[Solved] How to access progressBar from a QWizardPage subclass

Chris H

What error do you get, exactly, when you try to call
@ui->progressBar->setValue(value);@
from a member function (you certainly can't access it from a static function if it's a member variable!).

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Here is the error that I got when I try to call:

@
ui->progressBar->setValue(value);
@

...from a static function.

The error output:

In static member function 'static void MyQWizard::updateProgressBar(int)':
error: invalid use of member 'MyQWizard::ui' in static member function

...This error points to the line 42 of my code which have the follow declaration:

@
private:
Ui::CreateRepoWizard *ui;
@

...included "private:" for clarity.

Thanks for help.

Chris H

You cannot access a member variable from a static function: what error do you get when you try to do that from a member function?

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In the example that I wrote above you can see that the function:

myqwizard.cpp:
@
MyQWizard::MyQWizard(QWidget *parent) : QWizard(parent), ui(new Ui::CreateRepoWizard) {

...

}

...

void MyQWizard::updateProgressBar(const int value) {

  ui->progressBar->setValue(value);

}

...

@

...is a member of MyQWizard class and as I said, it was declared as a static function:

myqwizard.h:
@
public:
static void updateProgressBar(const int value);
@

I need this function be static, to be able to access it from progressPage(a QWizardPage subclass) without creating a new object of MyQWizard :

progresspage.cpp:
@

#include <myqwizard.h>

ProgressPage::ProgressPage(QWidget *parent) : QWizardPage(parent) {

...

}

...

MyQWizard::updateProgressBar(value);

...
@

Creating this member function as non-static will allow me to update the progressBar without problems, but it implies to create a new object of MyQWizard too, which doesn't have any sense in this scenario. Because I will be using a new instance of MyQWizard rather than the current, therefore I will be updating a different progressBar, that it's not the one that the wizard window shows.

Anyway thanks for the correction.

Chris H

There are a couple approaches you can use here: the first is to emit a signal in ProgressPage that indicates that it would like the progress bar updated, and connect to that in MyQWizard to do the update. A second approach is to get a pointer to MyQWizard from within ProgressPage (is MyQWizard a parent widget, perhaps?). I'd lean towards to first solution for encapsulation reasons, but either will work. Fundamentally, though, you must have an object to operate on: that's why you can't use a static function.

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As I said, thanks for the correction. I already understood that I can't use a static function. My next step will be try your suggestion, thanks again.

? Offline

Got it!!!

l used the signal-slot approach as you suggested and it worked at the first try. It was so easy that I feel ashamed right now, but well, I guess it's a matter of experience.

Thanks for your continuous help and support, Chris H.

astodolski

What did you use for the signal to emit? Value changed is a signal that is emitted from the progress bar. It looks like from your posting that you wanted to call MyQWizard::updateProgressBar(value); and you said you used a signal-slot solution. I was hoping to see what you used as a solution scheme.

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I don't have access to the original code right now, so I made an example for you to have an idea how I've solved this.

Note that I've promoted the object "ui->progressBarPage" to "ProgressPage".

Here is the code:

mywizard.h:

@#ifndef MYWIZARD_H
#define MYWIZARD_H

#include <QWizard>

namespace Ui {

class MyWizard;

}

class MyWizard : public QWizard
{

Q_OBJECT

public:

explicit MyWizard(QWidget *parent = 0);

~MyWizard();

public slots:

void updateProgressBar(const int value);

private:

Ui::MyWizard *ui;

};

#endif // MYWIZARD_H@

mywizard.cpp:

@#include "mywizard.h"
#include "ui_mywizard.h"

MyWizard::MyWizard(QWidget *parent) : QWizard(parent), ui(new Ui::MyWizard)
{

ui->setupUi(this);

ui->progressBar->reset();

connect(ui->progressBarPage, SIGNAL(updateProgressValue(int)), this, SLOT(updateProgressBar(int)));

}// Constructor

MyWizard::~MyWizard()
{

delete ui;

}// Destructor

void MyWizard::updateProgressBar(const int value)
{

ui->progressBar->setValue(value);

}// Update ProgressBar@

progresspage.h:

@#ifndef PROGRESSPAGE_H
#define PROGRESSPAGE_H

#include <QWizardPage>
#include <QTimer>

class ProgressPage : public QWizardPage
{

Q_OBJECT

public:

explicit ProgressPage(QWidget *parent = 0);

void initializePage();

signals:

void updateProgressValue(const int value);

private slots:

void updateValue();

private:

QTimer *timer;

int count;

};

#endif // PROGRESSPAGE_H@

progresspage.cpp:

@#include "progresspage.h"

ProgressPage::ProgressPage(QWidget *parent) : QWizardPage(parent)
{

timer = new QTimer(this);

count = 0;

connect(timer, SIGNAL(timeout()), this, SLOT(updateValue()));

}// Constructor

void ProgressPage::initializePage() {

timer->start(100);

}// initializePage

void ProgressPage::updateValue() {

if(count == 100) {

    timer->stop();

    return;

}// if

count++;

emit updateProgressValue(count);

}// updateValue@

Hope this can help you.

astodolski

Absolutely helps. Thanks very much.

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Glad to know it.