How to: Extend and Access the Application Model Nodes from Controllers

• Nov 19, 2025
• 4 minutes to read

Follow the instructions below to extend the Application Model in the following two ways:

• Add the IsGroupFooterVisible property to Views | <ListView> nodes. If set to true, the corresponding List View displays a Group Footer.
• Add the GroupFooterSummaryType property to column nodes (ListView | Columns | Column). This property specifies group summary type for the corresponding column.

For more information on how to extend the Application Model, refer to the following topic: Extend and Customize the Application Model in Code.

View Example: How to Extend the Application Model

Common Steps

Implement interfaces that expose the IsGroupFooterVisible and GroupFooterSummaryType properties:

using DevExpress.Data;
using System.ComponentModel;

namespace ExtendModel.Module {
    public interface IModelListViewExtender {
        bool IsGroupFooterVisible { get; set; }
    }
    public interface IModelColumnExtender {
        [DefaultValue(SummaryItemType.None)]
        SummaryItemType GroupFooterSummaryType { get; set; }
    }
}

Override the ModuleBase.ExtendModelInterfaces method of your base Module to extend the Application Model with declared interfaces:

using DevExpress.ExpressApp.Model;
// ...
namespace ExtendModel.Module;

public sealed partial class ExtendModelModule : ModuleBase {
    // ...
    public override void ExtendModelInterfaces(ModelInterfaceExtenders extenders) {
        base.ExtendModelInterfaces(extenders);
        extenders.Add<IModelListView, IModelListViewExtender>();
        extenders.Add<IModelColumn, IModelColumnExtender>();
    }
}

WinForms-Specific Steps

Inherit a WinGroupFooterViewController from the ViewController<ListView> type in the Windows Forms Module. This base class choice ensures the Controller activates in List Views only.

Override the protected OnViewControlsCreated method. If the IsGroupFooterVisible property is set to true for the current List View, display the group footer.

Note that users can change column summary types in the UI. Handle the View.ModelSaved event to save these changes to the Application Model when users close the current List View.

using DevExpress.Data;
using DevExpress.ExpressApp;
using DevExpress.ExpressApp.Win.Editors;
using DevExpress.XtraGrid.Views.Grid;
using ExtendModel.Module;

namespace ExtendModel.Win.Controllers {
    public class WinGroupFooterViewController : ViewController<DevExpress.ExpressApp.ListView> {
        private void View_ModelSaved(object sender, EventArgs e) {
            if (View.Model is IModelListViewExtender modelListView && modelListView.IsGroupFooterVisible) {
                if (View.Editor is GridListEditor gridListEditor) {
                    GridView gridView = gridListEditor.GridView;
                    for (int i = 0; i < gridView.GroupSummary.Count; i++) {
                        if (View.Model.Columns[
                            gridView.GroupSummary[i].FieldName] is IModelColumnExtender modelColumn) {
                            modelColumn.GroupFooterSummaryType = gridView.GroupSummary[i].SummaryType;
                        }
                    }
                }
            }
        }
        protected override void OnViewControlsCreated() {
            base.OnViewControlsCreated();
            if (View.Model is IModelListViewExtender modelListView && modelListView.IsGroupFooterVisible) {
                if (View.Editor is GridListEditor gridListEditor) {
                    GridView gridView = gridListEditor.GridView;
                    gridView.OptionsView.GroupFooterShowMode = GroupFooterShowMode.VisibleAlways;
                    foreach (var column in gridListEditor.Columns) {
                        if (column.ModelColumn is IModelColumnExtender modelColumnExtender && modelColumnExtender.GroupFooterSummaryType != SummaryItemType.None) {
                            gridView.GroupSummary.Add(modelColumnExtender.GroupFooterSummaryType, column.Id, column.Column);
                        }
                    }
                }
            }
        }
        protected override void OnActivated() {
            base.OnActivated();
            View.ModelSaved += View_ModelSaved;
        }
        protected override void OnDeactivated() {
            View.ModelSaved -= View_ModelSaved;
            base.OnDeactivated();
        }
    }
}

ASP.NET Core Blazor-Specific Steps

Inherit a BlazorGroupFooterViewController from the ViewController<ListView> type in the ASP.NET Core Blazor Module. This base class choice ensures that the controller is activated only in List Views.

Override the protected OnViewControlsCreated method. If the IsGroupFooterVisible property is set to true for the current List View, display the group footer.

Users cannot customize summary settings in ASP.NET Core Blazor UI. You do not need to handle the ModelSaved event.

C#

using DevExpress.Data;
using DevExpress.ExpressApp;
using DevExpress.ExpressApp.Blazor.Editors;
using ExtendModel.Module;

namespace ExtendModel.Blazor.Server.Controllers {
    public class BlazorGroupFooterViewController : ViewController<ListView> {
        protected override void OnViewControlsCreated() {
            base.OnViewControlsCreated();
            if (View.Model is IModelListViewExtender modelListView && modelListView.IsGroupFooterVisible && View.Editor is DxGridListEditor gridListEditor) {
                gridListEditor.GridModel.GroupFooterDisplayMode = DevExpress.Blazor.GridGroupFooterDisplayMode.Always;
                foreach (var column in gridListEditor.Columns) {
                    if (column.ModelColumn is IModelColumnExtender modelColumnExtender && modelColumnExtender.GroupFooterSummaryType != SummaryItemType.None) {
                        var summaryItem = (DxGridSummaryItemWrapper)gridListEditor.GridSummary.CreateItem(column.Id, modelColumnExtender.GroupFooterSummaryType);
                        summaryItem.SummaryItemModel.FooterColumnName = column.Id;
                        gridListEditor.GridSummary.GroupSummary.Add(summaryItem);
                    }
                }
            }
        }
    }
}

Run the Application

Rebuild your solution. Invoke the Model Editor for the base Module and navigate to a ListView node. Change the following settings:

• Set the IsGroupPanelVisible property to true to allow users to group data.
• Set the new IsGroupFooterVisible property to true to enable group footers.
• Specify summary types for Column nodes. Use the new GroupFooterSummaryType property.

Run the application. Open a List View with a group panel and group the List View by a column. You can see the footer with the specified summary types.