[Browsable(false)]
[DefaultValue(null)]
public RibbonPage SelectedPage { get; set; }

<DefaultValue(Nothing)>
<Browsable(False)>
Public Property SelectedPage As RibbonPage

using System.Drawing;
using DevExpress.XtraBars;
using DevExpress.XtraBars.Ribbon;
using DevExpress.XtraEditors;

namespace DXApplication19
{
    public partial class Form1 : XtraForm
    {
        public Form1()
        {
            InitializeComponent();
            // Create a RibbonControl.
            RibbonControl Ribbon = new RibbonControl();
            // Create the 'Home' page.
            RibbonPage pageHome = new RibbonPage("Home");
            Ribbon.Pages.Add(pageHome);
            // Create the 'Selection' page category.
            RibbonPageCategory catSelection = new RibbonPageCategory("Selection", Color.Orange, false);
            Ribbon.PageCategories.Add(catSelection);
            // Create 'Format' an 'Clipboard' contextual pages/tabs in the 'Selection' page category.
            RibbonPage contextPageFormat = new RibbonPage("Format");
            RibbonPage contextPageClipboard = new RibbonPage("Clipboard");
            catSelection.Pages.AddRange(new RibbonPage[] { contextPageFormat, contextPageClipboard });

            // Add the 'Edit' group with two bar items to the 'Format' page.
            RibbonPageGroup groupEdit = new RibbonPageGroup("Edit") { AllowTextClipping = false };
            // Add two bar items to the 'Edit' group.
            BarButtonItem itemCopy = new BarButtonItem(Ribbon.Manager, "Copy"){ RibbonStyle = RibbonItemStyles.Large};
            itemCopy.ImageOptions.SvgImage = svgImageCollection1["copy"];
            BarButtonItem itemCut = new BarButtonItem(Ribbon.Manager, "Cut") { RibbonStyle = RibbonItemStyles.Large };
            itemCut.ImageOptions.SvgImage = svgImageCollection1["cut"];
            groupEdit.ItemLinks.AddRange(new BarItem[] { itemCopy, itemCut });
            contextPageFormat.Groups.Add(groupEdit);
            Ribbon.ItemClick += new ItemClickEventHandler(Ribbon_ItemClick);

            // Add the RibbonControl to the form.
            this.Controls.Add(Ribbon);

            /* Contextual pages are hidden by default.
             * The following line displays the 'Selection' page category.
             */
            catSelection.Visible = true;
            // Activate the 'Format' contextual page/tab.
            Ribbon.SelectedPage = catSelection.Pages["Format"];
        }
        void Ribbon_ItemClick(object sender, ItemClickEventArgs e)
        {
            // Add your code to handle clicks on bar items.
        }
    }
}

Imports System.Drawing
Imports DevExpress.XtraBars
Imports DevExpress.XtraBars.Ribbon
Imports DevExpress.XtraEditors

Namespace DXApplication19
    Partial Public Class Form1
        Inherits XtraForm

        Public Sub New()
            InitializeComponent()
            ' Create a RibbonControl.
            Dim Ribbon As New RibbonControl()
            ' Create the 'Home' page.
            Dim pageHome As New RibbonPage("Home")
            Ribbon.Pages.Add(pageHome)
            ' Create the 'Selection' page category.
            Dim catSelection As New RibbonPageCategory("Selection", Color.Orange, False)
            Ribbon.PageCategories.Add(catSelection)
            ' Create 'Format' an 'Clipboard' contextual pages/tabs in the 'Selection' page category.
            Dim contextPageFormat As New RibbonPage("Format")
            Dim contextPageClipboard As New RibbonPage("Clipboard")
            catSelection.Pages.AddRange(New RibbonPage() { contextPageFormat, contextPageClipboard })

            ' Add the 'Edit' group with two bar items to the 'Format' page.
            Dim groupEdit As New RibbonPageGroup("Edit") With {.AllowTextClipping = False}
            ' Add two bar items to the 'Edit' group.
            Dim itemCopy As New BarButtonItem(Ribbon.Manager, "Copy") With {.RibbonStyle = RibbonItemStyles.Large}
            itemCopy.ImageOptions.SvgImage = svgImageCollection1("copy")
            Dim itemCut As New BarButtonItem(Ribbon.Manager, "Cut") With {.RibbonStyle = RibbonItemStyles.Large}
            itemCut.ImageOptions.SvgImage = svgImageCollection1("cut")
            groupEdit.ItemLinks.AddRange(New BarItem() { itemCopy, itemCut })
            contextPageFormat.Groups.Add(groupEdit)
            AddHandler Ribbon.ItemClick, AddressOf Ribbon_ItemClick

            ' Add the RibbonControl to the form.
            Me.Controls.Add(Ribbon)

' Contextual pages are hidden by default.
' * The following line displays the 'Selection' page category.
'             
            catSelection.Visible = True
            ' Activate the 'Format' contextual page/tab.
            Ribbon.SelectedPage = catSelection.Pages("Format")
        End Sub
        Private Sub Ribbon_ItemClick(ByVal sender As Object, ByVal e As ItemClickEventArgs)
            ' Add your code to handle clicks on bar items.
        End Sub
    End Class
End Namespace

spreadsheetControl1.LoadDocument("temperature.xlsx");
    ribbonControl1.SelectedPage = dataRibbonPage1;
}

InitializeRichEditControl();
ribbonControl.SelectedPage = homeRibbonPage1;
string path = @"DemoDoc.docx";

InitializeComponent();
ribbonControl1.SelectedPage = mailingsRibbonPage1;
richEditControl1.LoadDocument("invitation.rtf", DocumentFormat.Rtf);

InitializeComponent();
ribbonControl1.SelectedPage = formulaEngineRibbonPage1;
spreadsheetControl1.Document.DocumentSettings.R1C1ReferenceStyle = true;

void ribbonControl1_Merge(object sender, DevExpress.XtraBars.Ribbon.RibbonMergeEventArgs e) {
    ribbonControl1.SelectedPage = e.MergedChild.SelectedPage;
}

spreadsheetControl1.LoadDocument("temperature.xlsx")
    ribbonControl1.SelectedPage = dataRibbonPage1
End Sub

InitializeRichEditControl()
ribbonControl.SelectedPage = homeRibbonPage1
Dim path As String = "DemoDoc.docx"

InitializeComponent()
ribbonControl1.SelectedPage = mailingsRibbonPage1
richEditControl1.LoadDocument("invitation.rtf", DocumentFormat.Rtf)

InitializeComponent()
ribbonControl1.SelectedPage = formulaEngineRibbonPage1
spreadsheetControl1.Document.DocumentSettings.R1C1ReferenceStyle = True

Private Sub ribbonControl1_Merge(ByVal sender As Object, ByVal e As DevExpress.XtraBars.Ribbon.RibbonMergeEventArgs)
    ribbonControl1.SelectedPage = e.MergedChild.SelectedPage
End Sub