Get data from Azure push notification on Xamarin Forms Page

Question

I'm developing a Xamarin Forms app who gets data from prestashop webservices.

In order to make it work, you need to create a api key on the website and provide it to the app, but I think it will be a big problem to the average user to copy a 32 characters key from web to the app.

So I decided it's a good option to create a azure app service backend with a notification hub, when the user creates the api key, it goes to a xxx.azurewebsite.com paste the key, enter the customer notification hub id showed in the login screen of the app and then a push notification is send it to the app, the api key is captured stored and the user logs in.

I'm following this guide Add push notifications to your Xamarin.Forms app but I can't see how can I recive the notification in a currently open screen and capture it in a ViewModel class in the shared project.

Brandon Minnick Brandon Minnick · Accepted Answer · 2016-12-29T18:24:34

Here's some sample code that shows how to display a pop-up alert in Xamarin.Forms when you receive a Push Notification on either platform.

Xamarin.Forms Shared Code

Create a static class in the Xamarin.Forms shared code that triggers DisplayAlert. Then create a static method called ShowAlert that can be accessed from our platform-specific projects.

public static class PushNotificationHelpers
{
    public static async Task ShowAlert(string alert)
    {
        await Application.Current?.MainPage?.DisplayAlert("Push Notification Received", alert, "OK");
    }
}

iOS AppDelegate

To handle the Push Notification on iOS, you will override the ReceivedRemoteNotification method in the AppDelegate. The ReceivedRemoteNotification method is triggered every time the iOS app receives a push notification.

[Register("AppDelegate")]
public partial class AppDelegate : FormsApplicationDelegate
{
    .
    .
    .

    public override async void ReceivedRemoteNotification(UIApplication app, NSDictionary userInfo)
    {
        // Process a notification received while the app was already open
        await ProcessNotification(userInfo);
    }

    async Task ProcessNotification(NSDictionary userInfo)
    {
        if (userInfo == null)
            return;

        Console.WriteLine("Received Notification");

        var apsKey = new NSString("aps");

        if (userInfo.ContainsKey(apsKey))
        {

            var alertKey = new NSString("alert");

            var aps = (NSDictionary)userInfo.ObjectForKey(apsKey);

            if (aps.ContainsKey(alertKey))
            {
                var alert = (NSString)aps.ObjectForKey(alertKey);

                await PushNotificationHelpers.ShowAlert(alert.ToString());

                Console.WriteLine("Notification: " + alert);
            }
        }
    }
}

Android GcmServiceBase

To handle push notifications on Android, you will create a class that implements GcmServiceBase and overrides OnMessage. The OnMessage method is triggered every time the Android App receives a notification.

[Service(Name="com.sample.evolve.GcmService")] //Must use the service tag
public class GcmService : GcmServiceBase
{
    .
    .
    .

    protected override void OnMessage (Context context, Intent intent)
    {
        Console.WriteLine ("Received Notification");

        try
        {
            //Push Notification arrived - print out the keys/values
            if (intent != null || intent.Extras != null) 
            {

                var keyset = intent.Extras.KeySet ();

                foreach (var key in keyset)
                {
                    var message = intent.Extras.GetString(key);
                    Console.WriteLine("Key: {0}, Value: {1}", key, message);
                    if(key == "message")
                        await PushNotificationHelpers.ShowAlert(message);
                }
            }
        }
        catch(Exception ex)
        {
            Console.WriteLine ("Error parsing message: " + ex);
        }
    }
}

Sample App

The Xamarin Evolve app shows how to implement Push Notifications for a Xamarin.Forms app. I highly recommend perusing the Xamarin Evolve app source code to get a better understanding of the above sample code!