（仅供参考）
Option Explicit
Private Declare Function ShowWindow Lib "user32" (ByVal hwnd As Long, ByVal nCmdShow As Long) As Long
Private Declare Function FindWindow Lib "user32" Alias "FindWindowA" (ByVal lpClassName As String, ByVal lpWindowName As String) As Long
Private Declare Function IsIconic Lib "user32" (ByVal hwnd As Long) As Long
Private Declare Function SetForegroundWindow Lib "user32" (ByVal hwnd As Long) As Long
Const SW_RESTORE = 9
Private Const OPEN_APPLICATION = 0
Private Const SINGLE_INSTANCE_OPEN = 1
Sub Main()
Dim MultiInstResult As Integer
MultiInstResult = MultiInst
If MultiInstResult = OPEN_APPLICATION Then
Form1.Show
ElseIf MultiInstResult = SINGLE_INSTANCE_OPEN Then
End
End If
End Sub
Private Function MultiInst() As Integer
Dim hwndFound As Long
Dim strWindowName
strWindowName = App.Title
App.Title = "temp title"
hwndFound = FindWindow(vbNullString, strWindowName)
If hwndFound Then
MultiInst = SINGLE_INSTANCE_OPEN
MsgBox "A instance of the application is already open." & vbCrLf & vbCrLf & "Only one open instance allowed.", vbOKOnly + vbExclamation, "App Name"
If IsIconic(hwndFound) Then
ShowWindow hwndFound, SW_RESTORE
SetForegroundWindow hwndFound
Else
SetForegroundWindow hwndFound
End If
ElseIf hwndFound = 0 Then
App.Title = strWindowName
MultiInst = OPEN_APPLICATION
End If
End Function