How to: Display a List of Non-Persistent Objects in a Popup Dialog

Jul 11, 2023
5 minutes to read

This example demonstrates how to populate and display a list of objects that are not bound to the database (non-persistent objects). A sample application that stores a list of books will be created in this example. An Action that displays a list of duplicate books in a pop-up window will be added to this application.

Tip

A complete sample project is available in the DevExpress Code Examples database at https://supportcenter.devexpress.com/ticket/details/e980/how-to-display-a-list-of-non-persistent-objects.

Define the Book persistent class.

C#
VB.NET

[DefaultClassOptions]
public class Book : BaseObject {
    public Book(Session session) : base(session) { }
    public string Title {
        get { return GetPropertyValue<string>(nameof(Title)); }
        set { SetPropertyValue<string>(nameof(Title), value); }
    }
}

<DefaultClassOptions()> _
Public Class Book
    Inherits BaseObject
    Public Sub New(ByVal session As Session)
        MyBase.New(session)
    End Sub
    Public Property Title() As String
        Get
            Return GetPropertyValue(Of String)(NameOf(Title))
        End Get
        Set(ByVal value As String)
            SetPropertyValue(Of String)(NameOf(Title), value)
        End Set
    End Property
End Class

The Book class, as its name implies, is used to represent books. It inherits BaseObject, and thus it is persistent. It contains a single Title property, which stores a book’s title.

Define two non-persistent classes - Duplicate and DuplicatesList.
- C#
- VB.NET
```
[DomainComponent]
public class Duplicate {
    [Browsable(false), DevExpress.ExpressApp.Data.Key]
    public int Oid;
    public string Title { get; set; }
    public int Count { get; set; }
}
[DomainComponent]
public class DuplicatesList {
    private BindingList<Duplicate> duplicates;
    public DuplicatesList() {
        duplicates = new BindingList<Duplicate>();
    }
    public BindingList<Duplicate> Duplicates { get { return duplicates; } }
}
```
```
<DomainComponent> _
Public Class Duplicate
    <Browsable(False), DevExpress.ExpressApp.Data.Key> _
    Public Id As Integer
    Public Property Title() As String
    Public Property Count() As Integer
End Class
<DomainComponent> _
Public Class DuplicatesList
    Private _duplicates As BindingList(Of Duplicate)
    Public Sub New()
        _duplicates = New BindingList(Of Duplicate)()
    End Sub
    Public ReadOnly Property Duplicates() As BindingList(Of Duplicate)
        Get
            Return _duplicates
        End Get
    End Property
End Class
```
Note
The INotifyPropertyChanged, IXafEntityObject and IObjectSpaceLink interface implementations were omitted in this example. However, it is recommended to support these interfaces in real-world applications (see The Importance of Property Change Notifications for Automatic UI Updates and Non-Persistent Objects).

These classes are not inherited from an XPO base persistent class, and are not added to the Entity Framework Core data model. As a result, they are not persistent. Use the DomainComponentAttribute to add such classes to the Application Model. This affects application UI construction.

The Duplicate non-persistent class has three public properties - Title, Count, and Id. The Title property stores the title of a book. The Count property stores the total number of books with the title specified by the Title property. Id is a key property. A key property is required in a non-persistent class for correct ListView operation. To specify a key property, use the KeyAttribute. The DuplicatesList non-persistent class aggregates the duplicates via the Duplicates collection property of the BindingList<Duplicate> type.

Create the following ShowDuplicateBooksController View Controller.

C#
VB.NET

public class ShowDuplicateBooksController : ObjectViewController<ListView, Book> {
    public ShowDuplicateBooksController() {
        PopupWindowShowAction showDuplicatesAction = 
            new PopupWindowShowAction(this, "ShowDuplicateBooks", "View");
        showDuplicatesAction.CustomizePopupWindowParams += showDuplicatesAction_CustomizePopupWindowParams;
    }
    void showDuplicatesAction_CustomizePopupWindowParams(object sender, CustomizePopupWindowParamsEventArgs e) {
        Dictionary<string, int> dictionary = new Dictionary<string, int>();
        foreach(Book book in View.CollectionSource.List) {
            if(!string.IsNullOrEmpty(book.Title)) {
                if(dictionary.ContainsKey(book.Title)) {
                    dictionary[book.Title]++;
                }
                else 
                    dictionary.Add(book.Title, 1);
            }
        }
        var nonPersistentOS = Application.CreateObjectSpace(typeof(DuplicatesList));
        DuplicatesList duplicateList =nonPersistentOS.CreateObject<DuplicatesList>();
        int duplicateId = 0;
        foreach(KeyValuePair<string, int> record in dictionary) {
            if (record.Value > 1) {
                var dup = nonPersistentOS.CreateObject<Duplicate>();
                dup.Id = duplicateId;
                dup.Title = record.Key;
                dup.Count = record.Value;
                duplicateList.Duplicates.Add(dup);
                duplicateId++;
            }
        }
        nonPersistentOS.CommitChanges();
        DetailView detailView = Application.CreateDetailView(nonPersistentOS, duplicateList);
        detailView.ViewEditMode = DevExpress.ExpressApp.Editors.ViewEditMode.Edit;
        e.View = detailView;
        e.DialogController.SaveOnAccept = false;
        e.DialogController.CancelAction.Active["NothingToCancel"] = false;
    }
}

<DomainComponent> _
Public Class ShowDuplicateBooksController
    Inherits ObjectViewController(Of ListView, Book)
    Public Sub New()
        Dim showDuplicatesAction As New PopupWindowShowAction(Me, "ShowDuplicateBooks", "View")
        AddHandler showDuplicatesAction.CustomizePopupWindowParams, AddressOf showDuplicatesAction_CustomizePopupWindowParams
    End Sub
    Private Sub showDuplicatesAction_CustomizePopupWindowParams(ByVal sender As Object, ByVal e As CustomizePopupWindowParamsEventArgs)
        Dim dictionary As New Dictionary(Of String, Integer)()
        For Each book As Book In View.CollectionSource.List
            If Not String.IsNullOrEmpty(book.Title) Then
                If dictionary.ContainsKey(book.Title) Then
                    dictionary(book.Title) += 1
                Else
                    dictionary.Add(book.Title, 1)
                End If
            End If
        Next book
        Dim nonPersistentOS = Application.CreateObjectSpace(GetType(DuplicatesList))
        Dim duplicateList = nonPersistentOS.CreateObject(Of DuplicatesList)()
        Dim duplicateId As Integer = 0
        For Each record As KeyValuePair(Of String, Integer) In dictionary
            If record.Value > 1 Then
                Dim dup = nonPersistentOS.CreateObject(Of Duplicate)()
                dup.Id = duplicateId
                dup.Title = record.Key
                dup.Count = record.Value
                duplicateList.Duplicates.Add(dup)
                duplicateId += 1
            End If
        Next record
        nonPersistentOS.CommitChanges()
        e.View = Application.CreateDetailView(nonPersistentOS, duplicateList)
        detailView.ViewEditMode = DevExpress.ExpressApp.Editors.ViewEditMode.Edit
        e.View = detailView
        e.DialogController.SaveOnAccept = False
        e.DialogController.CancelAction.Active("NothingToCancel") = False
    End Sub
End Class

This Controller inherits ObjectViewController<ListView, Book>, and thus, targets List Views that display Books. In the Controller’s constructor, the ShowDuplicateBooks PopupWindowShowAction is created. In the Action’s PopupWindowShowAction.CustomizePopupWindowParams event handler, the Books are iterated to find the duplicates. For each duplicate book found, the Duplicate object is instantiated and added to the DuplicatesList.Duplicates collection. Note that a unique key value (Id) is assigned for each Duplicate. Finally, a DuplicatesList Detail View is created and passed to the handler’s CustomizePopupWindowParamsEventArgs.View parameter. As a result, a DuplicatesList object is displayed in a pop-up window when a user clicks ShowDuplicateBooks.