编辑:检查下面的解决方案。

我正在为我的应用程序设计一个登录屏幕，除了少数极端情况外，我大部分时间都在使用它。我已经进行了设置，以便我在应用程序委托(delegate) applicationDidBecomeActive: 方法中触发的 Storyboard中的 UITabBar 中有一个 segue。正如我所说，它在除我目前发现的一种边缘情况外的所有情况下都能正常工作。

我的应用程序使用一些模态视图 Controller (其中一些是 UIActivityViewControllers，如果有区别的话)来输入和编辑一些核心数据实体。如果在应用程序进入后台时打开这些模态视图 Controller 之一，它会在应用程序重新打开时始终显示，而我的登录名不会显示。我收到以下控制台消息

Warning: Attempt to present <UINavigationController: 0x1d51e320>  on <MPTabBarViewController: 0x1d5b4810> which is already presenting <UIActivityViewController: 0x1e38fc40>

这是我的代码

   - (void) displayLogin{
        NSLog(@"%s", __PRETTY_FUNCTION__);

        UITabBarController *tabBarController = (UITabBarController *)self.window.rootViewController;

        NSDate *lastDate = [[NSUserDefaults standardUserDefaults] objectForKey:MPLastCloseDate];
        NSTimeInterval timeDiff = [[NSDate date] timeIntervalSinceDate:lastDate];
        int seconds = timeDiff;

        if ([[NSUserDefaults standardUserDefaults] integerForKey:MPPassCodeDelay] == MPScreenLockAlways || seconds >= 300) {
            NSLog(@"Should see login");
            [tabBarController performSegueWithIdentifier:@"loginScreen" sender:self];
        }
    }

我完全理解这条消息告诉我的意思，标签栏已经呈现了一个模态 Controller ，所以它不能呈现另一个。所以我的问题是，是否有更好的方法来实现这一点，以便登录始终显示，甚至在模态视图之上？

好的，这是我目前的解决方案

根据 Bartu 的建议并要求由 Shawn 分享

我有一个工作的单例 loginManager 类，它需要在应用程序委托(delegate)中进行 1 次调用，并在任何可以调用以呈现为模态的 View Controller 中进行 1 次调用。我无法按照 ViewController 类别的建议弄清楚如何执行此操作，但是嘿，一些包含和方法调用还不错。我将它包含在 App-Prefix.pch 中，因此它随处可用。它是为 ARC 编写的，所以如果你喜欢管理自己的内存，你需要为此修改单例。最后一个警告，目前您需要为登录屏幕滚动自己的 viewController。只需在带有所有星星的实现中查找注释部分，然后将您自己的 View Controller 放在那里。我的仍然在我的应用程序 Storyboard 中，它基本上是 4 位数字 pin，用于检查钥匙串(keychain)中的匹配项并为正确的 pin 自行解雇。我可能会把它从我的 Storyboard 中拉出来并 nib 它，这样它就可以与 loginManager 打包在一起，并让它在未来的某个日期成为我的第一个 gitHub 项目。

您可以将其配置为在每次打开应用程序时或在延迟属性后显示登录信息。延迟时间也是一个以秒为单位设置的属性。它还会在几秒钟内阻止您的应用程序 UI，以便使用您的应用程序 Default.png 显示登录信息。这也可以使用属性进行配置。

我很想就此获得一些反馈，如果有人能告诉我如何做一个类别，这样就不需要在 viewControllers 中进行额外的调用，那就太好了!享受吧!

AppDelegate:

- (void)applicationDidBecomeActive:(UIApplication *)application
{
    // Restart any tasks that were paused (or not yet started) while the application was inactive. If the application was previously in the background, optionally refresh the user interface.
    [self.window makeKeyAndVisible];

    // these calls are all optional
    [[VHLoginManager loginManager] setShouldBlockUIWithSplashOnResume:NO];
    [[VHLoginManager loginManager] setSecondsRequiredToPassBeforeLockDown:1000];
    [[VHLoginManager loginManager] setScreenLockRequirment:VHLMScreenLockDelayed];

    // this is the only required call to run with defaults - always login and block UI with splash while login loads
    [[VHLoginManager loginManager] presentLogin];
}

任何在某些时候可能呈现为模态的 viewController

- (void)viewDidLoad
{
    [super viewDidLoad];
    [[VHLoginManager loginManager] registerViewControllerIfModal:self];
}

登录管理器类

标题:

//  VHLoginManager.h
//  Created by Victor Hudson on 5/31/13.
//  Copyright (c) 2013 Victor Hudson. All rights reserved.
//  Use if you like but be nice and leave my name 

#import <Foundation/Foundation.h>
#define VHLMLastCloseDate @"VHLMLastCloseDate"
#define VHLMPassCodeDelay @"VHLMPassCodeDelay"

typedef enum {
    VHLMScreenLockAlways = 0,
    VHLMScreenLockDelayed = 1,
} VHLMScreenLockRequirement;

@interface VHLoginManager : NSObject
@property (nonatomic) BOOL shouldBlockUIWithSplashOnResume;
// defaults to yes so app contents arent visible before the login screen appears
@property (nonatomic) int secondsRequiredToPassBeforeLockDown;
// defaults to 5 minutes (300)

#pragma mark - Class Methods
+ (VHLoginManager *)loginManager;
// returns the singleton login manager

#pragma mark - Manager Methods
- (void) presentLogin;
// will determine if login should be presented an do so if needed
- (void) registerViewControllerIfModal:(UIViewController *)controller;
// any view controllers that are presented modally should call this with self as controller in viewDidLoad - the pupose of this manager is so login shows even over top of modals
- (void) setScreenLockRequirment:(VHLMScreenLockRequirement) requirement;
// deafaults to always if not adjusted
@end

实现:

//  VHLoginManager.m
//  Created by Victor Hudson on 5/31/13.
//  Copyright (c) 2013 Victor Hudson. All rights reserved.
//  Use if you like but be nice and leave my name

#import "VHLoginManager.h"
static VHLoginManager *loginManager = nil;

@interface VHLoginManager ()
@property (nonatomic, strong) UIViewController *currentModalViewController;
@property (nonatomic) VHLMScreenLockRequirement screenLockrequirement;
@end

@implementation VHLoginManager
#pragma mark - Manager Methods
- (void) presentLogin
{
    // NSLog(@"%s", __PRETTY_FUNCTION__);
    if ([[NSUserDefaults standardUserDefaults] integerForKey:VHLMPassCodeDelay] == VHLMScreenLockAlways || [self timeSinceLastClose] >= self.secondsRequiredToPassBeforeLockDown) {
        //NSLog(@"User should see login");
        // determine who the presenting view controller should be
        UIViewController *viewController;
        if (self.currentModalViewController && self.currentModalViewController.presentingViewController != nil) {
            // NSLog(@"We have a modal view controller on top");
            viewController = self.currentModalViewController;
        } else {
            // NSLog(@"We have NO modal view controller on top");
            // get the root view controller of the app
            viewController = [[[UIApplication sharedApplication] keyWindow] rootViewController];
        }

//********************************************************************************************************************************************************************************
        // *** This is still tied into my app storyboard and should be made into a viewcontroller with nib to be portable with loginManager for now implement and present your own loginViewController
        UIStoryboard *storyboard = [UIStoryboard storyboardWithName:@"MainStoryboard_iPhone" bundle:nil];
        UINavigationController *navController = [storyboard instantiateViewControllerWithIdentifier:@"appLoginScreen"];
//********************************************************************************************************************************************************************************

        // present the login to user
        [viewController presentViewController:navController animated:NO completion:nil];
    }
}

- (void) setScreenLockRequirment:(VHLMScreenLockRequirement) requirement
{
    _screenLockrequirement = requirement;
    [[NSUserDefaults standardUserDefaults] setInteger:self.screenLockrequirement forKey:VHLMPassCodeDelay];
}

- (void) registerViewControllerIfModal:(UIViewController *)controller
{
    // NSLog(@"%s", __PRETTY_FUNCTION__);
    if (controller.presentingViewController) {
        NSLog(@"Registering a modalViewController");
        self.currentModalViewController = controller;
    }
}

#pragma mark - Private Methods

- (void) timeStampForBackground
{
    // NSLog(@"%s", __PRETTY_FUNCTION__);
    [[NSUserDefaults standardUserDefaults] setObject:[NSDate date] forKey:VHLMLastCloseDate];
    [self setDisplaySplashForBackgroundResume];
}

- (int) timeSinceLastClose
{
    return [[NSDate date] timeIntervalSinceDate:[[NSUserDefaults standardUserDefaults] objectForKey:VHLMLastCloseDate]];
}

#pragma mark Splash Screen management
- (void) setDisplaySplashForBackgroundResume
{
    // NSLog(@"%s", __PRETTY_FUNCTION__);
    if (self.shouldBlockUIWithSplashOnResume) {
        // dismiss all keyboards and input views
        UIView *topView = [[[[UIApplication sharedApplication] keyWindow] subviews] lastObject];
        [topView endEditing:YES];

        // Don't show a splash screen if the application is in UIApplicationStateInactive (lock/power button press)
        UIApplication *application = [UIApplication sharedApplication];
        if (application.applicationState == UIApplicationStateBackground) {
            UIImageView *splash = [[UIImageView alloc] initWithImage:[UIImage imageNamed:@"Default"]];
            splash.frame = application.keyWindow.bounds;
            [application.keyWindow addSubview:splash];
        }
    }
}

- (void) removeSplashScreen
{
    // NSLog(@"%s", __PRETTY_FUNCTION__);
    if (self.shouldBlockUIWithSplashOnResume) { // we should have a splash image up if true
                                                // so remove it
        UIWindow *thewindow = [[UIApplication sharedApplication] keyWindow];
        if ([[thewindow subviews] count] > 1) {
            [NSThread sleepForTimeInterval:1.0];
            [[[thewindow subviews] lastObject] removeFromSuperview];
        }
    }
}
#pragma mark - Class Management

//prevent additional instances
+ (id)allocWithZone:(NSZone *)zone
{
    return [self loginManager];
}

+ (VHLoginManager *)loginManager
{
    if (!loginManager) {
        //Create The singleton
        loginManager = [[super allocWithZone:NULL] init];
    }

    return loginManager;
}

- (id) init
{
    // If we already have an instance of loginManager
    if (loginManager) {
        //Return The Old One
        return loginManager;
    }

    self = [super init];
    if (self) {
        [[NSNotificationCenter defaultCenter] addObserver:self
                                                 selector:@selector(timeStampForBackground)
                                                     name:UIApplicationDidEnterBackgroundNotification
                                                   object:nil];
        [[NSNotificationCenter defaultCenter] addObserver:self
                                                 selector:@selector(removeSplashScreen)
                                                     name:UIApplicationDidBecomeActiveNotification
                                                   object:nil];
        self.shouldBlockUIWithSplashOnResume = YES;
        self.secondsRequiredToPassBeforeLockDown = 300;

        if (![[NSUserDefaults standardUserDefaults] integerForKey:VHLMPassCodeDelay]) {
            [self setScreenLockRequirment:VHLMScreenLockAlways];
        }
    }
    return self;
}
@end

最佳答案

不久前我遇到了同样的问题，我对这个问题的解决方案是引用您的应用委托(delegate)中当前呈现的任何模态视图。因此，您可以知道您的选项卡栏 Controller 是否已经呈现模态 Controller ，如果是这种情况，您可以在当前模态视图上呈现登录 View 。

关于ios - 在 iOS 上创建一个始终显示在所有 View 顶部的登录屏幕，我们在Stack Overflow上找到一个类似的问题： https://stackoverflow.com/questions/16839171/