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C#：Win32 Hooks（一）讓下一個彈出子窗體自動顯示在父窗體中心

編輯：C#入門知識

/* ----------------------------------------------------------
文件名稱：FormHelper.cs

using System;
using System.Runtime.InteropServices;
using System.Windows.Forms;

namespace Splash.Windows.Forms
{
    /// <summary>
    /// 窗體擴展功能：
    ///     1.子窗體自動顯示在父窗體中心位置
    /// </summary>
    public static class FormHelper
    {
        /// <summary>
        /// 子窗體自動顯示在父窗體中心位置
        /// </summary>
        /// <param name="owner">要中心化子窗體的窗體</param>
        /// <remarks>擴展方法</remarks>
        public static void CenterChild(this IWin32Window owner)
        {
            CenterChildHelper helper = new CenterChildHelper();
            helper.Run(owner);
        }

        /// <summary>
        /// 基於Hook實現子窗體自動顯示在父窗體中心位置
        /// </summary>
        private class CenterChildHelper
        {
            private const Int32 WH_CBT = 5;
            private const Int32 HCBT_ACTIVATE = 5;
            private const Int32 GWL_HINSTANCE = -6;

            private IntPtr _hhk;    // 鉤子句柄
            private IntPtr _parent; // 父窗體句柄
            private GCHandle _gch;

            public void Run(IWin32Window owner)
            {
                NativeMethods.CBTProc CenterChildHookProc = new NativeMethods.CBTProc(CenterChildCallBack);

                // 分配新的GCHandle，保護對象不被垃圾回收
                _gch = GCHandle.Alloc(CenterChildHookProc);

                _parent = owner.Handle; // 父窗體句柄

                // 注意：dwThreadId為System.Threading.Thread.CurrentThread.ManagedThreadId不起作用
                _hhk = NativeMethods.SetWindowsHookEx(WH_CBT, CenterChildHookProc, IntPtr.Zero, NativeMethods.GetCurrentThreadId());
            }

            private IntPtr CenterChildCallBack(Int32 nCode, IntPtr wParam, IntPtr lParam)
            {
                if (nCode == HCBT_ACTIVATE)
                {   // 父窗體
                    NativeMethods.RECT formRect;
                    NativeMethods.GetWindowRect(_parent, out formRect);

                    // 子窗體
                    NativeMethods.RECT messageBoxRect;
                    NativeMethods.GetWindowRect(wParam, out messageBoxRect);

                    Int32 width = messageBoxRect.right - messageBoxRect.left;       // 消息窗體寬度
                    Int32 height = messageBoxRect.bottom - messageBoxRect.top;      // 消息窗體高度
                    Int32 xPos = (formRect.left + formRect.right - width) >> 1;     // 消息窗體位於父窗體中心時左上角X坐標
                    Int32 yPos = (formRect.top + formRect.bottom - height) >> 1;    // 消息窗體位於父窗體中心時左上角Y坐標

                    // 將消息窗體移到父窗體中心
                    NativeMethods.MoveWindow(wParam, xPos, yPos, width, height, false);

                    // 卸載鉤子
                    NativeMethods.UnhookWindowsHookEx(_hhk);

                    // 釋放已分配的GCHandle
                    _gch.Free();
                }

                // 允許操作
                return IntPtr.Zero;
            }
        }

        private static class NativeMethods
        {
            [StructLayout(LayoutKind.Sequential)]
            internal struct RECT
            {
                public Int32 left;
                public Int32 top;
                public Int32 right;
                public Int32 bottom;
            }

            /// <summary>
            /// CBTProc委托聲明
            /// </summary>
            /// <param name="nCode">HCBT_ACTIVATE：系統將要激活一個窗口</param>
            /// <param name="wParam">要激活的窗口句柄</param>
            /// <param name="lParam">指向CBTACTIVATESTRUCT結構</param>
            /// <returns>
            ///     0：執行這個操作
            ///     1：阻止這個操作
            /// </returns>
            internal delegate IntPtr CBTProc(Int32 nCode, IntPtr wParam, IntPtr lParam);

            [DllImport("user32.dll", SetLastError = true)]
            internal static extern IntPtr SetWindowsHookEx(Int32 idHook, CBTProc lpfn, IntPtr hMod, Int32 dwThreadId);

            [DllImport("user32.dll")]
            [return: MarshalAs(UnmanagedType.Bool)]
            internal static extern Boolean UnhookWindowsHookEx(IntPtr hhk);

            [DllImport("user32.dll")]
            [return: MarshalAs(UnmanagedType.Bool)]
            internal static extern Boolean GetWindowRect(IntPtr hWnd, out RECT lpRect);

            [DllImport("user32.dll")]
            [return: MarshalAs(UnmanagedType.Bool)]
            internal static extern Boolean MoveWindow(IntPtr hWnd, Int32 X, Int32 Y, Int32 nWidth, Int32 nHeight, [MarshalAs(UnmanagedType.Bool)]Boolean bRepaint);

            [DllImport("kernel32.dll")]
            internal static extern Int32 GetCurrentThreadId();
        }
    }
}