是否可以禁用或阻止某个键，例如 Print Screen 键？

我的事件过滤器:

bool EventFilter::eventFilter(QObject *object, QEvent *event)
{
    qDebug() << "object:" << object << "type:" << event->type();
    return false;
}

我尝试在 qApp 中使用:

ui->setupUi(this);

EventFilter *evt = new EventFilter;

qApp->installEventFilter(evt);

但只返回来自应用程序小部件的事件:

object: QWidgetWindow(0x175bae50, name = "QWidgetClassWindow") type: QEvent::Type(PlatformSurface)
object: QWidget(0x175b02c0) type: QEvent::Type(PlatformSurface)
object: QWidget(0x175b02c0) type: QEvent::Type(WinIdChange)
object: QWidget(0x175b02c0) type: QEvent::Type(Create)
...

和:

ui->setupUi(this);

EventFilter *evt = new EventFilter;

QDesktopWidget *c = new QDesktopWidget;
c->installEventFilter(evt);

但只返回 2 个事件:

object: QDesktopWidget(0x174e0260, name = "desktop") type: QEvent::Type(PolishRequest)
object: QDesktopWidget(0x174e0260, name = "desktop") type: QEvent::Type(Polish)

不能拦截和/或阻止事件？谢谢

最佳答案

您可以安装 low-level keyboard hook拦截并阻止所有 Print Screen 按键。以下是在我的 windows 7 机器上测试的。

这是一个展示如何执行此操作的最小示例:

#include <QtWidgets>
#include <windows.h>
//link against user32.lib when compiling in MSVC
#ifdef _MSC_VER
#pragma comment(lib, "User32.lib")
#endif

class GlobalPrintScreenBlocker {
public:
    GlobalPrintScreenBlocker():mHKeyboardHook(NULL) {}
    //to avoid leaking the hook procedure handle
    ~GlobalPrintScreenBlocker(){ unblock(); }
    //hook callback function (called on every system-wide key press)
    static LRESULT CALLBACK LowLevelKeyboardProc(int nCode,
                                                 WPARAM wParam, LPARAM lParam) {
        if(nCode == HC_ACTION) {
            PKBDLLHOOKSTRUCT p = reinterpret_cast<PKBDLLHOOKSTRUCT>(lParam);
            if(p->vkCode == VK_SNAPSHOT) return 1; //block print-screen key
        }
        //this is not a message we are interested in
        return CallNextHookEx(NULL, //ignored paramater
                              nCode,
                              wParam,
                              lParam);
    }
    void block(){
        mHKeyboardHook = SetWindowsHookEx(WH_KEYBOARD_LL, //low-level keyboard hool
                                          &LowLevelKeyboardProc, //callback
                                          GetModuleHandle(NULL), 
                                          0);
    }
    void unblock(){
        if(mHKeyboardHook) UnhookWindowsHookEx(mHKeyboardHook);
        mHKeyboardHook = NULL;
    }

private:
    HHOOK mHKeyboardHook;
};

int main(int argc, char* argv[]) {
    QApplication a(argc, argv);

    GlobalPrintScreenBlocker blocker;
    QPushButton button("Disable ScreenShot");
    button.setCheckable(true);
    QObject::connect(&button, &QPushButton::toggled, [&](bool isChecked){
        if(isChecked)
            blocker.block();
        else
            blocker.unblock();
    });
    button.show();

    return a.exec();
}

Hook 在安装它的线程中被调用。这样做的好处是不必担心回调函数中的线程安全问题，并且 32 位进程和 64 位进程之间没有区别(所有进程最终都会通过发布消息到安装钩子(Hook)的线程的事件循环)。但是，这也有一个缺点，即如果您的线程正忙(正在执行其他任何事情)，则可能不会调用回调 Hook :

The hook procedure should process a message in less time than the data entry specified in the LowLevelHooksTimeout value ... The value is in milliseconds. If the hook procedure times out, the system passes the message to the next hook. However, on Windows 7 and later, the hook is silently removed without being called. There is no way for the application to know whether the hook is removed.

您可以通过分配一个单独的线程来安装/执行 Hook 来绕过这个限制。另外请注意，您的 Hook 的回调函数应尽可能少，以便它能够在时间限制内完成。

P.S.:我必须使用截图工具来创建上面的屏幕截图。 . .

关于c++ - 如何使用 Qt 禁用 Windows 中的键(全局)？，我们在Stack Overflow上找到一个类似的问题： https://stackoverflow.com/questions/45968724/