Help reqested: very simple keypressevent in mainwindow

[naizarak]

Hello

I've been trying to add a basic keyboard input handler to my mainwindow. The mainwindow has a few Qlabels and pushbuttons, nothing fancy.

I've tried adding the following code:

mainwindow.h
@ protected:
void keyPressEvent(QKeyEvent *event);@

mainwindow.cpp
@ void MainWindow::keyPressEvent(QKeyEvent *event)
{
std::cout << "pressed";
}@

But nothing happens when I press a key. I think there's something very simple that I'm missing, but I just can't figure it out. Trust me I've googled quite a bit on the topic but got nowhere. Any help would be greatly appreciated. Thanks.

[SGaist]

Hi and welcome to devnet,

What is your MainWindow ? A QWidget ? A QMainWindow ?

Does it get keyboard focus ?

Typically, if your one of your pushbuttons has the focus, your MainWindow won't receive any keyboard event

[naizarak]

Thanks for the reply.

My mainwindow class inherits from QMainWindow, and yes indeed, the very first pushbutton appears to receive focus by default.

Can you tell me what I need to run in order for the overall mainwindow to receive universal focus(if that makes sense).

[SGaist]

It doesn't really make sense (I.E. if you have QLineEdit, you'd rather want it to have the keyboard focus)

You can however use your MainWindow as a filter, search for event filter in the documentation.

Why do you need that "universal focus" ?

[naizarak]

I looked through the eventfilter documentation, and as I understand the filter must be added to an existing object. I'm not sure how that would work for me because I want the program to just catch keyboard input in general. It doesn't have to be tied to a specific control or GUI element.

Basically the program is open and running.
The user presses a key.
The program should catch this input and go from there.

[SGaist]

What kind of key ? A short cut ?

From what "state" to what "state" ?

You can filter events for several widgets in the same filter event

[naizarak]

Ah ok I think I'm not elaborating enough.

Basically my program is an extremely simple game.

There is a qlabel with a car image.

When the user presses an arrow key, the car-image label should be moved in an appropriate direction. My entire program consists of nothing but a main file, mainwindow.h inhering from qmainwindow, and the mainwindow.cpp. I'm not using widgets or anything like that.

This is purely conceptual at this point. I just want the program to be open, the user to press a key, the program to read this and then move the car. I don't know how to explain it any simpler lol.

Maybe if I just added my code...

@#ifndef MAINWINDOW_H
#define MAINWINDOW_H

#include <QMainWindow>
#include <QGraphicsScene>
#include <QGraphicsView>
#include <QPushButton>
#include <QMessageBox>
#include <QPixmap>
#include <QLabel>
#include <QTimer>
#include <QTextEdit>
#include <QInputDialog>
#include <QString>
#include <QEvent>
#include <QObject>
#include <QKeyEvent>

//class GUITile;
class MainWindow : public QMainWindow {
Q_OBJECT

public:
explicit MainWindow();

void show();

protected:
void keyPressEvent(QKeyEvent *event);

private:
QString name;
int roadSpeed;
int score;
int speed;
int lives;

int roadTimerCount;

bool gameRunning;
bool timerRunning;

QGraphicsScene *scene;
QGraphicsView *view;

QLabel *nameLabel;
QTextEdit *scoreField;

QTextEdit *speedField;
QTextEdit *livesField;

QPushButton *startButton;
QPushButton *pauseButton;
QPushButton *exitButton;
QPushButton *aboutButton;

QMessageBox *aboutBox;

QPixmap *cityMap;
QLabel *city;

QPixmap *roadMap;
QLabel *road;

QPixmap *roadMap2;
QLabel *road2;

QPixmap *playerMap;
QLabel *player;

QTimer *roadTimer;

private slots:
void startSlot();
void pauseSlot();
void exitSlot();

void aboutSlot();

void handleRoadTimer();

};

#endif
@

And in mainwindow.cpp:
@ void MainWindow::keyPressEvent(QKeyEvent *event)
{
std::cout << "pressed";
//just to test basic input. the actual event will be filtering for the arrow keys and space bar
}@

[SGaist]

Ok ! I see, then i think "grabKeyboard":http://qt-project.org/doc/qt-4.8/qwidget.html#grabKeyboard is your friend

[holygirl]

Will an installEventFilter help here?

Here's some code which might help.

In the constructor

@
installEventFilter(this)
@

and then a function

@
bool MainWindow::eventFilter(QObject *target, QEvent *event) {

if (event->type() == QEvent::KeyPress) {

    QKeyEvent *keyEvent = static_cast<QKeyEvent*>(event);

    switch (keyEvent->key())
    {

          case <whatever key you want>:
     }
     return QObject::eventFilter(target, event);
 }

}
@

Here, the key you wish to map can be specified as

@
Qt::Key_Up
Qt::Key_A
.
.
etc
@

Hope this is what you were looking for!