.NET (Core and Framework)

steve_9496613 wrote:

but I don't know how to do this.

Bastard Programmer from Hell
If you can't read my code, try converting it here[^]

Imports System.Reflection
Imports System.Runtime.InteropServices

Public Class SingleInstanceApplication

  <DllImport("Coredll.dll", SetLastError:=True)> _
  Public Shared Function CreateMutex(ByVal Attr As IntPtr, ByVal Own As Boolean, ByVal Name As String) As IntPtr
  End Function

  <DllImport("Coredll.dll", SetLastError:=True)> _
  Public Shared Function ReleaseMutex(ByVal hMutex As IntPtr) As Boolean
  End Function

  Const ERROR_ALREADY_EXISTS As Long = 183

  Public Shared Sub Run(ByVal frm As Form)
    Dim name As String = Assembly.GetExecutingAssembly().GetName().Name
    Dim mutexHandle As IntPtr = CreateMutex(IntPtr.Zero, True, name)
    Dim Rerror As Long = Marshal.GetLastWin32Error()

    'MessageBox.Show(name & " - " & mutexHandle.ToString & " - " & Rerror.ToString)  'just for debug

    If (Not Rerror = ERROR_ALREADY_EXISTS) Then
      Application.Run(frm)
    End If

    'MessageBox.Show("release mutex")  'just for debug

    ReleaseMutex(mutexHandle)

  End Sub
End Class

Public Class StartApp
  Public Shared Sub main()
    Try
      SingleInstanceApplication.Run(FormMain)
    Catch ex As Exception
      MessageBox.Show(ex.Message)
    End Try
  End Sub
End Class