C# と VB.NET の質問掲示板

■No99313 (魔界の仮面弁士 さん) に返信
> 以下は VB6 のサンプルですが、参考までに。
> https://www.vbforums.com/showthread.php?866647-MessageBox-without-Red-X-close-button

.NET のサンプルが意外に見つからなかったので URL を参考にサンプルを書いてみました。
こんな感じで使います。

using (var remover = new CloseButtonRemover()) {
    MessageBox.Show("TEST");
}

以下クラスです。

using Microsoft.Win32.SafeHandles;
using System;
using System.Runtime.InteropServices;
using System.Text;
using System.Windows.Forms;

class CloseButtonRemover : SafeHandleZeroOrMinusOneIsInvalid
{
    readonly HookProcDelegate hookProcDelegate;
    readonly MessageBoxWindow messageBoxWindow = new MessageBoxWindow();

    public CloseButtonRemover() : base(true) {
        hookProcDelegate = new HookProcDelegate(HookProc);
        handle = SetWindowsHookEx(WH_CALLWNDPROC, hookProcDelegate, IntPtr.Zero, GetCurrentThreadId());
    }

    protected override bool ReleaseHandle() {
        return UnhookWindowsHookEx(handle);
    }

    private IntPtr HookProc(int code, IntPtr wp, IntPtr lp) {
        var cwp = Marshal.PtrToStructure<CWPSTRUCT>(lp);
        if (cwp.message == WM_CREATE) {
            var sb = new StringBuilder(128);
            GetClassName(cwp.hwnd, sb, sb.Capacity);
            if (sb.ToString() == "#32770") {
                messageBoxWindow.AssignHandle(cwp.hwnd);
            }
        }
        return CallNextHookEx(handle, code, wp, lp);
    }

    class MessageBoxWindow : NativeWindow
    {
        protected override void WndProc(ref Message m) {
            switch (m.Msg) {
                case WM_INITDIALOG:
                    IntPtr hMenu = GetSystemMenu(m.HWnd, false);
                    DeleteMenu(hMenu, SC_CLOSE, MF_BYCOMMAND);
                    base.WndProc(ref m);
                    break;
                default:
                    base.WndProc(ref m);
                    break;
            }
        }

        const int WM_INITDIALOG = 0x0110;
        const int MF_BYCOMMAND = 0x0000;
        const int SC_CLOSE = 0xF060;

        [DllImport("user32.dll")]
        static extern IntPtr GetSystemMenu(IntPtr hWnd, bool bRevert);
        [DllImport("user32.dll")]
        static extern bool DeleteMenu(IntPtr hMenu, int position, int flags);
    }

    const int WM_CREATE = 0x0001;
    const int WH_CALLWNDPROC = 4;

    delegate IntPtr HookProcDelegate(int code, IntPtr wParam, IntPtr lParam);
    [DllImport("user32.dll", SetLastError = true)]
    static extern IntPtr SetWindowsHookEx(int hookType, HookProcDelegate lpfn, IntPtr hMod, uint dwThreadId);
    [DllImport("kernel32.dll")]
    static extern uint GetCurrentThreadId();
    [DllImport("user32.dll")]
    static extern IntPtr CallNextHookEx(IntPtr hhk, int nCode, IntPtr wParam, IntPtr lParam);
    [DllImport("user32.dll", SetLastError = true)]
    static extern bool UnhookWindowsHookEx(IntPtr hhk);
    [DllImport("user32.dll", SetLastError = true, CharSet = CharSet.Auto)]
    static extern int GetClassName(IntPtr hWnd, StringBuilder lpClassName, int nMaxCount);
    [StructLayout(LayoutKind.Sequential)]
    private struct CWPSTRUCT
    {
        public IntPtr lparam;
        public IntPtr wparam;
        public int message;
        public IntPtr hwnd;
    }
}