Format Multi-Font in System.Windows.Forms.RichTextBox with FlowDocument

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VB

RichTextBox

Hi,


I want to use Richtextbox to store text with format in SQL database. I love the way System.Windows.Forms.RichTextBox handle binding RTF format but i hate the way it change multi-font format. So I use flowdocument to handle multi-font format. Below is my code

Imports System.Windows.Forms
Imports System.Windows.Documents
Imports System.IO
Imports System.Text
.......
Private Sub chkbBold_Click(sender As Object, e As EventArgs) Handles chkbBold.Click
Try
Dim SelStart As Integer = rtbOtherInfo.SelectionStart
Dim SelLength As Integer = rtbOtherInfo.SelectionLength

Dim fdTmp As FlowDocument = New FlowDocument()
Dim inStream As MemoryStream = New MemoryStream(Encoding.ASCII.GetBytes(rtbOtherInfo.SelectedRtf))
Dim outStream As New MemoryStream
Dim textRangeTmp As TextRange = New TextRange(fdTmp.ContentStart, fdTmp.ContentEnd)

textRangeTmp.Load(inStream, DataFormats.Rtf)

'Toggle chkbBold state
If chkbItalic.Checked = True Then
textRangeTmp.ApplyPropertyValue(TextElement.FontWeightProperty, Windows.FontWeights.Bold)
Else
textRangeTmp.ApplyPropertyValue(TextElement.FontWeightProperty, Windows.FontWeights.Normal)
End If
textRangeTmp.Save(outStream, DataFormats.Rtf)


rtbOtherInfo.SelectedRtf = System.Text.ASCIIEncoding.Default.GetString(outStream.ToArray())
rtbOtherInfo.SelectionStart = SelStart
rtbOtherInfo.SelectionLength = SelLength
rtbOtherInfo.Focus()

Catch ex As Exception
MsgBox(ex.Message)
End Try
End Sub

But i see some schange behavior of richtextbox:
- in some selected text in richtextbox, this code work well, but in some case, there's nothing change in richtextbox after chkbBold_Click.
- some time I can set selected text to Bold but cannot set the selected text back to normal (with the same selected text)

Please kindly help to show me what im I wrong?
Please also kindly share you ideas.

Thank you all