I'm working with Unity C# for my personal project.
I have seperated Model and View. I want View to be automatically updated when somethings in model change.
So I made an Action object, and added all view-updating functions to it.
The thing is, there is super many fields in model. Adding the event to these fields would be really tedious job, and moreover, a single variable change will cause the whole UI to be updated, which may be a huge waste of perfomance.
But adding individual Action object to each of these fields would be much more tedious job.
All I want is that View is updated when Model is changed, and I think this event pattern is the best choice for my situation.
Are there any suggestions for my code design?
Unity has a great article on using ScriptableObjects to handle events like this. That being said, Unity uses an Entity-Component pattern, and retrofitting MVC pattern contradicts some of the optimizations that EC and Unity provide.
Related
I am having a hard time understanding how MVVM is used in case of more complex applications. All the examples I can find are extremely basic Apps.
Let's say I have a "Package Delivery" application. To perform a delivery I have to do 3 steps:
Scan the package
Enter any damages or problems with the package
Let the recipient sign on the device
All this information gets validated on the device and then sent to the backend.
In MVC I would implement this like this:
The DeliveryController handles all of the logic. This includes navigation between pages, fetching of API data and validating all of the data once it is all collected.
The controller acts as the "Connection" between the Views and collects all the information and brings it together.
But how would this be done in MVVM? Where would all the data be brought together? Most implementations of MVVM I can find do something like this:
In this, the data entered in each View would have to be passed to the next ViewModel until the end of the chain is reached. At that point the SignatureViewModel would do the validation and make the API call. That seems very weird and like it would get very confusing, since data would just be "passed through" multiple ViewModels just to have it at the end of the chain.
Another option I see would be that each ViewModel handles it's own data:
Here for instance the DamagesViewModel would validate and send the data it's own View handles. The big issue with this is that data does not get sent as a whole. Also there can not be any validation of the entire data before it is sent.
My last idea would look like this:
This adds a DeliveryViewModel that essentials acts like the DeliveryController does in MVC. It would handle which ViewModel to navigate to next, handle what API calls to make and validate all the data once it is entered.
To me (as someone who has mostly used MVC) this last options seems most sensible. But I also feel like it might miss the point of MVVM.
How is this usually done in MVVM? I would really appreciate any pointers. Links to articles that explain this well are much appreciated.
Also if anyone knows of any publicly available repositories or projects that have this kind of pattern in them, I would love to see them.
Even when using MVVM I still use some form of a controller and consider ViewModels as basically transformation of data to facilitate the view.
So for me there is still a service or controller layer that completely separates the middle and back end tier from the rest of the architecture.
View models come into play depending on the consumer/app - fetches data from the service tier, transforming the data, validating etc for the purpose of a consumer/app/etc.
I have struggled quite a bit with the same thing. Especially since I’ve used MVC quite a lot.
I think the most important thing to consider is that MVVM is not meant to solve exactly the same things as MVC. You can still implement a controller outside of this pattern to complement it. It also changes quite a lot the general design of the application.
One mean to do it that I have used is to implement the controller as a singleton that can be shared between VewModels. This controller can per example be injected into the ViewModels using dependency injection.
Viewmodels could then for exemple subscribe to events coming from the controller to update.
But this is one way to solve this problem among others.
MVVM is a way to organize code. It’s one way to separate your user interface from your logic.
I have found a blog where you can have a look where MVVM architecture is described perfectly.Though here writer demonstrates MVVM for windows form app but at least you can get some idea about architectural design of MVVM.
https://scottlilly.com/c-design-patterns-mvvm-model-view-viewmodel/
Also please have a look into this repo.
https://github.com/MarkWithall/worlds-simplest-csharp-wpf-mvvm-example
To better show my problem, I drew a graph of how my ViewModel hierarchy looks like so far:
ViewModel hierarchy
What I want to achieve is simply call a method from ScriptEditorViewModel and ask it, if the object, which is currently being edited inside EditObjectViewModel has been specified in the script.
Later I also want to send some information to ScriptEditorViewModel and make it generate a script for the object if it doesn't exist.
ScriptEditorViewModel and ProjectManagementViewModel are 2 separate tabs in my program, which are basically operating at the same time.
Is it possible to do that and if so, is it a good approach?
Note: I'm currently using ReactiveUI as my MVVM framework but any other MVVM solution is also welcome.
When using MVVM pattern, you want to decouple components.
In View part there is xaml with bindings to data and command present in ViewModel.
In ViewModel you should keep data that is presented and logic that does something with that data. It is not the wisest thing to couple multiple ViewModels - keep their logic separated. If you have a command method, all data it deals with should be present in its ViewModel. For anything more complex, you shoud consider communicating with some kind of service or database.
Hence comes the Model part. Here you want to create the model of something you want to store and not necessary present in a View.
I don't know if I understood your problem well, but including a database or any kind of 'persistence layer' into your solution should resolve the problem of accessing specific information. You can create some in-memory storage for start.
Almost every MVVM example I've come across has both the Model and ViewModel implementing INotifyPropertyChanged.
Other sources (ones which focus on domain modeling) seem to suggest that Models should be incredibly plain (something to do with separation of concerns?) with essentially no references to anything. Unfortunately, those sources don't use MVVM.
I'm trying to reconcile the two.
-I'm relatively new to programming and completely new to design patterns and the like so please try to go easy on me.
Edit: Let me rephrase my question. Given that the answer to the above seems to be "sometimes one and sometimes the other," WHEN should you do one and and when should you do the other. Also, how would each be implemented?
(That isn't answered in the other post. It just has them arguing with each other).
Models have to implement INotifyPropertyChanged to inform the view model that they have changed. If the model doesn't implement INotifyPropertyChanged (or another equivalent interface), then the view model is stuck using polling or other similarly inefficient methods to detect changes in the model state.
This MSDN page may be useful reading to further understand the roles of the various components that make up the MVVM pattern.
I have no idea if this is a best practice, but I have my ViewModel set up so that it is the only active entity. The Model is only directly changed when created by reading from a database (and then loaded into a ViewModel), or before saving to database (extracting from ViewModel, modifying Model properties that only matter to the database, like foreign keys).
If for some reason you desire being able to have multiple ViewModels connected to the same Model or have a need to change a Model from under a ViewModel, then you'd have a good reason to implement INotifyPropertyChanged on the Model.
I'm a relative amateur, so take what I say with a grain of salt. But this is what I've been gathering, and enforcing this separation has, I think, made my code cleaner and easier to understand and debug. So for my own projects, I'm going to try avoiding implementing INotifyPropertyChanged on my Models if I can avoid it.
I’ve an Interface with many textEdit fields. But any Fields have dependencies to others.
For example:
When textfield_1 is filled, textvield_3 and 4 disabled. But my Layout is Dynamic and I don’t want to Code this dependencies Hard.
Does anyone have an Idea or Solution to Save or hold this dependencies in my Application? And how can I check it.
If I understood your intent correctly I would say the basics would come from ViewModel (as in MVVM design pattern). You could go with the simple INotifyPropertyChanged route or something more "reactive" like RxUI: http://www.reactiveui.net/
All changes happen in the ViewModel (so you can also share it across platforms) and the UI just reacts to changes in the ViewModel data.
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The way it was explained was through the use of events and the publish/subscribe model. Basically, the model would just be the data and it would have no knowledge of the view/GUI/UI. The model is typically just an abstract object that operates on its data and can perform operations and whatnot.
The view is a different class that responds to changes in the model and usually displays this data to the user. Previously, I did not know how this could occur without coupling between the view and model but having it explained with events clears that confusion up a lot. Does this mean that the model contains public events that itself raises when something interesting happens? For example, if we were programming a game of Chess, when a piece was moved, the model would raise the event of PieceMoved with the necessary information (which piece, moved from where to where, etc.) and the view could subscribe to such an event and then show an animation of the piece moving from its old square to its new square.
The part that still confuses me is the exact nature of the controller. I'm having trouble understanding how it supplies the model and view with new information. I imagine the controller contains references to the model and view. Keeping with the Chess example, would the controller just respond to user input (for example to move a piece) and then just suggest to the model what piece wants to move to where? Then the model takes this information, sees if it's a legitimate move, and if so, update the model accordingly, raise the PieceMoved event, to which the view reacts and updates the graphical realm accordingly?
Lastly, how does the controller find out which piece is trying to be moved? It seems like that type of thing is heavily tied to the view (let's say moving involved first clicking the piece you wish to move and then the destination square). I imagine the controller would respond to a mouse click and sends those coordinates to the model but how would the model know how to translate those coordinates to find which piece was selected? Isn't that heavily tied to the view? It seems like the view would have to perform some logic processing instead of simply responding to the model and controller but then it wouldn't be a proper view anymore (instead a view/model mix).
The bad things about the MVC pattern are:
Everyone has her/his own version
It is a bit abstract to be grasped at first
The good things:
It is actually pretty simple
It is a fantastic way of dividing up most applications
To answer your question though:
The model
This is a easy one. The model should know only about itself. It is the board, the pieces and the rules of the game. You know you are building your model right if you could reuse it either in a desktop application or a web one.
The view
This isn't complex either. It is the visual part, and the one that deals with the user input. The most important concept to understand the role of views in the MVC pattern is that they must provide a way to make calls to the puclic interface of your system. In the chess game, it is the one that has to draw the elements and detect what the user is doing with the mouse/keyboard. When the user does something it is the view the responsible of calling the system: eg. "User1 wants to move piece from X to Y" (Important: most of the time you don't want the view to trigger a call like User1 clicked in coordinates x, y. Pixels are the realm of the view. The system has to receive orders that are independent of how they are graphically represented).
The controller
You're right, this one isn't that straightfoward. The controller is the one that has to process calls to the public interface to the system. In your example it will receive a call 'User1 moves from X to Y' and call a method in the appropiate object of the model (very likely the board in this case). Thus, the controller totally knows about the objects in the model. However it can also contain the code that is necessary in the application but that doesn't belong to the domain of your model. You have to check if the user has permission to access the system? You have to log that call into a file? Well, most of the time that kind of things go into the controller.
However, that's just my own version of MVC (I, like everyone else, also have my own too... :)
MVC is a pretty generic concept. There are tons of different ways that it has been implemented, and most of them have compromises of one sort or another.
The problem I see is that you are trying to take an esoteric concept and apply concrete implementation details to it. That's hard to do unless you have a very specific implementation in mind (asp.net MVC, fubuMVC, spring MVC, smalltalk MVC, whatever) and each one accomplishes things like notifications and event handling in a different manner.
If you're just talking about the MVC concept, then you have to deal with the MVC concepts in a generic way. I know it may be easier to understand if you have a concrete implementation, but then you go down the path of understanding the pattern (MVC) based on the understanding of the implementation, which can skew your understanding of the pattern itself.
So when you read about messages or events, you have to just think "some mechanism that is implementation defined". It could be a callback, or it could be a C# event, or it could be a Windows message, or it could be using the force ;)
EDIT:
Regarding your update, I will repeat. You can't answer implementation specific details about a generic concept. You would have to define a specific implementation for someone to be able to tell you how those implementation details are accomplished.
There's a lot of answers to this question, mainly because there are so many different MVC frameworks. Have a look at http://martinfowler.com/eaaDev/uiArchs.html for some examples. I can also give an MVVM perspective mainly since this is what I've been working on these days so this is how I'm thinking.
The Model layer is basically your data and your business logic. You might be talking to a database or a webservice here. If you end up writing a system, that is more than a just a GUI, this is your reusable code.
The ViewModel then sits on top the Model, and basically presents (ahem) the data as properties. It uses an INotifyPropertyChanged interface to tell the UI when data changes. If you have data that you are using to build something up before pushing it to the model layer, it lives here. You will normally expose the actions that you can perform in the UI as ICommnands.
The View layer is the least coupled, because it just uses binding to connect to the ViewModel. Things to visualise are properties that are bound with optional IValueConverters used to change its form, e.g.
Visibilty="{Binding IsVisible, Converter={StaticResource booleanToVisibiltyConverter}}"
Action UI elements are bound to the Commands on the ViewModel to kick off the ViewModel actions.
Command="{Binding DoSomething}"
So if you have a view (the chess board) and a controller for the chess board, the controller would house the events for it. When you move a piece it raises the PieceMoved event which should pass information to this event such as current position, and desired position.
For a very simple application you may not grasp the concept of models. One might have a billing model that could be reused on multiple views (such as a detail and create view). You wouldn't want to duplicate this code every time you needed it, so in your controller each event would reach out to the billing model that needed it. By creating a model you are encapsulating your code.