Check if a Key is Down with Qt

c++ qt event-handling keyboard-events
Armen Tsirunyan picture Armen Tsirunyan · Sep 13, 2011 · Viewed 17k times · Source

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

Nathan picture Nathan · Nov 4, 2014

This doesn't solve the general problem of detecting which keys are pressed, but if you are only looking for keyboard modifiers (shift, ctrl, alt, etc.), you can retrieve that through the static QApplication::keyboardModifiers() and QApplication::queryKeyboardModifiers() methods.

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