View Models - WPF MVVM TUTORIAL #3 

I love it when I do little things in my app naturally coz it feels right, then see an actual programmer doing it (but like a hundred times faster xD). This is a great series btw, It's pulling everything mvvm into focus for me. 👍👍👍

the part you are talking about how to glue the model data to a viewmodel (8:35) is just what I need! thank you for these helpful and good quality tutorial :)

Thank you for your tutorials! So far yours have been the best I've seen as they are easy to follow, well structured, and aren't pushing to add additional frameworks to do what MVVM was made to do. I'm watching your tutorials for a private project, we don't use WPF or MVVM where I work(yet), but I will be recommending your tutorials to my coworkers and friends that are developers.

Thank you So much. You are helping me in a different type of project of mine and actually, i could make my own progress thanks to your help. Thank you second time. 🙏

Great content and great pace! Third or fourth MVVM video I watch and by far the best!

Best WPF C# contents I have ever found in youtube after searching for months. Amazing all round tutorial with exactly the speed I wanted. Thanks a ton @SingletonSean

i have watched a few videos about MVVM tutorials now, yours is truely for everyone, the others just assume we already know everything else

Thanks for all SingletonSean! Amazing tutorials altough sometimes pretty fast. I'm mechanical engineer although I have strong bases in programming but not as strong in Software arquitecture. I think a great idea would be creating some graphics diagrams before you start to code directly. I really believe this would help to understand this course even better!

I am (also) a C# developer, but never used WPF before. Great video series. Always rechecking your videos, when I need something :D

Propchange snippet is so useful. Thanks for that.

I'm glad to hear that a new video has been uploaded.

The best MVVM tutorial on RU-vid!

he is a master in software. Respect.

Thanks a lot, it was a great lesson! I didn't think that it was possible to create a VM for Model to connect Model and ViewModel, it seemed to me a very interesting mechanism

Better than all the paid courses I know. Thank you from the bottom of my one braincell!

You are an MVVM master , my problem is that I can't digest such a lot of information, Please do you have any course where you explain logic step by step to master the MVVM pattern

amazing tutorial

Wow thank you for that snippet lol such a timesaver

Very nice!

I like your videos and appreciate the way you debug on line so we can see how you solve and diagnose issues, but was puzzled in this one at 13:20 where you comment that MVVM XAML views should not be using code behind, yet the very next step is you putting currentViewModel & datacontext into code behind on the Main Window - not sure what to take from that? If you view it as a temporary step before navigation is implemented, then it would have been simpler to put datacontext in each viewmodel leaving only currentViewModel to change on App.cs and that could have been declared in Xaml rather than code behind. If datacontext was declared earlier in each viewmodel (even if temporarily using xaml resources), it would have made autocompletion available on your views when binding text so your video of view creation would be much simpler - we would have understood the code much earlier.

Love the tutorials, but I have to say I had an issue when trying to bind my properties, I kept getting issues claiming "InvalidOperationException: A TwoWay or OneWayToSource binding cannot work on the read-only property 'Size' " I tried all binding options out of curiosity and continued to get the same result. I would love to use this method for making a large view for this form I've created.

This is a great video!! I have a question, at 11:28 we have generated mock data in ReservationListingViewModel constructor, I have real data coming from a data access layer method and I want to add this data into _reservations list as bulk but I cannot cast it. How can I accomplish this?

Absolutely amazing series, really helpful. Can I just ask one question? I have a view, in which I have a list of objects which we'll call Class A. As per your video I have created a viewmodel class of the model class A, so that it can interface with the view. But I also have a list, made up of another model class (Class B) inside the original class. I don't need to show this in the view, as each list item of Class A has a button to show the list of list items of Class B (so as a separate view), but now I'm implementing commands and I need to save list A, so I also need lists of B inside the viewmodel of A, but how do I do that? I'm sorry if it's not well explained, and thank you.

Thanks for video! Sounds funny on 0.5 speed)

Hey Sean, great video as always! The propchange snippet, does it really allow _lowercase field and Uppercase property automatically? I always failed setting up a snippet to do that. Also looking at yours i do not see the trick that is responsible for it. I would try but i have no PC right here.

Nice tutorial. But I would like to see how would you do when the application gets more complex. I mean when you need more methods to do specific stuffs and how you separate the viewmodel from the model. I'm asking this because I have an application that connects to an API that have to do a lot of stuffs and I have many methods in the view model because there is where I have other variables that I need and I cannot move them to the model. In short words maybe you can explain more the right way to separate models and view models when you need to use many different methods. Where and how to put them?

Hey Sean! When you created the ReservationViewModel that extended VMBase, why didn't you have to call OnPropertyChanged on the mapped properties from the Reservation model?

Hi, Hey Sean! I havae a question: on time 4:00 when you propchanged a property, you named the private one and suddenly the public one is also changed, how did you do this? Any Extension or Configuration? Thanks!

Hi Sean. Amazing roundup! Thanks for that a lot. Question though: in your setup, the view will not update changes inside the models entities. Only new or removed items is forwarded through the observable collection. How would you tunnel the property changed here? I'd bet you had a less messy implementation at hand than I have done it😉

Great one. I like the way you pronounce "item" haha

Hi Sean, a question regarding backing model access in ViewModels. I have a Model that is called Sound which is represented in a combobox in the UI through a list of SoundViewModels. SoundViewModel has the Sound model in its constructor and uses it to provide data to the view. When then selection in the combobox changes it updates its bound property on the backing ViewModel. However I need to access the Sound model inside the SoundViewModel to make changes in the domain. What would be the best approach here? Add the model as a public property on the SoundViewModel? This feels wrong as the Model would then be visible to the View.

6:40 - Why binding to a property that doesn't implement INotifyOnPropertyChanged can cause memory leaks?

Thanks for the nice explanation! 9:24, I notice that you exposed your private ObservableCollection field as an IEnumerable property. But that prevents the UI Binding from seeing the CollectionChanged events as you add or remove reservations, right? Don't you want the Binding to detect when reservations are added/removed?

Hi. Good quality tutorial. Just a little constructive feedback - maybe slow your presentation down a little? Learning theory dictates that learners need pauses and 'beats' to assimilate/accommodate information. Great quality stuff, but hampered by not taking a breath. I realise it's a sad result of contemporary pressures (everything has to be lightning fast and 'not too long' due to worsening attention spans).

At 11:22 you are adding Reservation Type Items to the Listview, but for some reason the only Object intellisense shows is the Reservation object. when I try to do a New RoomID, intellisense does not show it. Is there somewhere that I am missing a reference to these properties?

Do we have to have the properties on the ReservationViewModel?

I was wondering if viewmodelbase should be an abstract class like commandbase will be? If not could you say why?

I've seen both Models and ViewModels implement INotifyPropertyChanged. Is either one the "correct" way or if MVVM flexible in which does?

I have a question, this is not strictly about this video, but on the concept as a whole. How do changes in the model propogate to the UI layer? For example, if I'm implementing a counter for 'X days from fatal accidents'. I might have a DaysFromAccidentModel, which will have an int field. Then I'll do a DaysFromAccidentViewModel, to which I'll pass the model. And it will have a property that implements INotifyPropertyChanged that reads the value of the int in DaysFromAccidentModel. And finally I'll have a view DaysFromAccidentView that has a textBlock that binds to the ViewModel's property. I understand that if I change the counter in the UI it will trigger the InotifyPropertychanged interface and the change will be reflected in the viewmodel. But how will it be refected in the model itself? Also, how a change in the model be reflected in the UI? For example if I reset the counter in code and not from the UI, how will the view model know the value was changed?

How to refer to names of xaml elements (x:Name) of Views (that are defined under "views" folder for instance) from inside ViewModels??? Because there is no linkage as in the case of ".xaml & .xaml.cs " pairs when creating window classes. Any help appreciated.

Maybe someone can clarify this for me, at 15:09 Sean adds a binding setting to UpdateSourceTrigger on PropertyChanged. That seems like a lot of overhead to me, to re-instantiate our MakeReservationViewModel every time a new character is typed. Is this actually OK in practice and what is the reasoning to update the binding so frequently?

Placing all the view models as properties inside a MainViewModel wich serves as the root view model and works like a singleton is a good aproach?

I really like using the CallerMemberName attribute so that I don't have to remember to explicitly put in the property name in the setters. I also like to make the base class abstract and the OnPropertyChanged virtual. Its come in handy more than once protected virtual void OnPropertyChanged([CallerMemberName] string propertyName = null) { PropertyChanged?.Invoke(this, new PropertyChangedEventArgs(propertyName)); }

Thanks for the tutorials, very clear und teachful! I'm implementing a chess game using WPF, for the drag and drop of the pieces I need to implement the method that will handle the event in the xaml.cs file of the view, and I have to update the gamestate at the same time. But how do I access the gamestate (Model) if it is a bad practice to have a Datacontext of the Model in the controller (xaml.cs). Thanks for any response in advance

10:30, Why the list is binding in one ViewModel, and the values of the columns comes from another ViewModel?

What if we implemented INotifyPropertyChange directly in Models for properties, and for CurrentItem in ViewModel ? why need to create extra glue code?

6:35 Can, please, someone explain (or provide a link) why binding to an object that does not implement INotifyPropertyChange could result in memory leaks, especially when the properties are readonly.

Minute 07:40 - my Class RoomID is avalible but this is not correct, what am i doing wrong...? thanks for this usefull content!

Hello i got a problem if i remove startupUri programm starts but it doenst open the window. I did it like you show it, in the class app maybe someone can help

Hi, Do Anyone have idea why my textbox is readonly? I'm in the testing point at 14:00 min, and I can't write on the name textbox. Does it related to the fact that the textbox is binding? How do I solve it? P.S. So far great tutorial!

Why don't you bind View and ViewModels with the TwoWay binding instead of using INotifyChange ?

Why do you repeat all model-properties from type "Reservation" inside of your ReservationViewModel? I think it is not DRY. I do it because datatype-mismatch, so just use an UI-converter for this problem. :-)

No bloviate, just specifics!

got to 14:39 and the window is completely blank, I literally have no idea what's wrong help pls

14:34 Find Find error in Visual Studio

He's very fast like BMW M5

Mechanics question here - at ru-vid.com/video/%D0%B2%D0%B8%D0%B4%D0%B5%D0%BE-2FPFgW0xVB0.html you set up the public reservationViewModel properties with the '=>' operator since the _reservation object is readonly (you don't need to set). However, when I do this, I have to use "Mode=OneWay" in my binding on the view, or I get this: A TwoWay or OneWayToSource binding cannot work on the read-only property How is your code working without the "Mode=OneWay" attribute in your XAML?

Hi, I love your tutorials. I live in Iran and due to sanctions I can not be a member of your support channel, so some of your videos can not be played😐😐😐

Fantastic but please give us a second to read what you typed before the edit.

Youre really good. But its going too fast.

Thanks for the effort but on the other hand you are speaking no stop like the gamers, and not trying to explain it's just a show-off. Frankly, it will be more helpful if you keep the narration regular.

When manually adding the reservations in the ReservationListingViewModel for testing and demo purposes we are bypassing the the conflict handler. _reservations = new ObservableCollection(); _reservations.Add(new ReservationViewModel(new Reservation(new RoomID(1, 3), "Bob", DateTime.Now, DateTime.Now.AddDays(3)))); _reservations.Add(new ReservationViewModel(new Reservation(new RoomID(1, 3), "John", DateTime.Now, DateTime.Now.AddDays(3)))); You can add 2 conflicting reservations and error won't be raised. In order to test the Conflict raising error I would suggest to do it in one of 2 ways. For both of them we can create an instance of ReservationBook and add the reservations to it. This way we will fire the Conflict if such exists private readonly ReservationBook _reservationBook; _reservationBook = new ReservationBook(); _reservationBook.AddReservation(new Reservation(new RoomID(1, 3), "John", DateTime.Now, DateTime.Now.AddDays(1))); _reservationBook.AddReservation(new Reservation(new RoomID(1, 3), "Bob", DateTime.Now.AddDays(2), DateTime.Now.AddDays(5))); _reservationBook.AddReservation(new Reservation(new RoomID(3, 2), "Maria", DateTime.Now, DateTime.Now.AddDays(2))); _reservationBook.AddReservation(new Reservation(new RoomID(2, 3), "Lorain", DateTime.Now, DateTime.Now.AddDays(2))); 1. First way - private readonly ObservableCollection _reservations; _reservations = new ObservableCollection(); foreach (var reservation in _reservationBook.GetAllReservations()) _reservations.Add(new ReservationViewModel(reservation)); 2.Second way - similar but to use IEnumerable private readonly IEnumerable _reservations; _reservations = _reservationBook.GetAllReservations().Select(x => new ReservationViewModel(x));