05-EventAggregator

Using EventAggregator

In this sample, we will see how to create custom events, how to pass custom payload in events, how to subscribe to events both inside Xamarin.Forms app and on the native platform, and how to publish events all using Prism's EventAggregator.

Creating Events

To create an event, simply extend Prism.Events.PubSubEvent<T> with a T payload.

public class IsFunChangedEvent : PubSubEvent<bool> { }

Usage

Publish

_eventAggregator.GetEvent<IsFunChangedEvent> ().Publish (true);

Subcribe

_eventAggregator.GetEvent<IsFunChangedEvent> ().Subscribe (IsFunChanged);

void IsFunChanged(bool arg) 
{
    // Do something with the payload
}

Creating Events with Custom Payload

To create a custom payload for your event, simply extend System.EventArgs and set as payload for custom event,

public class NativeEventArgs : EventArgs
{
    public string Message { get; set; }
    public NativeEventArgs (string message)
    {
        Message = message;
    }
}

public class NativeEvent : PubSubEvent<NativeEventArgs> { }

Usage

Publish

_eventAggregator.GetEvent<NativeEvent> ().Publish (new NativeEventArgs("Xamarin.Forms"));

Subcribe

_eventAggregator.GetEvent<NativeEvent>().Subscribe(OnNameChangedEvent);

void OnNameChangedEvent(NativeEventArgs args) 
{
    Message = args.Message;
}

Subscribing To Events

As mentioned above, subscribing to events is quite simple inside Xamarin.Forms app.

_eventAggregator.GetEvent<IsFunChangedEvent> ().Subscribe (IsFunChanged);

void IsFunChanged(bool arg) 
{
    // Do something with the payload
}

Platform Subscriptions

To subscribe to an event published in Xamarin.Forms app at the platform level, resolve the IEventAggregator from the Xamarin.Forms.App() instance before loading it.

iOS

After initializing the Xamarin.Forms app in FinishedLaunching() method of AppDelegate.cs,

var application = new App (new iOSInitializer ());
var ea = application.Container.Resolve<IEventAggregator> ().GetEvent<NativeEvent>().Subscribe(OnNameChangedEvent);
LoadApplication (application);

Android

After initializing the Xamarin.Forms app in OnCreate() method of MainActivity.cs,

var application = new App (new AndroidInitializer ());
var ea = application.Container.Resolve<IEventAggregator> ().GetEvent<NativeEvent> ().Subscribe (OnNameChangedEvent);
LoadApplication (application);

UWP

After initializing the Xamarin.Forms app in OnLaunched() method of native App.xaml.cs, subsribe in the contructor of MainPage.xaml.cs,

var application = new UsingEventAggregator.App(new UwpInitialer());
var ea = application.Container.Resolve<IEventAggregator>().GetEvent<NativeEvent>().Subscribe(OnNativeEvent);
LoadApplication(application);