Question

When I run it it will just finish right away and not show anything. I can’t find anything wrong w/it and no one on #qt could either. I’ve got other apps working fine so I’m not sure. It’s got something to do with the createForm call, if I omit that call in the constructor I do get a default QWidget displayed.

captchit.pro

    #-------------------------------------------------
    #
    # Project created by QtCreator 2011-02-26T20:58:23
    #
    #-------------------------------------------------


QT       += core gui network

TARGET = captchit
TEMPLATE = app

SOURCES += main.cpp\
        widget.cpp

HEADERS  += widget.h

main.cpp

    #include "QtGui/QApplication"
    #include "widget.h"


int main(int argc, char *argv[])
{
    QApplication a(argc, argv);
    Widget mainWidget;
    mainWidget.show();

return a.exec();

}


widget.h


    #ifndef WIDGET_H
    #define WIDGET_H


#include <QWidget>

class QPixmap;

class QLabel;

class QLineEdit;

class QPushButton;
class Widget : public QWidget

{

    Q_OBJECT
public:

    Widget(QWidget *parent = 0);
private slots:

    void on_refreshButton_pressed();

    void on_submitButton_pressed();

    void on_closeButton_pressed();
private:

    QPixmap captchaImage;

    QLabel *imageLabel;

    QLabel *statusLabel;

    QLineEdit *captchaLineEdit;

    QPushButton *submitButton;

    QPushButton *refreshButton;

    QPushButton *closeButton;
void createForm();
void createActions();
void getCaptcha();
void submitCaptcha();

};
endif // WIDGET_H

widget.cpp


    #include "widget.h"
    #include "QtNetwork/QtNetwork"
    #include "QtGui"


void Widget::on_refreshButton_pressed()
{
    ;
}

void Widget::on_submitButton_pressed()
{
    ;
}

void Widget::on_closeButton_pressed()
{
    ;
}

// Create UI Components
void Widget::createForm()
{
    // Create Main Layout
    QVBoxLayout *mainLayout = new QVBoxLayout(this);

//    // set captcha pixmap to imageLabel for displaying
//    imageLabel->setPixmap(captchaImage);

// Create Buttons
QVBoxLayout *buttonLayout = new QVBoxLayout();
submitButton->setText("Submit");
refreshButton->setText("Refresh");
closeButton->setText("Close");
buttonLayout->addWidget(submitButton);
buttonLayout->addWidget(refreshButton);
buttonLayout->addWidget(closeButton);

// Complete Layouts
// lineEdit & submitStatus
QVBoxLayout *lineEditLayout = new QVBoxLayout();
lineEditLayout->addStretch();
lineEditLayout->addWidget(statusLabel);
lineEditLayout->addWidget(captchaLineEdit);
lineEditLayout->addStretch();

// Create Bottom Layout
QHBoxLayout *bottomLayout = new QHBoxLayout();
bottomLayout->addLayout(lineEditLayout);
bottomLayout->addLayout(buttonLayout);

// Add to mainLayout

//    mainLayout->addWidget(imageLabel);

    mainLayout->addLayout(bottomLayout);

    setLayout(mainLayout);

}
// Bind Slots and Signals

void Widget::createActions()

{

    ;

}
void Widget::getCaptcha()

{

    ;

}
void Widget::submitCaptcha()

{

    ;

}
Widget::Widget(QWidget *parent) :

    QWidget(parent)

{

    createForm();

//    createActions();

}

												

Answer 1

You need to initialize your private class members, probably in your constructor, before you use them.

Widget::Widget(QWidget* parent) :
    QWidget(parent)
{
    captchaImage = new QPixmap;
    imageLabel = new QLabel(this);
    statusLabel = new QLabel(this);
    captchaLineEdit = new QLineEdit(this);
    submitButton = new QPushButton(this);
    refreshButton = new QPushButton(this);
    closeButton = new QPushButton(this);

    createForm();
//    createActions();
}

Also note that QPixmap does not derive from QObject, so you’ll have to delete it manually. It may be better to remove the QPixmap *captchaImage member from your class and use temporary QPixmap objects in your code.