束，则必须禁用 TranslatesAutoresizingMaskIntoConstraints 到 false

使用下面的代码，它将绘制按钮，而不是设置titleLable.text，而是使用button1.setTitle("foo", forState: UIControlState.Normal)，因为这是将标题设置为按钮的方法

override func viewDidLoad() 

    view.backgroundColor = UIColor.grayColor()

    var button1 = UIButton()
    button1.setTranslatesAutoresizingMaskIntoConstraints(false)

    button1.setTitle("foo", forState: UIControlState.Normal)
    button1.backgroundColor = UIColor.redColor()

    var button2 = UIButton()
    button2.setTitle("bar", forState: UIControlState.Normal)
    button2.backgroundColor = UIColor.purpleColor()
    button2.setTranslatesAutoresizingMaskIntoConstraints(false)
    self.view.addSubview(button1)
    self.view.addSubview(button2)

    var bindings = [ "button1" : button1, "button2" : button2 ]
    // picked this arbitrarily ...
    var opt = NSLayoutFormatOptions.AlignAllTop

    var formatString = "[button1]-12-[button2]"
    var c = NSLayoutConstraint.constraintsWithVisualFormat(formatString, options: opt, metrics: nil, views: bindings)

    view.addConstraints(c)

 

【讨论】：

这很棒！感谢您抽出宝贵时间撰写建设性且有用的答案。