Event Aggregation in WPF - A TimCo Retail Manager Video 

Finally the pieces come together :-) As always another great video.

Hi Tim, this is a great course and in general you are my go-to guy to develop a more concrete understanding of .NET concepts. Many thanks and keep it up!

Great concept-explanations as always!

Very good and clear explenation. Good job!

Remarkable Work Tim!

I learned a lot till now. Thx Tim

Awesome course thus far, learning a lot about how view models and views work. This is my first time working with API's learning there too!

Tim, really appreciate in some of your videos at the end you go through the next steps. Allows me to try to implement the features myself before you tell us how to do it. So I have figured out how to pass our User’s name to the next view, and more complex, pulled a sql list, and figured out how to get past a deserialize Json error, then bind it to a drop down list. Can’t wait for the next video!

Thank you very much Tim really appreciated efforts

This session was very enlightening. I really dug into the Caliburn.Micro documentation in order to fully understand the lesson. I would suggest the same for anyone following this instructional series. The project that I am implementing has some similar functionality however, I am starting to veer off from the follow along training. This is some incredible material that you are putting out here Tim. I am looking forward to pulling the data thru from my tables and populating the information in my desktop UI. Really people, read the Caliburn Documentation. There is some really good jems of functionality that can be taken advantage of... Thanks Tim for the awesome lesson.

I tried to find out how Event Aggregation are working... and this video was very, very helpful! Thank you. And it came just in time :D I'm currently learning to work with WPF and C# for my new job and I have the feeling that your content will be very helpful ;)

@20:00 you can also just hit ctrl+r, ctrl+r twice; rename it; and hit enter and it'll be automatic.

Tim is a "Basket is half-full" kind of guy. ;-)

Many thanks for doing these Tim, much appreciated. I do have a couple of questions if I may. 1. As I've never done WPF it's all very new and really liking the caliburn system - Is there a similar system for Winforms as I believe caliburn is just for WPF - Can't recall if you mentioned it in a previous video. 2. In the ShellViewModel where you activate the Login View Model and get a new instance of it each time, what happens with the old instance of it - I guess we don't have to worry about memory leaks here and Caliburn deals with this for us. 3. Why when placing margins do we go left, top, right, bottom - couldn't they make it the same as CSS - They had to be awkward!

Hi Tim, since you usually ask for suggestions of what we would like to see in future videos, here's mine. I would like to see your way of managing the events from the UI, but not the "Click" event for a button, that is so easy with CM. What I mean, is an event that you specify event name and method name that handles it in your xaml. For example, MouseRightButtonUp for a button, SelectedChanged for a some list where an item can be selected, etc. If I use , it is recognised only if I implement the event in the view.xaml.cs code (well this is another doubt I have... how good is it to use the code behind when we use MVVM?). I've had a hard time finding the way to put it only in my ViewModel. I finally did but I think I did too much work and I'm not really sure if that is the best/an acceptable way. I could also just call the method in my view model from the code behind, but I thought CM would be there for me to have an almost empty xaml.cs code. Again, there is a concept concern here for me. If EventAggregation could be used, I don't know how I could raise the event, since in this video we are raising it from our .cs code. PS: Sorry for my long message.

Hi Tim, What are your thoughts on Clean Architecture and would you be willing to do a video on it and other design patterns?

Following along (and loving the course, thank you). For every spot you were changing LogOnEvent(Model) is there any downside to using Rename? (ctrl+R, ctrl+R)? At a glance it's changing the class, implementations and class name in one go.

Hi Tim, I should have seen this a bit sooner... Thanks for your clear explanation. Two opinions exist within our team on where to apply the EventAggregator: only on ViewModel level (it is just a caliburn thing and leave it within this context), or everywhere in the code where a pub-sub pattern is needed (it is a design pattern). Whats your opinion about this?

While walking through this a second time I misnamed my SalesView as SaleView But my models had a different name.. If you get a message about unable to find view, check the name of the view, you may need to change it in both the Xaml and CS file that accompanies it to get it to load.

I think your talk about the pros/cons of just injecting the container and resolving dependencies in the methods is an important one. I think it is important to point out a couple of other things related to this. If you specify all of your dependencies in the constructor then you are giving whoever consumes it no choice but to provide all of the relevant dependencies, rather than sticking in a container that MIGHT be able to give it what it needs later - The dependencies still need to be resolved, but it just pushes the buck in an unclear way in my opinion, and the consumer now has to look at the code itself to figure out what its dependencies are. This is not a good situation and leads to brittle code. Furthermore, specifying the dependencies up front makes unit testing a lot more straight-forward. In the video, you do inject the container, and your ShellViewModel becomes coupled to the Bootstrapper Configure method (Where the types are registered). What are your thoughts on this, and do you think there is another suitable way? Maybe injecting a factory for LoginViewModel instead - I'm new to this, so i'm just thinking out loud.

Can I use this event aggregation also for pushing events from helper classes? Like a method using a 3rd party dll creates a specific event, I will inform the VMs about this event to react to it? Example: I am using tapi3 to grab phone calls, when the tapi_event fires, I want to inform the VMs to change the UserControl.

Instead of injecting SimpleContainer to the ShellViewModel in the constructor, could you use Caliburn.Micro's static Service Locator IoC instead? And do you mean to use BindingList instead of Caliburn.Micro's BindableCollection (in LoginViewModel)?

Hi Tim, great series I am trying to branch out a little and display the First and Lastname from the LoggedInUserModel created in an earlier video as a Singleton I ask for that model using _loggedInUserModel = _container.GetInstance(); and I can see this is returned when I set approprate breakpoints. What I am strugling with is how do you then update the view with that data. I have used for instance in the view and have created a FirstName property in the ShellViewModel public string FirstName { get { if(_loggedInUserModel == null) { return "Not logged in"; } else { return _loggedInUserModel.FirstName; } } set { _loggedInUserModel.FirstName = value; NotifyOfPropertyChange(() => FirstName); } } The property never seems to be set and the view not updated when the Login form closes. Any hints?

EventHandle is awesome. Really powerful weapon: D! I could not understand it before, and i had a problem in my application with get user info to ShellView. Thanks! I have one question. If i want put registration page for new account. I should put business logic into APIHelper and do somethink like HttpResponseMessage to "api/Account/Register" ?

Hi Tim, in the ShellViewModel's constructor how are those objects passed in (or wired up)? It seems more and more items are added to the constructor yet we don't have to manually update any code that is consuming this constructor. How does this work? How does the program automatically know which objects to use to instantiate the ShellViewModel regardless of which classes you put in the constructor?

I have seen a static class in Caliburn.Micro which is "IoC" and I used it before to get a new view model without getting it in the constructor using the method IoC.Get(); Which would be the good practice to follow?

Hi, wouldn't it be better to specify that Conductor takes only objects that implement Screen instead of object?

In the APIHelper class, I removed the following lines from my GetLoggedInUserInfo method, as it is being done in the initialize method, and it works just fine. Is there a reason that we had to repeat it in the method, or a future video has taken care of it ..? apiClient.DefaultRequestHeaders.Accept.Clear(); apiClient.DefaultRequestHeaders.Accept.Add(new MediaTypeWithQualityHeaderValue("application/json"));

29:10 but you could set container as the only parameter in the constructor, and still have the backing properties, assigning them to containter.GetInstance() inside the constructor. Am I right?

Amazing videos Tim I really love it and I learned a lot I am following your project and picked some bits and pieces however when I jump between 2 user controls I noticed it still show new instances for example for example, you may fill the sales form with some data then you move to a different form "not the login" then go back to sales form and whatever textbox you left it filled it is now empty so I don't think that having those top variables holding the view models are actually working unless you fixed this in a different video please guide me which one exactly Thanks

In trying to understand the Button events, I cannot understand how the CanAddToCart is hooked into the AddToCart button. This surfaced when I noticed that the buttons are disabled. But if I return 'true' from CanAddToCart, the AddToCart button is enabled. This came about as I was trying to find a typo where the AddToCart button was becoming enabled in a future session. Upon reverting my code and reworking this lesson I am now in sync with the expected display of the SalesViewModel. However, when I toggle the return from CanAddToCart the AddToCart button enables and disables appropriately. I'm just not seeing how that property is wired to that specific button. On a side note, As a Patreon supporter, should I address this question to you from there?

Hi Tim, thank you for this video, I have a question which is not related to this video, can you or any of your followers advice me on a good reporting system which works with WPF using MVVM, also need to have an end user report designer.

Hi, I really like using dependency injection, thus I am asking myself whether it makes sense to also create an instance of LogOnEvent via DI in the LoginViewModel. Does this make any sense or would that would go a little too far as LogOnEvent does not contain any coding? Thanks for your thoughts.

Have you ever used the Framework Prism?

If you extract an interface from a collection of empty events, can you still pattern match?

what if from Sales page i want to navigate to other page with same view model ? How this could be accomplished?

hi tim so in my shellview i made a menu when i click on a button its shows another tab here's my code is that correct or should i use the event public ShellViewModel(DashViewModel dashvm, IncidentViewModel InciVM) { _dashvm = dashvm; _inciVM = InciVM; ActivateItem(_dashvm); } public void dash() { ActivateItem(_dashvm); } public void inci() { ActivateItem(_inciVM); }

I'm just going to drop this comment here since I'm not sure where this would go. Since we login during this video I figure it's an appropriate spot to mention something strange. When I try to login I have credentials from Windows 10 on a work computer being forced in as the username. My solution to this problem was to change the username and use that to login. Have you ever come up with any bugs like this and how would you suggest fixing something like that?

Hi Tim, Is it worth to learn making Windows apps nowadays? Or better start to learn ASP.NET web apps programming? Im starting with coding right now and im so confused what to choose and focus on

any chance to make Xamarin Forms in this way ?

I measured. It took 2:38 secs to substitute some tiny login form by the empty sales one. Isn't that too slow?

Will you ever make an android version of this app? If not, then how would I call the API and use it in Flutter? I'm planning to use Flutter for the mobile version because it's cross platform and has great performance. Will be really helpful if you replied!

I have a problem with SalesView, when im clicking the button, nothing happen. Login is fine, i got 200 and all data, next events are okay (debug goes throughout the event) but nothing displaying. Even when i change ActiveItem(_salesVM) to ActiveItem(_container.GetInstance

Why not just use ActivateItem(IoC.Get()); ?

Is it still useful to learn WPF in 2019? Isn’t WPF going away?

its getting too complicated. i guess Forms are much straight forward.

I'm getting a runtime error on this line: _events.Subscribe(this); The error message is: "System.NullReferenceException: 'Object reference not set to an instance of an object.'". _events is null. This is in ShellViewModel.cs. The function is "public ShellViewModel(IEventAggregator events, SalesViewModel salesVM, SimpleContainer container)". The events parameter is coming in as null. Anybody have any idea why?

For me I had to pick Async try { ErrorMessage = ""; var result = await _apiHelper.Authenticate(UserName, Password); // Capture more information about the user await _apiHelper.GetLoggedInUserInfo(result.Access_Token); await _events.PublishOnUIThreadAsync(new LogOnEvent()); } The option you picked wasn't available And public async Task HandleAsync(LogOnEvent message, CancellationToken cancellationToken) { await ActivateItemAsync(_salesVM); } but it worked as expected