M-V-VM, isn't the Model leaking into the View?
- by BFree
The point of M-V-VM as we all know is about speraration of concerns. In patterns like MVVM, MVC or MVP, the main purpose is to decouple the View from the Data thereby building more flexible components. I'll demonstrate first a very common scenario found in many WPF apps, and then I'll make my point:
Say we have some StockQuote application that streams a bunch of quotes and displays them on screen. Typically, you'd have this:
StockQuote.cs : (Model)
public class StockQuote
{
public string Symbol { get; set; }
public double Price { get; set; }
}
StockQuoteViewModel.cs : (ViewModel)
public class StockQuoteViewModel
{
private ObservableCollection<StockQuote> _quotes = new ObservableCollection<StockQuote>();
public ObservableCollection<StockQuote> Quotes
{
get
{
return _quotes;
}
}
}
StockQuoteView.xaml (View)
<Window x:Class="WpfApplication1.Window1"
xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
xmlns:local="clr-namespace:WpfApplication1"
Title="Window1" Height="300" Width="300">
<Window.DataContext>
<local:StockQuoteViewModel/>
</Window.DataContext>
<Window.Resources>
<DataTemplate x:Key="listBoxDateTemplate">
<StackPanel Orientation="Horizontal">
<TextBlock Text="{Binding Symbol}"/>
<TextBlock Text="{Binding Price}"/>
</StackPanel>
</DataTemplate>
</Window.Resources>
<Grid>
<ListBox ItemTemplate="{StaticResource listBoxDateTemplate}" ItemsSource="{Binding Quotes}"/>
</Grid>
</Window>
And then you'd have some kind of service that would feed the ObservableCollection with new StockQuotes.
My question is this: In this type of scenario, the StockQuote is considered the Model, and we're exposing that to the View through the ViewModel's ObservableCollection. Which basically means, our View has knowledge of the Model. Doesn't that violate the whole paradigm of M-V-VM? Or am I missing something here....?
