如何在Xamarin应用运行或手机未锁屏时接收推送通知

应用处于前台时系统默认不会自动弹出通知栏提示，你需要分别对Android和iOS端做额外配置即可实现全场景接收推送通知，具体实现方案如下：

Android端实现方案 #

Android平台应用前台运行时，推送的回调会触发FirebaseMessagingService的OnMessageReceived方法，你只需要在该方法内主动构建并弹出通知即可：

1. 首先确保已安装Xamarin.Firebase.Messaging NuGet包，且已正确配置Google服务相关文件
2. 实现自定义消息接收服务，代码示例如下：

[Service(Exported = false)]
[IntentFilter(new[] { "com.google.firebase.MESSAGING_EVENT" })]
public class CustomFirebaseMessagingService : FirebaseMessagingService
{
    public override void OnMessageReceived(RemoteMessage message)
    {
        base.OnMessageReceived(message);
        var notification = message.GetNotification();
        if (notification != null)
        {
            ShowNotification(notification.Title, notification.Body);
        }
    }

    private void ShowNotification(string title, string content)
    {
        string channelId = "app_push_channel";
        var intent = new Intent(this, typeof(MainActivity));
        intent.AddFlags(ActivityFlags.ClearTop);
        var pendingIntent = PendingIntent.GetActivity(this, 0, intent, PendingIntentFlags.OneShot | PendingIntentFlags.Immutable);

        var notificationBuilder = new NotificationCompat.Builder(this, channelId)
            .SetSmallIcon(Resource.Mipmap.ic_launcher)
            .SetContentTitle(title)
            .SetContentText(content)
            .SetAutoCancel(true)
            .SetContentIntent(pendingIntent)
            .SetPriority(NotificationCompat.PriorityHigh);

        var notificationManager = NotificationManager.FromContext(this);
        // Android 8.0及以上需要创建通知渠道
        if (Build.VERSION.SdkInt >= BuildVersionCodes.O)
        {
            var channel = new NotificationChannel(channelId, "应用推送", NotificationImportance.High)
            {
                Description = "应用常规推送通知渠道"
            };
            notificationManager.CreateNotificationChannel(channel);
        }
        // 生成随机ID避免通知覆盖
        notificationManager.Notify(new Random().Next(1000, 9999), notificationBuilder.Build());
    }
}

• 部分国产Android系统需要额外引导用户开启通知权限、自启动权限，否则前台也可能无法正常弹出通知

iOS端实现方案 #

iOS平台需要实现UNUserNotificationCenterDelegate的WillPresentNotification方法，配置前台运行时的通知展示规则即可：

1. 首先确保已在Entitlements.plist中开启Push Notifications功能，证书配置正确
2. 在AppDelegate中注册通知并配置代理，代码示例如下：

public override bool FinishedLaunching(UIApplication app, NSDictionary options)
{
    global::Xamarin.Forms.Forms.Init();
    LoadApplication(new App());

    // 申请通知权限
    UNUserNotificationCenter.Current.RequestAuthorization(
        UNAuthorizationOptions.Alert | UNAuthorizationOptions.Badge | UNAuthorizationOptions.Sound, 
        (granted, error) => 
        {
            if (granted)
            {
                InvokeOnMainThread(UIApplication.SharedApplication.RegisterForRemoteNotifications);
            }
        });
    // 设置通知代理
    UNUserNotificationCenter.Current.Delegate = new CustomNotificationDelegate();

    return base.FinishedLaunching(app, options);
}

// 自定义通知代理类
public class CustomNotificationDelegate : UNUserNotificationCenterDelegate
{
    public override void WillPresentNotification(UNUserNotificationCenter center, UNNotification notification, Action<UNNotificationPresentationOptions> completionHandler)
    {
        // 配置前台运行时也展示通知横幅、声音、角标
        completionHandler(UNNotificationPresentationOptions.Alert | UNNotificationPresentationOptions.Sound | UNNotificationPresentationOptions.Badge);
    }

    public override void DidReceiveNotificationResponse(UNUserNotificationCenter center, UNNotificationResponse response, Action completionHandler)
    {
        // 此处处理通知点击逻辑
        completionHandler();
    }
}

通用注意事项 #

• 推送分为通知消息和数据消息两种类型：通知消息系统默认仅在后台/锁屏时弹出，数据消息无论应用处于什么状态都会触发对应回调，需自行解析后弹出通知
• 可根据业务需求调整前台通知的展示样式，比如仅展示横幅、或仅播放提示音不弹出横幅

内容的提问来源于stack exchange，提问作者Zeeshan shaikh