Question

我正在向导航栏添加子视图，问题是我无法为其添加约束。我正在像这样崩溃

由于未捕获的异常终止应用程序＆＃39; NSGenericException＆＃39;，原因：＆＃39;无法激活项目约束;值：0.000000＆gt;和＆gt;因为他们没有共同的祖先。约束是否引用不同视图层次结构中的项目？这是非法的。＆＃39;

使用的代码在

之下

//create a slider and add it to the view
        let slider = UISlider()
        self.navigationController?.navigationBar.addSubview(slider)

        //pin the slider 20 points from the left edge of the the superview
        //from the left edge of the slider to the left edge of the superview
        //superview X coord is at 0 therefore 0 + 20 = 20 position
        let horizonalContraints = NSLayoutConstraint(item: slider, attribute:
            .LeadingMargin, relatedBy: .Equal, toItem: view,
            attribute: .LeadingMargin, multiplier: 1.0,
            constant: 20)

        //pin the slider 20 points from the right edge of the super view
        //negative because we want to pin -20 points from the end of the superview.
        //ex. if with of super view is 300, 300-20 = 280 position
        let horizonal2Contraints = NSLayoutConstraint(item: slider, attribute:
            .TrailingMargin, relatedBy: .Equal, toItem: view,
            attribute: .TrailingMargin, multiplier: 1.0, constant: -20)

        //pin 100 points from the top of the super
        let pinTop = NSLayoutConstraint(item: slider, attribute: .Top, relatedBy: .Equal,
            toItem: view, attribute: .Top, multiplier: 1.0, constant: 100)

        //when using autolayout we an a view, MUST ALWAYS SET setTranslatesAutoresizingMaskIntoConstraints
        //to false.
        slider.translatesAutoresizingMaskIntoConstraints = false
        slider.backgroundColor = UIColor.redColor()
        //IOS 8
        //activate the constrains.
        //we pass an array of all the contraints
        NSLayoutConstraint.activateConstraints([horizonalContraints, horizonal2Contraints,pinTop])

如果我使用行view.addSubview(slider)，上面的代码可以正常工作而不是

self.navigationController?.navigationBar.addSubview(slider)

但想法是在导航栏上的子视图中添加约束。欢迎任何想法

Answer 1

正如已经说过的例外，navigationBar不是'view'的子视图。它属于navigationcontroller。你可以做的是使用导航栏的超级视图：

let slider = UISlider()
self.navigationController?.navigationBar.addSubview(slider)
let targetView = self.navigationController?.navigationBar.superview

let horizonalContraints = NSLayoutConstraint(item: slider, attribute:
    .LeadingMargin, relatedBy: .Equal, toItem: targetView,
    attribute: .LeadingMargin, multiplier: 1.0,
    constant: 20)

let horizonal2Contraints = NSLayoutConstraint(item: slider, attribute:
    .TrailingMargin, relatedBy: .Equal, toItem: targetView,
    attribute: .TrailingMargin, multiplier: 1.0, constant: -20)


let pinTop = NSLayoutConstraint(item: slider, attribute: .Top, relatedBy: .Equal,
    toItem: targetView, attribute: .Top, multiplier: 1.0, constant: 10)


slider.translatesAutoresizingMaskIntoConstraints = false
slider.backgroundColor = UIColor.redColor()

NSLayoutConstraint.activateConstraints([horizonalContraints, horizonal2Contraints,pinTop])

删除了异常并且可能看起来像你想做的那样，但它绝对不是一个好的解决方案。如果您想要导航栏内的滑块，请将其添加到导航项目中。如果您希望它低于导航栏，请将其添加到视图中并将约束设置为顶部布局指南。

如何以编程方式在uinavigationbar子视图上添加约束

1 个答案: