In many ways I think of using the MVC pattern in WinForms, but I'd like to know if it's possible to bind controls with objects using the ObservableCollection type? If it's purely for WPF, what other alternatives are out there?
To put it into perspective, we're building a system which has business logic that I'd like to control the UI with, instead of making customizations for each requirement or workflow on the UI itself. We have around a few hundred potential forms which I'd like to start designing with the pattern in mind.
We're also building web interfaces for most of the processes, but in reality they're just watered-down versions of the Forms. If I can use the same framework which I can just bind to on the web form that would be awesome.
Thanks
What ObservableCollection does is that it implements INotifyPropertyChange and each control in WPF has the possibility to listen for it's bound data to raise the event from INotifyPropertyChange. You can read more here about why you can't use ObservableCollection they way you want to in WinForms.
Another way is to use the Model-View-Presenter pattern:
This pattern can also be used in ASP.NET.
There's an MSDN Magazine Article on: "Better Web Forms with the MVP Pattern" that I think you should look into. And here is an introduction to how you use MVP-pattern in asp.net.
Related
I have a WPF GUI application based on MVVM design and data binding. Now, I want to reuse the core code (i.e. the data model) in a Windows service, or a console UI app, or a WinForms app.
Is such a design reasonable? If yes, what are the pitfalls?
Or should I make a standalone data model instead, and interface WPF via wrappers?
UPDATE:
Sorry, I should have been more precise. Let me clarify: I don't doubt the very modularity thing =) My concern boils down to having my current DataModel implement INotifyPropertyChanged, use DispatcherTimers, etc. -- all that non-GUI but still WPF stuff. The model's business logic is based on it.
Is this (non-GUI WPF) design acceptable for reuse in the aforementioned cases, or should I abstract further, until no references to WPF would be required at all?
Yes, this is perfectly acceptable and most of the time it is desired!
When you build an MVVM app, it should be in at least 3 formal layers:
Presentation WPF, UI, xaml, behaviors. All that stuff. Not reusable
Application The view models and structure that supports your application rules. All that stuff. Not intended for reuse
Foundation Database access, business objects. Domain specific algorithms. Ideally this bit should be reusable anywhere
The foundation layer is the clever bit. This is where the meat in your application sandwich is. It makes perfect sense for this to be totally agnostic of UI technology. WPF, winforms, ASP. It shouldn't even need a UI.
Edit for question update:
Removing all references to WPF is hard because sometimes you need a CollectionViewSource on your view models for grouping/filtering of results. That is a WPF class.
It is very tempting to view your seperation-of-concerns as 'just dont reference wpf' and that helps but it can make life difficult. Instead, try to be disciplined with the type of behaviors you are putting in. If you find yourself writing 'clever' (domain) code on a view model, shift it to the foundation layer as a business object method or extension. Similarly, if you find yourself implementing IValueConverter often, perhaps you should make better use of view models.
One thing is for sure, your foundation layer should never, ever, ever reference WPF.
Such a design is very reasonable! You can create a portable C# library for all .NET technologies including WPF, WinRT, ASP MVC, etc which can contain your models. Obviously you'll need to wrap these portable models into a viewmodel anyway, but IPropertyChanged is implemented in all XAML flavors.
In MVC a model can have multiple views, in WPF a XAML code-behind model is tight to 1 single XAML (view) isn't WPF/XAML flawed from the start in respect to MVC ?
I recommend looking at MVVM for use with WPF.
You're comparing MVC with Windows Forms to WPF with code behind - which is comparing an architectural pattern to a technology (without using a pattern). This is an unfair comparison.
I wrote a series on MVVM starting from a Windows Forms perspective that may help with understanding this. You'll find that the separation of View and ViewModel possible with WPF is far cleaner and simpler to implement than the Controller of MVC. It actually allows even more decoupled architectures with less implementation work.
Good question!
In MVC you state that a model can have multiple views, which is true. However, each view would have its own controller.
In MVVM a model can have multiple views, and in this case each may have their own view model.
However, in practical terms, if a ViewModel does not have any concepts that are highly specific to a certain view, it is entirely possible to re-use view models. In fact, I wrote an article on cross-platform XAML applications where I re-used code between three apps, one on WP7, one in Silverlight, the other WPF:
http://blogs.msdn.com/b/mikeormond/archive/2010/12/09/writing-cross-platform-xaml-applications.aspx
The views for each were very different, however I was able to re-use both the models AND the view models for all three apps.
WPF/XAML is a technology, and MVC is design pattern, it's good when technology is not limiting you to a specific pattern, and allows developer to choose what pattern to use. Same as programing languages allow's you to use any design pattern.
You can use MVC, MVP, MVVM, or YourMegaPattern with XAML\WPF. Technology should be above patterns, it's frameworks that are usually bound to a specific pattern.
For example you can take ASP .NET techology, and MVC framework based on it.
What aspects and practices specific to WPF could be most useful (and not inconceivable to implement) in non-WPF GUI programming?
I was introduced to the command pattern by learning the WPF commands. It forms the basis for the UI - code separation, which I believe should be utilized in other applications.
Updating of the view via events. Databinding magic happens due to INotifyPropertyChanged and INotifyCollectionChanged. Writing a non-WPF app that, rather than blocking on queries, updated its data through either these interfaces or a custom one is a solid practice that can help ensure good separation of responsibilities as well as testability.
MVVM or Model-View-ViewModel is a fantastic design pattern and one that I hope will become widespread on the internet.
On that, have a look at Steve Sanderson's Knockout UI javascript library.
Ok, it's not entirely specific to WPF (it is used in silverlight as well), but I find IDataErrorInfo to be extremely useful outside of WPF / Silverlight. For my ASP.NET MVC applications my ViewModels implement IDataErrorInfo (for complex validations that are uncomfortable to solve using the validation attributes - such as if field A has a particular value, and field B has a particular value, then C can only be in a small subset of values). Then I have an extension method on my controllers that adds those data validation errors to the ModelState. Works like a charm.
MVVM is most commonly used with WPF because it is perfectly suited for it. But what about Windows Forms? Is there an established and commonly used approach / design pattern like this for Windows Forms too? One that works explicitly well with Windows Forms? Is there a book or an article that describes this well? Maybe MVP or MVC based?
I have tried MVP and it seems to work great with windows forms too.
This book has an example of windows forms with MVP pattern (sample payroll application). The application is not that complex but will give you an idea about how to go about creating it.
Agile Principles, Patterns, and Practices in C#...
You can get the source code at
Source Code
EDIT:
There are two variations of the MVP pattern
(a) Passive view and (b) supervising controller
For complex databinding scenarios I prefer to go with the Supervising controller pattern.
In supervising controller pattern the databinding responsibility rest with the view. So,for treeview/datagrid this should be in the respective views, only view agnostic logic should moved on to the presenter.
I'll recommend having a look at the following MVP framework
MVC# - An MVP framework
Don't go by the name (it's an MVP framework).
Simple winforms MVP video
Winforms - MVP
An example of dealing with dropdown list
MVP - DropDownList
Simple treeview binding example (poor man's binding). You can add any treeview specific logic in BindTree().
Below is the code snippet.... not tested, directly keyed in from thought....
public interface IYourView
{
void BindTree(Model model);
}
public class YourView : System.Windows.Forms, IYourView
{
private Presenter presenter;
public YourView()
{
presenter = new YourPresenter(this);
}
public override OnLoad()
{
presenter.OnLoad();
}
public void BindTree(Model model)
{
// Binding logic goes here....
}
}
public class YourPresenter
{
private IYourView view;
public YourPresenter(IYourView view)
{
this.view = view;
}
public void OnLoad()
{
// Get data from service.... or whatever soruce
Model model = service.GetData(...);
view.BindTree(model);
}
}
As it has already said, i always worked in a MVP pattern when using Winforms. But the design pattern you will use not mean you will use right. There is loads of anti-pattern attached to MVP.
If you want to starts everything in a good manner, you have to use the framework for building smart client. So i will recommend to use that design and practices: Smart Client Software Factory http://www.codeplex.com/smartclient
You have a discussion here about the current smart client frameworks : http://codebetter.com/blogs/glenn.block/archive/2008/05/10/prism-cab-and-winforms-futures.aspx
PS: I like this post on the MVP anti-patterns: http://blog.mattwynne.net/2007/06/13/mvp-smells/
Hope this helps
The Model-View-ViewModel (MVVM) Pattern is a design pattern. Per definition a design pattern shows a common solution in the object-oriented world and this solution can be applied in various platforms (WPF, WinForms, Java Swing, etc.). I agree that MVVM is best used with WPF because it leverages the strong binding capabilities. However, Windows Forms supports data binding as well.
The WAF Windows Forms Adapter shows how to apply the MVVM Pattern in a Windows Forms application.
I have written about a variation of MVP/MVVM design patterns called MVP-VM, which is a tailor made solution for winforms applications that require full testing coverage and use data binding as main mechanism for keeping the presentation updated with model data.
MVVM for .NET Winforms
MVVM (Model View View Model)
introduces similar approach for
separating the presentation from the
data in an environment that empowers
data binding (WPF). Since .NET
framework 2.0 already offers advanced
data binding infrastructure that also
allows design time binding of
application objects - the ‘View Model’
entity can fit quite well in MVP based
environment.
I asked this same question to two of my techies co-workers: is MVVM for WindowsForms possible? Both gave me the exact same answer: "No way! WindowsForms is missing the rich bindings of WPF and Silverlight (OneTime, OneWay, TwoWay, OnewayToSource) and it is also missing the TypeConverters."
Screen Activator Pattern for WindowsForms - you can find it here, ported from Caliburn.Micro by jagui
Rich Bindings and TypeConverters - Truss by Kent Boogaart, does it in an UI independent way
Commands - WPF Application Framework (WAF) has a WafWinFormsAdapter project that takes care of some MVVM stuff namely commands
Again, can we have MVVM for WinForms?
Yes we can. We have all the pieces. We just have to glue them together.
I believe that MVP is a pattern well-suited to WinForms development - as is partly evidenced by it's use in CAB - Microsoft's framework for WinForms.
I use MVP in WinForms to extract code out of the View - because I can't test the View code. And also to enable code that needs to be reused (or is duplicated) to stay out of the View where it can't be shared.
I can refer to my own project where I use the MVP pattern ExceptionReporter.NET. Though I'm sure I don't use it perfectly.
You mentioned MVVM working for WPF - I think the reason for that is because of strong data-binding support. If you were not using data-binding in WPF (and it's certainly not compulsory) then you could choose MVP. The point being that MVP is a strong choice for any client-side application. And possibly a 'better' choice, even in WPF, if you plan on sharing code between projects that aren't WPF.
For more evidence of the value of using MVP in WinForms see Boodhoo's video presentation on using MVP:
http://www.bestechvideos.com/2008/06/29/dnrtv-show-14-jean-paul-boodhoo-on-model-view-presenter
And an MSDN article by the same author at http://msdn.microsoft.com/en-us/magazine/cc188690.aspx
The BindTree method seems a little
flawed to me. Suddenly the the View
knows abou the Model. Is that a good
thing? There must be tons of poeple
being confronted with these kind of
problems. I am surprised that there
aren't any books about it. Since there
are books about everything in the .NET
world.
These Design not about hiding the model rather precisely defining the interactions between the different layers of the applications. You can change the backend completely and as long as you pass a Model through Bindtree your UI will continue to work.
Now class Model may be a poor choice of a name in the example that Rajesh gives. It can be TreeData, or RecordsData. However you define it, it has what you need to using the binding mechanism of Winforms to bind a specific control to the underlying data.
The best site to browse for this kind of material is here. Martin Fowler has collected a variety of useful UI design pattern and enterprise design patterns.
Again the key to this is the use of interfaces to precisely define how each layer interact with each other.
In my own application (a CAD/CAM applications used to run metal cutting machines) my structure looks like this.
Forms implementing form interfaces
UIDLL with views implementing view
interfaces that interact with forms
through the form interface. The
specific views register themselves
with UIViewDLL Views executes Command Objects found
in command libraries that interact
with the Model.
Command libraries; lists of
commands implementing ICommand.
The command that interact with
views do so through the interfaces
exposed in UIViewDLL.
UIViewDLL; exposes the View Interfaces
used by the commands.
Model; the classes and collection that
make up core data structures of my
application. For me these are things
like material, cuttingpaths, shape,
sheets, torches, etc.
Utility; a DLL that has commonly used
utility classes used by my company
that span different application. For
example complex math functions.
You can use Enterprise Architecture, Patterns and Practices as the starting point, although they are slightly dated.
Under General Guidance there is Application Architecture for .NET: Designing Applications and Services, which is a good introduction to .NET ways and layered N-tier application.
alt text http://i.msdn.microsoft.com/ms954595.f00aa01%28en-us%2CMSDN.10%29.gif
For more formal "patterns", there is Enterprise Solution Patterns Using Microsoft .NET.
(source: microsoft.com)
To name a few,
Model-View-Controller
Intercepting Filter
Three-Layered Services Application
The first good explanation of UI design patterns I read was in Jeremy Miller's blog - Building Your Own CAB. It describes the common patterns - Passive View, MVP, etc. and addresses some of the ways you might implement them in C#.
You can try MugenMvvmToolkit that allows to use a "pure MVVM" for WinForms.
Due to the fact that it supports bindings on all platforms, all of the native binding features available for WPF platform available on all platforms (include WinForms).
I don't develop too many desktop / Windows Forms applications, but it had occurred to me that there may be some benefit to using the MVC (Model View Controller) pattern for Windows Forms .NET development.
Has anyone implemented MVC in Windows Forms? If so, do you have any tips on the design?
What I've done in the past is use something similar, Model-View-Presenter.
[NOTE: This article used to be available on the web. To see it now, you'll need to download the CHM, and then view the file properties and click Unblock. Then you can open the CHM and find the article. Thanks a million, Microsoft! sigh]
The form is the view, and I have an IView interface for it. All the processing happens in the presenter, which is just a class. The form creates a new presenter, and passes itself as the presenter's IView. This way for testing you can pass in a fake IView instead, and then send commands to it from the presenter and detect the results.
If I were to use a full-fledged Model-View-Controller, I guess I'd do it this way:
The form is the view. It sends commands to the model, raises events which the controller can subscribe to, and subscribes to events from the model.
The controller is a class that subscribes to the view's events and sends commands to the view and to the model.
The model raises events that the view subscribes to.
This would fit with the classic MVC diagram. The biggest disadvantage is that with events, it can be hard to tell who's subscribing to what. The MVP pattern uses methods instead of events (at least the way I've implemented it). When the form/view raises an event (e.g. someButton.Click), the form simply calls a method on the presenter to run the logic for it. The view and model don't have any direct connection at all; they both have to go through the presenter.
Well, actually Windows Forms implements a "free-style" version of MVC, much like some movies implement some crappy "free-style" interpretation of some classic books (Romeo & Juliet come to mind).
I'm not saying Windows Forms' implementation is bad, it's just... different.
If you use Windows Forms and proper OOP techniques, and maybe an ORM like EntitySpaces for your database access, then you could say that:
The ORM/OOP infrastructure is the Model
The Forms are the Views
The event handlers are the Controller
Although having both View and Controller represented by the same object make separating code from representation way more difficult (there's no easy way to plug-in a "GTK+ view" in a class derived from Microsoft.Windows.Forms.Form).
What you can do, if you are careful enough. Is keep your form code completely separate from your controller/model code by only writing GUI related stuff in the event handlers, and all other business logic in a separate class. In that case, if you ever wanted to use GTK+ to write another View layer, you would only need to rewrite the GUI code.
Windows Forms isn't designed from the ground up to use MVC. You have two options.
First, you can roll your own implementation of MVC.
Second, you can use an MVC framework designed for Windows Forms.
The first is simple to start doing, but the further in you get, the more complex it is. I'd suggest looking for a good, preexisting and well-tested, MVC framework designed to work with Windows Forms. I believe this blog post is a decent starting point.
For anybody starting out, I'd suggest skipping Windows Forms and developing against WPF, if you have the option. It's a much better framework for creating the UI. There are many MVC frameworks being developed for WPF, including this one and that one.
According to Microsoft, the UIP Application Block mentioned by #jasonbunting is "archived." Instead, look at the Smart Client Application Block or the even newer Smart Client Software Factory, which supports both WinForms and WPF SmartParts.
Check into the User Interface Process (UIP) Application Block. I don't know much about it but looked at it a few years ago. There may be newer versions, check around.
"The UIP Application Block is based on the model-view-controller (MVC) pattern."
Take a look at the MS Patterns and Practices Smart Client application block which has some guidance and classes which walk you through implementing a model view presenter patter in windows forms - take a look at the reference application included.
For WPF this is being superseced by the prism project
The software factories approach is a great way to learn best practices