如果你的应用程序处于前台状态，这意味着你正在使用同一个应用程序。所以通常没有必要在顶部显示通知。

但如果你想显示通知在那种情况下你必须创建你的自定义警报视图或自定义视图像Toast或其他东西来向用户显示你已经收到通知。

如果你的应用中有这样的功能，你也可以在顶部显示一个徽章。

下面是当应用程序处于活动状态(前台或打开)时接收推送通知的代码。UNUserNotificationCenter文档

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

如果您需要访问通知的userInfo，请使用代码:notification.request.content.userInfo

用于swift 5解析推送通知字典

    func application(_ application: UIApplication, didReceiveRemoteNotification data: [AnyHashable : Any]) {
            if application.applicationState == .active {
                if let aps1 = data["aps"] as? NSDictionary {
                    if let dict = aps1["alert"] as? NSDictionary {
                        if let strTitle = dict["title"] as? String , let strBody = dict["body"] as? String {
                            if let topVC = UIApplication.getTopViewController() {
                                //Apply your own logic as per requirement
                                print("strTitle ::\(strTitle) , strBody :: \(strBody)")
                            }
                        }
                    }
                }
            }
        }

获取topBanner所在的top viewController

extension UIApplication {

    class func getTopViewController(base: UIViewController? = UIApplication.shared.keyWindow?.rootViewController) -> UIViewController? {

        if let nav = base as? UINavigationController {
            return getTopViewController(base: nav.visibleViewController)

        } else if let tab = base as? UITabBarController, let selected = tab.selectedViewController {
            return getTopViewController(base: selected)

        } else if let presented = base?.presentedViewController {
            return getTopViewController(base: presented)
        }
        return base
    }
}

添加completionHandler行委托方法为我解决了同样的问题:

//Called when a notification is delivered to a foreground app.
@available(iOS 10.0, *)
func userNotificationCenter(_ center: UNUserNotificationCenter, willPresent notification: UNNotification, withCompletionHandler completionHandler: @escaping (UNNotificationPresentationOptions) -> Void) {

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

如果应用程序在前台运行，iOS不会显示通知横幅/警报。这是故意的。你必须编写一些代码来处理应用程序在前台接收通知的情况。您应该以最合适的方式显示通知(例如，向UITabBar图标添加徽章号，模拟notification Center横幅等)。

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];          
    }    
}