Supply Predefined Values for the String Property Editor Dynamically (WinForms)

• Oct 17, 2023
• 4 minutes to read

This topic describes implementation of a custom Property Editor for a Windows Forms application. A custom Property Editor used to edit a business object’s CultureCode (locale) property of the String type is implemented here. The dropdown list of the Property Editor’s control will display the cultures installed in an end-user’s Windows operating system.

Note

You can also specify predefined values in the Model Editor using the IModelCommonMemberViewItem.PredefinedValues property. This approach is much simpler because it does not require extra coding, but you will be unable to update the values list dynamically in code in this instance.

The image below shows the resulting Property Editor:

By default, XAF creates the StringPropertyEditor for String type properties. This Property Editor displays a dropdown list of items if the corresponding BOModel | <Class> | OwnMembers | <Member> node’s RowCount property is set to 0 and the PredefinedValues property contains a predefined list values for the dropdown. However, if you do not know the values before run time it is necessary to implement a custom Property Editor.

Since you are going to use a control supplied by DevExpress, implement a custom Property Editor by overriding the DXPropertyEditor class methods. You can inherit this class directly, or inherit one of its descendants (e.g., StringPropertyEditor). Note that your editor should be public. So, the following methods must be overridden.

1. Override the CreateControlCore method to return the ComboBoxEdit control.
2. Override the CreateRepositoryItem method to return RepositoryItemComboBox type item, because it is the appropriate type for the ComboBoxEdit control.
3. Override the SetupRepositoryItem method to populate the control’s dropdown list with items. We use the CultureInfo.GetCultures method to retrieve the cultures installed.

To specify that the implemented Property Editor can be used for the String type properties, the PropertyEditor attribute is applied:

C#

using System;
using System.Globalization;

using DevExpress.ExpressApp;
using DevExpress.ExpressApp.Editors;
using DevExpress.ExpressApp.Win.Editors;
using DevExpress.XtraEditors;
using DevExpress.XtraEditors.Controls;
using DevExpress.XtraEditors.Repository;
using DevExpress.ExpressApp.Model;
//...
[PropertyEditor(typeof(String), "CultureInfoPropertyEditor", false)]
public class CustomStringEditor : StringPropertyEditor {
    public CustomStringEditor(Type objectType, IModelMemberViewItem info)
        : base(objectType, info) {
    }
    protected override object CreateControlCore() {
        return new ComboBoxEdit();
    }
    protected override RepositoryItem CreateRepositoryItem() {
        return new RepositoryItemComboBox();
    }
    protected override void SetupRepositoryItem(
        DevExpress.XtraEditors.Repository.RepositoryItem item) {
        base.SetupRepositoryItem(item);
        foreach (CultureInfo culture in CultureInfo.GetCultures(
            CultureTypes.InstalledWin32Cultures)) {
            ((RepositoryItemComboBox)item).Items.Add(
                culture.EnglishName + "(" + culture.Name + ")");
        }
        ((RepositoryItemComboBox)item).TextEditStyle = TextEditStyles.DisableTextEditor;
    }
}

VB.NET

Imports System
Imports System.Globalization

Imports DevExpress.ExpressApp
Imports DevExpress.ExpressApp.Editors
Imports DevExpress.ExpressApp.Win.Editors
Imports DevExpress.XtraEditors
Imports DevExpress.XtraEditors.Controls
Imports DevExpress.XtraEditors.Repository
Imports DevExpress.ExpressApp.Model
'...
<PropertyEditor(GetType(String), "CultureInfoPropertyEditor", False)> _
Public Class CustomStringEditor
    Inherits StringPropertyEditor
    Public Sub New(ByVal objectType As Type, ByVal info As IModelMemberViewItem)
        MyBase.New(objectType, info)
    End Sub
    Protected Overrides Function CreateControlCore() As Object
        Return New ComboBoxEdit()
    End Function
    Protected Overrides Function CreateRepositoryItem() As RepositoryItem
        Return New RepositoryItemComboBox()
    End Function
    Protected Overrides Sub SetupRepositoryItem( _
    ByVal item As DevExpress.XtraEditors.Repository.RepositoryItem)
        MyBase.SetupRepositoryItem(item)
        For Each culture As CultureInfo In CultureInfo.GetCultures( _
        CultureTypes.InstalledWin32Cultures)
            CType(item, RepositoryItemComboBox).Items.Add( _
            culture.EnglishName & "(" & culture.Name & ")")
        Next culture
        CType(item, RepositoryItemComboBox).TextEditStyle = TextEditStyles.DisableTextEditor
    End Sub
End Class

Apply the EditorAliasAttribute attribute to use the implemented Property Editor for a business object’s CultureCode property:

C#

using DevExpress.ExpressApp.Model;
//...
[EditorAlias("CultureInfoPropertyEditor")]
public String CultureCode {
   get { return GetPropertyValue<String>(nameof(CultureCode)); }
   set { SetPropertyValue(nameof(CultureCode), value); }
}

VB.NET

Imports DevExpress.ExpressApp.Model
'...
<EditorAlias("CultureInfoPropertyEditor")> _
Public Property CultureCode() As String
   Get
      Return GetPropertyValue(Of String)(NameOf(CultureCode))
   End Get
   Set(ByVal value As String)
      SetPropertyValue(NameOf(CultureCode), value)
   End Set
End Property

Here, the EditorAlias attribute changes the PropertyEditorType property of the Application Model’s IModelMember node, that defines the CultureCode property. Alternatively, you can do it via the Model Editor.

You can also implement IComplexViewItem in this Property Editor. This interface allows the editor to access the XafApplication instance and use an Object Space to load data from an application database.

Note

You can see the code demonstrated here along with more examples on custom property editors in the Feature Center Demo installed with XAF.