Question

I want to replace a regular link with a hyperlink in my RichTextBox, all of the information is given to me via a outside library (LinkEntity). But I don’t know how to actually go about replacing the text.

I have this, but it does not work right, sometimes it throws a value cannot be null exception, and sometimes it just replaces the wrong part of the link.

        Dim Start As TextPointer = TweetText.Document.ContentStart
        Dim StartPos As TextPointer = Start.GetPositionAtOffset(LinkEntity.StartIndex)
        Dim EndPos As TextPointer = Start.GetPositionAtOffset(LinkEntity.EndIndex)
        Dim h As New Hyperlink(StartPos, EndPos)
        AddHandler h.MouseLeftButtonDown, AddressOf Hyperclick_Link
        h.NavigateUri = New Uri(LinkEntity.Url)
        h.Cursor = Cursors.Hand

The exception throws because StartPos and EndPos are nothing, even though the Start and End index have a valid value.

Answer 1

I found the problem, TweetText.Document did not have a value when I was calling it when declaring the StartPos and EndPos. My Final code looks like:

Dim FlowDocument As New FlowDocument
Dim Paragraph As New Paragraph
Paragraph.Inlines.Add(myfireactions.FormatTweet(Tweet))
FlowDocument.Blocks.Add(Paragraph)

Dim Start As TextPointer = FlowDocument.ContentStart
Dim StartPos As TextPointer = Start.GetPositionAtOffset(LinkEntity.StartIndex + 2)
Dim EndIndexInt As Integer = LinkEntity.StartIndex + LinkEntity.DisplayUrl.Length + 2
Dim EndPos As TextPointer = Start.GetPositionAtOffset(EndIndexInt, LogicalDirection.Backward)
Dim h As New Hyperlink(StartPos, EndPos)
AddHandler h.MouseLeftButtonDown, AddressOf Hyperclick_Link
h.NavigateUri = New Uri(LinkEntity.Url)
h.Cursor = Cursors.Hand

TweetText.Document = FlowDocument