managing-wpf-collectionview-mvvm

# 5.6 MVVM Pattern with CollectionView

## Project Structure

The templates folder contains a .NET 9 WPF project example.

```
templates/
├── WpfCollectionViewSample.Core/           ← Pure C# models and interfaces
│   ├── Member.cs
│   ├── IMemberCollectionService.cs
│   └── WpfCollectionViewSample.Core.csproj
├── WpfCollectionViewSample.ViewModels/     ← ViewModel (no WPF references)
│   ├── MainViewModel.cs
│   ├── GlobalUsings.cs
│   └── WpfCollectionViewSample.ViewModels.csproj
├── WpfCollectionViewSample.WpfServices/    ← WPF Service Layer
│   ├── MemberCollectionService.cs
│   ├── GlobalUsings.cs
│   └── WpfCollectionViewSample.WpfServices.csproj
└── WpfCollectionViewSample.App/            ← WPF Application
    ├── Views/
    │   ├── MainWindow.xaml
    │   └── MainWindow.xaml.cs
    ├── App.xaml
    ├── App.xaml.cs
    ├── GlobalUsings.cs
    └── WpfCollectionViewSample.App.csproj
```

#### 5.6.1 Problem Scenario

When a single source collection needs to be filtered with different conditions across multiple Views while adhering to MVVM principles

#### 5.6.2 Core Principles

- **ViewModel must not reference WPF-related assemblies** (MVVM violation)
- **Encapsulate `CollectionViewSource` access through Service Layer**
- **ViewModel uses only `IEnumerable` or pure BCL types**

#### 5.6.3 Architecture Layer Structure

```
View (XAML)
    ↓ DataBinding
ViewModel Layer (uses IEnumerable, no WPF assembly reference)
    ↓ IEnumerable interface
Service Layer (uses CollectionViewSource directly)
    ↓
Data Layer (ObservableCollection<T>)
```

#### 5.6.4 Implementation Pattern

**1. Service Layer (CollectionViewFactory/Store)**

```csharp
// Services/MemberCollectionService.cs
// This class can reference PresentationFramework
namespace MyApp.Services;

public sealed class MemberCollectionService
{
    private ObservableCollection<Member> Source { get; } = [];

    // Factory Method: Create filtered view
    // Returns IEnumerable so ViewModel doesn't know WPF types