Dependency Injection

• Aug 12, 2022
• 3 minutes to read

Bind a View to a View Model

To bind a view to a view model, create a MarkupExtension that resolves the correct ViewModel type:

C#

public class DISource : MarkupExtension {
    public static Func<Type, object, string, object> Resolver { get; set; }

    public Type Type { get; set; }
    public object Key { get; set; }
    public string Name { get; set; }

    public override object ProvideValue(IServiceProvider serviceProvider) => Resolver?.Invoke(Type, Key, Name);
}

Register the resolver at the application startup:

C#

protected override void OnStartup(StartupEventArgs e) {
    base.OnStartup(e);
    DISource.Resolver = Resolve;
}
object Resolve(Type type, object key, string name) {
    if(type == null)
        return null;
    if(key != null)
        return Container.ResolveKeyed(key, type);
    if(name != null)
        return Container.ResolveNamed(name, type);
    return Container.Resolve(type);
}

Specify the DataContext in XAML in the following manner:

XAML

DataContext="{common:DISource Type=common:MainViewModel}"

Examples

• Services:

  View Example

• POCO:

  View Example

Use POCO View Models with Dependency Injection

To use a POCO View Model in a Dependency Injection container, utilize the ViewModelSource.GetPOCOType method to register the POCO type generated at runtime:

C#

container.RegisterType(typeof(IMainViewModel),
                    ViewModelSource.GetPOCOType(typeof(MainViewModel)));

View Example

Use Services with Dependency Injection

The recommended technique to use DevExpress services with Dependency Injection varies depending on whether the service has an associated visual element.

• If the service is attached to a specific visual element, add the following custom AttachServiceBehavior to register it:

  C#

  public class AttachServiceBehavior : Behavior<DependencyObject> {
      public static readonly DependencyProperty AtachableServiceProperty =
          DependencyProperty.Register(nameof(AtachableService), typeof(ServiceBase),
          typeof(AttachServiceBehavior), new PropertyMetadata(null, OnAtachableServiceChanged));
  
      static void OnAtachableServiceChanged(DependencyObject d, DependencyPropertyChangedEventArgs e) {
          (e.OldValue as ServiceBase)?.Detach();
          ((AttachServiceBehavior)d).AttachService();
      }
      public ServiceBase AtachableService {
          get => (ServiceBase)GetValue(AtachableServiceProperty);
          set => SetValue(AtachableServiceProperty, value);
      }
  
      protected override void OnAttached() {
          base.OnAttached();
          AttachService();
      }
      protected override void OnDetaching() {
          base.OnDetaching();
          AtachableService?.Detach();
      }
  
      void AttachService() {
          if(AtachableService == null || AssociatedObject == null)
              return;
          if(AtachableService.IsAttached)
              AtachableService.Detach();
          AtachableService.Attach(AssociatedObject);
      }
  }
  

  Add a public property that corresponds to the service to the View Model:

  C#

  public class MainViewModel {
      public INavigationService NavigationService { get; }
  
      public MainViewModel(INavigationService navigationService) =>
          NavigationService = navigationService;
  }
  

  Use the AttachServiceBehavior to attach the service to a visual element:

  XAML

  <dxwui:NavigationFrame>
      <dxmvvm:Interaction.Behaviors>
          <common:AttachServiceBehavior Service="{Binding NavigationService}"/>
      </dxmvvm:Interaction.Behaviors>
  </dxwui:NavigationFrame>
  

  View Example

• If the service does not need to be attached to a specific visual element (such as Message Box Services), you can use the following technique instead:

  1. Register the service in the Dependency Injection container:

     C#

     container.RegisterSingleton(typeof(IMessageBoxService), typeof(DXMessageBoxService));
     

  2. Specify the corresponding View Model property:

     C#

     public class MainViewModel {
         IMessageBoxService messageBoxService;
         public MainViewModel(IMessageBoxService dialogService) {
             this.messageBoxService = messageBoxService;
         }
     }
     

Tip

If you configure the service to work with a specific View, Dependency Injection is not recommended. Use the technique described in the following section instead: Implement Services in Your Application.