当应用程序在前台显示横幅消息时，使用以下方法。

iOS 10, Swift 3/4:

// This method will be called when app received push notifications in foreground
func userNotificationCenter(_ center: UNUserNotificationCenter, willPresent notification: UNNotification, withCompletionHandler completionHandler: @escaping (UNNotificationPresentationOptions) -> Void) 
{
    completionHandler([.alert, .badge, .sound])
}

iOS 10, Swift 2.3:

@available(iOS 10.0, *)
func userNotificationCenter(center: UNUserNotificationCenter, willPresentNotification notification: UNNotification, withCompletionHandler completionHandler: (UNNotificationPresentationOptions) -> Void)
{
    //Handle the notification
    completionHandler(
       [UNNotificationPresentationOptions.Alert,
        UNNotificationPresentationOptions.Sound,
        UNNotificationPresentationOptions.Badge])
}

你还必须将你的应用委托注册为通知中心的委托:

import UserNotifications

// snip!

class AppDelegate : UIResponder, UIApplicationDelegate, UNUserNotificationCenterDelegate

// snip!

   func application(_ application: UIApplication, didFinishLaunchingWithOptions launchOptions: [UIApplication.LaunchOptionsKey: Any]?) -> Bool {

      // set the delegate in didFinishLaunchingWithOptions
      UNUserNotificationCenter.current().delegate = self
      ...
   }

您可以创建自己的通知，模仿横幅警报。

一种方法是创建一个自定义的uiview，看起来像横幅，可以动画和响应触摸。考虑到这一点，你可以创建更好的横幅，甚至更多的功能。

或者你可以寻找一个api来帮你做这件事，并把它们作为podfile添加到你的项目中。

以下是我使用过的一些方法:

https://github.com/terryworona/TWMessageBarManager

https://github.com/toursprung/TSMessages

下面的代码将为您工作:

- (void)application:(UIApplication *)application didReceiveRemoteNotification:(NSDictionary *)userInfo  {
    application.applicationIconBadgeNumber = 0;             
    //self.textView.text = [userInfo description];
    // We can determine whether an application is launched as a result of the user tapping the action
    // button or whether the notification was delivered to the already-running application by examining
    // the application state.

    if (application.applicationState == UIApplicationStateActive) {                
        // Nothing to do if applicationState is Inactive, the iOS already displayed an alert view.                
        UIAlertView *alertView = [[UIAlertView alloc] initWithTitle:@"Did receive a Remote Notification" message:[NSString stringWithFormat:@"Your App name received this notification while it was running:\n%@",[[userInfo objectForKey:@"aps"] objectForKey:@"alert"]]delegate:self cancelButtonTitle:@"OK" otherButtonTitles:nil];
        [alertView show];          
    }    
}

Swift 5

1)使用UNUserNotificationCenterDelegate确认委托到AppDelegate 2)在didFinishLaunch中UNUserNotificationCenter.current().delegate = self 3)在AppDelegate中实现如下方法。

func userNotificationCenter(_ center: UNUserNotificationCenter,
                                willPresent notification: UNNotification,
                                withCompletionHandler completionHandler: @escaping (UNNotificationPresentationOptions) -> Void) {
     print("Push notification received in foreground.")
     completionHandler([.alert, .sound, .badge])
}

就是这样!

如上所述，您应该使用UserNotification.framework来实现这一点。但出于我的目的，我必须在app中显示它，我想要iOS 11风格，所以我创建了一个小助手视图，可能对某些人有用。

GitHub iOS 11推送通知视图。

最好的方法是通过使用扩展AppDelegate: UNUserNotificationCenterDelegate在AppDelegate中添加UNUserNotificationCenterDelegate 该扩展告诉应用程序能够在使用时获得通知

并实现这个方法

func userNotificationCenter(_ center: UNUserNotificationCenter, willPresent notification: UNNotification, withCompletionHandler completionHandler: @escaping (UNNotificationPresentationOptions) -> Void) {
        completionHandler(.alert)
    }

只有当应用程序在前台时，才会在委托上调用此方法。

最后的实现:

extension AppDelegate: UNUserNotificationCenterDelegate {
    func userNotificationCenter(_ center: UNUserNotificationCenter, willPresent notification: UNNotification, withCompletionHandler completionHandler: @escaping (UNNotificationPresentationOptions) -> Void) {
        completionHandler(.alert)
    }
}

要调用这个，你必须在AppDelegate中在didFinishLaunchingWithOptions中设置委托添加这一行

UNUserNotificationCenter.current().delegate = self

你可以修改

completionHandler(.alert) 

与

completionHandler([.alert, .badge, .sound]))