我想以编程方式向 UISearchController 添加前导、尾随、底部和宽度约束。这是我的代码:

@IBOutlet weak var navigationBar: UIView!

// create search bar
searchBar = UISearchController(searchResultsController: nil)
navigationBar.addSubview(searchBar.searchBar)
searchBar.searchBar.translatesAutoresizingMaskIntoConstraints = false

let leftConstraint = NSLayoutConstraint(item: searchBar.searchBar, attribute: .Leading, relatedBy: .Equal, toItem: navigationBar, attribute: .Leading, multiplier: 1, constant: 0)

let rightConstraint = NSLayoutConstraint(item: searchBar.searchBar, attribute: .Trailing, relatedBy: .Equal, toItem: navigationBar, attribute: .Trailing, multiplier: 1, constant: 0)

let bottomConstraint = NSLayoutConstraint(item: searchBar.searchBar, attribute: .Bottom, relatedBy: .Equal, toItem: navigationBar, attribute: .Bottom, multiplier: 1, constant: 0)

let heightConstraint = NSLayoutConstraint(item: searchBar.searchBar, attribute: .Height, relatedBy: .Equal, toItem: nil, attribute: .NotAnAttribute, multiplier: 1, constant: 44)

navigationBar.addConstraints([leftConstraint, rightConstraint, bottomConstraint, widthConstraint])

运行应用程序时，搜索栏正确显示，但当我按下搜索栏时，它会缩小，如果我再按一次，应用程序就会崩溃。这是输出:

2015-08-12 20:20:37.696 Contacts++[96997:8547485] The view hierarchy is not prepared for the constraint: <NSLayoutConstraint:0x7fb22580c7a0 UIView:0x7fb225817b20.leading == UIView:0x7fb223449860.leading>
    When added to a view, the constraint's items must be descendants of that view (or the view itself). This will crash if the constraint needs to be resolved before the view hierarchy is assembled. Break on -[UIView(UIConstraintBasedLayout) _viewHierarchyUnpreparedForConstraint:] to debug.
2015-08-12 20:20:37.697 Contacts++[96997:8547485] *** Assertion failure in -[UIView _layoutEngine_didAddLayoutConstraint:roundingAdjustment:mutuallyExclusiveConstraints:], /BuildRoot/Library/Caches/com.apple.xbs/Sources/UIKit_Sim/UIKit-3491.2.5/NSLayoutConstraint_UIKitAdditions.m:590

最佳答案

为什么需要创建“UISearchController”的实例并获取它的 searchBar？

为什么不直接从 UISearchBar 制作 searchBar？

// create a searchBar from UISearchBar
let searchBar = UISearchBar(frame: CGRectZero)

// add searchBar to navigationBar
navigationController?.navigationBar.addSubview(searchBar)

// call sizeToFit.. this will set the frame of the searchBar to exactly the same as the size of the allowable frame of the navigationBar
searchBar.sizeToFit()

// now reframe the searchBar to add some margins
var frame = searchBar.frame
frame.origin.x = 20
frame.size.width -= 40
searchBar.frame = frame // set new frame with margins

注意:您不需要任何这些约束来实现这一点。

但如果您真的更喜欢约束，这里是没有崩溃的约束代码。

let searchBar = UISearchBar(frame: CGRectZero)
navigationController?.navigationBar.addSubview(searchBar)
searchBar.setTranslatesAutoresizingMaskIntoConstraints(false)

let leftConstraint = NSLayoutConstraint(item: searchBar, attribute: .Leading, relatedBy: .Equal, toItem: navigationController?.navigationBar, attribute: .Leading, multiplier: 1, constant: 20) // add margin

let bottomConstraint = NSLayoutConstraint(item: searchBar, attribute: .Bottom, relatedBy: .Equal, toItem: navigationController?.navigationBar, attribute: .Bottom, multiplier: 1, constant: 1)

let topConstraint = NSLayoutConstraint(item: searchBar, attribute: .Top, relatedBy: .Equal, toItem: navigationController?.navigationBar, attribute: .Top, multiplier: 1, constant: 1)

let widthConstraint = NSLayoutConstraint(item: searchBar, attribute: .Width, relatedBy: .Equal, toItem: nil, attribute: .NotAnAttribute, multiplier: 1, constant: self.view.frame.size.width - 40) // - margins from both sides

navigationController?.navigationBar.addConstraints([leftConstraint, bottomConstraint, topConstraint, widthConstraint])

关于ios - 添加 UISearchController 并以编程方式使用约束定位它，我们在Stack Overflow上找到一个类似的问题： https://stackoverflow.com/questions/31948982/