c++ - 将类中的方法作为参数传递

Question

我有这样的课

class Keyboard
{
public:
    Keyboard(void);
    ~Keyboard(void);
    void SetHook(HINSTANCE hInstance);
    LRESULT CALLBACK keyboardHookProc(int nCode, WPARAM wParam, LPARAM lParam);
};


LRESULT CALLBACK Keyboard::keyboardHookProc(int nCode, WPARAM wParam, LPARAM lParam)
{
    bool bControlKeyDown=0;
    bool caps = GetKeyState(VK_CAPITAL) < 0;

...

void Keyboard::SetHook(HINSTANCE hInstance)
{
    KeyboardHook = SetWindowsHookEx(WH_KEYBOARD_LL, Keyboard::keyboardHookProc, hInstance, NULL);
}

但声明

KeyboardHook = SetWindowsHookEx(WH_KEYBOARD_LL, Keyboard::keyboardHookProc, hInstance, NULL);

导致编译错误

Error   7   error C3867: 'Keyboard::keyboardHookProc': function call missing argument list; use '&Keyboard::keyboardHookProc' to create a pointer to member

如果我更改为 '&Keyboard::keyboardHookProc' 它也会出错，当我转换为 '(HOOKPROC) &Keyboard::keyboardHookProc' 它也会出错

任何人请帮助

Answer 1

这是 C 回调的常见错误。

Keyboard::keyboardHookProc必须是静态的。

[更新]

如果Keyboard要Keyboard对static Keyboard::keyboardHookProc. 如果你有一个Keyboard，你可能会使用singleton模式，如果没有，那么每个静态方法都必须有自己的Keyboard对象。

[更新2]

将对象与全局函数链接的一种方法是通过模板对象引用。但这仅适用于全局对象：

class Keyboard
{
public:
    Keyboard();
    ~Keyboard(void);
    LRESULT keyboardHookProc(int nCode, WPARAM wParam, LPARAM lParam);
};

LRESULT Keyboard::keyboardHookProc(int nCode, WPARAM wParam, LPARAM lParam)
{
}
// global function interface 
template <Keyboard& k>
LRESULT CALLBACK keyboardHookProc(int nCode, WPARAM wParam, LPARAM lParam)
{
   return k.keyboardHookProc(nCode, wParam, lParam);
}


Keyboard k; // global keyboard

int main()
{
   // this works
   SetWindowsHookEx(0, keyboardHookProc<k>, NULL, NULL);
}