使用 Qt 检查密钥是否已关闭

Question

I am playing around with some graphics, and I have implemented simple camera movement with the arrow keys. My first approach was to override keyPressEvent to do something like this:

switch(key)
{
   case up: MoveCameraForward(step); break;
   case left: MoveCameraLeft(step); break;
   ...
}

This doesn't work as I wish it would. When I press and hold, for example, the forward key, the camera moves forward "step" units, then halts for a while and then continues moving. I am guessing that this is how the event is generated, in order to avoid multiple events in case of a little bit long keypress.

So, I need to poll the keyboard in my Paint() routine. I haven't found how to do it with Qt. I thought of having a map<Key, bool> which would be updated in keyPressEvent and keyReleaseEvent and poll that map in Paint() . Any better ideas? Thanks for any insights.

Answer 1

这并不能解决检测按下哪些键的一般问题，但如果您只是在寻找键盘修饰符（shift、ctrl、alt 等），您可以通过静态QApplication::keyboardModifiers()和QApplication::queryKeyboardModifiers()检索它QApplication::queryKeyboardModifiers()方法。

Answer 2

So, I need to poll the keyboard in my Paint() routine. I haven't found how to do it with Qt. I thought of having a map which would be updated in keyPressEvent and keyReleaseEvent and poll that map in Paint().

Your second method is what I would have done, except that I would use a continuous, periodic QTimer event to poll the keyboard-pressed map and call QWidget::Update() function when necessary to invalidate the display widget instead. Performing non-painting operations inside Paint() is strongly discouraged for many reasons but I do not know how to explain that well.

Answer 3

There is no Qt API for checking whether a key is pressed or not. You may have to write separate code for different platforms and add a bit of #ifdef logic.

On Windows you can use GetKeyState() and GetKeyboardState() , both declared in windows.h .

Answer 4

This is not straight forward when using Qt, but the Gluon team has been working on exactly that problem (along with a bunch of others). GluonInput solves the issue, and is available as part of Gluon: http://gluon.gamingfreedom.org/ It is also a nice, Qt-like API, so while it's an extra dependency, it should be possible for you to use it.

Answer 5

This is caused by auto repeation of keys:

When I press and hold, for example, the forward key, the camera moves forward "step" units, then halts for a while and then continues moving.

In QT5 you can detect key held down by function isAutoRepeat() of QKeyEvent object. If the key is held down then isAutoRepeat() will return true . for example:

void MainWindow::keyPressEvent(QKeyEvent *event)
{
    if (event->isAutoRepeat())
    {
        return;
    }

    if (!event->isAutoRepeat())
    {
        qDebug() << "[MainWindow::keyPressEvent()] " << event->key() << "; " << event->isAutoRepeat();
    }
}

void MainWindow::keyReleaseEvent(QKeyEvent *event)
{
    if (event->isAutoRepeat())
    {
        return;
    }
    qDebug() << "[MainWindow::keyReleaseEvent()] " << event->key() << "; " << event->isAutoRepeat();
}

Answer 6

在 Qt5 中使用 QGuiApplication::keyboardModifiers() 和 QGuiApplication::queryKeyboardModifiers() 作为键盘修饰符