How to retrieve a PNS Handle from the Platform Notification Service?

Question

I have an Xamarin.iOS application that is connecting an Azure backend service and I want my service to send notifications to the client applications.

The Microsoft documentation explains how to set up the Notification Hub for different scenario. I think I am getting most of it, however I am not sure I understood the very first part, which is for the iOS application to Retrieve PNS Handle from the Platform Notification Service, as shown in the following picture:

It looks like this is some task that must be performed by the client application alone and then communicate this to the backend service for the registration.

I have a feeling that it happens at the 10th step of this section, when iOS calls the application back on the method RegisteredForRemoteNotifications. In that callback, the application is given a deviceToken:

public override void RegisteredForRemoteNotifications(UIApplication application, NSData deviceToken)
{
    Hub = new SBNotificationHub(Constants.ListenConnectionString, Constants.NotificationHubName);

    Hub.UnregisterAllAsync (deviceToken, (error) => {
        if (error != null)
        {
            System.Diagnostics.Debug.WriteLine("Error calling Unregister: {0}", error.ToString());
            return;
        }

        NSSet tags = null; // create tags if you want
        Hub.RegisterNativeAsync(deviceToken, tags, (errorCallback) => {
            if (errorCallback != null)
                System.Diagnostics.Debug.WriteLine("RegisterNativeAsync error: " + errorCallback.ToString());
        });
    });
}

Question

Is that deviceToken the PNS Handle that I need to send to the backend service to start the registration process? If not, how am I supposed to contact the PNS to get the Handle?

Answer 1

The information is in the documentation but not in an obvious form for a C# developer.

In Objective-C, the deviceToken is provided by the iOS application, as mentioned by @LucasZ, after it got registered against the PNS.

However I can't just send this deviceToken right away as it will not be accepted by the AppleRegistrationDescription class used in my Service.

It took me a while to get more familiar with Objective-C to figure out that this token was actually transformed before being sent to Azure:

NSSet* tagsSet = tags?tags:[[NSSet alloc] init];

NSString *deviceTokenString = [[token description]
        stringByTrimmingCharactersInSet:[NSCharacterSet characterSetWithCharactersInString:@"<>"]];

    deviceTokenString = [[deviceTokenString stringByReplacingOccurrencesOfString:@" " withString:@""] uppercaseString];

I have implemented something similar in C#:

public override void RegisteredForRemoteNotifications(UIApplication application, NSData deviceToken)
{
    string pnsHandle = deviceToken.Description
                                  .Replace("<", string.Empty)
                                  .Replace(">", string.Empty)
                                  .Replace(" ", string.Empty)
                                  .ToUpper(); 

    Hub = new SBNotificationHub(Constants.ListenConnectionString, Constants.NotificationHubName);

    Hub.UnregisterAllAsync (pnsHandle, (error) => 
    {
        if (error != null)
        {
            System.Diagnostics.Debug.WriteLine("Error calling Unregister: {0}", error.ToString());
            return;
        }

        // In my use case, the tags are assigned by the server based on privileges.
        NSSet tags = null;

        Hub.RegisterNativeAsync(pnsHandle, tags, (errorCallback) => 
        {
            if (errorCallback != null)
                System.Diagnostics.Debug.WriteLine("RegisterNativeAsync error: " + errorCallback.ToString());
        });
    });
}

To answer my question, yes, the deviceToken is the PNS Handle but it must be formatted.