FIX: Can't Set SelStart Property of RichTextBox to

SYMPTOMS

You cannot set the SelStart property of RichTextBox controls that contain text greater than 32K (32768) characters in length to a value greater than 32767 and less than the text length. Although this is a legal range, SelStart is automatically set to the text length. Consequently, you cannot make selections within this range.

STATUS

Microsoft has confirmed this to be a bug in the Microsoft products listed at the beginning of this article. This bug has been fixed in Visual Basic 5.0.

RESOLUTION

Use the SendMessage API of USER32 with the EM_EXSETSEL parameter to set the SelStart position:

   Private Const WM_USER = &H400
   Private Const EM_EXSETSEL = (WM_USER + 55)

   Private Declare Function SendMessage Lib "USER32" Alias "SendMessageA"
   (ByVal hwnd As Long, ByVal wMsg As Long, ByVal wParam As Long, lParam As
   Long) As Long

   Private Sub Command1_Click()
   Dim x As String

       x = String(32800, "a")
       RichTextBox1.Text = x

       '''[THE NORMAL WAY] RichTextBox1.SelStart = 32790
       SendMessage RichTextBox1.hwnd, EM_EXSETSEL, 0, 32790
       RichTextBox1.SelLength = 10

       MsgBox RichTextBox1.SelText

   End Sub

MORE INFORMATION

Steps to Reproduce Problem

Start a new project in Visual Basic. Form1 is created by default.
Place a RichTextBox, RichTextBox1, on Form1.
Place a CommandButton, Command1, on Form1.

Place the following code in the Click event of Command1:

   Private Sub Command1_Click()
   Dim x As String

       x = String(32800, "a")
       RichTextBox1.Text = x

       RichTextBox1.SelStart = 32790
       RichTextBox1.SelLength = 10

       MsgBox RichTextBox1.SelText

   End Sub