Imports Microsoft.Office.Interop.Excel
Public Class Form1
    Dim MiaApp As Application
    Dim WithEvents fileXl As Workbook
    Dim foglio As Worksheet

    Private Sub Button1_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles Button1.Click
        Me.Visible = False
        MiaApp = New Application
        MiaApp.Visible = True
        fileXl = MiaApp.Workbooks.Add
        foglio = fileXl.Worksheets.Add
    End Sub

    Private Sub fileXl_BeforeClose(ByRef Cancel As Boolean) Handles fileXl.BeforeClose
        Control.CheckForIllegalCrossThreadCalls = False
        MiaApp.Quit()
        Me.Visible = True
        Me.Focus()
        Control.CheckForIllegalCrossThreadCalls = True
    End Sub
End Class