如何使用自动布局以编程方式将活动指标定位到其超级视图的中心？

为什么下面的代码不能用于将活动指标定位到其超级中心的中心：

UIActivityIndicatorView *activityIndicator = [[UIActivityIndicatorView alloc] initWithActivityIndicatorStyle:UIActivityIndicatorViewStyleWhiteLarge]; [self.mysuperview addSubview:activityIndicator]; [activityIndicator addConstraints:[NSLayoutConstraint constraintsWithVisualFormat:@"|-(>=20)-[view(==100)]-(>=20)-|" options:NSLayoutFormatAlignAllCenterX | NSLayoutFormatAlignAllCenterY metrics:nil views:@{@"view" : self.mysuperview}]]; 

活动指示器位于左上angular的某处，绝对不在中心。

==================更新：find解决scheme：我必须在创build指标后closures自动调整约束，然后在给定工作的所有解决scheme：

  [activityIndicator setTranslatesAutoresizingMaskIntoConstraints:NO]; 

我在@Vignesh给出的链接上find了，所以我接受他/她的回答。

Answer 1

你可以试试这个，

  UIView *superview = self.mysuperview; NSDictionary *variables = NSDictionaryOfVariableBindings(activityIndicator, superview); NSArray *constraints = [NSLayoutConstraint constraintsWithVisualFormat:@"V:[superview]-(<=1)-[activityIndicator]" options: NSLayoutFormatAlignAllCenterX metrics:nil views:variables]; [self.view addConstraints:constraints]; constraints = [NSLayoutConstraint constraintsWithVisualFormat:@"H:[superview]-(<=1)-[activityIndicator]" options: NSLayoutFormatAlignAllCenterY metrics:nil views:variables]; [self.view addConstraints:constraints]; 

从这里采取。

Answer 2

以下四个Swift 3代码示例演示了如何使用Auto布局将UIView集中到UIViewController的UIView中。

所有样本产生相同的结果，但根据您的需要和口味，您可以select其中一个。

如果你的UIActivityIndicatorView的superview不是self.view ，你只需要用你自己的（unwrapped） superview代替每个self.view调用。

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1. NSLayoutConstraint风格

 import UIKit class ViewController: UIViewController { override func viewDidLoad() { super.viewDidLoad() let indicatorView = UIActivityIndicatorView(activityIndicatorStyle: .gray) indicatorView.isHidden = false indicatorView.translatesAutoresizingMaskIntoConstraints = false self.view.addSubview(indicatorView) // Auto layout let horizontalConstraint = NSLayoutConstraint(item: indicatorView, attribute: .centerX, relatedBy: .equal, toItem: self.view, attribute: .centerX, multiplier: 1, constant: 0) let verticalConstraint = NSLayoutConstraint(item: indicatorView, attribute: .centerY, relatedBy: .equal, toItem: self.view, attribute: .centerY, multiplier: 1, constant: 0) NSLayoutConstraint.activate([horizontalConstraint, verticalConstraint]) /* // You can replace NSLayoutConstraint activate(_:) call with the following lines: self.view.addConstraint(horizontalConstraint) self.view.addConstraint(verticalConstraint) */ } } 

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2. UIViewAutoresizing风格

在运行时，Spring和Struts将被转换成相应的自动布局约束。

 import UIKit class ViewController: UIViewController { override func viewDidLoad() { super.viewDidLoad() let indicatorView = UIActivityIndicatorView(activityIndicatorStyle: .gray) indicatorView.isHidden = false indicatorView.translatesAutoresizingMaskIntoConstraints = true // default is true self.view.addSubview(indicatorView) // Springs and struts indicatorView.center = CGPoint(x: self.view.bounds.midX, y: self.view.bounds.midY) indicatorView.autoresizingMask = [ .flexibleLeftMargin, .flexibleRightMargin, .flexibleTopMargin, .flexibleBottomMargin ] } } 

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3.视觉格式语言风格

 import UIKit class ViewController: UIViewController { override func viewDidLoad() { super.viewDidLoad() let indicatorView = UIActivityIndicatorView(activityIndicatorStyle: .gray) indicatorView.isHidden = false indicatorView.translatesAutoresizingMaskIntoConstraints = false self.view.addSubview(indicatorView) // Auto layout let views: [String: Any] = ["superview": self.view, "indicatorView": indicatorView] let horizontalConstraints = NSLayoutConstraint .constraints(withVisualFormat: "H:[superview]-(<=0)-[indicatorView]", options: .alignAllCenterY, metrics: nil, views: views) let verticalConstraints = NSLayoutConstraint .constraints(withVisualFormat: "V:[superview]-(<=0)-[indicatorView]", options: .alignAllCenterX, metrics: nil, views: views) self.view.addConstraints(horizontalConstraints) self.view.addConstraints(verticalConstraints) } } 

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4. NSLayoutAnchor风格（需要iOS 9）

 import UIKit class ViewController: UIViewController { override func viewDidLoad() { super.viewDidLoad() let indicatorView = UIActivityIndicatorView(activityIndicatorStyle: .gray) indicatorView.isHidden = false indicatorView.translatesAutoresizingMaskIntoConstraints = false self.view.addSubview(indicatorView) // Auto layout let horizontalConstraint = indicatorView .centerXAnchor.constraint(equalTo: self.view.centerXAnchor) let verticalConstraint = indicatorView .centerYAnchor.constraint(equalTo: self.view.centerYAnchor) NSLayoutConstraint.activate([horizontalConstraint, verticalConstraint]) /* // You can replace NSLayoutConstraint activate(_:) call with the following lines: self.view.addConstraint(horizontalConstraint) self.view.addConstraint(verticalConstraint) */ } } 

Answer 3

它在angular落里满足了它的要求，因为你并不是说每一边的差距都是一样的。 试试这个：

 [self.superview addConstraint:[NSLayoutConstraint constraintWithItem:activityIndicator attribute:NSLayoutAttributeCenterX relatedBy:NSLayoutRelationEqual toItem:self.superview attribute:NSLayoutAttributeCenterX multiplier:1.0 constant:0.0]]; 

并垂直居中做这个：

 [self.superview addConstraint:[NSLayoutConstraint constraintWithItem:activityIndicator attribute:NSLayoutAttributeCenterY relatedBy:NSLayoutRelationEqual toItem:self.superview attribute:NSLayoutAttributeCenterY multiplier:1.0 constant:0.0]]; 

另外，我强烈build议使用FLKAutoLayout项目来简化所有这些：

https://github.com/dkduck/FLKAutoLayout

那你可以这样做：

 [activityIndicator alignCenterXWithView:self.superview predicate:nil]; [activityIndicator alignCenterYWithView:self.superview predicate:nil]; 

哪个好:)

Answer 4

我集中在我的活动指标在其超级视图中，通过在界面生成器中添加一个为零的alpha（在我的视图控制器类IBOutlet）。 然后，我添加约束将其集中在X轴和Y轴。 最后，我添加了宽度和高度约束来消除自动布局错误。

在我的视图控制器的startActivityIndi​​cator方法中，我将活动指示符的alpha设置为1，并在其上调用startAnimating方法。 在我的stopActivityIndi​​cator方法中，我调用了stopAnimating方法，并将活动指示符的alpha值设置为零。