How to remove vb.net Richtextbox lines that not contains specific text? - vb.net

Question

I use the next code to remove lines from Richtextboxes but that way i can only tell what line to remove. I need to remove all lines that not contains specific text, can this be done with some edits of my code?
1st piece:
Private Property lineToBeRemovedlineToBeRemoved As Integer
2nd piece:
Dim lineToBeRemoved As Integer = 0
lineToBeRemovedlineToBeRemoved = lineToBeRemoved - 0
Dim str As String = RichTextBox1.Lines(lineToBeRemoved)
RichTextBox1.Find(str & vbCr)
RichTextBox1.SelectedText = ""

Answer 1

This code will remove any line from a richtextbox RichTextbox1 that does not contain "Test" on it. Remember to add Imports System.Text.RegularExpressions to the top of your code.
Private Sub RemoveLines()
Dim lines As New List(Of String)
lines = RichTextBox1.Lines.ToList
Dim FilterText = "Test"
For i As Integer = lines.Count - 1 To 0 Step -1
If Not Regex.IsMatch(lines(i), FilterText) Then
lines.RemoveAt(i)
End If
Next
RichTextBox1.Lines = lines.ToArray
End Sub

Answer 2

You code is not close. You should start over. Use a for loop to go through the RichTextBox lines. If the text is not in a line, then delete it. Tip: It may be easier to go from the last line to the first to avoid problems when deleting.

Answer 3

Private Sub Button1_Click(sender As Object, e As EventArgs) Handles Button1.Click
RTB.Select(RTB.GetFirstCharIndexFromLine(2), RTB.Lines(2).Count)
RTB.SelectionLength = RTB.Lines(2).Length + 1
RTB.SelectedText = ""
End Sub

Answer 4

Try this code, I applied to my prog and it work good.
When use, just ... call dels("unwanted") ==> Line which contain unwanted word will disappear.
Private Sub dels(sw As String)
Dim ud As String = "" 'for keep all we need
Dim cn As Integer = 0 'for avoid empty line
For Each line As String In RichTextBox1.Lines 'for every line in reichtextbox
If Len(line) > 5 Then 'if that line got more than 5 character
If InStr(line.ToLower, sw.ToLower) < 1 Then 'transform them to lower case for better resulted
If cn = 1 Then ud = ud + vbCrLf 'not place new-line if it is first
ud = ud + line 'keep this line if not match ne want delete
cn = 1 'turn-off first line signal
End If
End If
Next
RichTextBox1.Clear() 'empty richtextbox
RichTextBox1.AppendText(ud) 'update richtextbox with the unwanted
End Sub