Create a Custom Service

• Aug 10, 2023
• 4 minutes to read

This topic describes how to create a custom service if predefined services do not suit your requirements.

Note

If you need to implement the logic that should access a UI element in the View Model code, you can use the UIObjectService instead.

Follow the steps below to create a custom service, attach it to a control, and access this service in the View Model:

1. Create a service interface with methods that should be called from the View Model:

   C#

   public interface IGridUpdateService {
       void BeginUpdate();
       void EndUpdate();
   }
   

   VB.NET

   Public Interface IGridUpdateService
       Sub BeginUpdate()
       Sub EndUpdate()
   End Interface
   

2. Create a ServiceBase class descendant that implements your interface:

   C#

   using DevExpress.Mvvm.UI;
   // ...
   public class GridUpdateService : ServiceBase, IGridUpdateService {
       public void BeginUpdate() {
           // ...
       }
       public void EndUpdate() {
           // ...
       }
   }
   

   VB.NET

   Imports DevExpress.Mvvm.UI
   ' ...
   Public Class GridUpdateService
       Inherits ServiceBase
       Implements IGridUpdateService
   
       Public Sub BeginUpdate() Implements IGridUpdateService.BeginUpdate
           ' ...
       End Sub
   
       Public Sub EndUpdate() Implements IGridUpdateService.EndUpdate
           ' ...
       End Sub
   End Class
   

3. Use the AssociatedObject property to access the associated control:

   C#

   using DevExpress.Xpf.Grid;
   // ...
   public class GridUpdateService : ServiceBase, IGridUpdateService {
       GridControl GridControl => AssociatedObject as GridControl;
   
       public void BeginUpdate() {
           Dispatcher.Invoke(new Action(() => {
               if (GridControl != null) {
                   GridControl.BeginDataUpdate();
               }
           }));
       }
   
       public void EndUpdate() {
           Dispatcher.Invoke(new Action(() => {
               if (GridControl != null) {
                   GridControl.EndDataUpdate();
               }
           }));
       }
   }
   

   VB.NET

   Imports DevExpress.Xpf.Grid
   ' ...
   Public Class GridUpdateService
       Inherits ServiceBase
       Implements IGridUpdateService
   
       Private ReadOnly Property GridControl As GridControl
           Get
               Return TryCast(AssociatedObject, GridControl)
           End Get
       End Property
   
       Public Sub BeginUpdate() Implements IGridUpdateService.BeginUpdate
           Dispatcher.Invoke(New Action(Sub()
               If GridControl IsNot Nothing Then
                   GridControl.BeginDataUpdate()
               End If
           End Sub))
       End Sub
   
       Public Sub EndUpdate() Implements IGridUpdateService.EndUpdate
           Dispatcher.Invoke(New Action(Sub()
               If GridControl IsNot Nothing Then
                   GridControl.EndDataUpdate()
               End If
           End Sub))
       End Sub
   End Class
   

   In this example, the Dispatcher object is used to call methods of the associated control in the UI thread.

4. Add your service to the Behaviors collection to attach it to a control:

   XAML

   <Window ...
           xmlns:dxg="http://schemas.devexpress.com/winfx/2008/xaml/grid"
           xmlns:local="clr-namespace:DXGridThreads"
           xmlns:dxmvvm="http://schemas.devexpress.com/winfx/2008/xaml/mvvm">
       <Window.DataContext>
           <local:ViewModel />
       </Window.DataContext>
       <dxg:GridControl AutoGenerateColumns="AddNew" 
                        ItemsSource="{Binding Source}">
           <dxmvvm:Interaction.Behaviors>
               <local:GridUpdateService/>
           </dxmvvm:Interaction.Behaviors>
       </dxg:GridControl>
   </Window>
   

5. Access your service in the View Model:

   C#

   using DevExpress.Mvvm;
   // ...
   public class ViewModel : ViewModelBase {
       public IGridUpdateService GridUpdateService { get { return GetService<IGridUpdateService>(); } }
   
       void TimerCallback(object state) {
           lock(SyncRoot) {
               if(GridUpdateService != null) {
                   GridUpdateService.BeginUpdate();
                   foreach(DataItem item in Source) {
                       item.Value = random.Next(100);
                   }
                   GridUpdateService.EndUpdate();
               }
           }
       }
   }
   

   VB.NET

   Imports DevExpress.Mvvm
   ' ...
   Public Class ViewModel
       Inherits ViewModelBase
   
       Public ReadOnly Property GridUpdateService As IGridUpdateService
           Get
               Return GetService(Of IGridUpdateService)()
           End Get
       End Property
   
       Private Sub TimerCallback(ByVal state As Object)
           SyncLock SyncRoot
               If GridUpdateService IsNot Nothing Then
                   GridUpdateService.BeginUpdate()
                   For Each item As DataItem In Source
                       item.Value = random.Next(100)
                   Next
   
                   GridUpdateService.EndUpdate()
               End If
           End SyncLock
       End Sub
   End Class
   

6. (Optional) Add a DependencyProperty to your service. This property is set at the View level and you can use its value within the service:

   C#

   public class GridUpdateService : ServiceBase, IGridUpdateService {
       public static readonly DependencyProperty UpdatedTextProperty =
           DependencyProperty.Register("UpdatedText", typeof(string), typeof(GridUpdateService), new PropertyMetadata("Updated"));
   
       public string UpdatedText {
           get { return (string)GetValue(UpdatedTextProperty); }
           set { SetValue(UpdatedTextProperty, value); }
       }
       // ...
   }
   

   VB.NET

   Public Class GridUpdateService
       Inherits ServiceBase
       Implements IGridUpdateService
   
       Public Shared ReadOnly UpdatedTextProperty As DependencyProperty = 
           DependencyProperty.Register("UpdatedText", GetType(String), GetType(GridUpdateService), New PropertyMetadata("Updated"))
   
       Public Property UpdatedText As String
           Get
               Return CStr(GetValue(UpdatedTextProperty))
           End Get
           Set(ByVal value As String)
               SetValue(UpdatedTextProperty, value)
           End Set
       End Property
       ' ...
   End Class
   

   XAML

   <dxmvvm:Interaction.Behaviors>
       <local:GridUpdateService UpdatedText="Modified"/>
   </dxmvvm:Interaction.Behaviors>
   

7. (Optional) Override OnAttached and OnDetaching methods to subscribe and unsubscribe from associated control events:

   C#

   public class GridUpdateService : ServiceBase, IGridUpdateService {
       GridControl GridControl => AssociatedObject as GridControl;
   
       protected override void OnAttached() {
           base.OnAttached();
           GridControl.CustomColumnDisplayText += GridControl_CustomColumnDisplayText;
       }
   
       private void GridControl_CustomColumnDisplayText(object sender, CustomColumnDisplayTextEventArgs e) {
           // ...
       }
   
       protected override void OnDetaching() {
           GridControl.CustomColumnDisplayText -= GridControl_CustomColumnDisplayText;
           base.OnDetaching();
       }
   }
   

   VB.NET

   Public Class GridUpdateService
       Inherits ServiceBase
       Implements IGridUpdateService
   
       Private ReadOnly Property GridControl As GridControl
           Get
               Return TryCast(AssociatedObject, GridControl)
           End Get
       End Property
   
       Protected Overrides Sub OnAttached()
           MyBase.OnAttached()
           GridControl.CustomColumnDisplayText += AddressOf GridControl_CustomColumnDisplayText
       End Sub
   
       Private Sub GridControl_CustomColumnDisplayText(ByVal sender As Object, ByVal e As CustomColumnDisplayTextEventArgs)
       ' ...
       End Sub
   
       Protected Overrides Sub OnDetaching()
           GridControl.CustomColumnDisplayText -= AddressOf GridControl_CustomColumnDisplayText
           MyBase.OnDetaching()
       End Sub
   End Class
   

The complete sample project is available in the following GitHub repository:

View Example: Data Grid for WPF - How to Update Data in a Separate Thread