Optimization - open excel file from VB.NET using interop

Question

I have a simple app, which is something like a launcher for my macro enabled excel workbook. I made it for easier distribution, to be able to check if excel installed and also to make it look and behave like a standalone application.

I am using Office Interop which, according to MS, has many performance issues. But still, have you got any idea what I could improve to perform faster?

Imports System.Threading
Imports Microsoft.Win32
Imports Microsoft.Office.Interop.Excel
Module Module1
Public Sub Main()
 On Error GoTo ErrorHandler
 Dim singleInstance As Boolean = False
 Dim mutex As New Mutex(True, My.Application.Info.AssemblyName, 
 singleInstance)
 Dim excelKey As RegistryKey = Registry.ClassesRoot.OpenSubKey("Excel.Application")
 Dim excelInstalled As Boolean = If(excelKey Is Nothing, False, True)
 If excelInstalled = True And singleInstance = True Then
 SplashForm.Show()
 Dim MyAppPath As String = My.Application.Info.DirectoryPath
 Dim ExcelFilePath As String = IO.Path.Combine(My.Computer.FileSystem.SpecialDirectories.MyDocuments, "Správce rozpisů 2019\" & "Rozpis1.xlsb")
 If Not IO.File.Exists(ExcelFilePath) Then
 Dim ExcelfileBackupPath As String = IO.Path.Combine(MyAppPath, "bundle\backup\" & "Rozpis1.xlsb")
 If IO.File.Exists(ExcelfileBackupPath) Then
 My.Computer.FileSystem.CopyFile(ExcelfileBackupPath, ExcelFilePath, True)
 Call Open(ExcelFilePath)
 Else
 SplashForm.Close()
 ErrorForm.ShowDialog()
 End
 End If
 Else
 Call Open(ExcelFilePath)
 End If
 SplashForm.Close()
 ElseIf excelInstalled = False Then
 SplashForm.Close()
 CompatibilityErrorForm.ShowDialog()
 ElseIf singleInstance = False Then
 MsgBox("Správce rozpisů je již spuštěn.", vbInformation, "Aplikace je již spuštěna")
 End If
 Exit Sub
ErrorHandler:
 MsgBox("Při spouštění Správce rozpisů došlo k chybě.", vbCritical, "Došlo k chybě")
 Resume Next
End Sub
Sub Open(openThis As String)
 Dim xls As Application = New Application With {
 .WindowState = XlWindowState.xlMaximized
 }
 Dim workbook As Workbook = xls.Workbooks.Open(openThis)
 xls.Visible = True
End Sub
End Module

Answer 1

Interop is surely enough for this purpose. To manipulate workbooks, fill in 10.000th of cells then I usually use SpreadsheetLight (http://spreadsheetlight.com/), a free, MIT licensed .NET library that works on the XML level of the Excel files and is incredibly fast compared to the Application.Excel object.

From the point of code review, I think you could dive a bit more into VB​.NET, your code still has the feeling of being VB6 or VBA. Why don't you switch to try/catch error handling for example? I assure you, you are going to like it. And as a rule of thumb, never compile any path/file names into your application, put them into app.config (especially if this is a standalone application) or into start parameters (especially if this application is called from within an enterprise database application).