VB.NET问题：怎么让For...Next...循环加速？

Question

我设计了一个程序，在RichTextBox的TextChanged事件，通过For...Next...枚举每个字符，将其中的尖括号（<>）、双引号（""）中的文字换成不同的颜色。
这是我的代码：

Public Class FrmEdit
    Private Sub CodeTextBox_TextChanged(sender As Object, e As EventArgs) Handles CodeTextBox.TextChanged
        If CodeTextBox.Text = "" Then Exit Sub
        CodeTextBox.ForeColor = Color.Black
        CodeTextBox.SelectAll() : CodeTextBox.SelectionFont = Me.Font
        TipProgressBar.Visible = True
        TipProgressBar.Maximum = CodeTextBox.TextLength - 1
        TipProgressBar.Minimum = 0
        TipProgressBar.Value = 0

        Dim AngleBracketsOn As Boolean = False
        Dim DoubleQuotesOn As Boolean = False

        For i As Integer = 0 To CodeTextBox.TextLength - 1
            CodeTextBox.SelectionStart = i
            CodeTextBox.SelectionLength = 1

            If CodeTextBox.SelectedText = "<" Then
                AngleBracketsOn = True
                CodeTextBox.SelectionLength = CodeTextBox.TextLength - i
                CodeTextBox.SelectionColor = Color.Purple
            End If
            If CodeTextBox.SelectedText = ">" Then
                If AngleBracketsOn = True Then
                    AngleBracketsOn = False
                    CodeTextBox.SelectionStart = i + 1
                    CodeTextBox.SelectionLength = CodeTextBox.TextLength - i - 1
                    CodeTextBox.SelectionColor = Color.Black
                End If
            End If

            If CodeTextBox.SelectedText = """" Then
                If DoubleQuotesOn = False Then
                    DoubleQuotesOn = True
                    CodeTextBox.SelectionLength = CodeTextBox.TextLength - i
                    CodeTextBox.SelectionColor = Color.Blue
                Else
                    DoubleQuotesOn = False
                    CodeTextBox.SelectionStart = i + 1
                    CodeTextBox.SelectionLength = CodeTextBox.TextLength - i - 1
                    CodeTextBox.SelectionColor = Color.Black
                End If
            End If

            TipProgressBar.Value = i
        Next

        CodeTextBox.SelectionLength = 0
        CodeTextBox.SelectionStart = CodeTextBox.TextLength
        TipProgressBar.Visible = False
    End Sub
End Class

我复制了一段百度翻译网页（http://fanyi.baidu.com/#en/zh/）的源代码，卡了9分钟才完成。不知道有没有更好的办法，可以加快程序的速度？求大神帮忙！

Answer 1

For i As Integer = 0 To CodeTextBox.Text.Length - 1
    Dim char1 As Char = CodeTextBox.Text(i)
    CodeTextBox.Select(i, 1)
    Select Case char1
        Case "<"c
            CodeTextBox.SelectionColor = Color.Red
            Exit Select
        ...
        Case Else
            CodeTextBox.SelectionColor = Color.Black
            Exit Select
    End Select
Next

CodeTextBox.SelectionLength = 0
CodeTextBox.SelectionStart = CodeTextBox.TextLength