22

为什么以下代码不适用于将活动指示器定位到其超级视图的中心：

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角的某处，绝对不在中心。

================== 更新：找到解决方案：我必须在创建指标后关闭自动调整大小约束，然后关闭所有给定工作的解决方案：

 [activityIndicator setTranslatesAutoresizingMaskIntoConstraints:NO];

我在@Vignesh 给出的链接上找到了它，所以我接受他/她的回答。

4

4 回答 4

23

以下四个 Swift 5/iOS 12 代码示例展示了如何使用Auto layoutUIActivityIndicatorView使UIViewa居中。UIViewController

所有样品产生相同的结果，但根据您的需要和口味，您可以选择其中一种。

如果您UIActivityIndicatorView的 superview 不是self.view，您只需self.view用您自己的（未包装的）替换每个调用superview。

1.NSLayoutConstraint初始化风格

import UIKit

class ViewController: UIViewController {

    override func viewDidLoad() {
        super.viewDidLoad()

        let indicatorView = UIActivityIndicatorView(style: .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)
         */
    }

}

2.UIViewAutoresizing风格

Springs 和 Struts 将在运行时转换为相应的自动布局约束。

import UIKit

class ViewController: UIViewController {

    override func viewDidLoad() {
        super.viewDidLoad()

        let indicatorView = UIActivityIndicatorView(style: .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
        ]
    }

}

3.视觉格式语言风格

import UIKit

class ViewController: UIViewController {

    override func viewDidLoad() {
        super.viewDidLoad()

        let indicatorView = UIActivityIndicatorView(style: .gray)
        indicatorView.isHidden = false
        indicatorView.translatesAutoresizingMaskIntoConstraints = false
        self.view.addSubview(indicatorView)

        // Auto layout
        let views = ["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)
    }

}

4.NSLayoutAnchor风格（需要iOS 9）

import UIKit

class ViewController: UIViewController {

    override func viewDidLoad() {
        super.viewDidLoad()

        let indicatorView = UIActivityIndicatorView(style: .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)
         */
    }

}
于 2016-01-05T21:56:29.607 回答
6

它通过在角落里来满足它的要求，因为你并不是说每一侧的间隙必须相同。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]];

并垂直居中这样做：

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

或者，我强烈建议使用 FLKAutoLayout 项目来简化这一切：

https://github.com/dkduck/FLKAutoLayout

然后你可以这样做：

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

这很好:)

于 2013-10-17T15:49:41.267 回答
2

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];

取自这里。

于 2013-10-17T15:52:48.563 回答
0

我将我的活动指示器集中在它的超级视图中，方法是在 Interface Builder 中添加它，alpha 为零（并在我的视图控制器类中为它添加一个 IBOutlet）。然后我添加了约束使其在 X 和 Y 轴上居中。最后，我为其添加了宽度和高度约束以消除自动布局错误。

在我的视图控制器的 startActivityIndi​​cator 方法中，我将活动指示器的 alpha 设置为 1 并在其上调用 startAnimating 方法。在我的 stopActivityIndi​​cator 方法中，我调用它的 stopAnimating 方法并将活动指示器的 alpha 设置回零。

于 2015-11-02T00:30:24.823 回答