[RESOLVED] Change multiple selected fonts in richtextbox vb.net

[hackerspk]

I know theres a way to change the font size of mixed text in a RTB using API but not sure how to change the font name, anyway came up with this...

Public Class Form1
    Private Sub Form1_Load(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles MyBase.Load
        RichTextBox1.SelectionFont = New Font("Tahoma", 12.0F)
        RichTextBox1.SelectedText = "ABCD EFG HIJKL "
        RichTextBox1.SelectionFont = New Font("Courier New", 14.25F)
        RichTextBox1.SelectedText = "123 4567 890!"
    End Sub

    Private Sub Button1_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles Button1.Click
        ChangeSelTextFont(RichTextBox1, "Segoe Script")
    End Sub

    '---
    Private Const WM_SETREDRAW As Integer = &HB
    <System.Runtime.InteropServices.DllImport("user32.dll")> _
    Private Shared Function SendMessage(ByVal hWnd As IntPtr, ByVal Msg As Integer, ByVal wParam As Integer, ByVal lParam As Integer) As Integer
    End Function

    Private Sub ChangeSelTextFont(rtb As RichTextBox, fontName As String)
        ' get selected length
        Dim rtbEnd As Integer = rtb.SelectionLength
        If rtbEnd = 0 Then Return ' nothin to do
        ' selection start
        Dim rtbStart As Integer = rtb.SelectionStart
        ' lock rtb redraw
        SendMessage(rtb.Handle, WM_SETREDRAW, 0, 0)
        ' Change font of each char in select text
        rtb.SelectionLength = 1
        For i As Integer = rtbStart To rtbStart + (rtbEnd - 1)
            rtb.SelectionStart = i
            rtb.SelectionFont = New Font(fontName, rtb.SelectionFont.Size, rtb.SelectionFont.Style)
        Next
        ' reselect text
        rtb.SelectionStart = rtbStart
        rtb.SelectionLength = rtbEnd
        ' unlock/redraw
        SendMessage(rtb.Handle, WM_SETREDRAW, 1, 0)
        rtb.Invalidate()
    End Sub
End Class

Thanks for help but,
this code work great if we have a limited text in our selection. but its worthless with large selection of text like 100000 characters. I have more than 1 lack characters in my richtextbox. any correction please?