QWidget "access violation" exeption

Question

A have a class, inherited from QWidget and Ui_Form (automaticaly generated class, appears when you create a .ui in Qt). It looks like

class MyClass: public QWidget, public Ui_Form {}

Ui_Form has some members, which connected with relevant widgets in the .ui file (for example, QLineEdits, QButtons, etc).

class Ui_Form {
public:
QLineEdit *fileNameEdit;

    void setupUi(QWidget *Form) {
    fileNameEdit = new QLineEdit(layoutWidget);
    fileNameEdit->setObjectName(QStringLiteral("fileNameEdit"));
    }
}

As MyClass is inherited from Ui_Form, I can use this membes. But, when I try to do something, I have an exeption "Access violation reading location". For example:

fileNameEdit->setText("String");

Can somebody give an advice?

Answer 1

The way you are incorporating the Ui_Form part is not how Qt proposes it by default. If you look into this button example you can see how the ui part is incorporated diferently:

Header file

#ifndef BUTTON_H
#define BUTTON_H

#include <QWidget>

namespace Ui {
class Button;
}

class Button : public QWidget
{
    Q_OBJECT

public:
    explicit Button(int n, QWidget *parent = 0);
    ~Button();

private slots:
    void removeRequested();

signals:
    void remove(Button* button);
private:
    Ui::Button *ui;
};

#endif // BUTTON_H

CPP code

#include "button.h"
#include "ui_button.h"

Button::Button(int n, QWidget *parent) :
    QWidget(parent),
    ui(new Ui::Button)
{
    ui->setupUi(this);
    ui->pushButton->setText("Remove button "+QString::number(n));
    addAction(ui->actionRemove);
    connect(ui->actionRemove,SIGNAL(triggered()),this,SLOT(removeRequested()));
    connect(ui->pushButton,SIGNAL(clicked()),this,SLOT(removeRequested()));
}

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

void Button::removeRequested()
{
    emit remove(this);
}

The main difference is that I believe you are not calling Ui_From::setupUi function. It is clear to me that you do not need to follow the Qt suggested template (incorporating the ui as a class member rather than inheriting from it), however, it is much clearer from my point of view if you follow the Qt suggestions.