Search items in listview in vb.net

Public Class Form1


    Public output As New List(Of Class1)
    Private Sub Form1_Load(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles MyBase.Load
        Dim index As Integer
        Dim row1 As String() = {"978945251.pdf.ssdswew", "37Mb", "3/7/2013", "ssdswew"}
        Dim row2 As String() = {"978945251.pdf.ssdsdsddew", "37Mb", "3/7/2013", "ssdsdsddew"}
        Dim row3 As String() = {"978945270.pdf.ssdswew", "37Mb", "3/7/2013", "ssdswew"}
        Dim row4 As String() = {"978945251.pdf.ssdghhsdde", "37Mb", "3/7/2013", "ssdsdghgfhsddew"}
        Dim lst As ListViewItem
        lst = New ListViewItem(row1)
        ListView1.Items.Add(lst)
        lst = New ListViewItem(row2)
        ListView1.Items.Add(lst)
        lst = New ListViewItem(row3)
        ListView1.Items.Add(lst)
        lst = New ListViewItem(row4)
        ListView1.Items.Add(lst)
    End Sub

    Private Sub Button1_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles Button1.Click
        Dim temp As String = String.Empty
        For Each lv As ListViewItem In ListView1.Items
            temp = lv.SubItems(3).Text
            If (Isfound(temp) = False) Then
                output.Add(AdddistinctRow(lv))
            End If
        Next
    End Sub

    Public Function Isfound(ByVal val As String) As Boolean
        Dim flag As Boolean = False
        Dim index As Integer = 0
       
            For index = 0 To output.Count - 1
            If (output(index).Format.Equals(val) = True) Then
                flag = True
            End If
        Next
        Return flag
    End Function

    Public Function AdddistinctRow(ByVal lst As ListViewItem) As Class1
        Dim obj As New Class1
        obj.Name = lst.SubItems(0).Text
        obj.Size = lst.SubItems(1).Text
        obj.Dates = lst.SubItems(2).Text
        obj.Format = lst.SubItems(3).Text
        Return obj
    End Function
End Class

Public Class Class1
    Private _name As String
    Public Property Name() As String
        Set(ByVal value As String)
            _name = value
        End Set
        Get
            Return _name
        End Get
    End Property

    Private _Size As String
    Public Property Size() As String
        Get
            Return _Size
        End Get
        Set(ByVal value As String)
            _Size = value
        End Set
    End Property

    Private _Date As DateTime
    Public Property Dates() As DateTime
        Get
            Return _Date
        End Get
        Set(ByVal value As DateTime)
            _Date = value
        End Set
    End Property
    Private _Format As String
    Public Property Format() As String
        Get
            Return _Format
        End Get
        Set(ByVal value As String)
            _Format = value
        End Set
    End Property
End Class