How to: Extend the Application Model

• Feb 25, 2022
• 6 minutes to read

To demonstrate how to extend the Application Model, this topic details how to display a Group Footer for List Views. An IsGroupFooterVisible property will be added to the to the Views | <ListView> node. When set to true for a ListView, a special Controller will enable the group footer. To specify a summary type for different columns, a GroupFooterSummaryType property will be added to the ListView | Columns | Column node. For general information on extending the Application Model, refer to the Extend and Customize the Application Model in Code help topic.

Note

Mobile applications do not support the Group Footer. However, you can implement the approach described in this topic to extend your Application Model for other purposes.

Tip

A complete sample project is available in the DevExpress Code Examples database at How to Extend the Application Model.

• Implement the interfaces exposing the IsGroupFooterVisible and GroupFooterSummaryType properties.

  C#

  using DevExpress.Data;
  //...
  public interface IModelListViewExtender {
      bool IsGroupFooterVisible { get; set; }
  }
  public interface IModelColumnExtender {
      [DefaultValue(SummaryItemType.None)]
      SummaryItemType GroupFooterSummaryType { get; set; }
  }
  

  VB.NET

  Imports DevExpress.Data
  '...
  Public Interface IModelListViewExtender
      Property IsGroupFooterVisible() As Boolean
  End Interface
  Public Interface IModelColumnExtender
      <DefaultValue(SummaryItemType.None)> _
      Property GroupFooterSummaryType() As SummaryItemType
  End Interface
  

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

  C#

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

  VB.NET

  Imports DevExpress.ExpressApp.Model
  '...
  Public NotInheritable Partial Class ExtendModelModule
      Inherits ModuleBase
      '...
      Public Overrides Sub ExtendModelInterfaces(ByVal extenders As ModelInterfaceExtenders)
          MyBase.ExtendModelInterfaces(extenders)
          extenders.Add(Of IModelListView, IModelListViewExtender)()
          extenders.Add(Of IModelColumn, IModelColumnExtender)()
      End Sub
  End Class
  

• Create a WinGroupFooterViewController ViewController in the Windows Forms Module. Inherit it from the ViewController<ListView> type, since this Controller must be activated in List Views only.

• Override the protected OnViewControlsCreated method to display the group footer, if the IsGroupFooterVisible property is set to true for the current List View. Additionally, when the Controller is activated, handle the View.ModelSaved event to save the group footer summary type for different columns into Application Model, when the current List View is closing.

  C#

  using System;
  using System.ComponentModel;
  using DevExpress.Data;
  using DevExpress.ExpressApp;
  using DevExpress.ExpressApp.Model;
  using DevExpress.ExpressApp.Win.Editors;
  using DevExpress.XtraGrid.Views.Grid;
  using DevExpress.XtraGrid.Columns;
  //...
  public class WinGroupFooterViewController : ViewController<ListView> {
      private void View_ModelSaved(object sender, EventArgs e) {
          IModelListViewExtender modelListView = View.Model as IModelListViewExtender;
          if(modelListView != null && modelListView.IsGroupFooterVisible) {
              GridListEditor gridListEditor = View.Editor as GridListEditor;
              if(gridListEditor != null) {
                  GridView gridView = gridListEditor.GridView;
                  for(int i = 0; i < gridView.GroupSummary.Count; i++) {
                      IModelColumnExtender modelColumn = View.Model.Columns[
                          gridView.GroupSummary[i].FieldName] as IModelColumnExtender;
                      if(modelColumn != null) {
                          modelColumn.GroupFooterSummaryType = gridView.GroupSummary[i].SummaryType;
                      }
                  }
              }
          }
      }
      protected override void OnViewControlsCreated() {
          base.OnViewControlsCreated();
          IModelListViewExtender modelListView = View.Model as IModelListViewExtender;
          if(modelListView != null && modelListView.IsGroupFooterVisible) {
              GridListEditor gridListEditor = View.Editor as GridListEditor;
              if(gridListEditor != null) {
                  GridView gridView = gridListEditor.GridView;
                  gridView.GroupFooterShowMode = GroupFooterShowMode.VisibleAlways;
                  foreach(IModelColumn modelColumn in View.Model.Columns) {
                      IModelColumnExtender modelColumnExtender = modelColumn as IModelColumnExtender;
                      if(modelColumnExtender != null && 
                          modelColumnExtender.GroupFooterSummaryType != SummaryItemType.None) {
                          GridColumn gridColumn = gridView.Columns[
                              modelColumn.ModelMember.MemberInfo.BindingName];
                          gridView.GroupSummary.Add(modelColumnExtender.GroupFooterSummaryType, 
                              modelColumn.Id, gridColumn);
                      }
                  }
              }
          }
      }
      protected override void OnActivated() {
          base.OnActivated();
          View.ModelSaved += View_ModelSaved;
      }
      protected override void OnDeactivated() {
          View.ModelSaved -= View_ModelSaved;
          base.OnDeactivated();
      }
  }
  

  VB.NET

  Imports Microsoft.VisualBasic
  Imports System
  Imports System.ComponentModel
  Imports DevExpress.Data
  Imports DevExpress.ExpressApp
  Imports DevExpress.ExpressApp.Model
  Imports DevExpress.ExpressApp.Win.Editors
  Imports DevExpress.XtraGrid.Views.Grid
  Imports DevExpress.XtraGrid.Columns
  '...
  Public Class WinGroupFooterViewController
      Inherits ViewController(Of ListView)
      Private Sub View_ModelSaved(ByVal sender As Object, ByVal e As EventArgs)
          Dim modelListView As IModelListViewExtender = TryCast(View.Model, IModelListViewExtender)
          If modelListView IsNot Nothing AndAlso modelListView.IsGroupFooterVisible Then
              Dim gridListEditor As GridListEditor = TryCast(View.Editor, GridListEditor)
              If gridListEditor IsNot Nothing Then
                  Dim gridView As GridView = gridListEditor.GridView
                  For i As Integer = 0 To gridView.GroupSummary.Count - 1
                      Dim modelColumn As IModelColumnExtender = TryCast(CType(View.Model.Columns, _
                      IModelList(of IModelColumn))(gridView.GroupSummary(i).FieldName), _
                      IModelColumnExtender)
                      If modelColumn IsNot Nothing Then
                          modelColumn.GroupFooterSummaryType = gridView.GroupSummary(i).SummaryType
                      End If
                  Next i
              End If
          End If
      End Sub
      Protected Overrides Overloads Sub OnViewControlsCreated()
          MyBase.OnViewControlsCreated()
          Dim modelListView As IModelListViewExtender = TryCast(View.Model, IModelListViewExtender)
          If modelListView IsNot Nothing AndAlso modelListView.IsGroupFooterVisible Then
              Dim gridListEditor As GridListEditor = TryCast(View.Editor, GridListEditor)
              If gridListEditor IsNot Nothing Then
                  Dim gridView As GridView = gridListEditor.GridView
                  gridView.GroupFooterShowMode = GroupFooterShowMode.VisibleAlways
                  For Each modelColumn As IModelColumn In View.Model.Columns
                      Dim modelColumnExtender As IModelColumnExtender = _
                      TryCast(modelColumn, IModelColumnExtender)
                      If modelColumnExtender IsNot Nothing AndAlso _
                      modelColumnExtender.GroupFooterSummaryType <> SummaryItemType.None Then
                          Dim gridColumn As GridColumn = _
                          gridView.Columns(modelColumn.ModelMember.MemberInfo.BindingName)
                          gridView.GroupSummary.Add( _
                          modelColumnExtender.GroupFooterSummaryType, modelColumn.Id, gridColumn)
                      End If
                  Next modelColumn
              End If
          End If
      End Sub
      Protected Overrides Overloads Sub OnActivated()
          MyBase.OnActivated()
          AddHandler View.ModelSaved, AddressOf View_ModelSaved
      End Sub
      Protected Overrides Overloads Sub OnDeactivated()
          RemoveHandler View.ModelSaved, AddressOf View_ModelSaved
          MyBase.OnDeactivated()
      End Sub
  End Class
  

• Create a WebGroupFooterViewController ViewController in the ASP.NET Web Module. Inherit it from the ViewController<ListView> type, since this Controller must be activated in List Views only.

• Override the protected OnViewControlsCreated method to display the group footer, if the IsGroupFooterVisible property is set to true for the current List View. There is no need to handle the ModelSaved event since end-users cannot customize summary types for different columns in the ASP.NET UI.

  C#

  using System;
  using DevExpress.Data;
  using DevExpress.ExpressApp;
  using DevExpress.ExpressApp.Model;
  using DevExpress.ExpressApp.Web.Editors.ASPx;
  using DevExpress.Web.ASPxGridView;
  //...
  public class WebGroupFooterViewController : ViewController<ListView> {
      protected override void OnViewControlsCreated() {
          base.OnViewControlsCreated();
          IModelListViewExtender modelListView = View.Model as IModelListViewExtender;
          if(modelListView != null && modelListView.IsGroupFooterVisible) {
              ASPxGridListEditor gridListEditor = View.Editor as ASPxGridListEditor;
              if(gridListEditor != null) {
                  ASPxGridView gridView = gridListEditor.Grid;
                  gridView.Settings.ShowGroupFooter = GridViewGroupFooterMode.VisibleAlways;
                  foreach(IModelColumn modelColumn in View.Model.Columns) {
                      IModelColumnExtender modelColumnExtender = modelColumn as IModelColumnExtender;
                      if(modelColumnExtender != null && 
                          modelColumnExtender.GroupFooterSummaryType != SummaryItemType.None) {
                          string fieldName = modelColumn.ModelMember.MemberInfo.BindingName;
                          ASPxSummaryItem summaryItem = null;
                          foreach(ASPxSummaryItem currentItem in gridView.GroupSummary) {
                              if(currentItem.FieldName == fieldName) {
                                  currentItem.ShowInGroupFooterColumn = modelColumn.Caption;
                                  summaryItem = currentItem;
                                  break;
                              }
                          }
                          if(summaryItem == null) {
                              summaryItem = new ASPxSummaryItem(
                                  fieldName, modelColumnExtender.GroupFooterSummaryType);
                              summaryItem.ShowInGroupFooterColumn = modelColumn.Caption;
                              gridView.GroupSummary.Add(summaryItem);
                          }
                      }
                  }
              }
          }
      }
  }
  

  VB.NET

  Imports Microsoft.VisualBasic
  Imports System
  Imports DevExpress.Data
  Imports DevExpress.ExpressApp
  Imports DevExpress.ExpressApp.Model
  Imports DevExpress.ExpressApp.Web.Editors.ASPx
  Imports DevExpress.Web.ASPxGridView
  '...
  Public Class WebGroupFooterViewController
      Inherits ViewController(Of ListView)
      Protected Overrides Sub OnViewControlsCreated()
          MyBase.OnViewControlsCreated()
          Dim modelListView As IModelListViewExtender = TryCast(View.Model, IModelListViewExtender)
          If modelListView IsNot Nothing AndAlso modelListView.IsGroupFooterVisible Then
              Dim gridListEditor As ASPxGridListEditor = TryCast(View.Editor, ASPxGridListEditor)
              If gridListEditor IsNot Nothing Then
                  Dim gridView As ASPxGridView = gridListEditor.Grid
                  gridView.Settings.ShowGroupFooter = GridViewGroupFooterMode.VisibleAlways
                  For Each modelColumn As IModelColumn In View.Model.Columns
                      Dim modelColumnExtender As IModelColumnExtender = _
                      TryCast(modelColumn, IModelColumnExtender)
                      If modelColumnExtender IsNot Nothing AndAlso _
                      modelColumnExtender.GroupFooterSummaryType <> SummaryItemType.None Then
                          Dim fieldName As String = modelColumn.ModelMember.MemberInfo.BindingName
                          Dim summaryItem As ASPxSummaryItem = Nothing
                          For Each currentItem As ASPxSummaryItem In gridView.GroupSummary
                              If currentItem.FieldName = fieldName Then
                                  currentItem.ShowInGroupFooterColumn = modelColumn.Caption
                                  summaryItem = currentItem
                                  Exit For
                              End If
                          Next currentItem
                          If summaryItem Is Nothing Then
                              summaryItem = New ASPxSummaryItem( _
                              fieldName, modelColumnExtender.GroupFooterSummaryType)
                              summaryItem.ShowInGroupFooterColumn = modelColumn.Caption
                              gridView.GroupSummary.Add(summaryItem)
                          End If
                      End If
                  Next modelColumn
              End If
          End If
      End Sub
  End Class
  

• Rebuild you solution and invoke the Model Editor for the base Module. Set a ListView node’s IsGroupPanelVisible property to true to be able to group the List View’s columns. Set the newly added IsGroupFooterVisible property to true. Specify summary types for the ListView node’s Column nodes.
• Run the application. Display the List View with a group panel and group the List View by a column. The footer with the specified summary types will be displayed.