Program runs but nothing displays Qt c++

Question

Hi my program runs with no errors but nothing is displayed on screen, a window is meant to pop up which runs another program with a QProcess, this program runs fine. code follows:

header file:

#ifndef WIDGET_H
#define WIDGET_H

#include <QWidget>
#include <QtGui>
#include <QTimer>

namespace Ui {
    class Widget;
}

class Widget : public QWidget
{
    Q_OBJECT

public:
    explicit Widget(QWidget *parent = 0);
    ~Widget();
private slots:
    void setTimer();
    void displayAdvice();
    void cancelTimer();
    void addAdvice();
    void processDone(int);
private:
    QLabel* timerLbl;
    QLineEdit* timerEdt;
    QTextEdit* adviceEdt;
    QPushButton* okBtn;
    QPushButton* cancelBtn;
    QTimer* timer;
    QProcess *process;
    void setupGui();


private:
    Ui::Widget *ui;
};

#endif // WIDGET_H

widget.cpp

#include "widget.h"
#include "ui_widget.h"

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

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

void Widget::setupGui()
{
    timerLbl = new QLabel("Timer set interval in seconds");
    timerEdt = new QLineEdit();
    adviceEdt = new QTextEdit();
    this->adviceEdt->setReadOnly(true);
    okBtn = new QPushButton("OK");
    cancelBtn = new QPushButton("Cancel");
    QVBoxLayout* layout = new QVBoxLayout();
    layout->addWidget(timerLbl);
    layout->addWidget(timerEdt);
    layout->addWidget(okBtn);
    layout->addWidget(adviceEdt);
    layout->addWidget(cancelBtn);
    this->setWindowTitle("Advice");
    this->setLayout(layout);

    connect(okBtn,SIGNAL(clicked()), this, SLOT(setTimer()));
    connect(cancelBtn, SIGNAL(clicked()), this, SLOT(cancelTimer()));
    connect(timer, SIGNAL(timeout()),this, SLOT(displayAdvice()));

}

void Widget::setTimer()
{
    timer = new QTimer(this);
    connect(timer, SIGNAL(timeout()),this, SLOT(cancelTimer()));
    QString setting = this->timerEdt->text();
    bool ok;
    int set = setting.toInt(&ok,10);
    set = set * 1000;
    timer->setInterval(set);
    timer->start();
    timerEdt->setReadOnly(true);
    okBtn->setDown(true);
}

void Widget::cancelTimer()
{
    timer->stop();
    adviceEdt->clear();
    okBtn->setDown(false);
    timerEdt->clear();
    timerEdt->setReadOnly(false);
}

void Widget::displayAdvice()
{
    process = new QProcess(this);
    process->start("C:/Users/Dmon/Desktop/47039949 COS3711 Assignment 2/Question 4/Ass2Q4Part1-build-desktop/debug/Ass2Q4Part1.exe");
    connect(process, SIGNAL(readyReadStandardOutput()),this, SLOT(addAdvice()));
    connect(process, SIGNAL(finished(int)),this, SLOT(processDone(int)));
}

void Widget::addAdvice()
{
    QByteArray data = process->readAllStandardOutput();
    QString strToWrite = data;
    this->adviceEdt->clear();
    this->adviceEdt->append(strToWrite);
}

void Widget::processDone(int)
{
    process->close();
    process->deleteLater();
    process=0;
}

main.cpp

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

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

    return a.exec();
}

Program runs with nothing displayed then eventually exits with no errors after about 15 seconds.

Answer 1

Your problem is that you're already using a user interface coming from the form file (.ui file). You need to decide which one you wish to use.

To fix your code, all you need to do is remove all references to the Ui namespace. Simply remove the below:

namespace Ui {
    class Widget;
}
//
private:
    Ui::Widget *ui;
//
#include "ui_widget.h"
//
delete ui;

Also, note that this line is working with a null or undefined pointer value - you never create the timer instance:

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

Finally, there's no reason whatsoever to allocate the member widgets on the heap. It does, in fact, waste a bit of heap memory since QWidget instances are very small.

Here's how your code could look. I've put it all in a single file, to keep it short. You obviously don't need it in a single file. I've also made the UI a bit more compliant with usual expectations. E.g. controls that can't be interacted with should be disabled.

// main.cpp
#include <QApplication>
#include <QtWidgets>
#include <QTimer>

class Widget : public QWidget
{
   Q_OBJECT
public:
   explicit Widget(QWidget *parent = 0);
private slots:
   void setTimer();
   void displayAdvice();
   void cancelTimer();
   void addAdvice();
   void processDone(int);
private:
   QLabel m_timerLbl;
   QLineEdit m_timerEdt;
   QTextEdit m_adviceEdt;
   QPushButton m_okBtn;
   QPushButton m_cancelBtn;
   QTimer m_timer;
   QProcess m_process;
   void setupGui();
};

Widget::Widget(QWidget *parent) :
   QWidget(parent)
{
   setupGui();
}

void Widget::setupGui()
{
   m_timerLbl.setText("Timer set interval in seconds");
   m_adviceEdt.setReadOnly(true);
   m_okBtn.setText("OK");
   m_cancelBtn.setText("Cancel");
   m_cancelBtn.setEnabled(false);
   QVBoxLayout* layout = new QVBoxLayout(this);
   layout->addWidget(&m_timerLbl);
   layout->addWidget(&m_timerEdt);
   layout->addWidget(&m_okBtn);
   layout->addWidget(&m_adviceEdt);
   layout->addWidget(&m_cancelBtn);
   setWindowTitle("Advice");

   connect(&m_okBtn, SIGNAL(clicked()), SLOT(setTimer()));
   connect(&m_cancelBtn, SIGNAL(clicked()), SLOT(cancelTimer()));
   connect(&m_timer, SIGNAL(timeout()), SLOT(displayAdvice()));
   connect(&m_timer, SIGNAL(timeout()), SLOT(cancelTimer()));

   connect(&m_process, SIGNAL(readyReadStandardOutput()), SLOT(addAdvice()));
   connect(&m_process, SIGNAL(finished(int)), SLOT(processDone(int)));
}

void Widget::setTimer()
{
   QString const setting = m_timerEdt.text();
   bool ok;
   int set = setting.toInt(&ok,10) * 1000;
   m_timer.setInterval(set);
   m_timer.start();
   m_timerEdt.setEnabled(false);
   m_okBtn.setEnabled(false);
   m_cancelBtn.setEnabled(true);
}

void Widget::cancelTimer()
{
   m_timer.stop();
   m_adviceEdt.clear();
   m_timerEdt.clear();
   m_okBtn.setEnabled(true);
   m_timerEdt.setEnabled(true);
   m_cancelBtn.setEnabled(false);
}

void Widget::displayAdvice()
{
   m_process.start("bash", QStringList() << "-c" << "echo 'Hello!'");
#if 0
   m_process.start(QDir::homePath() +
                   "/Desktop/47039949 COS3711 Assignment 2/Question 4/Ass2Q4Part1-build-desktop/debug/Ass2Q4Part1.exe");
#endif
}

void Widget::addAdvice()
{
   QByteArray const data = m_process.readAllStandardOutput();
   m_adviceEdt.setPlainText(QString::fromLocal8Bit(data));
}

void Widget::processDone(int)
{
   m_process.close();
}

int main(int argc, char *argv[])
{
   QApplication a(argc, argv);
   Widget w;
   w.show();
   return a.exec();
}

#include "main.moc"