创建时隐藏的表单不接收广播消息

Question

我创建了一个旨在运行单个实例的程序，其中包含一个隐藏的表单，直到收到广播消息。错误是除非在创建时显示表单，否则不会收到消息。为什么要在这个阶段展示表格？我举了一个例子。程序的第一个运行实例创建表单，其他实例向它广播消息。

using System;

using System.Runtime.InteropServices;

using System.Threading;

using System.Windows.Forms;

namespace HiddenProgram

{

public class Program : ApplicationContext

{

    [DllImport("user32")]

    static extern bool PostMessage(IntPtr hwnd, int msg, IntPtr wparam, IntPtr lparam);

    [DllImport("user32")]

    static extern int RegisterWindowMessage(string message);

    const int HWND_BROADCAST = 0xffff;

    public static readonly int WM_SHOWME = Program.RegisterWindowMessage("com.holroyd.Gateway.Show");

    public static Program Instance;

    static Mutex mutex = new Mutex(true, "{9BFB3652-CCE9-42A2-8CDE-BBC40A0F5213}");

    MyForm form;

    [STAThread]

    static void Main()

    {

        Application.EnableVisualStyles();

        Application.SetCompatibleTextRenderingDefault(false);

        if (!mutex.WaitOne(TimeSpan.Zero, true))

        {

            // Show the single instance window

            PostMessage(

                (IntPtr)HWND_BROADCAST,

                WM_SHOWME,

                IntPtr.Zero,

                IntPtr.Zero);

        }

        else

        {

            // Create the hidden window

            Instance = new Program();

            Application.Run(Instance);

            mutex.ReleaseMutex();

        }

    }

    Program()

    {

        form = new MyForm();

        form.FormClosing += form_FormClosing;

        // One of the following two seem necessary to get the broadcast message

        form.Show();

        //MainForm = form;

    }

    void form_FormClosing(object sender, FormClosingEventArgs e)

    {

        ExitThread();

    }

}

public class MyForm : Form

{

    protected override void WndProc(ref Message m)

    {

        if (m.Msg == Program.WM_SHOWME)

            Visible = !Visible;

        else

            base.WndProc(ref m);

    }

}

Answer 1

要创建一个在收到广播消息之前保持隐藏的窗体，从窗体的构造函数调用 CreateHandle()，以创建底层窗口，以便接收来自程序的其他实例的广播消息。using System;using System.Runtime.InteropServices;using System.Threading;using System.Windows.Forms;namespace HiddenProgram{public class Program : ApplicationContext{    [DllImport("user32")]    static extern bool PostMessage(IntPtr hwnd, int msg, IntPtr wparam, IntPtr lparam);    [DllImport("user32")]    static extern int RegisterWindowMessage(string message);    const int HWND_BROADCAST = 0xffff;    public static readonly int WM_SHOWME = Program.RegisterWindowMessage("com.holroyd.Gateway.Show");    static Mutex mutex = new Mutex(true, "{9BFB3652-CCE9-42A2-8CDE-BBC40A0F5213}");    MyForm form;    [STAThread]    static void Main()    {        Application.EnableVisualStyles();        Application.SetCompatibleTextRenderingDefault(false);        if (!mutex.WaitOne(TimeSpan.Zero, true))        {            // Show the single instance window            PostMessage(                (IntPtr)HWND_BROADCAST,                WM_SHOWME,                IntPtr.Zero,                IntPtr.Zero);        }        else        {            // Create the hidden window            Application.Run(new Program());            mutex.ReleaseMutex();        }    }    Program()    {        form = new MyForm();        form.FormClosing += form_FormClosing;    }    void form_FormClosing(object sender, FormClosingEventArgs e)    {        ExitThread();    }}public class MyForm : Form{    public MyForm()    {        CreateHandle();    }    protected override void WndProc(ref Message m)    {        if (m.Msg == Program.WM_SHOWME)            Visible = !Visible;        else            base.WndProc(ref m);    }}}