Transitioning between menu screens with QStateMachine - c++

Question

I am considering transitioning between menu screens in a game by using QStateMachine. However, I'm unsure how to kick off some code (e.g. show() a QWidget) upon a transition between states occurring. I can do it quite easily with plain old signals (see commented out code), but I figure that I could probably do some fancy animation upon switching screens using transitions.
Here's my code:
Edit: updated as per Koying's suggestion.
ApplicationWindow.h:
#include <QtGui>
#include <QStateMachine>
#include "MainMenu.h"
#include "LoadGameMenu.h"
class ApplicationWindow : public QMainWindow
{
Q_OBJECT
public:
ApplicationWindow();
private slots:
void mainMenuButtonClicked();
void loadGameMenuButtonClicked();
private:
MainMenu* mainMenu;
LoadGameMenu* loadGameMenu;
QStateMachine stateMachine;
QStackedWidget* stack;
};
ApplicationWindow.cpp:
ApplicationWindow::ApplicationWindow()
{
resize(800, 600);
stack = new QStackedWidget(this);
mainMenu = new MainMenu();
setCentralWidget(mainMenu);
loadGameMenu = new LoadGameMenu();
QState* mainMenuState = new QState();
QState* loadGameMenuState = new QState();
QAbstractTransition* loadTransition = mainMenuState->addTransition(
mainMenu, SIGNAL(loadGameClicked()), loadGameMenuState);
connect(loadTransition, SIGNAL(triggered()), this, SLOT(loadGameMenuButtonClicked()));
QAbstractTransition* mainMenuTransition = loadGameMenuState->addTransition(
loadGameMenu, SIGNAL(backToMainMenuClicked()), mainMenuState);
connect(mainMenuTransition, SIGNAL(triggered()), this, SLOT(mainMenuButtonClicked()));
stateMachine.addState(mainMenuState);
stateMachine.addState(loadGameMenuState);
stateMachine.setInitialState(mainMenuState);
stateMachine.start();
}
void ApplicationWindow::mainMenuButtonClicked()
{
setCentralWidget(mainMenu);
}
void ApplicationWindow::loadGameMenuButtonClicked()
{
setCentralWidget(loadGameMenu);
}
LoadGameMenu.h:
#include <QtGui>
class LoadGameMenu : public QWidget
{
Q_OBJECT
public:
LoadGameMenu();
signals:
void backToMainMenuClicked();
private:
QPushButton* loadGameButton;
QPushButton* backToMainMenuButton;
};
LoadGameMenu.cpp:
#include "LoadGameMenu.h"
LoadGameMenu::LoadGameMenu()
{
loadGameButton = new QPushButton(tr("Load"));
backToMainMenuButton = new QPushButton(tr("Main Menu"));
QObject::connect(backToMainMenuButton, SIGNAL(clicked()),
this, SIGNAL(backToMainMenuClicked()));
QVBoxLayout* layout = new QVBoxLayout();
layout->addWidget(loadGameButton);
layout->addWidget(backToMainMenuButton);
layout->setContentsMargins(300, 400, 300, 200);
setLayout(layout);
}
MainMenu.h:
#include <QtGui>
class MainMenu : public QWidget
{
Q_OBJECT
public:
MainMenu();
signals:
void newGameClicked();
void loadGameClicked();
private slots:
void exit();
private:
QPushButton* newGameButton;
QPushButton* loadGameButton;
QPushButton* exitGameButton;
QMenu* fileMenu;
};
MainMenu.cpp:
#include "MainMenu.h"
MainMenu::MainMenu()
{
newGameButton = new QPushButton(tr("New Game"), this);
loadGameButton = new QPushButton(tr("Load Game"));
exitGameButton = new QPushButton(tr("Exit"));
QObject::connect(newGameButton, SIGNAL(clicked()), this, SIGNAL(newGameClicked()));
QObject::connect(loadGameButton, SIGNAL(clicked()), this, SIGNAL(loadGameClicked()));
QObject::connect(exitGameButton, SIGNAL(clicked()), qApp, SLOT(quit()));
QVBoxLayout* layout = new QVBoxLayout();
layout->addWidget(newGameButton);
layout->addWidget(loadGameButton);
layout->addWidget(exitGameButton);
layout->setContentsMargins(300, 200, 300, 200);
setLayout(layout);
}
void MainMenu::exit()
{
if( QMessageBox::question(
this,
tr("Exit?"),
tr("Do you really want to exit the game?"),
QMessageBox::Yes | QMessageBox::No,
QMessageBox::No
) == QMessageBox::Yes
)
{
qApp->quit();
}
}
main.cpp:
#include <QtGui>
#include "ApplicationWindow.h"
int main(int argv, char **args)
{
QApplication app(argv, args);
ApplicationWindow window;
window.show();
return app.exec();
}
So, how do I trigger some behaviour or action when a transition occurs?
Cheers.

Answer 1

To actually do something on a state transition, you have to connect to the triggered() signal of the transition, e.g.
QAbstractTransition* trMainLoad = mainMenuState->addTransition(mainMenu, SIGNAL(loadGameClicked()), loadGameMenuState);
connect(trMainLoad , SIGNAL(triggered()), SLOT(...));