在不同屏幕之间切换

Question

I have an application with a few screens that I would like to load on application launch and keep in memory while the program is running. I want to be able to switch between screens on a button click, hiding the current screen while showing the next screen. There is not a direct path through the application, the user may go back and forth through screens in the application. I'm using Qt and new to c++.

The following is skeleton code I would like to get to work (or get advice about a better way to do it). I'm doing it this way in order to avoid memory leaks from creating new instances of the dialogs when moving back and forth through the application a number of times.

When I compile this, I get an error Undefined Reference to 'Screen2' in Screen2->show(); in Dialog1::on_pushButton_clicked() in dialog1.cpp. I tried everything I could to get this to compile without success. Why isn't Screen2 a valid pointer in dialog1.cpp?

I have a Manager which is run from Main and initialises the dialogs.

manager.cpp:

#include "manager.h"
#include "ui_manager.h"

Manager::Manager(QWidget *parent) :
QDialog(parent),
ui(new Ui::Manager)
{
    ui->setupUi(this);
    Screen1 = new Dialog1(this);
    Screen2 = new Dialog2(this);
    Screen1->show();
}

Manager::~Manager()
{
    delete ui;
}

manager.h:

#ifndef MANAGER_H
#define MANAGER_H
#include <QDialog>
#include "dialog1.h"
#include "dialog2.h"

namespace Ui {
    class Manager;
}

class Manager : public QDialog
{
    Q_OBJECT

public:
    explicit Manager(QWidget *parent = 0);
    ~Manager();

    Dialog1 *Screen1;
    Dialog2 *Screen2;

private:
    Ui::Manager *ui;
};

#endif // MANAGER_H

dialog1.cpp:

#include "dialog1.h"
#include "ui_dialog1.h"
#include "manager.h"
#include "dialog2.h"
#include <QDebug>

extern Dialog1 *Screen1;
extern Dialog2 *Screen2;

Dialog1::Dialog1(QWidget *parent) :
    QDialog(parent),
    ui(new Ui::Dialog1)
{
    ui->setupUi(this);
}

Dialog1::~Dialog1()
{
    delete ui;
}

void Dialog1::on_pushButton_clicked()
{
    Screen2->show();
}

dialog1.h:

#ifndef DIALOG1_H
#define DIALOG1_H

#include <QDialog>
#include "dialog2.h"

class Manager;

namespace Ui {
    class Dialog1;
}

class Dialog1 : public QDialog
{
    Q_OBJECT

public:
    explicit Dialog1(QWidget *parent = 0);
    ~Dialog1();

private slots:
    void on_pushButton_clicked();

private:
    Ui::Dialog1 *ui;
};

#endif // DIALOG1_H

dialog2.cpp:

#include "dialog2.h"
#include "ui_dialog2.h"
#include "dialog1.h"
#include "manager.h"

extern Dialog1 *Screen1;
extern Dialog2 *Screen2;

Dialog2::Dialog2(QWidget *parent) :
    QDialog(parent),
    ui(new Ui::Dialog2)
{
    ui->setupUi(this);
}

Dialog2::~Dialog2()
{
    delete ui;
}

void Dialog2::on_pushButton_clicked()
{
    Screen1->show();
}

All help appreciated!

Regards, James

Answer 1

I'll explain you easiest way to get it work.

1. Make screen1 and screen2 private members of manager class.
2. Add signal buttonPressed() to both screens.
3. Emit signal on button press in each dialog.
4. Add slot to manager class to handle button press in dialogs
5. connect signals of dialogs to manager slot

6. Remove this in both dialogs:

    extern Dialog1 *Screen1; extern Dialog2 *Screen2; 

You can not access them directly because thee are members of your manager object.

As a result you will be able to add as many screens as you want. Each screen won't know anything about others (you were trying to do so).