Dim file As New IO.FileInfo(saveFileDialog1.FileName)

<Serializable()>
Public Class Task
    Property Value1 As String
    Property Value2 As MemoryStream
    Property Value3 As TaskChild
    ......
End Class
<Serializable()>
Public Class TaskChild
   .......
End Class

   Private mInstance As Task
   Public Shared Sub Load()
        If IO.File.Exists("user.dat") Then
            Try
                Dim binFormat As BinaryFormatter = New BinaryFormatter
                Using fStream As New FileStream("user.dat", FileMode.Open, FileAccess.Read, FileShare.None)
                    mInstance = binFormat.Deserialize(fStream)
                End Using
            Catch ex As Exception
                MessageBox.Show(ex.Message, ex.Message, MessageBoxButton.OK, MessageBoxImage.Error)
            End Try
        End If
        If IsNothing(mInstance) Then
            mInstance = New Task
        End If
    End Sub
    Public Shared Sub Save()
        Try
            Dim binFormat As BinaryFormatter = New BinaryFormatter
            Using fStream As New FileStream("user.dat", FileMode.Create, FileAccess.Write, FileShare.None)
                binFormat.Serialize(fStream, mInstance)
            End Using
        Catch ex As Exception
            MessageBox.Show(ex.Message, "Сохранение параметров", MessageBoxButton.OK, MessageBoxImage.Error)
        End Try
    End Sub