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)。

正如@Danial Martine所说，iOS不会显示通知横幅/提醒。这是故意的。但如果真要这么做，还有一个办法。我也用同样的方法做到了这一点。

1.从parse FrameWork下载解析框架

2.导入# Import <Parse/Parse.h> .h

3.将以下代码添加到您的didReceiveRemoteNotification方法

 - (void)application:(UIApplication *)application
didReceiveRemoteNotification:(NSDictionary *)userInfo
{
    [PFPush handlePush:userInfo];
}

PFPush会注意如何处理远程通知。如果App在前台，这显示警报，否则它显示在顶部的通知。

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。

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!

在你的应用委托中使用下面的代码

import UIKit
import UserNotifications
@UIApplicationMain
class AppDelegate: UIResponder, UIApplicationDelegate, UNUserNotificationCenterDelegate {
 var currentToken: String?
 var window: UIWindow?
 func application(_ application: UIApplication, didFinishLaunchingWithOptions launchOptions: [UIApplicationLaunchOptionsKey: Any]?) -> Bool {
        // Override point for customization after application launch.
        application.registerForRemoteNotifications()
        let center = UNUserNotificationCenter.current()
        center.requestAuthorization(options: [.alert, .sound, .badge]) { (granted, error) in

            // Enable or disable features based on authorization.
            if granted == true
            {
                print("Allow")
                UIApplication.shared.registerForRemoteNotifications()
            }
            else
            {
                print("Don't Allow")
            }
        }
        UNUserNotificationCenter.current().delegate = self

        return true
    }
func application(_ application: UIApplication, didRegisterForRemoteNotificationsWithDeviceToken deviceToken: Data){
        let tokenParts = deviceToken.map { data -> String in
            return String(format: "%02.2hhx", data)
        }
        let token = tokenParts.joined()
        currentToken = token  //get device token to delegate variable

    }
 public class var shared: AppDelegate {
        return UIApplication.shared.delegate as! AppDelegate
    }
 func userNotificationCenter(_ center: UNUserNotificationCenter, willPresent notification: UNNotification, withCompletionHandler completionHandler: @escaping (UNNotificationPresentationOptions) -> Void) {
         completionHandler([.alert, .badge, .sound])
    }
}

Xcode 10 Swift 4.2

当你的应用程序在前台时，显示推送通知

步骤1:在AppDelegate类中添加delegate UNUserNotificationCenterDelegate。

class AppDelegate: UIResponder, UIApplicationDelegate, UNUserNotificationCenterDelegate {

步骤2:设置UNUserNotificationCenter委托

let notificationCenter = UNUserNotificationCenter.current()
notificationCenter.delegate = self

第三步:这一步将允许你的应用程序显示推送通知，即使你的应用程序在前台

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

    }

步骤4:该步骤是可选的。检查你的应用程序是否在前台，如果在前台，然后显示本地推送通知。

func application(_ application: UIApplication,didReceiveRemoteNotification userInfo: [AnyHashable: Any],fetchCompletionHandler completionHandler:@escaping (UIBackgroundFetchResult) -> Void) {

        let state : UIApplicationState = application.applicationState
        if (state == .inactive || state == .background) {
            // go to screen relevant to Notification content
            print("background")
        } else {
            // App is in UIApplicationStateActive (running in foreground)
            print("foreground")
            showLocalNotification()
        }
    }

本地通知功能-

fileprivate func showLocalNotification() {

        //creating the notification content
        let content = UNMutableNotificationContent()

        //adding title, subtitle, body and badge
        content.title = "App Update"
        //content.subtitle = "local notification"
        content.body = "New version of app update is available."
        //content.badge = 1
        content.sound = UNNotificationSound.default()

        //getting the notification trigger
        //it will be called after 5 seconds
        let trigger = UNTimeIntervalNotificationTrigger(timeInterval: 1, repeats: false)

        //getting the notification request
        let request = UNNotificationRequest(identifier: "SimplifiedIOSNotification", content: content, trigger: trigger)

        //adding the notification to notification center
        notificationCenter.add(request, withCompletionHandler: nil)
    }