Why is this an issue?

Most checks against an IndexOf value compare it with -1 because 0 is a valid index.

strings.IndexOf(someString) = -1  ' Test for "index not found"
strings.IndexOf(someString) < 0   ' Test for "index not found"
strings.IndexOf(someString) >= 0  ' Test for "index found"

Any checks which look for values > 0 ignore the first element, which is likely a bug. If the intent is merely to check the inclusion of a value in a String, List, or array, consider using the Contains method instead.

strings.Contains(someString) ' Boolean result

This rule raises an issue when the output value of any of the following methods is tested against > 0:

someArray.IndexOf(someItem) > 0        ' Noncompliant: index 0 missing
someString.IndexOfAny(charsArray) > 0  ' Noncompliant: index 0 missing
someList.LastIndexOf(someItem) > 0     ' Noncompliant: index 0 missing
someString.LastIndexOf(charsArray) > 0 ' Noncompliant: index 0 missing

How to fix it

Code examples

Noncompliant code example

Dim Color As String = "blue"
Dim Name As String = "ishmael"

Dim Strings As New List(Of String)
Strings.Add(Color)
Strings.Add(Name)
Dim StringArray As String() = Strings.ToArray()

If Strings.IndexOf(Color) > 0 Then ' Noncompliant
  ' ...
End If

If Name.IndexOf("ish") > 0 Then ' Noncompliant
  ' ...
End If

If Name.IndexOf("ae") > 0 Then ' Noncompliant
  ' ...
End If

If Array.IndexOf(StringArray, Color) > 0 Then ' Noncompliant
  ' ...
End If

Compliant solution

Dim Color As String = "blue"
Dim Name As String = "ishmael"

Dim Strings As New List(Of String)
Strings.Add(Color)
Strings.Add(Name)
Dim StringArray As String() = Strings.ToArray()

If Strings.IndexOf(Color) > -1 Then
  ' ...
End If

If Name.IndexOf("ish") >= 0 Then
  ' ...
End If

If Name.Contains("ae") Then
  ' ...
End If

If Array.IndexOf(StringArray, Color) >= 0 Then
  ' ...
End If

Resources

Documentation