Single Instance using Mutex in NET

问题

How to make vb Form a single instance use Mutex. For the developers!

Hi, I searched in the net how to make a single instance startup form in VB Net not in c# code. Here is my solution:

1. In the project select "Add class..."
2. Rename the new class in "NativeMethods.vb" and put this code:

Add this reference: Imports System.Runtime.InteropServices

    Public Const HWND_BROADCAST As Integer = &HFFFF
        Public Shared ReadOnly WM_SHOWME As Integer = RegisterWindowMessage("WM_SHOWME")
        <DllImport("user32")>
        Public Shared Function PostMessage(ByVal hwnd As IntPtr, ByVal msg As Integer, ByVal wparam As IntPtr, ByVal lparam As IntPtr) As Boolean
        End Function
        <DllImport("user32")>
        Public Shared Function RegisterWindowMessage(ByVal message As String) As Integer
End Function

3. In the project select "Add class..."
4. Rename the new class in "main.vb" and put this code:

Add this reference: Imports System.Threading

Public Sub Main()
        Dim Mutex As Mutex = New Mutex(True, "{8F6F0AC4-B9A1-45fd-A8CF-72F04E6BDE8F}")
        If Mutex.WaitOne(TimeSpan.Zero, True) Then
            Application.EnableVisualStyles()
            Application.SetCompatibleTextRenderingDefault(False)
            Application.Run(New Form1())
            Mutex.ReleaseMutex()
        Else
            MessageBox.Show("Another instance of this Application is already running.", "Attention Requested", MessageBoxButtons.OK, MessageBoxIcon.Exclamation)
            NativeMethods.PostMessage(CType(NativeMethods.HWND_BROADCAST, IntPtr), NativeMethods.WM_SHOWME, IntPtr.Zero, IntPtr.Zero)
        End If
    End Sub

5. On the Form1 enter the following lines:

    Private Const SW_HIDE As Integer = 0
    Private Const SW_SHOWNORMAL As Integer = 1
    Private Const SW_SHOWMINIMIZED As Integer = 2
    Private Const SW_SHOWMAXIMIZED As Integer = 3
    Private Const SW_SHOWNOACTIVATE As Integer = 4
    Private Const SW_RESTORE As Integer = 9
    Private Const SW_SHOWDEFAULT As Integer = 10

    Protected Overrides Sub WndProc(ByRef m As Message)
            Const WM_SYSCOMMAND As Integer = &H112
            Const SC_RESTORE As Integer = &HF120
            Const SC_MINIMIZE As Integer = &HF020
            If m.Msg = NativeMethods.WM_SHOWME Then
                ShowMe()
            End If
            If m.Msg = WM_SYSCOMMAND AndAlso CInt(m.WParam) = SC_RESTORE Then
            End If
            If m.Msg = WM_SYSCOMMAND AndAlso CInt(m.WParam) = SC_MINIMIZE Then
            End If
            MyBase.WndProc(m)
        End Sub

    Private Sub ShowMe()
            If WindowState = FormWindowState.Minimized Then
                WindowState = FormWindowState.Normal
            End If
            Show()
            Dim top As Boolean = TopMost
            TopMost = True
            TopMost = top
            'Here you can call your own function. For example if your application uses the command line!
        End Sub

6. In the project select "Properties project name..."
7. Remove the check mark on: "Enable Application FrameWork"
8. In the start object select: "Sub Main"
9. Save the project, create the solution and start it

This solution works very well and has been tested on Windows 7/8.1 and 10 32/64 Bit. If anyone finds a better solution, please post it. Thanks and Best Regards.

回答1:

In the WinForms project properties, why not just check the Make single instance application?

来源：https://stackoverflow.com/questions/57116228/single-instance-using-mutex-in-net