Check if a list of strings contains a value

Question

I have:

Public lsAuthors As List(Of String)

I want to add values to this list, but before adding I need to check if the exact value is alre

Answer 1

The generic List has a method called Contains that returns true if the default comparer for the choosen type finds an element matching the searching criteria.

For a List(Of String) this is the normal string comparison, so your code could be

Dim newAuthor = "Edgar Allan Poe"
if Not lsAuthors.Contains(newAuthor) Then
    lsAuthors.Add(newAuthor)
End If 

As a side note, the default comparison for strings considers two strings different if they don't have the same case. So if your try to add an author named "edgar allan poe" and you already have added one with the name "Edgar Allan Poe" the barebone Contains fails to notice that they are the same.
If you have to manage this situation then you need

....
if Not lsAuthors.Contains(newAuthor, StringComparer.CurrentCultureIgnoreCase) Then
    .....