c++ - SetWindowSubclass 内的 msftedit.dll RichEdit 控件出现错误 "Access violation reading location 0x00000008"

Question

我在单独的子类文件中有编辑控件。在开始使用 SetWindowSubclass 函数后(我是 C++ 的新手，之前我使用 SetWindowLongPtr 进行子类化，它工作正常但有人建议我开始使用 SetWindowSubclass)，我遇到了这个问题:

编译程序后，应用程序绘制了一个空窗口，该窗口立即停止响应(我必须通过任务管理器将其关闭)。输出窗口中的结果错误:

Exception thrown at 0x635F3DEF (msftedit.dll) in TaskTracklist.exe: 0xC0000005: Access violation reading location 0x00000008.

完整代码:

#include "stdafx.h"
#include <windows.h>
#include <commctrl.h>
#include <richedit.h>
#include <string.h>
#include "SearchEditBox.h"

/*global vars*/
LPCWSTR SearchEditBox::editBoxDefText = L"Search...";
bool SearchEditBox::firstLoad = false;
int SearchEditBox::width = 0;
int SearchEditBox::height = 0;
HWND SearchEditBox::editBox;

/*functions*/
LRESULT CALLBACK EditBoxProc(HWND hwnd, UINT uMsg, WPARAM wParam, LPARAM lParam, UINT_PTR uint_ptr, DWORD dwRefData);
void ChangeEdit(const HWND hwnd, const bool change);

/*set-get functions*/
HWND SearchEditBox::getEditBox()
{
    return SearchEditBox::editBox;
}

SearchEditBox * SearchEditBox::CreateEditBox(HINSTANCE hInst, HWND hwnd, int pos_x, int pos_y, int width, int height) {
    SearchEditBox * p_SearchEditBox = new SearchEditBox;

    LoadLibrary(TEXT("Msftedit.dll")); //enables RichEdit field
    SearchEditBox::editBox = CreateWindowEx(0, (L"RICHEDIT50W"), editBoxDefText, WS_VISIBLE | WS_CHILD, pos_x + 6, pos_y + 4, width, height, hwnd, NULL, (HINSTANCE)GetWindowLong(hwnd, GWL_HINSTANCE), p_SearchEditBox);
    SearchEditBox::width = width;
    SearchEditBox::height = height;

    if (SearchEditBox::editBox == NULL)
    {
        delete p_SearchEditBox;
        MessageBox(NULL, L"Problem creating the Search box.", L"Error", 0);
        return 0;
    }

    SetWindowSubclass(SearchEditBox::editBox, SearchEditBox::EditBoxProc, 0, 0);

    return p_SearchEditBox;
}

LRESULT CALLBACK SearchEditBox::EditBoxProc(HWND hwnd, UINT uMsg, WPARAM wParam, LPARAM lParam, UINT_PTR uIdSubclass, DWORD dwRefData)
{
    PAINTSTRUCT ps;
    HDC hdc;
    switch (uMsg)
    {
        case WM_SETFOCUS:
        {
            LPWSTR getText = new TCHAR[10];
            GetWindowText(hwnd, getText, 10);
            if (_tcscmp(getText, editBoxDefText) == 0)
            {
                SearchEditBox::ChangeEdit(hwnd, 1);
            }
            delete getText;
            break;
        }
        case WM_KILLFOCUS:
        {
            LPWSTR getText = new TCHAR[10];
            if (GetWindowText(hwnd, getText, 10) == 0)
            {
                SearchEditBox::ChangeEdit(hwnd, 0);
            }
            ::SetFocus(NULL);
            delete getText;
            break;
        }
        case WM_LBUTTONDBLCLK:
            SearchEditBox::ChangeEdit(hwnd, 1);
            break;
        case WM_PAINT:
        {
            hdc = BeginPaint(hwnd, &ps);

            RECT rc;
            InvalidateRect(hwnd, &rc, 0);
            if (SearchEditBox::firstLoad == false)
            {
                SearchEditBox::ChangeEdit(hwnd, 0);
                ::SetFocus(NULL);
                SearchEditBox::firstLoad = true;
            }
            HBRUSH hBrush = CreateSolidBrush(RGB(33, 33, 33));
            SelectObject(hdc, hBrush);
            RoundRect(hdc, -6, -4, SearchEditBox::width + 7, SearchEditBox::height + 4, 5, 5);
            EndPaint(hwnd, &ps);
            break;
        }
    }
    return DefSubclassProc(hwnd, uMsg, lParam, wParam);
}

我很清楚问题出在与 SetWindowSubclass 函数联机的 RichEdit 控件上。

尽管我没有找到任何与 Msftedit.dll 相关的错误特别相关的主题，但我从这些文章(here 和 here 和 here)中了解到我可能引用了 NULL 指针，但这对我来说没有意义，因为那时我会从 SetWindowSubclass 函数上方的这一点得到错误(我不知道):

    if (SearchEditBox::editBox == NULL)
    {
        delete p_SearchEditBox;
        MessageBox(NULL, L"Problem creating the Search box.", L"Error", 0);
        return 0;
    }

我还认为问题可能出在外部函数(意思是在 comctl32 中定义的函数，而不是在类内部定义的函数)访问类特定变量(指针不会为 NULL，但它可能无法访问以某种方式添加到函数中)所以我尝试为 SetWindowSubclass 函数创建局部变量(这也不起作用):

HWND newHWND = SearchEditBox::editBox;
SetWindowSubclass(newHWND, SearchEditBox::EditBoxProc, 0, 0);

使用函数 getEditBox() 也没有解决这个问题。

我还尝试在控件声明中使用 MSFTEDIT_CLASS 而不是 (L"RICHEDIT50W")(认为问题可能出在控件本身内部)但这也无济于事，并且尝试不同的版本(例如 RICHEDIT51W 或 RICHEDIT80W)导致错误(因此我必须使用适用于 VS2015 的正确 RichEdit 版本)。

我还尝试在 CreateEditBox 中声明 HWND editBox(使其成为局部变量)，但这也无济于事。

我使用 VS 的免费社区版。

编辑:从代码中清除了我不成功尝试的一些遗留问题。

Answer 1

Exception thrown at 0x635F3DEF (msftedit.dll) in TaskTracklist.exe: 0xC0000005: Access violation reading location 0x00000008.

地址 0 附近的访问冲突通常意味着正在通过 NULL 对象指针访问类/记录数据成员。

Even though I did not find any topic related specifically to this error in connection to Msftedit.dll, I understood from these articles (...) that I may be referencing to NULL pointer, but that does not make sense to me because then I would get error from this bit just above SetWindowSubclass function (which I don't)

问题与访问 NULL HWND 句柄无关。它与访问 NULL 对象指针 有关。而且您的代码中确实有对象指针，因此您需要弄清楚哪个是 NULL。当 AccessViolation 发生时，使用调试器查看在内存地址 0x635F3DEF 处运行的代码，这应该会引导您找到代码中的哪一行崩溃。

话虽如此，EditBoxProc() 的最后一个参数需要是 DWORD_PTR 而不是 DWORD，并且您正在传递wParam 和 lParam 值到 DefSubclassProc() 的顺序错误。

此外，您的 WM_KILLFOCUS 和 WM_PAINT 处理程序不应调用 SetFocus()，并且您的 WM_PAINT 处理程序不应调用 InvalidateRect()。

我建议您重写您的 SearchEditBox 类，使其数据成员不再是 static。在类中将它们设置为 static 可防止您创建多个具有单个 HWND 的 SearchEditBox 对象。数据成员不需要是static。您可以将 SearchEditBox* 指针作为子类的 dwRefData 参数传递，这样 EditBoxProc() 就可以访问 SearchEditBox 对象及其非静态成员。

尝试更像这样的东西:

搜索编辑框.h

#ifndef SearchEditBoxH
#define SearchEditBoxH

class SearchEditBox
{
private:
    bool firstPaint;
    int width;
    int height;
    HWND editBox;

    SearchEditBox();
    void ChangeEdit(const bool change);

    static LRESULT CALLBACK EditBoxProc(HWND hwnd, UINT uMsg, WPARAM wParam, LPARAM lParam, UINT_PTR uint_ptr, DWORD_PTR dwRefData);

public:
    ~SearchEditBox();

    HWND getEditBox()

    static SearchEditBox* CreateEditBox(HINSTANCE hInst, HWND hwnd, int pos_x, int pos_y, int width, int height);
};

#endif

搜索编辑框.cpp

#include "stdafx.h"
#include <windows.h>
#include <commctrl.h>
#include <richedit.h>
#include <string.h>
#include "SearchEditBox.h"

/*global vars*/
static LPCTSTR editBoxDefText = TEXT("Search...");

SearchEditBox::SearchEditBox()
{
    firstPaint = false;
    width = 0;
    height = 0;
    editBox = NULL;
}

SearchEditBox::~SearchEditBox()
{
    if (editBox)
        DestroyWindow(editBox);
}

void SearchEditBox::ChangeEdit(const bool change)
{
    //...
}

HWND SearchEditBox::getEditBox()
{
    return editBox;
}

SearchEditBox* SearchEditBox::CreateEditBox(HINSTANCE hInst, HWND hwnd, int pos_x, int pos_y, int width, int height)
{
    // make sure RichEdit 4.1 is enabled
    if (!GetModuleHandle(TEXT("Msftedit.dll")))
    {
        if (!LoadLibrary(TEXT("Msftedit.dll")))
        {
            MessageBox(NULL, L"Problem loading Msftedit.dll.", L"Error", 0);
            return 0;
        }
    }

    SearchEditBox *pSearchEditBox = new SearchEditBox;

    pSearchEditBox->editBox = CreateWindowEx(0, MSFTEDIT_CLASS, editBoxDefText, WS_VISIBLE | WS_CHILD, pos_x + 6, pos_y + 4, width, height, hwnd, NULL, (HINSTANCE) GetWindowLong(hwnd, GWL_HINSTANCE), p_SearchEditBox);
    if (!pSearchEditBox->editBox)
    {
        delete pSearchEditBox;
        MessageBox(NULL, L"Problem creating the Search box.", L"Error", 0);
        return 0;
    }

    if (!SetWindowSubclass(pSearchEditBox->editBox, SearchEditBox::EditBoxProc, 0, (DWORD_PTR)p_SearchEditBox))
    {
        delete pSearchEditBox;
        MessageBox(NULL, L"Problem subclassing the Search box.", L"Error", 0);
        return 0;
    }

    pSearchEditBox->width = width;
    pSearchEditBox->height = height;

    return pSearchEditBox;
}

LRESULT CALLBACK SearchEditBox::EditBoxProc(HWND hwnd, UINT uMsg, WPARAM wParam, LPARAM lParam, UINT_PTR uIdSubclass, DWORD_PTR dwRefData)
{
    SearchEditBox *pSearchEditBox = (SearchEditBox*) dwRefData;

    switch (uMsg)
    {
        case WM_NCDESTROY:
            RemoveWindowSubclass(hwnd, SearchEditBox::EditBoxProc, uIdSubclass);
            pSearchEditBox->editBox = NULL;
            break;

        case WM_SIZE:
            pSearchEditBox->width = LOWORD(lParam);
            pSearchEditBox->height = HIWORD(lParam);
            break;

        case WM_SETFOCUS:
        {
            TCHAR getText[10];
            GetWindowText(hwnd, getText, 10);

            if (_tcscmp(getText, editBoxDefText) == 0)
                pSearchEditBox->ChangeEdit(true);

            break;
        }

        case WM_KILLFOCUS:
        {
            TCHAR getText[10];
            if (GetWindowText(hwnd, getText, 10) == 0)
                pSearchEditBox->ChangeEdit(false);
            break;
        }

        case WM_LBUTTONDBLCLK:
            pSearchEditBox->ChangeEdit(true);
            break;

        case WM_PAINT:
        {
            if (!pSearchEditBox->firstPaint)
            {
                pSearchEditBox->firstPaint = true;
                pSearchEditBox->ChangeEdit(false);
            }

            PAINTSTRUCT ps;
            HDC hdc = BeginPaint(hwnd, &ps);
            HBRUSH hBrush = CreateSolidBrush(RGB(33, 33, 33));
            SelectObject(hdc, hBrush);
            RoundRect(hdc, -6, -4, pSearchEditBox->width + 7, pSearchEditBox->height + 4, 5, 5);
            EndPaint(hwnd, &ps);

            break;
        }
    }

    return DefSubclassProc(hwnd, uMsg, wParam, lParam);
}