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• How to implement menuitems that depend on current selection in WPF MVVM explorer-like application

  - by Doug

  I am new to WPF and MVVM, and I am working on an application utilizing both. The application is similar to windows explorer, so consider an app with a main window with menu (ShellViewModel), a tree control (TreeViewModel), and a list control (ListViewModel). I want to implement menu items such as Edit - Delete, which deletes the currently selected item (which may be in the tree or in the list). I am using Josh Smith's RelayCommand, and binding the menuitem to a DeleteItemCommand in the ShellViewModel is easy. It seems like implementing the DeleteItemCommand, however, requires some fairly tight coupling between the ShellViewModel and the two child view models (TreeViewModel and ListViewModel) to keep track of the focus/selection and direct the action to the proper child for implementation. That seems wrong to me, and makes me think I'm missing something. Writing a focus manager and/or selection manager to do the bookkeeping does not seem too hard, and could be done without coupling the classes together. The windowing system is already keeping track of which view has the focus, and it seems like I'd be duplicating code. What I'm not sure about is how I would route the command from the ShellViewModel down to either the ListViewModel or the TreeViewModel to do the actual work without making a mess of the code. Some day, the application will be extended to include more than two children, and I want the shell to be as ignorant of the children as possible to make that extension as painless as possible. Looking at some sample WPF/MVVM applications (Karl Shifflett's CipherText, Josh Smith's MVVM Demo, etc.), I haven't seen any code that does this (or I didn't understand it). Regardless of whether you think my approach is way off base or I'm just missing a small nuance, please share your thoughts and help me get back on track. Thanks!

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• WPF MVVM Trigger Animation on MainWindow close

  - by Scott

  I'm using trying to implement MVVM in my app. I have a MainWindow.xaml and a MainWindowViewModel. I'm in the process of removing all of the code-behind code from the MainWindow.xaml but I'm stuck on one final piece. In my pre-MVVM setup I started an animation in the MainWindow.xaml.cs that would fade out the form before closing it. Since Closing is not a RoutedEvent, I had to use code-behind to get this to work. My VM has the following two properties that can be bound: ClosingWindow and CloseWindow. My goal was to bind a DataTrigger in my MainWindowStyle to the ClosingWindow property of the VM. When ClosingWindow was set to True, it would start an animation using the following XAML: <DataTrigger Binding="{Binding ClosingWindow}" Value="True"> <DataTrigger.EnterActions> <BeginStoryboard> <Storyboard> <DoubleAnimation Storyboard.TargetProperty="Opacity" From="1" To="0" Duration="0:0:2"/> </Storyboard> </BeginStoryboard> </DataTrigger.EnterActions> </DataTrigger> Somehow (insert magic here) I was going to set CloseWindow on the VM, via Binding, to True when the animation completed, which would then use an AttachedBehavior to Close the Window. The AttachedBehavior works perfectly when I just set CloseWindow directly using the following XAML: <DataTrigger Binding="{Binding CloseWindow}" Value="True"> <Setter Property="ab:WindowCloseBehavior.Close" Value="True"/> </DataTrigger> ...but I want to reproduce the form fade before the form actually closes. So there are two issues that I've run into: First, the animation doesn't work. I enter the trigger correctly (I've taken out the animation and put a Setter statement in there that changes the Title of the MainWindow to "Closing" and it changes correctly when ClosingWindow = True) but the DoubleAnimation never does anything. Second, there's no way to set the value of CloseWindow once the animation is complete. I looked at Marlon Grech's animation code but that won't work on DataTriggers. I can't publish a RoutedEvent because my VM doesn't descend from UIElement, and I've been Googling all day trying to come up with a clever, MVVM-friendly way to do this with no luck. So any ideas why that animation doesn't do anything? And more importantly, how would you solve the entire problem of animating a form fade on close from the VM? I don't doubt that my entire solution to this problem might be whacked so I'm open to just about anything.

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• Drag and Drop in MVVM with ScatterView

  - by Rich McGuire

  I'm trying to implement drag and drop functionality in a Surface Application that is built using the MVVM pattern. I'm struggling to come up with a means to implement this while adhering to the MVVM pattern. Though I'm trying to do this within a Surface Application I think the solution is general enough to apply to WPF as well. I'm trying to produce the following functionality: User contacts a FrameworkElement within a ScatterViewItem to begin a drag operation (a specific part of the ScatterViewItem initiates the drag/drop functionality) When the drag operation begins a copy of that ScatterViewItem is created and imposed upon the original ScatterViewItem, the copy is what the user will drag and ultimately drop The user can drop the item onto another ScatterViewItem (placed in a separate ScatterView) The overall interaction is quite similar to the ShoppingCart application provided in the Surface SDK, except that the source objects are contained within a ScatterView rather than a ListBox. I'm unsure how to proceeded in order to enable the proper communication between my ViewModels in order to provide this functionality. The main issue I've encountered is replicating the ScatterViewItem when the user contacts the FrameworkElement.

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• WPF MVVM: TextBox and default Button binding does update too late

  - by Sam

  I've got a simple WPF dialog with these two controls: <TextBox Text="{Binding MyText}"/> <Button Command="{Binding MyCommand}" IsDefault="True"/> Now, when I enter some text in the TextBox and click the button using the mouse, everything works like expected: the TextBox will set MyText and MyCommand is called. But when I enter some text and hit enter to "click" the default button, it does not work. Since on hitting enter the focus does not leave the TextBox, the binding will not be refresh MyText. So when MyCommand is called (which works), MyText will contain old data. How do I fix this in MVVM? In classic code-behind I probably just would call "MyButton.Focus()" in the MyCommand handler, but in MVVM the MyCommand handler does know nothing about the button. So what now`?

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• Automapper use in a MVVM application

  - by Echiban

  I am building a MVVM application. The model / entity (I am using NHibernate) is already done, and I am thinking of using AutoMapper to map between the ViewModel and Model. However this clause scares the jebus out of me: (from http://www.lostechies.com/blogs/jimmy_bogard/archive/2009/01/22/automapper-the-object-object-mapper.aspx) Blockquote AutoMapper enforces that for each type map (source/destination pair), all of the properties on the destination type are matched up with something on the source type To me, the logical choice is to map from model to viewmodel, (and I'll let viewmodel manually assign to model), but the quote basically kills the idea since the viewmodel will definitely have properties that don't exist on the model. How have you been using Automapper in a MVVM app? Please help!

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• MVVM Light Toolkit samples

  - by Neir0

  Does anyone know opensource WPF applications created using MVVM Light Toolkit?

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• Error window show modal in MVVM WPF

  - by bluebit

  Hi guys I have implemented my MVVM error message as a message dialog that subscribes to error messages via a mediator class, so that other viewmodels can notify it if any errors occur. When an error occurs, I set the visibility attribute in the viewmodel to Visible, to display the error window. This is all bound in the Error window from the viewmodel. However, this window is NOT modal! I need to show it as a dialog and not just set the visibility to true - is there any kind of binding I can do, even if I have to extend the functionality of the window? I'd rather not break MVVM if I can avoid it. Thanks!

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• MVVM/ViewModels and handling Authorization

  - by vdh_ant

  Hey guys Just wondering how how people handle Authorization when using MVVM and/or View Models. If I wasn't using VM's I would be passing back the Model and it would have a property which I could check if a user can edit a given object/property but when using MVVM I am disconnecting myself from the business object... and thus doen't know what the security should be any more. Is this a case where the mapper should be aware of the Authorization that is in place and don't copy across the data if the Authorization check fails. If this was the case I am guessing that the mapper would have to see some properties on the VM to let the interface know which fields are missing data because of the Authorization failure. If this does occur within the mapper, how does this fit in with things like AutoMapper, etc. Cheers Anthony

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• MVVM View-First Approach How Change View

  - by CodeWeasel

  Hi everybody, Does anybody have an idea how to change screens (views) in a MVVM View-First-Approach (The view instantiates the ViewModel: DataContext="{Binding Source={StaticResource VMLocator}, Path=Find[EntranceViewModel]}" ) For example: In my MainWindow (Shell) I show a entrance view with a Button "GoToBeach". <Window> <DockPanel> <TextBox DockPanel.Dock="Top" Text="{Binding Title}" /> <view.EntranceView DockPanel.Dock="Top" /> </DockPanel> </Window> When the button is clicked I want to get rid of the "EntranceView" and show the "BeachView". I am really curious if somebody knows a way to keep the View-First Approach and change the screen (view) to the "BeachView". I know there are several ways to implement it in a ViewModel-First Approach, but that is not the question. Perhabs I missed something in my mvvm investigation and can't see the wood for the trees... otherwise i am hoping for a inspiring discussion.

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• What makes MVVM uniquely suited to WPF?

  - by Reed Copsey

  The Model-View-ViewModel is very popular with WPF and Silverlight. I've been using this for my most recent projects, and am a very large fan. I understand that it's a refinement of MVP. However, I am wondering exactly what unique characteristics of WPF (and Silverlight) allow MVVM to work, and prevent (or at least make difficult) this pattern from working using other frameworks or technologies. I know MVVM has a strong dependency on the powerful data binding technology within WPF. This is the one feature which many articles and blogs seem to mention as being the key to WPF providing the means of the strong separation of View from ViewModel. However, data binding exists in many forms in other UI frameworks. There are even projects like Truss that provide WPF-style databinding to POCO in .NET. What features, other than data binding, make WPF and Silverlight uniquely suited to Model-View-ViewModel?

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• MVVM - RaisePropertyChanged turning code into a mess

  - by vidalsasoon

  New to MVVM so please excuse my ignorance. I THINK i'm using it right but I find my ViewModel has too many of these: RaisePropertyChanged("SomeProperty") Every time I set a property I have to raise that damned property changed. I miss the days where I could just go: public int SomeInteger { get; private set;} These days I have to stick the "RaisePropertyChanged" in everywhere or my UI does not reflect the changes :( Am I doing it wrong or are other people getting annoyed with the excessive number of magic strings and old school property setters? Should I be using dependency properties instead? (I doubt that would help the code bloat anyway) Despite these problems I still think MVVM is the way to go so I guess that's something.

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• WPF MVVM: Convention over Configuration for ResourceDictionary ?

  - by Jeffrey Knight

  Update In the wiki spirit of StackOverflow, here's an update: I spiked Joe White's IValueConverter suggestion below. It works like a charm. I've written a "quickstart" example of this that automates the mapping of ViewModels-Views using some cheap string replacement. If no View is found to represent the ViewModel, it defaults to an "Under Construction" page. I'm dubbing this approach "WPF MVVM White" since it was Joe White's idea. Here are a couple screenshots. The first image is a case of "[SomeControlName]ViewModel" has a corresponding "[SomeControlName]View", based on pure naming convention. The second is a case where the ModelView doesn't have any views to represent it. No more ResourceDictionaries with long ViewModel to View mappings. It's pure naming convention now. I'm hosting a download of the project here: http://rootsilver.com/files/Mvvm.White.Quickstart.zip I'll follow up with a longer blog post walk through. Original Post I read Josh Smith's fantastic MSDN article on WPF MVVM over the weekend. It's destined to be a cult classic. It took me a while to wrap my head around the magic of asking WPF to render the ViewModel. It's like saying "Here's a class, WPF. Go figure out which UI to use to present it." For those who missed this magic, WPF can do this by looking up the View for ModelView in the ResourceDictionary mapping and pulling out the corresponding View. (Scroll down to Figure 10 Supplying a View ). The first thing that jumps out at me immediately is that there's already a strong naming convention of: classNameView ("View" suffix) classNameViewModel ("ViewModel" suffix) My question is: Since the ResourceDictionary can be manipulated programatically, I"m wondering if anyone has managed to Regex.Replace the whole thing away, so the lookup is automatic, and any new View/ViewModels get resolved by virtue of their naming convention? [Edit] What I'm imagining is a hook/interception into ResourceDictionary. ... Also considering a method at startup that uses interop to pull out *View$ and *ViewModel$ class names to build the DataTemplate dictionary in code: //build list foreach .... String.Format("<DataTemplate DataType=\"{x:Type vm:{0} }\"><v:{1} /></DataTemplate>", ...)

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• WPF databinding update comboxbox2 based on selection change in combobox1 with MVVM

  - by cody

  I have a combo box that I have bound to a list that exists in my viewmodel. Now when a users makes a selection in that combo box I want a second combo box to update its content. So, for example, combobox1 is States and combobox2 should contain only the Zipcodes of that state. But in my case I don't have a predefined lists before hand for combobox2, I need to go fetch from a db. Also, if needed, I could get all the potential values for combobox2 (for each combobox1 value) before hand, but I'd like to avoiding that if I can. How do I implement in WPF and using MVVM? I'm fairly new to this whole wpf\databinding\mvvm world.

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• MVVM Light Messenger Class

  - by Veer

  Can anybody provide samples/links/simple-illustrations/videos/demos on how to use the messenger class in MVVM Light?

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• Why should I use MVVM when it breaks built in riaservices functionality

  - by Jakob

  I'm struggling to grasp why MVVM is really a good pattern to implement in riaserivces, To me there's nothing but trouble to it, it just add's another tier that I have to code. I Get that I could change the UI, but really I don't need to. Instead i won't be able to user out of the box functionality with riaservices, datagrid, dataform all controls require some implementation. Why can't it just be simple? Is there really no way to get MVVM to automatically set "IsBusy" and all the dataform edit functionality. It's like reinventing the wheel to me, and it seems that I'd be able to write code much faster just using riaservices

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• Windows Phone 7, MVVM, Silverlight and navigation best practice / patterns and strategies

  - by Matt F

  Whilst building a Windows Phone 7 app. using the MVVM pattern we've struggled to get to grips with a pattern or technique to centralise navigation logic that will fit with MVVM. To give an example, everytime the app. calls our web service we check that the logon token we've assigned the app. earlier hasn't expired. We always return some status to the phone from the web service and one of those might be Enum.AuthenticationExpired. If we receive that I'd imagine we'd alert the user and navigate back to the login screen. (this is one of many examples of status we might receive) Now, wanting to keep things DRY, that sort of logic feels like it should be in one place. Therein lies my question. How should I go about modelling navigation that relies on (essentially) switch or if statements to tell us where to navigate to next without repeating that in every view. Are there recognised patterns or techniques that someone could recommend? Thanks

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• Real winforms/wpf projects which use MVC, MVP, MVVM

  - by Belousov Pavel

  Hello everybody, I have looked some videos and read some articles about MVC, MVP, MVVM. I think, that I understood basic principles and differences. But it seems to me that samples in articles and videos are very easy. I think that it's easy to learn how to apply these patterns when you can look on some projects. So I'd like to look on real projects(Winforms/WPF), which use MVC, MVP or MVVM. Could you provide me links to sources of such projects? (If it is open source) It will be great if projects will have unit tests for Controller/Presenter/ViewModel, because it's one of my problem when I develop applications. Thanks in advance.

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• problem in basic implementation of MVVM pattern - Services

  - by netmajor

  I watch some video and read articles about MVVM pattern and start thinking how should I implement it in my Silverlight app. So at first I create Silverlight application. I think that for clear view I create 3 folders: View - for each user control page in my app, ViewModel - for c# class which will querying date and Model- Entity Data Model of my SQL Server or Oracle Database. And now I am confused, cause I want to implement *WCF/RIA Services/Web services* in my project. In which folder should I put in class of services? I see in examples that Services take date and filtering it and then output data was binding in View - so It looks as ViewModel. But I was sure that someone use Services in Model and that I want to do. But how? Can someone explain me implementing Services as Model? Is my point of view at MVVM is correctly?

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• MVVM (ICommand) in Silverlight

  - by Andrey Khataev

  Hello! Please, don't judge strictly if this question was discussed previously or indirectly answered in huge nearby prism and mvvm blogs. In WPF implementation of RelayCommand or DelegateCommand classes there is a such eventhandler /// <summary> /// Occurs whenever the state of the application changes such that the result of a call to <see cref="CanExecute"/> may return a different value. /// </summary> public event EventHandler CanExecuteChanged { add { CommandManager.RequerySuggested += value; } remove { CommandManager.RequerySuggested -= value; } } but in SL subset of namespaces there are no CommandManager class. And this is where I'm stuck. I haven't yet found an workaround for this in MVVM adoptation for SL (PRISM is so complex for me yet). Different simple HelloWorldMVVM apps don't deal with at all. Thanks in advance and sorry for my English -)

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• Binding command to button in silverlight 4 using mvvm

  - by Archie

  Hello, I have a user control called HomePage.xaml. I'm creating a model instance (using MVVM pattern) in the code behind file in the constructor of page as MainViewModel model = new MainViewModel(); I have a button in HomePage.xaml which I want to bind to the command inside MainViewModel called GetData() and want to populate the data in datagrid. MainViewModel has an ObservableCollection which I would use to bind the data in datagrid. Populating the data in datagrid without binding command works fine. I'm binding the button as: <StackPanel x:Name="stkPanelInput" Orientation="Horizontal" VerticalAlignment="Center" HorizontalAlignment="Center"> <Button x:Name="buttonGetData" Width="70" Content="GetData" Command="{Binding GetData}" Click="buttonGetData_Click"/> </StackPanel> How shall I bind the command using MVVM? Thanks.

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• MVVM View reference to ViewModel

  - by BrettRobi

  I'm using MVVM in a WPF app. I'm very new to both. Let me state that I am not a purest in the MVVM pattern, I am trying to use as many best practices as I can but am trying to make what I think are reasonable compromises to make it work in our environment. For example, I am not trying to achieve 0% code in my View codebehind. I have a couple of questions about best practices. 1) I understand I don't want my VM to know about the attached View, but is it reasonable for the View to have a reference to its VM? 2) If a control in a View opens another View (such as a dialog) should I handle this in the View? It seems wrong to handle it in the VM since then the VM has some knowledge of a specific View.

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• what's the difference between MVVM and Prism v2

  - by jaffal

  Hello, what's the difference between MVVM and prism v2 design pattern to develop SL and WPF applications?

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• Why should I use MVVM when it breaks built in functionality

  - by Jakob

  I'm struggling to grasp why MVVM is really a good pattern to implement in riaserivces, To me there's nothing but trouble to it, it just add's another tier that I have to code. I Get that I could change the UI, but really I don't need to. Instead i won't be able to user out of the box functionality with riaservices, datagrid, dataform all controls require some implementation. Why can't it just be simple? Is there really no way to get MVVM to automatically set "IsBusy" and all the dataform edit functionality. It's like reinventing the wheel to me, and it seems that I'd be able to write code much faster just using riaservices

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• What is the best practice for accessing Model using MVVM pattern

  - by Dzenand

  I have a database that communicates with webservices with my Model (own thread) and exposes Data Objects. My UI application consists of different Views and ViewModels and Custom Controls. I'm using ServiceProvider (IServiceProvider) to access the Model and route the events to the UI thread. Communication between the ViewModels is handeled by a Messenger. Is this way to go? I was also wondering what is the best way to strucutre the DataObjects At the moment i have the DataObjects that have a hierarchy structure but does not support INotifyProperty though the children list are of type of ObservableCollection. I have no possiblity to implement notifypropertychange on the properties. I was wondering the best way of making them MVVM friendly. Implementing a partial class and adding all the properties or commands that are necessary or wrapping all the DataObjects and keep the Model list and MVVM list in sync. All thoughts and ideas are appreciated.

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• WPF MVVM - Correct way to consume a web service asynchronously

  - by byte

  I have implemented MVVM in my WPF application. I was wondering what is the correct way to consume a Web Service from WPF MVVM app. So far, I have created a DataAccess interface and a class that implements this interface. This would serve as a facade / proxy to the web service. The ViewModel gets a reference to this class as the constructor parameter so it can make any calls to get/set data, in this case it will be a Web service call. I would appreciate if you can guide me with some hints and / or direct me to some online resource.

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