I am working on an application where every object also has a view which is displayed to user. User uses this view to modify the object through click events.
My question is what is the most convenient way to setup the communication between an object's view and its underlying data ?
Currently, my objects extend the graphical package I am using in order to be able to use the click events so that they can be modified and also added to the view. Is there a better way to achieve this ? I know that I can use MVC/MVP but not really sure how I can apply it in a situation like this.
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I have to convert a decent sized Winforms application into a WPF app following the MVVM pattern. I'm not sure what the best way to do this is.
The application is built around a third party map control.
Multiple windows: A main window that displays the map, and other windows that allow the user to change properties of the map (add layers, change styles, etc).
My plan was to create a viewmodel for each window, and have a base viewmodel containing the map control itself and any properties/methods that needed to be shared.
The main thing I'm not sure about is how to handle the map operations that are built into the control. For instance, there is a MapMouse_Down event. Normally I would just put this in the code behind if I wasn't following MVVM, and handle it there. Is that the correct way to handle this?
Normally I would just put this in the code behind if I wasn't following MVVM, and handle it there. Is that the correct way to handle this?
You could keep anything that is purely view related in the code-behind of the views but anything that is testable application logic should be implemented in view models. View-related stuff may for example be animations and any code that changes the behaviour or appearance of a control in some way, like for example setting some width or colour.
There are different ways to handle "events" in MVVM depending on what kind of controls you are using but you would generally defined commands in the view model and invoked these from the view. Please refer to this blog post for more information.
Having a separate view model for each different type of window is ideal.
View models should never contain controls. They should contain only abstractions of the controls. If all of your windows have mapping components, only then should your base window view model have an abstraction of the mapping control. (An example of the sort of abstraction I'm talking about: Imagine a view that where the user should enter a name. The view will have a TextBox which has a Text property. The view model will have a Name property. The view will bind the TextBox's Text property to the view model's Name property. Figuring out the right abstractions for larger applications is one of the challenges of MVVM.)
It's perfectly fine to have event handlers in your view if your controls don't support data binding or they don't have ICommand support. But the event handler in your view should do as little as possible, instead just transferring control over to your view model, which will update its abstract representation of the view, which the view will then re-synchronize to through data bindings or manual synchronization logic.
WPF is different for Winforms, the approach is based on the binding of proprety .
Below an Example of using MVVM.
Easy MVVM Example
In my main window I have several user controls. One for the menu and one which has variable content depending on the menu choice. What is a good way to handle this with MVVM? Should both user controls have their own view models? But then how do I get the information from the menu view model to the content view model? Or should I use only one view model for the whole window?
This leads to a more general question: If I am using the same information in several places in my program, how do I handle that? How can two seperate views access the same model instance? Do I need to make that model static?
Should both user controls have their own view models?
Unless the controls in question are very process driven controls, it is best to have the controls work off of their declared dependency properties solely and not have indvidual VMs.
same information in several places in my program, how do I handle that?
Don't overthink it, create one VM, initialize and place it onto the application as a static and then access it from other VMs which need it.
Then anywhere in the code one can get the running app via from the global Application.Current Property (System.Windows) which will have the static VM property which will hold the shared VM.
I've done several WPF application(not using MVVM) in the past and I had always to implement my own system of navigation between view(instantiate the view once, and then load in a container component, with refreshing required components of my view).
It works, but:
It's always custom, so if a new developer comes he has to learn of it how it works
I'm pretty sure that It's not the most optimized(most of things haven't been done in background worker, ...)
It's a time loss
So I was wondering if there is an official way to handle this ? I don't exactly how, but I was thinking to a navigation component, which can act a little like a tab panel, or a little like the MVC framework in asp.net, we can call a specified controller for an action and some parameters.
Maybe deactiviting bindings when they aren't in the current view
You can use DataTemplates/Styles to customize content of your control ( not only apearance, but data, cause that what you're asking for I presume)
http://msdn.microsoft.com/en-us/library/ms742521.aspx
You can have one Host control and at runtime change its appearance based on events/ states.
Like an example can have a look here:
http://code.google.com/p/svnradar/ how this program manages a appearance of Group and Flat view of repository information.
Another example:
Podder of Josh Smith
http://joshsmithonwpf.wordpress.com/2008/03/05/podder-v2-has-been-released/
Hope this helps.
You may be interested by Lakana, a lightweight (but powerful) framework that can handle for you all the navigation concerns !
Riana
I'm trying to create a strategy for handling popup forms for use throughout any part of my application. My understanding so far is that I will need a single UserControl in the root of my MainWindow. This will be bound to its own ViewModel which will handle the messages that are sent within the app.
I'm using MVVM Light, and I'm fairly new to the Messenger class.
Imagine a Master/Details scenario, where a list a objects are contained within a ListBox. Selecting one of these items and clicking an Edit button would display a UserControl which covers the whole screen. The user can then edit the selected item, and click OK to commit the change.
I want the UserControl that is opened to be "generic" in a way that I can throw any (probably a ViewModel) at it... for it to render the ViewModel via a DataTemplate and handle all the object changes. Clicking OK will callback to the sending class and persist the change as before.
Some situations where this would be useful are...
Display error messages with no required user input (other than OK to close it)
Display an edit form for a data item
Confirmation dialogs (much like a standard MessageBox)
Can anyone provide any code samples of how I might acheive this?
When designing a UI with MVVM the goal is to separate the concerns of the View from the concerns of the ViewModel. Ideally, the ViewModel should not rely on any view components. However, this is the idal and another rule of MVVM is that you should design your application as you wish.
In the area providing a service showing dialogs there are two different approaches floating arround:
Implementing the DialogService on the View (e.g. see http://geekswithblogs.net/lbugnion/archive/2011/04/13/deep-dive-mvvm-samples-mix11-deepdivemvvm.aspx Sample 03).
Implementing a service component that does is not attached to the view (e.g. see http://blog.roboblob.com/2010/01/19/modal-dialogs-with-mvvm-and-silverlight-4/)
Both approaches rely on an interface that defines the functionality the service provides. The implementation for this Service is then injected into the ViewModel.
Also, do both approaches have their specific advantages and disadvantages.
The first approach works also well for WP7, however, it requires a common view base class as this contains the implementation of the view service.
The second approach works well for SilverLight and WPF and appleals as it keeps the service separate from the view and does not impose any restictions on the view.
Another possible solution is to use messaging to show the dialogs.
Whatever approach you are using try to keep the View and the ViewModel de-coupled by using an IoC (inversion of control) pattern, i.e. define an interface so that you can use different implementations. To bind the services into the ViewModel use injection, i.e. passing the service into the constructor of the ViewModel or by setting a property.
I recently started learning MVVM for a WPF app I was creating, I used this article as a basis for showing dialogs, if you download the sample project then it is actually quite a nice decoupled method, it is nicely abstracted and to get a view you pass an instance of a viewmodel. I extended it somewhat for my own means, I also used the WPFExtendedToolkit MessageBox for warnings, errors etc because the standard win32 MessageBox is fugly.
With regards to dynamic forms then you'll want to investigate the ItemsControl, and in your ViewModels have a Collection of Data Items which need to be edited by the user for the ItemsControl to bind to. I have a dialog for editing actions and their parameters in a workflow system designer where the dialog list of actions was totally dynamic. This was done by exposing a collection of my items with their data types so I could then use a DataTemplateSelector to select DataTemplates which contained the correct types of controls, i.e. a datatype of DateTime showed a DatePicker.
Hope That Helps
From the perspective of a developer coming in to 'maintain' that generic code, it sounds like a pain. From what you've described, I would give the form and the dialog the same view model and create a specific XAML template for the dialog that you want to show.
basically my project is an MDI Winform application where a user can customize the interface by adding various controls and changing the layout. I would like to be able to save the state of the application for each user.
I have done quite a bit of searching and found these:
How to auto save and auto load all properties in winforms C#?
Save WinForm or Controls to File
Basically from what I understand, the best approach is to serialize the data to XML, however winform controls are not serializable, so I would have use surrogate classes:
http://www.codeproject.com/KB/dotnet/Surrogate_Serialization.aspx
Now, do I need to write a surrogate class for each of my controls? I would need to write some sort of a recursive algorithm to save all my controls, what is the best approach to do accomplish that? How would I then restore all the windows, should I use the memento design pattern for that? If I want to implement multiple users later, should I use Nhibernate to store all the object data in a database? I am still trying to wrap my head around the problem and if anyone has any experience or advice I would greatly appreciate it, thanks
You don't want to serialize the actual control instances. They should be created and destroyed along with the Form they reside in. Rather look at what you let the user customize. Layout and position? Very well, save out the Top and Left coordinates for each control along with a control identifier. Do you let the user add new controls? Save their ids along with a type identifier so when its time to reload you are able to recreate the controls at their previous position.
Whether you use XML or some other format, there is no best approach or best practice, choose what makes sense for your project. XML happens to be an easy to go with format with great support in the .Net Framework.
I know there is a software, LinsUI Layout Manager, which handle your problems very well. They have free version for interested developers. You can check the site.
Cheer