Creating a modern WPF application involves a blend of robust architectural patterns and frameworks to ensure maintainability, scalability, and flexibility. This article discusses the development of a WPF application using the MVVM (Model-View-ViewModel) pattern, EF Core for database integration, a plugin architecture, and Autofac for dependency injection. A key focus will be on implementing a robust user management system that includes authentication, authorization, and role management. Additionally, we will explore communication between plugins using an event aggregator and a shared service provider, and demonstrate plugin versioning and loading in the main window.
Architectural Overview
The main components of our application include:
- MVVM Pattern: Separation of concerns between UI and business logic.
- EF Core: Database access and management.
- Plugin Architecture: Extensibility through dynamically loaded plugins.
- Autofac: Dependency injection management.
- Event Aggregator and Shared Service Provider: Facilitating communication between plugins.
Implementing the Main Application
Configuring Dependency Injection with Autofac
Autofac allows us to manage dependencies in a flexible and extendable way. Below is an example configuration for the DI container:
public class Bootstrapper
{
public IContainer Bootstrap()
{
var builder = new ContainerBuilder();
// Register MVVM components
builder.RegisterType<MainViewModel>().AsSelf();
builder.RegisterType<MainWindow>().AsSelf();
// Register EF Core DbContext
builder.RegisterType<AppDbContext>().AsSelf().InstancePerLifetimeScope();
// Register Plugin Loader
builder.RegisterType<PluginLoader>().As<IPluginLoader>();
// Register Event Aggregator
builder.RegisterType<EventAggregator>().As<IEventAggregator>().SingleInstance();
// Register AuthService
builder.RegisterType<AuthService>().As<IAuthService>().InstancePerLifetimeScope();
return builder.Build();
}
}
Loading Plugins and Displaying the Landing Page
The application loads plugins during startup and displays a simple landing page. Here’s how plugins are loaded:
public interface IPlugin
{
void Initialize(IContainer container);
}
public class PluginLoader : IPluginLoader
{
private readonly IContainer _container;
public PluginLoader(IContainer container)
{
_container = container;
}
public void LoadPlugins(string path)
{
var pluginAssemblies = Directory.GetFiles(path, "*.dll")
.Select(Assembly.LoadFrom);
foreach (var assembly in pluginAssemblies)
{
var pluginTypes = assembly.GetTypes().Where(t => typeof(IPlugin).IsAssignableFrom(t) && !t.IsAbstract);
foreach (var pluginType in pluginTypes)
{
var plugin = (IPlugin)Activator.CreateInstance(pluginType);
plugin.Initialize(_container);
}
}
}
}
To display the landing page, we ensure that the MainWindow is correctly set up:
public partial class MainWindow : Window
{
private readonly IPluginLoader _pluginLoader;
public MainWindow(IPluginLoader pluginLoader)
{
InitializeComponent();
_pluginLoader = pluginLoader;
Loaded += OnLoaded;
}
private void OnLoaded(object sender, RoutedEventArgs e)
{
_pluginLoader.LoadPlugins("Plugins");
// Display landing page content
DataContext = new MainViewModel();
}
}
Implementing User Management
Data Models for User Management
We start by defining the data models for users, roles, and their relationships:
public class User
{
public int Id { get; set; }
public string Username { get; set; }
public string PasswordHash { get; set; }
public ICollection<UserRole> UserRoles { get; set; }
}
public class Role
{
public int Id { get; set; }
public string Name { get; set; }
public ICollection<UserRole> UserRoles { get; set; }
}
public class UserRole
{
public int UserId { get; set; }
public User User { get; set; }
public int RoleId { get; set; }
public Role Role { get; set; }
}
Authentication and Authorization Service
The AuthService handles authentication and authorization:
public interface IAuthService
{
User Authenticate(string username, string password);
bool Authorize(User user, string role);
}
public class AuthService : IAuthService
{
private readonly AppDbContext _context;
public AuthService(AppDbContext context)
{
_context = context;
}
public User Authenticate(string username, string password)
{
var user = _context.Users.Include(u => u.UserRoles).ThenInclude(ur => ur.Role)
.FirstOrDefault(u => u.Username == username);
if (user == null || !VerifyPassword(user.PasswordHash, password))
{
return null;
}
return user;
}
public bool Authorize(User user, string role)
{
return user.UserRoles.Any(ur => ur.Role.Name == role);
}
private bool VerifyPassword(string hashedPassword, string password)
{
// Implement password verification logic here
return true;
}
}
Plugin Communication with Event Aggregator
Event Aggregator
An event aggregator facilitates decoupled communication between plugins:
public interface IEventAggregator
{
void Publish<TEvent>(TEvent eventToPublish);
void Subscribe<TEvent>(Action<TEvent> eventHandler);
}
public class EventAggregator : IEventAggregator
{
private readonly ConcurrentDictionary<Type, List<object>> _subscribers = new();
public void Publish<TEvent>(TEvent eventToPublish)
{
if (_subscribers.TryGetValue(typeof(TEvent), out var handlers))
{
foreach (var handler in handlers.OfType<Action<TEvent>>())
{
handler(eventToPublish);
}
}
}
public void Subscribe<TEvent>(Action<TEvent> eventHandler)
{
_subscribers.AddOrUpdate(
typeof(TEvent),
_ => new List<object> { eventHandler },
(_, handlers) => { handlers.Add(eventHandler); return handlers; }
);
}
}
Plugin Versioning and Loading
Plugin Metadata and Version Checking
To ensure plugins are compatible, we implement version checking:
public interface IPluginMetadata
{
string Name { get; }
Version Version { get; }
}
[AttributeUsage(AttributeTargets.Class, AllowMultiple = false)]
public class PluginAttribute : Attribute, IPluginMetadata
{
public string Name { get; }
public Version Version { get; }
public PluginAttribute(string name, string version)
{
Name = name;
Version = Version.Parse(version);
}
}
public class PluginLoader : IPluginLoader
{
private readonly IContainer _container;
public PluginLoader(IContainer container)
{
_container = container;
}
public void LoadPlugins(string path)
{
var pluginAssemblies = Directory.GetFiles(path, "*.dll")
.Select(Assembly.LoadFrom);
foreach (var assembly in pluginAssemblies)
{
var pluginTypes = assembly.GetTypes()
.Where(t => typeof(IPlugin).IsAssignableFrom(t) &&
t.GetCustomAttribute<PluginAttribute>() != null);
foreach (var pluginType in pluginTypes)
{
var metadata = pluginType.GetCustomAttribute<PluginAttribute>();
if (IsCompatible(metadata))
{
var plugin = (IPlugin)Activator.CreateInstance(pluginType);
plugin.Initialize(_container);
}
}
}
}
private bool IsCompatible(IPluginMetadata metadata)
{
// Implement compatibility check logic here
return true;
}
}
Conclusion
The architecture outlined above provides a robust foundation for developing a modular and extensible WPF application. By integrating the MVVM pattern, EF Core, a plugin architecture, and Autofac, the application becomes highly maintainable and future-proof. Implementing a comprehensive user management system, along with thread-safe plugin communication, ensures usability and reliability. A well-planned plugin versioning strategy keeps the application compatible and extensible.
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