如何使用自动布局以编程方式将活动指示器定位到其超级视图的中心？

Question

为什么以下代码不能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个位置,绝对不在中心位置.

==================更新:找到解决方案:我必须在创建指标后关闭自动调整约束,然后在给定工作的所有解决方案中关闭:

 [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.

Answer 1

以下四种雨燕3代码样本显示如何中心一个UIActivityIndicatorView内部UIView的UIViewController与自动布局.

所有样品都会产生相同的结果,但根据您的需要和口味,您可以选择其中一种.

如果您UIActivityIndicatorView的超级视图不是self.view,您只需self.view用自己的(未打开的)替换每个呼叫superview.

1. NSLayoutConstraint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)
         */
    }

}

Answer 2

因为你并没有说明每一方的差距必须相同,所以它在角落里满足了它的要求.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]];

垂直居中也是这样做的:

[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项目来简化所有这些:

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];

哪个好:)

Answer 3

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。