Issue with System.Array.FindAll ()

Question

Did vb6 years ago. Trying to upgrade brain to VB.NET

Private Sub BtnFindAll_Click(sender As Object, e As EventArgs) Handles BtnFindAll.Click

    Dim AutosArray() As String = {"Chrysler", "Corvette", "Lincoln", "Buick", "Ford", "Fiat", "Chevrolet", "Mercury"}
    Dim BooBee() As String

    ' The below line gets the error...
    BooBee = System.Array.FindAll(AutosArray, AddressOf MatchFunction)

    ' The below line gets the same error...
    'Dim BooBee() As String = Array.FindAll(AutosArray, AddressOf MatchFunction)

End Sub

Private Function MatchFunction(ByVal strAuto As String) As String
    If strAuto.IndexOf("c") > 1 Then
        Return strAuto
    End If
End Function

When I click on BtnFindAll I get the below error message:

Exception Unhandled System.InvalidCastException: 'Conversion from string "" to type 'Boolean' is not valid.'

Inner Exception FormatException: Input string was not in a correct format.

Steve · Accepted Answer · 2019-09-29 21:24:43Z

1

The MatchFunction should return a boolean to be compatible with the FindAll method

Something like this

Private Function MatchFunction(ByVal strAuto As String) As Boolean
    If strAuto.IndexOf("c") > 1 Then
        Return True
    Else
        Return False
    End If
End Function

You can read this point in the Remarks section of the FindAll documentation

Consider also that now there is another option to extract that information with a single line using Linq

BooBee = AutosArray.Where(Function(x) x.IndexOf("c") > 1).ToArray()

edited Sep 29, 2019 at 21:24

answered Sep 29, 2019 at 21:17

Steve

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