c – 尝试为Windows API包装器实现事件处理程序时遇到问题

朋友们,我正在尝试实现 Windows API的包装,我想从父窗口捕获子窗口事件,所以我做了一个简单的事件处理程序.我使用函数指针来存储回调函数.我用静态函数做了.请参阅下面的代码.

class Widget;
typedef void (*EventProc)(MSG* EventArgs);
class Widget
{
public:
    /// Constructors destructor and methods for Registering and Creating Windows
    static LRESULT CALLBACK MainProc(HWND hWnd,UINT msg,WParaM wParam,LParaM lParam)
    {
        MSG struct_msg;
        struct_msg.hWnd=hWnd;
        struct_msg.message=msg;
        struct_msg.wParam=wParam;
        struct_msg.lParam=lParam;

        Widget* wid=(Widget*)GetWidgetPointerFromHWND(hWnd);

        switch(msg)
        {
            case WM_CREATE:
                if(Created!=NULL)
                    (*(wid->Created))(&struct_msg);break;
            case WM_DESTROY:
                if(Destroyed!=NULL)
                    (*(wid->Destroyed))(&struct_msg);break;
            default:
                return DefWindowProc(hWnd,msg,wParam,lParam);
        }
        return 0;
    }
    EventProc Created;
    EventProc Destroyed;

};

class CustomControl: public Widget
{
    /// Constructor destructor and other methods

};

class Window: public Widget
{
public:

    static void ChildCreated(Widget* Sender,Widget* Self,MSG* EventArgs)
    {
        MessageBox(0,0);
    }

    Window()
    {
        control1=new CustomControl(100,100,200,200); //left,top,width,height
        this->AddChild(control1);
        control1->Created = ChildCreated; 
    }
private:
    CustomControl control1;
};

这是有效的,但由于静态函数没有这个指针,我无法访问类Window中的变量和成员函数.
我想将一个成员函数作为回调函数(Event Handler).
我希望你明白我想要解决的问题.请帮我.

解决方法

您在此示例中显示的主要想法是正确的.

您可以创建一些静态WndProc函数和映射,将HWND映射到您的类.

创建窗口小部件的新实例时,将其添加到映射.在销毁时,您将其从映射中删除.

在您的WndProc函数中,您可以从映射中获取类的实例,并调用该实例的虚拟事件处理函数：

class WidgetBase
{
public:
    WidgetBase()
    {
        _handle = CreateWindow(/*...*/,&WidgetBase::MainProc,/*...*/);
        _widgets.insert(std::make_pair(handle,this);
    }
    virtual ~WidgetsBase() 
    {
       _widgets.remove(handle);
    }
protected:
    HWND _handle;
    virtual LRESULT handleEvents(UINT msg,LParaM lParam)
    {
         return DefWindowProc(_handle,hWnd,lParam);
    }
private:
    static std::map<HWND,WidgetBase*> _widgets;

    static WidgetBase* GetWidgetPointerFromHWND(HWND handle)
    {
        // some error handling should be put there
        return _widgets[handle];
    }

    static LRESULT CALLBACK MainProc(HWND hWnd,LParaM lParam)
    {
        WidgetBase* wid=GetWidgetPointerFromHWND(hWnd);
        if (wid) {
            return wid->handleEvents(msg,lParam);
        }
        else {
            return DefWindowProc(hWnd,lParam);
        }
    }
};
std::map<HWND,WidgetBase*> WidgetBase::_widgets;

然后在派生类中,您只需要覆盖handleEvents函数：

class Derived: public WidgetBase
{
protected:
virtual LRESULT handleEvents(UINT msg,LParaM lParam)
    {
         // This is your event handler,that is memeber function
         //...
         return WidgetBase::handleEvents(msg,lParam);
    }
};