Categorized List

• Dec 22, 2023
• 5 minutes to read

When data is displayed as a tree, you may need to show the objects associated with the currently selected node in the same List View. XAF enables you to do this by implementing the ICategorizedItem interface in the associated objects, and using the CategorizedListEditor provided by the TreeList Editors module. This topic demonstrates how to perform this task using the business classes defined in the Display a Tree List using the ITreeNode Interface topic.

Tip

A complete sample project is available in the DevExpress Code Examples database at https://supportcenter.devexpress.com/ticket/details/e1125/xaf-winforms-how-to-use-tree-list-editors-to-display-list-views.

In the Display a Tree List using the ITreeNode Interface topic, the ProjectGroup, Project and ProjectArea classes are implemented by inheriting from an abstract Category class, which implements the ITreeNode interface. Now, we will implement the Issue class that will be related to the Category class by the Many-to-One relationship. In addition, to display the Issue List View via the CategorizedListEditor, the Issue class will implement the ICategorizedItem interface. For details on this interface and the CategorizedListEditor, refer to the TreeList Editors Module Overview topic.

Implement the Issue class as shown in the code below:

C# (EF Core)

using DevExpress.Persistent.Base.General;
using System.ComponentModel.DataAnnotations;
//...
[DefaultClassOptions]
public class Issue : BaseObject, ICategorizedItem {
   public virtual Category Category { get; set; }
   public virtual string Subject { get; set; }
   public virtual string Description { get; set; }

   ITreeNode ICategorizedItem.Category {
      get {
          return Category;
      }
      set {
         Category = (Category)value;
      }
   }
}

// Make sure that you use options.UseChangeTrackingProxies() in your DbContext settings.

C# (XPO)

using DevExpress.Persistent.Base.General;
//...
[DefaultClassOptions]
public class Issue : BaseObject, ICategorizedItem {
   private Category category;
   private string subject;
   private string description;
   public Issue(Session session) : base(session) {}
   public Issue(Session session, string subject) : base(session) {
      this.subject = subject;
   }
   [Association("Category-Issues")]
   public Category Category {
      get {
         return category;
      }
      set {
         SetPropertyValue(nameof(Category), ref category, value);
      }
   }
   public string Subject {
      get {
         return subject;
      }
      set {
         SetPropertyValue(nameof(Subject), ref subject, value);
      }
   }
   public string Description {
      get {
         return description;
      }
      set {
         SetPropertyValue(nameof(Description), ref description, value);
      }
   }
   ITreeNode ICategorizedItem.Category {
      get {
          return Category;
      }
      set {
         Category = (Category)value;
      }
   }
}

VB.NET (XPO)

Imports DevExpress.Persistent.Base.General
'...
<DefaultClassOptions> _
Public Class Issue
      Inherits BaseObject
      Implements ICategorizedItem
   Private fCategory As Category
   Private fSubject As String
   Private fDescription As String
   Public Sub New(ByVal session As Session)
      MyBase.New(session)
   End Sub
   Public Sub New(ByVal session As Session, ByVal fSubject As String)
      MyBase.New(session)
      Me.fSubject = fSubject
   End Sub
   <Association("Category-Issues")> _
   Public Property Category() As Category
      Get
         Return fCategory
      End Get
      Set
         SetPropertyValue(NameOf(Category), fCategory, Value)
      End Set
   End Property
   Public Property Subject() As String
      Get
         Return fSubject
      End Get
      Set
         SetPropertyValue(NameOf(Subject), fSubject, Value)
      End Set
   End Property
   Public Property Description() As String
      Get
         Return fDescription
      End Get
      Set
         SetPropertyValue(NameOf(Description), fDescription, Value)
      End Set
   End Property
   Private Property ICategorizedItem_Category() As ITreeNode Implements ICategorizedItem.Category
      Get
         Return Category
      End Get
      Set
         Category = CType(Value, Category)
      End Set
   End Property
End Class

Note

The public property that is returned by the private Category property, which implicitly implements the ICategorizedItem interface, must be called “Category”. This is currently required by the internal infrastructure.

Modify the Category class to add an association with Issue objects:

C# (EF Core)

[NavigationItem]
public abstract class Category : BaseObject, ITreeNode {
    public virtual IList<Issue> Issues { get; set; } = new ObservableCollection<Issue>();
    private List<Issue> allIssues;

    [NotMapped]
    public IList<Issue> AllIssues {
        get {
            if(allIssues == null) {
                allIssues = new List<Issue>();
                CollectIssuesRecursive(this, allIssues);
            }
            return allIssues;
        }
    }

    private void CollectIssuesRecursive(Category issueCategory, List<Issue> target) {
        target.AddRange(issueCategory.Issues);
        foreach(Category childCategory in issueCategory.Children) {
            CollectIssuesRecursive(childCategory, target);
        }
    }
   //...
}

// Make sure that you use options.UseChangeTrackingProxies() in your DbContext settings.

C# (XPO)

[NavigationItem]
public abstract class Category : BaseObject, ITreeNode {
   [Association("Category-Issues")]
   public XPCollection<Issue> Issues {
      get {
         return GetCollection<Issue>(nameof(Issues));
      }
   }
   private XPCollection<Issue> allIssues;
   public XPCollection<Issue> AllIssues {
      get {
         if (allIssues == null) {
            allIssues = new XPCollection<Issue>(Session, false);
            CollectIssuesRecursive(this, allIssues);
            allIssues.BindingBehavior = CollectionBindingBehavior.AllowNone;
         }
         return allIssues; 
      }
   }   
   private void CollectIssuesRecursive(Category issueCategory, XPCollection<Issue> target) {
      target.AddRange(issueCategory.Issues);
      foreach (Category childCategory in issueCategory.Children) {
         CollectIssuesRecursive(childCategory, target);
      }
   }
  //...
}

VB.NET (XPO)

<NavigationItem> _
Public MustInherit Class Category
      Inherits BaseObject
      Implements ITreeNode
   <Association("Category-Issues")> _
   Public ReadOnly Property Issues() As XPCollection(Of Issue)
      Get
         Return GetCollection(Of Issue)(NameOf(Issues))
      End Get
   End Property
   Private fAllIssues As XPCollection(Of Issue)
   Public ReadOnly Property AllIssues() As XPCollection(Of Issue)
      Get
         If fAllIssues Is Nothing Then
            fAllIssues = New XPCollection(Of Issue)(Session, False)
            CollectIssuesRecursive(Me, fAllIssues)
            fAllIssues.BindingBehavior = CollectionBindingBehavior.AllowNone
         End If
         Return fAllIssues
      End Get
   End Property
   Private Sub CollectIssuesRecursive(ByVal issueCategory As Category, _
         ByVal target As XPCollection(Of Issue))
      target.AddRange(issueCategory.Issues)
      For Each childCategory As Category In issueCategory.Children
      CollectIssuesRecursive(childCategory, target)
      Next childCategory
   End Sub
  '...
End Class

Check that the TreeList Editors module is added to the Windows Forms application project, and run the application. Invoke the Issue List View. Select a tree node in the tree list to the left and execute the New Action, to create an Issue for the corresponding Category object. To the right of the tree list, a list of Issue objects associated with the currently selected tree node is displayed.