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• ViewModel create in MVVM - my look at it

  - by netmajor

  When I want to implement ViewModel I should cut everything c# code from my Silverlight code behind(next delete .cs file and leave only .xaml file) and paste it in new class in new folder ViewModel ? It is good way of separate View from logic ?

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• Bi-directional view model syncing with "live" collections and properties (MVVM)

  - by Schneider

  I am getting my knickers in a twist recently about View Models (VM). Just like this guy I have come to the conclusion that the collections I need to expose on my VM typically contain a different type to the collections exposed on my business objects. Hence there must be a bi-directional mapping or transformation between these two types. (Just to complicate things, on my project this data is "Live" such that as soon as you change a property it gets transmitted to other computers) I can just about cope with that concept, using a framework like Truss, although I suspect there will be a nasty surprise somewhere within. Not only must objects be transformed but a synchronization between these two collections is required. (Just to complicate things I can think of cases where the VM collection might be a subset or union of business object collections, not simply a 1:1 synchronization). I can see how to do a one-way "live" sync, using a replicating ObservableCollection or something like CLINQ. The problem then becomes: What is the best way to create/delete items? Bi-directinal sync does not seem to be on the cards - I have found no such examples, and the only class that supports anything remotely like that is the ListCollectionView. Would bi-directional sync even be a sensible way to add back into the business object collection? All the samples I have seen never seem to tackle anything this "complex". So my question is: How do you solve this? Is there some technique to update the model collections from the VM? What is the best general approach to this?

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• Data binding manually update in WPF MVVM

  - by Benny

  My ViewModel: class ViewModel { public string FileName {get;set;} } and in my View I bind a label's content to ViewModel's FileName. now When I do drag-drop a file to my View, How can I update the label's Content property, so that the ViewMode's FileName also get updated via binding? Directly set the label's Content property won't work, it just simply clear the binding.

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• NHibernate MVVM Session Best Practice

  - by LnDCobra

  What is the best place to store the NHibernate session if we only need one? In the main windows view model? In the app? In the DataAccess Class?

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• Refreshing Read-Only (Chained) Property in MVVM

  - by Wonko the Sane

  I'm thinking this should be easy, but I can't seem to figure this out. Take these properties from an example ViewModel (ObservableViewModel implements INotifyPropertyChanged): class NameViewModel : ObservableViewModel { Boolean mShowFullName = false; string mFirstName = "Wonko"; string mLastName = "DeSane"; private readonly DelegateCommand mToggleName; public NameViewModel() { mToggleName = new DelegateCommand(() => ShowFullName = !mShowFullName); } public ICommand ToggleNameCommand { get { return mToggleName; } } public Boolean ShowFullName { get { return mShowFullName; } set { SetPropertyValue("ShowFullName", ref mShowFullName, value); } } public string Name { get { return (mShowFullName ? this.FullName : this.Initials); } } public string FullName { get { return mFirstName + " " + mLastName; } } public string Initials { get { return mFirstName.Substring(0, 1) + "." + mLastName.Substring(0, 1) + "."; } } } The guts of such a [insert your adjective here] View using this ViewModel might look like: <TextBlock x:Name="txtName" Grid.Row="0" Text="{Binding Name}" /> <Button x:Name="btnToggleName" Command="{Binding ToggleNameCommand}" Content="Toggle Name" Grid.Row="1" /> The problem I am seeing is when the ToggleNameCommand is fired. The ShowFullName property is properly updated by the command, but the Name binding is never updated in the View. What am I missing? How can I force the binding to update? Do I need to implement the Name properties as DependencyProperties (and therefore derive from DependencyObject)? Seems a little heavyweight to me, and I'm hoping for a simpler solution. Thanks, wTs

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• WPF MVVM Property Change Animation

  - by cjibo

  I am looking for a clean way to start an animation that will have dynamic values. Basically I want to do an animation where an element changes width based on the data of another element. Say I have a TextBlock that's Text Property is Binding. When this property changes I want a visual element say a Rectangle for our sake to do a DoubleAnimation changing the width from previous value to the new value. I am trying to stay away from putting code in my view if possible. I've looked into DataTriggers but they seem to require that you know what the value would be such as an Enum. In my case it is just the value changing that needs to trigger a storyboard and the animation would need to start at the current(previous) value and move nicely to the new value. Any ideas. Maybe I just missed a property.

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• A view model mvvm design issue

  - by Chen Kinnrot

  the best way to explain is with example so: this is the model public class Person { public int age; public string name; } this is the view model public class PersonVM { } my question is: should the vm expose the person to the datga template or encapsulate the model properties with his own properties?

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• C# - Silverlight - MVVM

  - by cmaduro

  I want to use UserControl as the base for my views, but I cannot add functionality to my views because they are based on UserControl. How do I create my own view class by using a subclassed version of UserControl.

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• drag-drop and data binding in MVVM

  - by Benny

  My ViewModel: class ViewModel { public string FileName {get;set;} } and in my View I bind a label's content to ViewModel's FileName. now When I do drag-drop a file to my View, How can I update the label's Content property, so that the ViewMode's FileName also get updated via binding? Directly set the label's Content property won't work, it just simply clear the binding.

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• MVVM and division of amongst multiple developers

  - by nlawalker

  Can anyone speak to the ease of dividing work amongst multiple developers when designing and building a medium- to large-complexity Silverlight or WPF application? My team is finding it difficult to cleanly split work when you've got, for example, a number of controls that provide different visualizations of a Model/ViewModel that's fairly complex and has a lot of properties and methods for interacting with data. It seems like a very big portion of the work ends up being the design and build of the Model/ViewModel, and much less inside each of the controls, which are naturally what are easy to ration out to multiple people.

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• MVVM and avoiding Monolithic God object

  - by bufferz

  I am in the completion stage of a large project that has several large components: image acquisition, image processing, data storage, factory I/O (automation project) and several others. Each of these components is reasonably independent, but for the project to run as a whole I need at least one instance of each component. Each component also has a ViewModel and View (WPF) for monitoring status and changing things. My question is the safest, most efficient, and most maintainable method of instantiating all of these objects, subscribing one class to an Event in another, and having a common ViewModel and View for all of this. Would it best if I have a class called God that has a private instance of all of these objects? I've done this in the past and regretted it. Or would it be better if God relied on Singleton instances of these objects to get the ball rolling. Alternatively, should Program.cs (or wherever Main(...) is) instantiate all of these components, and pass them to God as parameters and then let Him (snicker) and His ViewModel deal with the particulars of running this projects. Any other suggestions I would love to hear. Thank you!

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• Silverlight textblock binding question + MVVM

  - by AdrianDN

  Hello everyone, I'm trying to create a simple textblock control and I'm trying to insert a property from my ViewModel in the middle of the string. E.G. "Hello, My name is XX, bla, bla." (XX is a property from my ViewModel) <TextBlock Text="Hello, My name is {Binding SelectedUser.Name}, bla, bla." /> Is that possible? Regards, Adrian

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• Selecting the usercontrol to the relating datatemplate in mvvm

  - by msfanboy

  Hello, I have lets say a WeeklyViewUserControl.xaml and a DailyViewUserControl.xaml. Normally I used stuff like this to switch content: <DataTemplate DataType="{x:Type ViewModel:LessonPlannerViewModel}"> <View:LessonPlannerDailyUC/> </DataTemplate> This worked so far. But now I have still the WeeklyViewUC which uses 90 % of the LessonPlannerViewModel code so I want to make this additionally: <DataTemplate DataType="{x:Type ViewModel:LessonPlannerViewModel}"> <View:LessonPlannerWeeklyUC/> </DataTemplate> but this can not work, because from where does the ContentControl know that VM (LessonPlannerViewModel) should display a DailyViewUC or a WeeklyViewUC ? <ContentControl Content="{Binding VM}" />

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• WPF MVVM TreeView item source losing context after command

  - by user3955716

  I have a treeview which contains files, every view model holds an item source which is an ObservableCollection with files items: public ObservableCollection<CMItemFileNode> SubItemNode On each item i have context menu options (Delete, Execute..). If i move from one viewModel to another the ObservableCollection of files updated correctly and presented correctly but, when i perform a context menu command like delete file item, the command execute good but when i move to another view model (which holds SubItemNode ObservableCollection of is own) after the command executed the WPF still thinks i'm in the last view model i was in and not the one i'm really on. Very important to mention is that when i update to .net 4.5 (which unfortunantly i can't do) everything is ok and the ObservableCollection addresses the correct view model. Here is the treeView: <TreeView x:Name="Files" Margin="0,5,5,0" Grid.Row="6" Grid.Column="2" ItemsSource="{Binding SubItemNode}" HorizontalAlignment="Stretch" HorizontalContentAlignment="Stretch" VerticalAlignment="Stretch" Height="300" Grid.RowSpan="6" Width="300" dd:DragDrop.IsDragSource="True" dd:DragDrop.IsDropTarget="True" dd:DragDrop.DropHandler="{Binding}" dd:DragDrop.UseDefaultDragAdorner="True"> <TreeView.Resources> <Style TargetType="{x:Type TreeView}"> <Setter Property="local:CMTreeViewFilesBehavior.IsTreeViewFilesBehavior" Value="True"/> </Style> <Style TargetType="{x:Type TreeViewItem}"> <Setter Property="IsSelected" Value="{Binding IsSelected}" /> <Setter Property="local:CMTreeViewFilesItemBehavior.IsTreeViewFilesItemBehavior" Value="True"/> </Style> <SolidColorBrush x:Key="{x:Static SystemColors.HighlightBrushKey}" Color="Transparent" /> <SolidColorBrush x:Key="{x:Static SystemColors.HighlightTextBrushKey}" Color="Black" /> </TreeView.Resources> <TreeView.ContextMenu> <ContextMenu> <MenuItem Header="View File" Command="{Binding ExecuteFileCommand}" /> <Separator /> <MenuItem Header="Delete all" Command="{Binding DeleteAllFilesCommand}" /> <MenuItem Header="Delete selected" Command="{Binding DeleteSelectedFilesCommand}" /> </ContextMenu> </TreeView.ContextMenu> <TreeView.ItemTemplate> <HierarchicalDataTemplate ItemsSource="{Binding SubItemNode}" > <Grid> <Grid.ColumnDefinitions> <ColumnDefinition Width="Auto"/> <ColumnDefinition Width="*"/> </Grid.ColumnDefinitions> <Image Grid.Column="0" Margin="2" Width="32" Height="18" Source="{Binding Path=Icon}" HorizontalAlignment="Left" VerticalAlignment="Center" /> <TextBlock Text="{Binding Path=Name}" Grid.Column="1" Margin="2" VerticalAlignment="Center" Foreground="{Binding Path=Status, Converter={StaticResource ItemFileStatusToColor}}" FontWeight="{Binding Path=IsSelected, Converter={StaticResource BoolToFontWidth}}"/> </Grid> </HierarchicalDataTemplate> </TreeView.ItemTemplate> </TreeView> Am I doing somthing wrong? and why in .net 4.5 it works well ?

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• Silverlight 4 Treeview MVVM WCF

  - by Coppermine

  I'm having an issue with the treeview control from the silverlight 4 toolkit. I can't get it to view to display my data correctly, the toplevel items are shown but the childnodes are nowhere to be seen. More info: I have a wcf service that delivers a list of Categories with nested subcategories to my viewmodel (I made sure to explicitly include my subcategory data). My viewmodel has an observable list property (wich is named Categories) with this data from my WCF service. My ViewModel: _http://pastebin.com/0TpMW3mR My XAML: http://pastebin.com/QCwVeyYu

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• MVVM Binding To Property == Null

  - by LnDCobra

  I want to show some elements when a property is not null. What is the best way of achieving this? The following is my ViewModel: class ViewModel : ViewModelBase { public Trade Trade { get { return _trade; } set { SetField(ref _trade, value, () => Trade); } } private Trade _trade; } ViewModelBase inherits INotifyPropertyChanged and contains SetField() The Following is the Trade class: public class Trade : INotifyPropertyChaged { public virtual Company Company { get { return _company; } set { SetField(ref _company, value, () => Company); } } private Company _company; ...... } This is part of my View.xaml <GroupBox Visibility="{Binding Path=Trade.Company, Converter={StaticResource boolToVisConverter}}" /> I would like this groupbox to show only if Trade.Company is not null (so when a user selects a company). Would I need to create a custom converter to check for null and return the correct visibility or is there one in .NET?

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• Display Consistent Value of an Item using MVVM and WPF

  - by Blake Blackwell

  In my list view control (or any other WPF control that will fit the situation), I would like to have one TextBlock that stays consistent for all items while another TextBlock that changes based on the value in the ObservableCollection. Here is how my code is currently laid out: XAML <ListView ItemsSource="{Binding Path=MyItems, Mode=TwoWay}"> <ListView.ItemTemplate> <DataTemplate> <StackPanel Orientation="Horizontal"> <TextBlock x:Name="StrVal" Text="{Binding StrVal}" /> <TextBlock x:Name="ConstVal" Text="{Binding MyVM.ConstVal}" /> </StackPanel> </DataTemplate> </ListView.ItemTemplate> </ListView> Model public class MyItem { public string StrVal { get; set; } } ViewModel public class MyVM { public MyVM() { ObservableCollection<MyItem> myItems = new ObservableCollection<MyItem>(); for (int i = 0 ; i < 10; i++) myItems.Add(new MyItem { StrVal = i.ToString()}); MyItems = myItems; ConstVal = "1"; } public string ConstVal { get; set; } public ObservableCollection<MyItem> MyItems { get; set; } } Code Behind this.DataContext = new MyVM(); The StrVal property repeats correctly in the ListView, but the ConstVal TextBlock does not show the ConstVal that is contained in the VM. I would guess that this is because the ItemsSource of the ListView is MyItems and I can't reference other variables outside of what is contained in the MyItems. My question is: How do I get ConstVal to show the value in the ViewModel for all listviewitems that will be controlled by the Observable Collection of MyItems.

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• MVVM: Tutorial from start to finish?

  - by JP

  Although I'm an experienced C#/Winforms developer, I'm looking for a WPF tutorial that doesn't assume any previous WPF knowledge. Please post any links you have to WPF tutorials.

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• C# generics with MVVM, pulling the T out of <T>

  - by bufferz

  My Model is a generic class that contains a (for example) Value property which can be int, float, string, bool, etc. So naturally this class is represented something like Model<T>. For the sake of collections Model<T> implements the interface IModel, although IModel is itself empty of any content. My ViewModel contains and instance of Model<T> and it is passed in through ViewModel's constructor. I still want to know what T is in ViewModel, so when I expose Model to the View I know the datatype of Model's buried Value property. The class for ViewModel ends up looking like the following: class ViewModel<T> { private Model<T> _model; public ViewModel(Model<T> model) { ....blah.... } public T ModelsValue {get; set; } } This works fine, but is limited. So now I need to expose a collection of IModels with varying Ts to my View, so I'm trying to set up an ObservableCollection of new ViewModel<T>s to a changing list of IModels. The problem is, I can't figure out how to get T from Model<T> from IModel to construct ViewModel<T>(Model<T>) at runtime. In the VS2010 debugger I can mouseover any IModel object and see its full Model<int> for example at runtime so I know the data is in there. Any ideas?

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• C# MVVM Calculating Total

  - by LnDCobra

  I need to calculate a trade value based on the selected price and quantity. How can The following is my ViewModel: class ViewModel : ViewModelBase { public Trade Trade { get { return _trade; } set { SetField(ref _trade, value, () => Trade); } } private Trade _trade; public decimal TradeValue { get { return Trade.Amount * Trade.Price; } } } ViewModelBase inherits INotifyPropertyChanged and contains SetField() The Following is the Trade class: public class Trade : INotifyPropertyChaged { public virtual Decimal Amount { get { return _amount; } set { SetField(ref _amount, value, () => Amount); } } private Decimal _amount; public virtual Decimal Price { get { return _price; } set { SetField(ref _price, value, () => Price); } } private Decimal _price; ...... } I know due to the design my TradeValue only gets calculated once (when its first requested) and UI doesn't get updated when amount/price changes. What is the best way of achieving this? Any help greatly appreciated.

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• Silverlight ~ MVVM ~ Dynamic setting of Style property based on model value

  - by eponymous23

  I have a class called Question that represents a question and it's answer. I have an application that renders an ObservableCollection of Question objects. Each Question is rendered as a StackPanel that contains a TextBlock for the question verbiage, and a TextBox for the user to enter in an answer. The questions are rendered using an ItemsControl, and I have initially set the Style of the Questions's StackPanel using a StaticResource key called 'IncorrectQuestion' (defined in UserControl.Resources section of the page). In the UserControl.Resources section, I've also defined a key calld 'CorrectQuestion' which I need to somehow apply to the Question's StackPanel when the user correctly answers the question. My problem is I'm not sure how to dynamically change the Style of the StackPanel, specifically within the constraints of a ViewModel class (i.e. I don't want to put any style selection code in the View's code-behind). My Question class has an IsCorrect property which is accurately being set when the correction is answered. I'd like to somehow reflect the IsCorrect value in the form of a Style selection. How do I do that?

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• MVVM,WPF: How to set a item as selected in a combobox

  - by msfanboy

  It seems nobody has yet found a way to set the comboboxitem as selected with a SelectedItem="Binding Property". Is the solution to use a IsSelected Property in the ViewModel object within the combobox itemssource ?

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• Multiple volumetric lights

  - by notabene

  I recently read this GPU GEMS 3 article Volumetric Light Scattering as a Post-Process. I like the idea to add volumetric light property to realtime render i'm working on. Question is will it work for multiple lights? Our renderer uses one render pass per light and uses additive blending to sum incoming light. I'm mostly convinced that it have to work nice. Do you agree? Maybe there can be problem where light rays crosses each other.

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• Distinguishing between UI command & domain commands

  - by SonOfPirate

  I am building a WPF client application using the MVVM pattern that provides an interface on top of an existing set of business logic residing in a library which is shared with other applications. The business library followed a domain-driven architecture using CQRS to separate the read and write models (no event sourcing). The combination of technologies and patterns has brought up an interesting conundrum: The MVVM pattern uses the command pattern for handling user-interaction with the view models. .NET provides an ICommand interface which is implemented by most MVVM frameworks, like MVVM Light's RelayCommand and Prism's DelegateCommand. For example, the view model would expose a number of command objects as properties that are bound to the UI and respond when the user performs actions like clicking buttons. Many implementations of the CQRS use the command pattern to isolate and encapsulate individual behaviors. In my business library, we have implemented the write model as command / command-handler pairs. As such, when we want to do some work, such as create a new order, we 'issue' a command (CreateOrderCommand) which is routed to the command-handler responsible for executing the command. This is great, clearly explained in many sources and I am good with it. However, take this scenario: I have a ToolbarViewModel which exposes a CreateNewOrderCommand property. This ICommand object is bound to a button in the UI. When clicked, the UI command creates and issues a new CreateOrderCommand object to the domain which is handled by the CreateOrderCommandHandler. This is difficult to explain to other developers and I am finding myself getting tongue-tied because everything is a command. I'm sure I'm not the first developer to have patterns overlap like this where the naming/terminology also overlap. How have you approached distinguishing your commands used in the UI from those used in the domain? (Edit: I should mention that the business library is UI-agnostic, i.e. no UI technology-specific code exists, or will exists, in this library.)

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• MVVM Light Toolkit V3 SP1 for Windows Phone 7

  - by Laurent Bugnion

  He he I start to sound like Microsoft… Anyway… I just released a service pack (SP1) for MVVM Light Toolkit V3. Why? Well mostly because I worked a bit more with the Windows Phone 7 tools that were released at MIX0, and I noticed a few things that could be better in the Windows Phone 7 template. Also, I only found out at MIX that you can actually install custom project templates for Visual Studio Express. For some reason I thought it was not possible. The best way to solve these issues is through a service pack, which consists of a few zip files. Simply follow the instructions on the “Installing Manually” page. You can go ahead and overwrite the files that were installed with V3, all the file structure and names are exactly the same. What? So what do you get in this service pack that was not already in V3? (for more info about what’s new in V3, check the What’s New page). Project and Item templates for Visual Studio 10 Express (phone edition). Unzip these files in your “My Documents” folder, and you can now create a new MVVM Light application in the WinPhone7 version of Visual Studio 2010 Express. Signed assemblies: All the assemblies are now signed, which is a requirement in certain build configurations. XML documentation files: Thanks to Matt Casto for pinging me and reminding me that I had forgotten to include them (doh). New and improved Windows Phone 7 assemblies and templates: This one deserves its own section (see below). What was wrong with the old Silverlight 3 assemblies in Windows Phone 7 projects? It was kind of weird. Functionality wise, it was working just right. However, if you noticed, the EventToCommand behavior was not visible in the Assets tab of Expression Blend, under Behaviors, where it should normally have been. The reason was that even though the Windows Phone 7 is using Silverlight 3, the System.Windows.Interactivity that Blend was expecting is the version that is normally used in Silverlight 4. Yeah, I know, it’s weird. This led me to create a specific version of these assemblies for the phone. The assemblies are located into C:\Program Files\Laurent Bugnion (GalaSoft)\Mvvm Light Toolkit\Binaries\WP7. There are 3 DLLs: GalaSoft.MvvmLight.WP7.dll with RelayCommand, Messenger and ViewModelBase GalaSoft.MvvmLight.Extras.WP7.dll with EventToCommand and DispatcherHelper System.Windows.Interactivity.dll which is the same DLL installed in the Blend SDK, and which is needed for the EventToCommand behavior to work. Happy coding! That’s all! Download and install the service pack according to the instructions on the Installation page, and create your first MVVM Light application for the phone (a blog post will follow later with more details).   Laurent Bugnion (GalaSoft) Subscribe | Twitter | Facebook | Flickr | LinkedIn

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