Вот как вы можете это сделать (обратите внимание, что строка выбора SelectNodes была исправлена):
Dim threadLinks As IEnumerable(Of HtmlNode) = doc.DocumentNode.SelectNodes("//input")
' Use a stringbuilder to hold all of the retrieved information
Dim sbText As New System.Text.StringBuilder(5000)
If threadLinks IsNot Nothing Then
For Each link In threadLinks
' Add information about each found input on a new line
sbText.Append("Id = ").Append(link.Id)
' The class is held in an attribute, so ensure the attribute exists before using it
If link.Attributes.Contains("Class") Then
' Add the value of the class attribute to the output
sbText.Append(", Class = ").Append(link.Attributes("Class").Value)
End If
' Separate this item from the next by adding a new line
sbText.AppendLine()
Next
End If
' Finally, send the retrieved information to the textbox.
RichTextBox1.Text = sbText.ToString