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I'm currently working with a WPF application and has several problems. So far I've been putting all the business logic in a single ViewModel and what I noticed now is that ViewModel doesn't have a particular context.

An example would be:

 <telerik:RadSplitContainer Orientation="Vertical" telerik:DockingPanel.InitialSize="750,200">
 <telerik:RadPaneGroup IsContentPreserved="False" telerik:ProportionalStackPanel.RelativeSize="200,300" >
 <telerik:RadPane 
 <ContentControl ContentTemplate="StaticResource CategoryTemplate" 
 Content="Binding CategoryViewModel" />
 </telerik:RadPane>
 </telerik:RadPaneGroup>
 <telerik:RadPaneGroup IsContentPreserved="False" telerik:ProportionalStackPanel.RelativeSize="100,120">
 <telerik:RadPane Header="Items list" 
 CanUserClose="False" CanUserPin="False"
 CanDockInDocumentHost="True">
 <ContentControl ContentTemplate="StaticResource ItemsListTemplate" 
 Content="Binding ItemsViewModel" />
 </telerik:RadPane>
 </telerik:RadPaneGroup>
 </telerik:RadSplitContainer>

However, this is how the mainwindows.xaml look like, which is built up by multiple views which is specified as a datatemplate. At this moment I decided to extract the business logic from the huge common viewmodel and create a ViewModel for each View.

I have two views, one for category and one for items corresponding to the category. These two views contain a gridview which show the categorys in CategoryView and Items corresponding to the category.

The viewmodel which contains all the items is at initial empty, and the category just retrieves all existing categories from DB. I also have a SelectedCategory in CategoryViewModel which contain the grid row item I choose.

The thing I want to do is at a selection of a row in the grid in categoryView, I want the CategoryViewModel to tell the ItemsViewModel to retrieve its items corresponding to the categoryID I'm retrieving from CategoryViewModel. Then refresh the itemscollection in the itemsViewModel with INotifyPropertychanged and refresh the view on the grid.

My mainView view and viewmodel:

 public MainViewModel()
 
 this.InitializeCommands();
 this.ItemsViewModel = new ItemsViewModel();
 this.CategoryViewModel = new CategoryViewModel();

 

 public ViewModelBase CategoryViewModel
 
 get return this._categoryViewModel; 
 set
 
 if (this._categoryViewModel != value)
 
 this._categoryViewModel = value;
 
 
 

 public ViewModelBase ItemsViewModel
 
 get
 
 if (this._itemsViewModel == null)
 
 this._itemsViewModel;
 
 return this._itemsViewModel;
 
 set
 
 if (this._itemsViewModel != value)
 
 this._itemsViewModel = value;
 
 
 

An example of another view datatemplate which is used in MainView:

<DataTemplate x:Key="NewsTemplate">
 <Grid Margin="10">
 <Grid.RowDefinitions>
 <RowDefinition Height="Auto" />
 <RowDefinition Height="Auto" />
 <RowDefinition Height="*" />
 <RowDefinition Height="Auto" />
 </Grid.RowDefinitions>
 <telerik:RadBusyIndicator x:Name="BusyIndicator">
 <telerik:RadGridView Name="gridView"
 ItemsSource="Binding 
 Category"
 SelectedItem="Binding SelectedCategory, Mode=TwoWay"> 
 <telerik:RadGridView.Columns>
 <telerik:GridViewDataColumn DataMemberBinding=Binding Name" Header="Name"/> 
 </telerik:RadGridView>
 </telerik:RadBusyIndicator>
 </Grid>
</DataTemplate>`

Added viewmodel for items:

 public ObservableCollection<Item> GetItems
 
 get
 
 this._getItems = GetFromDb.GetItems(CategoryID)

 return this._getItems;
 
 set
 
 if (this._getItems != value)
 
 this._getItems = value;
 this.OnPropertyChanged("GetItems");
 
 
 

 public QueryableCollectionView Items
 
 get
 
 return this._items = new QueryableCollectionView(GetItems(CategoryID));
 
 set
 
 if (this._items != value)
 
 this._items = value;
 this.OnPropertyChanged(() => Items);
 
 
 

MainViewModel (if you look over I got a method GetFromDb.GetItems(CategoryID) which retrieves the items):

 public MainViewModel()
 
 this.InitializeCommands(); 
 this.CategoryViewModel = new CategoryViewModel();
 this.ItemsViewModel = new ItemsViewModel();

 this.CategoryViewModel.OnChanged += (s, e) => 

 //this one?
 this.ItemsViewModel.ContractMetaDatas(CategoryViewModel.ID)
 //this one?
 this.ItemsViewModel.ContractMetaDatas = new QueryableCollectionView(GetFromDb.GetItems(CategoryID));
 ;
 

How can I achieve this?

The thing I want to do is at a selection of a row in the grid in categoryView, I want the CategoryViewModel to tell the ItemsViewModel to retrieve its items corresponding to the categoryID I'm retrieving from CategoryViewModel. Then refresh the itemscollection in the itemsViewModel with INotifyPropertychanged and refresh the view on the grid.

How can I achieve this?

Well, basically you can use a typical setup with events:

Fire an event from your CategoryViewModel and handle it in the overall container.

 public class MainViewModel: INotifyPropertyChanged
 
 public CategoryViewModel CategoryViewModel get;set;
 public ItemsViewModel ItemsViewModel get;set;

 public MainViewModel()
 
 this.InitializeCommands();
 this.ItemsViewModel = new ItemsViewModel();
 this.CategoryViewModel = new CategoryViewModel();
 //wire up the event 
 this.CategoryViewModel.OnChanged += (s,e) => 
 //perform update here
 this.ItemsViewModel.UpdateWithId(this.CategoryViewModel.SelectedId);
 ;
 

 ///...
 

The category:

public class CategoryViewModel : INotifyPropertyChanged

 //fire this when appropiate
 public event EventHandler OnChanged;
 ///...