List.Contains

[NinjaNic]

Hello everyone!

If I have a list and want to search to see if it has a specific item in it, I use List.contains. However I found out that one cannot search for a custom made object. Why is this so? How can I fix it?

Thanks all,

~Nic

Option Strict On
Option Explicit On
 
Public Class Form1
 
    Dim List1 As New List(Of ComplexObject)
 
    Private Sub ButtonAdd_Click(sender As Object, e As EventArgs) Handles ButtonAdd.Click
 
        With List1
 
            .Add(New ComplexObject(New Point(5, 5), 10, "string1"))
            .Add(New ComplexObject(New Point(6, 10), 20, "string2"))
            .Add(New ComplexObject(New Point(8, 15), 30, "string3"))
            .Add(New ComplexObject(New Point(10, 20), 40, "string4"))
 
        End With
 
        MsgBox(List1.Count & " items on list.")
 
    End Sub
 
    Private Sub ButtonCheck_Click(sender As Object, e As EventArgs) Handles ButtonCheck.Click
 
        Dim N As New ComplexObject(New Point(8, 15), 30, "string3")
 
        If List1.Contains(N) Then
            MsgBox("Yes")
        Else
            MsgBox("No")
        End If
 
    End Sub
 
    Private Sub ButtonRemove_Click(sender As Object, e As EventArgs) Handles ButtonRemove.Click
 
        List1.Clear()
 
        MsgBox(List1.Count & " items on list.")
 
    End Sub
 
End Class
 
Public Class ComplexObject
 
    Dim P As Point
    Dim N As Int32
    Dim S As String
 
    Public Sub New(P_New As Point, N_New As Int32, S_New As String)
 
        P = P_New
        N = N_New
        S = S_New
 
    End Sub
 
End Class

[IanRyder]

Hi,

You need to override the Equals Method to test for the equality of a complex object. Have a look at the Find Method below which demonstrates how to do this:-

List(Of T).Find Method (Predicate(Of T))

Hope that helps.

Cheers,

Ian