最近本人在搞个程序,一个小功能是需要在程序开始时判断是否有已存在的实例在运行,如果有就告诉那个实例去打开文件(传递个字符串过去)然后结束当前实例.功能就是自动在一个MDI窗口中打开多个文档.
最开始我设想用DDE实现,忽然发现VB2010已经舍弃DDE了,大悲
后来又想到用写文件和注册表的方法,一想效率太低,用socket在没网卡的机子上就是个悲剧,而且这个程序和网络没关系,用socket容易触发防火墙的提示
然后我又用Sendmessage函数+Windows消息+内存映射文件,终于成功了,问题是现在需要.Net4.0支持,很多学校电脑只有.Net3.5,我演示的时候会悲剧......现在求助各位,如何用Sendmessage传递个字符串参数?wParam和lParam都是数字类型的,没法传递字符串,我试过传递指针和结构,都悲剧....
这是我的程序:


Public Class Form1
    <Runtime.InteropServices.DllImport("user32.dll", CharSet:=Runtime.InteropServices.CharSet.Unicode, entrypoint:="SendMessageW")> _
    Public Shared Function SendMessage(ByVal hwnd As Integer, ByVal wMsg As Integer, ByVal wParam As IntPtr, ByVal lParam As Integer) As Integer
    End Function
    Protected Overrides Sub DefWndProc(ByRef m As System.Windows.Forms.Message)
        Select Case m.Msg
            Case &H400
                If m.WParam = 3180 Then
                    Dim s As New IO.StreamReader(IO.MemoryMappedFiles.MemoryMappedFile.CreateOrOpen("asdn.open", 1024).CreateViewStream())
                    openfile(s.ReadToEnd)
                End If
            Case Else
                MyBase.DefWndProc(m)
        End Select
    End Sub

    Sub openfile(f)
        Text = f
    End Sub
    Private Sub Form1_Load(sender As System.Object, e As System.EventArgs) Handles MyBase.Load
        If My.Application.CommandLineArgs.Count = 1 Then
            Dim Proc_List As Process() = Process.GetProcessesByName(Process.GetCurrentProcess().ProcessName)
            If Proc_List.Length > 1 Then
                For Each i As Process In Proc_List
                    If XXXX <> Process.GetCurrentProcess().Id Then
                        Dim s As New IO.StreamWriter(IO.MemoryMappedFiles.MemoryMappedFile.CreateOrOpen("asdn.open", 1024).CreateViewStream())
                        s.Write(My.Application.CommandLineArgs(0))
                        s.Flush()
                        s.Close()
                        SendMessage(i.MainWindowHandle, &H400, 3180, 0)
                    End If
                Next
                Me.Close()
            Else
                openfile(My.Application.CommandLineArgs(0))
            End If
        End If
    End Sub
End Class