Dim index As Integer = 0
Dim i As Integer = 0
Dim isUpdating As Boolean

Private Sub Form1_Load(sender As Object, e As EventArgs) Handles MyBase.Load
　　isUpdating = True
　　C1DockingTab1.CanMoveTabs = True
　　C1DockingTab1.SelectedIndex = 0
　　Timer1.Interval = 300
　　isUpdating = False
End Sub

Private Sub C1DockingTab1_SelectedIndexChanging(sender As Object, e As C1.Win.C1Command.SelectedIndexChangingEventArgs) Handles C1DockingTab1.SelectedIndexChanging
　　If isUpdating = False Then
　　　　Console.WriteLine(e.NewIndex)
　　　　index = e.NewIndex
　　　　Timer1.Start()
　　End If
End Sub

Private Sub Timer1_Tick(sender As Object, e As EventArgs) Handles Timer1.Tick
　　Timer1.Stop()
　　isUpdating = True
　　Dim tabPage As C1DockingTabPage = New C1DockingTabPage()
　　tabPage.Text = "test" + i.ToString
　　i = i + 1
　　C1DockingTab1.TabPages.Insert((index + 1), tabPage)
　　C1DockingTab1.SelectedIndex = index
　　C1DockingTab1.ScrollToSelectedTab()
　　isUpdating = False
End Sub

int index = 0;
int i = 0;
bool isUpdating = false;

public Form1()
{
　　InitializeComponent();
　　c1DockingTab1.CanMoveTabs = true;
　　c1DockingTab1.SelectedIndex = 0;
　　timer.Interval = 300;
}

private void C1DockingTab1_SelectedIndexChanging(object sender, C1.Win.C1Command.SelectedIndexChangingEventArgs e)
{
　　if (!isUpdating)
　　{
　　　　Console.WriteLine(e.NewIndex);
　　　　index = e.NewIndex;
　　　　timer.Start();
　　}
}

private void Timer_Tick(object sender, EventArgs e)
{
　　timer.Stop();
　　isUpdating = true;
　　C1DockingTabPage tabPage = new C1DockingTabPage();
　　tabPage.Text = $"test{(i++)}";
　　c1DockingTab1.TabPages.Insert(index + 1, tabPage);
　　c1DockingTab1.SelectedIndex = index;
　　c1DockingTab1.ScrollToSelectedTab();
　　isUpdating = false;
}