How do I use delegates within Xamarin (specifically UNUserNotificationCenterDelegate) - xamarin

Question

I need to use the iOS 10 features in UNUserNotificationCenterDelegate. How can I implement this delegate in c# / Xamarin?

Answer 1

When using the an UNUserNotificationCenterDelegate, make sure that you assign it in the WillFinishLaunching or the FinishedLaunching methods in your app's UIApplicationDelegate.
You must assign your delegate object to the UNUserNotificationCenter object no later before your app finishes launching.
Ref: UNUserNotificationCenterDelegate
AppDelegate.cs Example
public override bool FinishedLaunching(UIApplication application, NSDictionary launchOptions)
{
UNUserNotificationCenter.Current.RequestAuthorization(UNAuthorizationOptions.Alert, (approved, err) =>
{
// Handle the user approval or refusal of your notifications...
});
UNUserNotificationCenter.Current.Delegate = new MyUNUserNotificationCenterDelegate();
return true;
}
In that example, I am creating/assigning a delegate class named MyUNUserNotificationCenterDelegate, so you need to implement that class.
MyUNUserNotificationCenterDelegate class example:
This UNUserNotificationCenterDelegate example will capture each local notification sent and toggle between showing it on the lock screen or outputting the details to the syslog.
public class MyUNUserNotificationCenterDelegate : UNUserNotificationCenterDelegate
{
bool toggle;
public override void WillPresentNotification(UNUserNotificationCenter center, UNNotification notification, Action<UNNotificationPresentationOptions> completionHandler)
{
if (toggle)
completionHandler(UNNotificationPresentationOptions.Alert);
else
{
Console.WriteLine(notification);
completionHandler(UNNotificationPresentationOptions.None);
}
toggle = !toggle;
}
}
Now you will actually need to send some notifications, this sets up a simple repeating notification:
Create/Schedule Local Notification:
// Schedule a repeating Notification...
var content = new UNMutableNotificationContent();
content.Title = new NSString("From SushiHangover");
content.Body = new NSString("StackOverflow rocks");
content.Sound = UNNotificationSound.Default;
var trigger = UNTimeIntervalNotificationTrigger.CreateTrigger(timeInterval: 60, repeats: true);
var request = UNNotificationRequest.FromIdentifier(identifier: "FiveSecond", content: content, trigger: trigger);
UNUserNotificationCenter.Current.AddNotificationRequest(request, (NSError error) =>
{
if (error != null) Console.WriteLine(error);
});
Every 60 seconds a notification is dispatched and if you are on the lock screen you will receive an alert every 120 seconds...
Recommend reading to understand how you Xamarin.iOS/C# to interact with delegates, protocols, and events:
iOS uses Objective-C delegates to implement the delegation pattern, in which one object passes work off to another. The object doing the work is the delegate of the first object. An object tells its delegate to do work by sending it messages after certain things happen. Sending a message like this in Objective-C is functionally equivalent to calling a method in C#. A delegate implements methods in response to these calls, and so provides functionality to the application.
Ref: Xamarin.iOS and Delegates