使用更安全的方法去子类化控件

在很长一段时间内，我们都习惯使用SetWindowLong去子类化控件，但是这种方法存在很多缺点，具体可以看MSDN文档的介绍。

这是列举出的四个缺点：

• 窗口过程只能更换一次。
• 创建子类后很难删除它。
• 将私有数据与窗口相关联是低效的。
• 要调用子类链中的下一个过程，不能转换旧窗口过程并调用它，必须使用CallWindowProc函数调用它。

所以现在我们需要使用SetWindowSubClass函数去子类化控件。

如何使用呢？ 

// Test_SetWindowSubclass.cpp : Defines the entry point for the application.
//

#include "stdafx.h"
#include "Test_SetWindowSubclass.h"
#include <commctrl.h>
#pragma comment(lib,"Comctl32.lib")

#define MAX_LOADSTRING 100
#define IDC_OWNERDRAWBUTTON 101

// Global Variables:
HINSTANCE hInst;                                // current instance
WCHAR szTitle[MAX_LOADSTRING];                  // The title bar text
WCHAR szWindowClass[MAX_LOADSTRING];            // the main window class name
HWND hWndStatic;
// Forward declarations of functions included in this code module:
ATOM                MyRegisterClass(HINSTANCE hInstance);
BOOL                InitInstance(HINSTANCE, int);
LRESULT CALLBACK    WndProc(HWND, UINT, WPARAM, LPARAM);
INT_PTR CALLBACK    About(HWND, UINT, WPARAM, LPARAM);
LRESULT CALLBACK OwnerDrawButtonProc(HWND hWnd, UINT uMsg, WPARAM wParam,
	LPARAM lParam, UINT_PTR uIdSubclass, DWORD_PTR dwRefData);

int APIENTRY wWinMain(_In_ HINSTANCE hInstance,
                     _In_opt_ HINSTANCE hPrevInstance,
                     _In_ LPWSTR    lpCmdLine,
                     _In_ int       nCmdShow)
{
    UNREFERENCED_PARAMETER(hPrevInstance);
    UNREFERENCED_PARAMETER(lpCmdLine);

    // TODO: Place code here.

    // Initialize global strings
    LoadStringW(hInstance, IDS_APP_TITLE, szTitle, MAX_LOADSTRING);
    LoadStringW(hInstance, IDC_TESTSETWINDOWSUBCLASS, szWindowClass, MAX_LOADSTRING);
    MyRegisterClass(hInstance);

    // Perform application initialization:
    if (!InitInstance (hInstance, nCmdShow))
    {
        return FALSE;
    }

    HACCEL hAccelTable = LoadAccelerators(hInstance, MAKEINTRESOURCE(IDC_TESTSETWINDOWSUBCLASS));

    MSG msg;

    // Main message loop:
    while (GetMessage(&msg, nullptr, 0, 0))
    {
        if (!TranslateAccelerator(msg.hwnd, hAccelTable, &msg))
        {
            TranslateMessage(&msg);
            DispatchMessage(&msg);
        }
    }

    return (int) msg.wParam;
}



//
//  FUNCTION: MyRegisterClass()
//
//  PURPOSE: Registers the window class.
//
ATOM MyRegisterClass(HINSTANCE hInstance)
{
    WNDCLASSEXW wcex;

    wcex.cbSize = sizeof(WNDCLASSEX);

    wcex.style          = CS_HREDRAW | CS_VREDRAW;
    wcex.lpfnWndProc    = WndProc;
    wcex.cbClsExtra     = 0;
    wcex.cbWndExtra     = 0;
    wcex.hInstance      = hInstance;
    wcex.hIcon          = LoadIcon(hInstance, MAKEINTRESOURCE(IDI_TESTSETWINDOWSUBCLASS));
    wcex.hCursor        = LoadCursor(nullptr, IDC_ARROW);
    wcex.hbrBackground  = (HBRUSH)(COLOR_WINDOW+1);
    wcex.lpszMenuName   = MAKEINTRESOURCEW(IDC_TESTSETWINDOWSUBCLASS);
    wcex.lpszClassName  = szWindowClass;
    wcex.hIconSm        = LoadIcon(wcex.hInstance, MAKEINTRESOURCE(IDI_SMALL));

    return RegisterClassExW(&wcex);
}

//
//   FUNCTION: InitInstance(HINSTANCE, int)
//
//   PURPOSE: Saves instance handle and creates main window
//
//   COMMENTS:
//
//        In this function, we save the instance handle in a global variable and
//        create and display the main program window.
//
BOOL InitInstance(HINSTANCE hInstance, int nCmdShow)
{
   hInst = hInstance; // Store instance handle in our global variable

   HWND hWnd = CreateWindowW(szWindowClass, szTitle, WS_OVERLAPPEDWINDOW,
      CW_USEDEFAULT, 0, CW_USEDEFAULT, 0, nullptr, nullptr, hInstance, nullptr);
  
 //  hWndStatic = CreateDialog(hInst, MAKEINTRESOURCE(IDC_OWNERDRAWBUTTON), hWnd, DialogProc);


   if (!hWnd)
   {
      return FALSE;
   }

   ShowWindow(hWnd, nCmdShow);
   UpdateWindow(hWnd);

   return TRUE;
}

//
//  FUNCTION: WndProc(HWND, UINT, WPARAM, LPARAM)
//
//  PURPOSE: Processes messages for the main window.
//
//  WM_COMMAND  - process the application menu
//  WM_PAINT    - Paint the main window
//  WM_DESTROY  - post a quit message and return
//
//
LRESULT CALLBACK WndProc(HWND hWnd, UINT message, WPARAM wParam, LPARAM lParam)
{
    switch (message)
    {
	case WM_CREATE:
	   {
		   hWndStatic = CreateWindowEx(0, L"Static", NULL, WS_CHILD | WS_VISIBLE | SS_LEFT, 10, 130, 200, 40, hWnd, (HMENU)IDC_OWNERDRAWBUTTON, hInst, NULL);
		   BOOL X = SetWindowSubclass(hWndStatic, &OwnerDrawButtonProc, IDC_OWNERDRAWBUTTON, 0);
		return TRUE;
	}
	break;
    case WM_COMMAND:
        {
            int wmId = LOWORD(wParam);
            // Parse the menu selections:
            switch (wmId)
            {
            case IDM_ABOUT:
                DialogBox(hInst, MAKEINTRESOURCE(IDD_ABOUTBOX), hWnd, About);
                break;
            case IDM_EXIT:
                DestroyWindow(hWnd);
                break;
            default:
                return DefWindowProc(hWnd, message, wParam, lParam);
            }
        }
        break;
	
    case WM_PAINT:
        {
            PAINTSTRUCT ps;
            HDC hdc = BeginPaint(hWnd, &ps);
            // TODO: Add any drawing code that uses hdc here...
            EndPaint(hWnd, &ps);
        }
        break;
    case WM_DESTROY:
        PostQuitMessage(0);
        break;
    default:
        return DefWindowProc(hWnd, message, wParam, lParam);
    }
    return 0;
}

// Message handler for about box.
INT_PTR CALLBACK About(HWND hDlg, UINT message, WPARAM wParam, LPARAM lParam)
{
    UNREFERENCED_PARAMETER(lParam);
    switch (message)
    {
    case WM_INITDIALOG:
        return (INT_PTR)TRUE;

    case WM_COMMAND:
        if (LOWORD(wParam) == IDOK || LOWORD(wParam) == IDCANCEL)
        {
            EndDialog(hDlg, LOWORD(wParam));
            return (INT_PTR)TRUE;
        }
        break;
    }
    return (INT_PTR)FALSE;
}

TCHAR szText[] = _T("TestString");
LRESULT CALLBACK OwnerDrawButtonProc(HWND hWnd, UINT uMsg, WPARAM wParam,
	LPARAM lParam, UINT_PTR uIdSubclass, DWORD_PTR dwRefData)
{
	switch (uMsg)
	{
	case WM_PAINT:
	{
		RECT rc;
		PAINTSTRUCT ps;
		HDC hdc = BeginPaint(hWnd, &ps);
		GetClientRect(hWnd, &rc);
		SetBkMode(hdc, TRANSPARENT);
		DrawText(hdc, szText, _tcslen(szText), &rc, DT_CENTER | DT_VCENTER);
		EndPaint(hWnd, &ps);
		return 0;
	}
	case WM_NCDESTROY:
		RemoveWindowSubclass(hWnd, &OwnerDrawButtonProc, 1);
		break;
	}
	return DefSubclassProc(hWnd, uMsg, wParam, lParam);
}

我先将完整使用的代码附上，再说几个需要注意的地方。

第一，在创建子控件的时候，最好在WM_CREATE事件里面创建，并且在创建完后要紧跟SetWindowSubClass函数

第二，在创建子控件的回调函数时，要注意函数的各项参数，不要漏了。

第三，在WM_NCDESTROY事件中添加RemoveWindowSubClass函数，这个函数是删除子类回调。

第四，我在摸索WM_INITDIALOG事件时，发现只有使用CreateDialog函数创建对话框才能触发这个事件，其余的创建控件的普通函数只能触发通用的WM_CREATE事件。