C ++ Winapi - 在类中包装子类的回调

Question

我想创建一个用于创建静态控件的类。问题是当子类化控件时，回调应该是静态的，这意味着我将无法访问回调中的非静态变量和函数。

我一直在努力使我的代码正常工作，但仍然没有成功。

MyClass.cpp

#include "MyClass.h"

MyClass::MyClass(){
    non_static_variable = 0; //default is zero.
}

LRESULT CALLBACK MyClass::SubClassProc(HWND hwnd, UINT uMsg, WPARAM wParam, LPARAM lParam, UINT_PTR uIdSubclass, DWORD_PTR dwRefData) {

    MyClass* pThis = reinterpret_cast<MyClass*>(dwRefData);
    
    char buffer[5];
    sprintf_s(buffer, "The value of non_static_variable is: %d \n", pThis->non_static_variable);
    OutputDebugStringA(buffer);    
        
    switch (uMsg) {
        case WM_PAINT: {
            // do nothing for now
            return 0;
        }

        case WM_NCDESTROY: {
            RemoveWindowSubclass(hwnd, SubClassProc, uIdSubclass);
            break;
        }
    }        
    return DefSubclassProc(hwnd, uMsg, wParam, lParam);
}

void MyClass::CreateStaticControl(HWND WindowHandle) {
    
    StaticControl = CreateWindowEx(0, L"STATIC", NULL, WS_CHILD | WS_VISIBLE | SS_OWNERDRAW, x, y, width, height, WindowHandle, NULL, NULL, this); 
    SetWindowSubclass(StaticControl, &SubClassProc, ID, reinterpret_cast<DWORD_PTR>(this));
}

void MyClass::SetValue(int value){
    non_static_variable = value; //test if I can access this in callback
}

MyClass.h

#include "header.h"

public:
    MyClass();

    void CreateStaticControl(HWND window);
    void SetValue(int value);
    static LRESULT CALLBACK SubClassProc(HWND hWnd, UINT msg, WPARAM wParam, LPARAM lParam, UINT_PTR uIdSubclass, DWORD_PTR dwRefData);

private:
    int non_static_variable;
    HWND StaticControl;

};

然后从我的主窗口过程中调用我的WM_CREATE 中的类，我是这样使用它的。

...
case WM_CREATE:{
   MyClass myClass;
   myClass.CreateStaticControl(hwnd);
   myClass.SetValue(888);
   break;
}

您可能认为这是其他人的重复，我发现了很多，但由于这是关于子类化的，我无权访问 WM_NCCREATE 我无法正确设置我的类的指针。谁能帮帮我？

编辑：我输入了我拥有的确切代码。

Answer 1

您可以使用SetWindowSubclass() 的dwRefData 参数将this 指针传递给回调的dwRefData 参数。然后，您可以对该参数进行类型转换以访问非静态成员。根本不需要使用GWLP_USERDATA（尤其是在设置GWLP_USERDATA 时没有正确使用回调的lParam）。

试试这个：

MyClass.h

class MyClass {

public:
    MyClass();

    void CreateStaticControl(HWND window);
    static LRESULT CALLBACK SubClassProc(HWND hWnd, UINT msg, WPARAM wParam, LPARAM lParam, UINT_PTR uIdSubclass, DWORD_PTR dwRefData);

private:
    int non_static_variable;
    HWND StaticControl;

};

MyClass.cpp：

void MyClass::CreateStaticControl(HWND WindowHandle) {
    StaticControl = CreateWindowEx(0, L"STATIC", NULL, WS_CHILD | WS_VISIBLE | SS_OWNERDRAW, x, y, width, height, WindowHandle, NULL, NULL, this); 
    SetWindowSubclass(StaticControl, &SubClassProc, ID, reinterpret_cast<DWORD_PTR>(this));
}

LRESULT CALLBACK MyClass::SubClassProc(HWND hwnd, UINT uMsg, WPARAM wParam, LPARAM lParam, UINT_PTR uIdSubclass, DWORD_PTR dwRefData) {

    MyClass* pThis = reinterpret_cast<MyClass*>(dwRefData);
        
    switch (uMsg) {
        case WM_PAINT: {
                
            // use pThis->non_static_variable as needed...
                
            return 0;
        }

        case WM_NCDESTROY: {
            RemoveWindowSubclass(hwnd, SubClassProc, uIdSubclass);
            break;
        }
    }        

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