[just.coder]

كود :

Dim s As String = "0"
        For i As Integer = 0 To ListBox1.Items.Count - 1
            If ListBox1.Items.Item(i) = OpenFileDialog1.FileName Then
                s = "1"
            End If
        Next
        If s = "0" Then
            ListBox1.Items.Add(OpenFileDialog1.FileName)
        Else
            MsgBox(OpenFileDialog1.FileName & "موجود مسبقا لايمكن اضفاتو", MsgBoxStyle.Critical)
        End If