Why am I not getting a display in my Qt Widget?

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(); }

This isn't your problem, but why do you have a bunch of empty statements with semicolons? — Michael Aaron Safyan

Terence Simpson Terence Simpson · Accepted Answer · 2011-02-27T05:16:56

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.

Why am I not getting a display in my Qt Widget?

endif // WIDGET_H

2 Answers