如何在UIAlertController的中心显示活动指示器？

Question

我目前UIAlertController正在屏幕上显示.警报视图应仅显示2个元素,标题和UIActivityIndicatorView警报中心.以下是显示警报及其元素的功能.

func displaySignUpPendingAlert() -> UIAlertController {
        //Create the UIAlertController
        let pending = UIAlertController(title: "Creating New User", message: nil, preferredStyle: .Alert)
        //Create the activity indicator to display in it.
        let indicator = UIActivityIndicatorView(frame: CGRectMake(pending.view.frame.width / 2.0, pending.view.frame.height / 2.0, 20.0, 20.0))
        indicator.center = CGPointMake(pending.view.frame.width / 2.0, pending.view.frame.height / 2.0)
        //Add the activity indicator to the alert's view
        pending.view.addSubview(indicator)
        //Start animating
        indicator.startAnimating()

        self.presentViewController(pending, animated: true, completion: nil)
        return pending
    }

但是,活动指示器不会显示在视图的中心,实际上它显示在屏幕的右下方,远离视图.这是什么原因？

编辑:我知道我可以硬编码指标位置的数字,但我希望警报可以在多个屏幕尺寸和方向的多个设备上工作.

Answer 1

确保在创建视图时设置frame属性.

func displaySignUpPendingAlert() -> UIAlertController {
        //create an alert controller
        let pending = UIAlertController(title: "Creating New User", message: nil, preferredStyle: .Alert)

        //create an activity indicator
        let indicator = UIActivityIndicatorView(frame: pending.view.bounds)
        indicator.autoresizingMask = [.flexibleWidth, .flexibleHeight]

        //add the activity indicator as a subview of the alert controller's view
        pending.view.addSubview(indicator)
        indicator.isUserInteractionEnabled = false // required otherwise if there buttons in the UIAlertController you will not be able to press them
        indicator.startAnimating()

        self.presentViewController(pending, animated: true, completion: nil)

        return pending
}

致@ 62Shark:

let pending = UIAlertController(title: "Creating New User", message: nil, preferredStyle: .Alert)

let indicator = UIActivityIndicatorView()
indicator.setTranslatesAutoresizingMaskIntoConstraints(false)
pending.view.addSubview(indicator)

let views = ["pending" : pending.view, "indicator" : indicator]
var constraints = NSLayoutConstraint.constraintsWithVisualFormat("V:[indicator]-(-50)-|", options: nil, metrics: nil, views: views)
constraints += NSLayoutConstraint.constraintsWithVisualFormat("H:|[indicator]|", options: nil, metrics: nil, views: views)
pending.view.addConstraints(constraints)

indicator.userInteractionEnabled = false
indicator.startAnimating()

self.presentViewController(pending, animated: true, completion: nil)

Answer 2

如果有人有兴趣,我将答案转换为目标C:

UIAlertController *pending = [UIAlertController alertControllerWithTitle:nil
                                                               message:@"Please wait...\n\n"
                                                        preferredStyle:UIAlertControllerStyleAlert];
UIActivityIndicatorView* indicator = [[UIActivityIndicatorView alloc] initWithActivityIndicatorStyle:UIActivityIndicatorViewStyleWhiteLarge];
indicator.color = [UIColor blackColor];
indicator.translatesAutoresizingMaskIntoConstraints=NO;
[pending.view addSubview:indicator];
NSDictionary * views = @{@"pending" : pending.view, @"indicator" : indicator};

NSArray * constraintsVertical = [NSLayoutConstraint constraintsWithVisualFormat:@"V:[indicator]-(20)-|" options:0 metrics:nil views:views];
NSArray * constraintsHorizontal = [NSLayoutConstraint constraintsWithVisualFormat:@"H:|[indicator]|" options:0 metrics:nil views:views];
NSArray * constraints = [constraintsVertical arrayByAddingObjectsFromArray:constraintsHorizontal];
[pending.view addConstraints:constraints];
[indicator setUserInteractionEnabled:NO];
[indicator startAnimating];
[self presentViewController:pending animated:YES completion:nil];

干杯

Answer 3

TL;博士

所有其他答案都是关闭:)请参阅文档:

重要

UIAlertController类旨在按原样使用,不支持子类化.此类的视图层次结构是私有的, 不得修改.

问题

问题不在于UIAlertController.这是一个非常简单的UI,一个或两个堆栈视图,具体取决于您是否希望将UIActivityIndi​​catorView留在标题标签或标题下.演示动画是我们想要的.

下面的代码基于WWDC会话A Look Inside Presentation Controllers.

重新创建演示控制器:

@interface LOActivityAlertControllerPresentationController : UIPresentationController
@end

@interface LOActivityAlertControllerPresentationController ()
@property (nonatomic) UIView *dimmerView;
@end

@implementation LOActivityAlertControllerPresentationController

- (instancetype)initWithPresentedViewController:(UIViewController *)presentedViewController presentingViewController:(UIViewController *)presentingViewController
{
    self = [super initWithPresentedViewController:presentedViewController presentingViewController:presentingViewController];
    if (self)
    {
        _dimmerView = [[UIView alloc] init];
        _dimmerView.autoresizingMask = UIViewAutoresizingFlexibleWidth | UIViewAutoresizingFlexibleHeight;
        _dimmerView.backgroundColor = [UIColor colorWithWhite:0 alpha:0.4];


        UIView *presentedView = [self presentedView];
        presentedView.layer.cornerRadius = 8.0;

        UIInterpolatingMotionEffect *centerXMotionEffect = [[UIInterpolatingMotionEffect alloc] initWithKeyPath:@"center.x" type:UIInterpolatingMotionEffectTypeTiltAlongHorizontalAxis];
        centerXMotionEffect.minimumRelativeValue = @(-10.0);
        centerXMotionEffect.maximumRelativeValue = @(10.0);

        UIInterpolatingMotionEffect *centerYMotionEffect = [[UIInterpolatingMotionEffect alloc] initWithKeyPath:@"center.y" type:UIInterpolatingMotionEffectTypeTiltAlongVerticalAxis];
        centerYMotionEffect.minimumRelativeValue = @(-10.0);
        centerYMotionEffect.maximumRelativeValue = @(10.0);

        UIMotionEffectGroup *group = [[UIMotionEffectGroup alloc] init];
        group.motionEffects = [NSArray arrayWithObjects:centerXMotionEffect, centerYMotionEffect, nil];

        [presentedView addMotionEffect:group];
    }
    return self;

}

- (CGRect)frameOfPresentedViewInContainerView
{
    UIView *containerView = [self containerView];
    UIView *presentedView = [self presentedView];

    CGSize size = [presentedView systemLayoutSizeFittingSize:UILayoutFittingCompressedSize];
    CGRect frame = CGRectZero;
    frame.origin = CGPointMake(CGRectGetMidX([containerView frame]) - (size.width / 2.0),
                               CGRectGetMidY([containerView frame]) - (size.height / 2.0));
    frame.size = size;

    return frame;
}

- (void)presentationTransitionWillBegin
{
    UIViewController *presentingViewController = [self presentingViewController];
    UIView *containerView = [self containerView];
    UIView *presentedView = [self presentedView];
    UIView *dimmerView = [self dimmerView];

    dimmerView.alpha = 0.0;
    dimmerView.frame = [containerView bounds];
    [containerView insertSubview:dimmerView atIndex:0];

    presentedView.center = [containerView center];

    [[presentingViewController transitionCoordinator] animateAlongsideTransition:^(id<UIViewControllerTransitionCoordinatorContext> context) {

        dimmerView.alpha = 1.0;

    } completion:NULL];
}

- (void)containerViewWillLayoutSubviews
{
    [super containerViewWillLayoutSubviews];

    UIView *containerView = [self containerView];
    UIView *presentedView = [self presentedView];
    UIView *dimmerView = [self dimmerView];

    dimmerView.frame = [containerView bounds];
    presentedView.frame = [self frameOfPresentedViewInContainerView];
}

- (void)dismissalTransitionWillBegin
{
    UIViewController *presentingViewController = [self presentingViewController];
    UIView *dimmerView = [self dimmerView];

    [[presentingViewController transitionCoordinator] animateAlongsideTransition:^(id<UIViewControllerTransitionCoordinatorContext> context) {

        dimmerView.alpha = 0.0;

    } completion:NULL];
}


@end

动画过渡:

@interface LOActivityAlertControllerAnimatedTransitioning : NSObject <UIViewControllerAnimatedTransitioning>

@property (getter=isPresentation) BOOL presentation;

@end

@implementation LOActivityAlertControllerAnimatedTransitioning

- (void)animateTransition:(nonnull id<UIViewControllerContextTransitioning>)transitionContext
{
    UIView *containerView = [transitionContext containerView];
    UIView *fromView = [transitionContext viewForKey:UITransitionContextFromViewKey];
    UIView *toView = [transitionContext viewForKey:UITransitionContextToViewKey];
    if (_presentation)
    {
        [containerView addSubview:toView];
        toView.transform = CGAffineTransformMakeScale(1.6, 1.6);
        toView.alpha = 0.0;
        [UIView animateWithDuration:0.2 animations:^{

            toView.alpha = 1.0;
            toView.transform = CGAffineTransformIdentity;

        } completion:^(BOOL finished) {

            [transitionContext completeTransition:YES];

        }];
    }
    else
    {
        [UIView animateWithDuration:0.2 animations:^{

            fromView.alpha = 0.0;

        } completion:^(BOOL finished) {

            [fromView removeFromSuperview];
            [transitionContext completeTransition:YES];

        }];
    }
}

- (NSTimeInterval)transitionDuration:(nullable id<UIViewControllerContextTransitioning>)transitionContext
{
    return 0.2;
}

@end

UIViewController使用XIB的样本子类,品尝季节:

@interface LOActivityAlertController : UIViewController <UIViewControllerTransitioningDelegate>

@property (nonatomic, strong) IBOutlet UIActivityIndicatorView *activityIndicatorView;
@property (nonatomic, strong) IBOutlet UILabel *titleLabel;

@end

@implementation LOActivityAlertController

@dynamic title;

+ (instancetype)alertControllerWithTitle:(NSString *)title
{
    LOActivityAlertController *alert = [LOActivityAlertController new];
    alert.title = title;
    return alert;
}

- (instancetype)init
{
    self = [super init];
    if (self)
    {
        self.transitioningDelegate = self;
        self.modalPresentationStyle = UIModalPresentationCustom;
    }
    return self;
}

- (void)viewDidLoad
{
    [super viewDidLoad];

    self.titleLabel.text = self.title;
}

#pragma mark Properties

- (void)setTitle:(NSString *)title
{
    [super setTitle:title];

    self.titleLabel.text = title;
}

#pragma mark UIViewControllerTransitioningDelegate

- (UIPresentationController *)presentationControllerForPresentedViewController:(UIViewController *)presented
                                                      presentingViewController:(UIViewController *)presenting
                                                          sourceViewController:(UIViewController *)source
{
    LOActivityAlertControllerPresentationController *myPresentation = nil;
    myPresentation = [[LOActivityAlertControllerPresentationController alloc]
                      initWithPresentedViewController:presented presentingViewController:presenting];

    return myPresentation;
}

- (id <UIViewControllerAnimatedTransitioning>)animationControllerForPresentedController:(UIViewController *)presented presentingController:(UIViewController *)presenting sourceController:(UIViewController *)source;
{
    LOActivityAlertControllerAnimatedTransitioning *transitioning = [LOActivityAlertControllerAnimatedTransitioning new];
    transitioning.presentation = YES;
    return transitioning;
}

- (id <UIViewControllerAnimatedTransitioning>)animationControllerForDismissedController:(UIViewController *)dismissed
{
    LOActivityAlertControllerAnimatedTransitioning *transitioning = [LOActivityAlertControllerAnimatedTransitioning new];
    return transitioning;
}

@end

屏幕录制

Bug Reporter

rdar:// 37433306:创建UIAlertController表示控制器并转换委托公共API以启用重用.

Answer 4

我必须实现NSLayoutConstraints 把 放在UIActivityIndicatorView中心UIAlertController

对于斯威夫特：

let loadingAlertController: UIAlertController = UIAlertController(title: "Loading", message: nil, preferredStyle: .alert)
let activityIndicator: UIActivityIndicatorView = UIActivityIndicatorView(style: .gray)
activityIndicator.translatesAutoresizingMaskIntoConstraints = false
    
loadingAlertController.view.addSubview(activityIndicator)
    
let xConstraint: NSLayoutConstraint = NSLayoutConstraint(item: activityIndicator, attribute: .centerX, relatedBy: .equal, toItem: loadingAlertController.view, attribute: .centerX, multiplier: 1, constant: 0)
let yConstraint: NSLayoutConstraint = NSLayoutConstraint(item: activityIndicator, attribute: .centerY, relatedBy: .equal, toItem: loadingAlertController.view, attribute: .centerY, multiplier: 1.4, constant: 0)
    
NSLayoutConstraint.activate([ xConstraint, yConstraint])
activityIndicator.isUserInteractionEnabled = false
activityIndicator.startAnimating()
    
let height: NSLayoutConstraint = NSLayoutConstraint(item: loadingAlertController.view, attribute: NSLayoutConstraint.Attribute.height, relatedBy: NSLayoutConstraint.Relation.equal, toItem: nil, attribute: NSLayoutConstraint.Attribute.notAnAttribute, multiplier: 1, constant: 80)
loadingAlertController.view.addConstraint(height)

self.present(loadingAlertController, animated: true, completion: nil)

结果：

Answer 5

Swift 5.0 解决方案

let alert = UIAlertController(title: "Sender ...", message: nil, preferredStyle: .alert)
let activityIndicator = UIActivityIndicatorView(style: .gray)
activityIndicator.translatesAutoresizingMaskIntoConstraints = false
activityIndicator.isUserInteractionEnabled = false
activityIndicator.startAnimating()

alert.view.addSubview(activityIndicator)
alert.view.heightAnchor.constraint(equalToConstant: 95).isActive = true

activityIndicator.centerXAnchor.constraint(equalTo: alert.view.centerXAnchor, constant: 0).isActive = true
activityIndicator.bottomAnchor.constraint(equalTo: alert.view.bottomAnchor, constant: -20).isActive = true

present(alert, animated: true)