Error when trying to update TableView

[Ferric]

Hi,

I am new to Qt programming and Im having problems trying to insert new data into a QTableView, via a QStandardItemModel,

Specifically, I am having trouble trying to update the table from within a function "void Loader::addChannelToTable() "

#include <QtGui>
#include "loader.h"
#include <QString>
#include <QTextStream>
#include "qextserialport.h"
#include "addDialog.h"
#include <QtGui/QApplication>
#include <QCoreApplication>
#include <QString>
#include <QTextStream>
#include <QThread>
#include <QTime>
#include <QtGlobal>
#include <qdatetime.h>
#include <QByteArray>
#include <QBitArray> // probably shouldnt use as RS232 works with bytes.
#include <QStandardItem>
#include <QStandardItemModel>
#include <QVariant>
#include <QModelIndex>
 
 
Loader::Loader(QWidget *parent)
    : QWidget(parent)
 {
 
 
    QTableView *channelsView = new QTableView();
            QStandardItemModel *model = new QStandardItemModel(4,2);
 
//               for (int row = 0; row < 4; ++row) {
//                 for (int column = 0; column < 2; ++column) {
//                     QStandardItem *item = new QStandardItem(QString("%0, %1").arg(row).arg(column));
//                     //QStandardItem *item = new QStandardItem(QString("row %0, column %1").arg(row).arg(column));
//                    model->setItem(row, column, item); //This item is put in the model by using the setItem(int, int, QStandardItem*) method.
//                }
//             }                                      //When I uncomment this section the Table is updated
 
     channelsView->setModel(model);
 
 
     QLabel *titleLabel = new QLabel(tr("COMMUNICATIONS"));
     QLabel *descriptionLabel = new QLabel(tr("Determines Distribution"));
     QLabel *netNameLabel = new QLabel(tr("Net Name:"));
     QLabel *currentChannelsLabel = new QLabel(tr("Descriptionfor Net:"));
     QLabel *cloningLabel = new QLabel(tr("Enable Cloning"));
     netNameLine = new QLineEdit;
     currentChannelsText = new QTextEdit;
     QPushButton *saveButton = new QPushButton(tr("Save Configuration Data As..."));
     QPushButton *uploadButton = new QPushButton(tr("Upload Configuration "));
     QPushButton *quitButton = new QPushButton(tr("Quit"));
     QPushButton *addChannelButton = new QPushButton(tr("Add Channel")); // the 'tr' is for translate...
     QPushButton *removeChannelButton = new QPushButton(tr("Remove Channel"));
     QCheckBox *cloningEnabled = new QCheckBox();
     QHBoxLayout *secondLayout = new QHBoxLayout();
     secondLayout->addWidget(saveButton);
     secondLayout->addWidget(uploadButton);
     secondLayout->addWidget(quitButton);
 
     QHBoxLayout *thirdLayout = new QHBoxLayout();
     thirdLayout->addWidget(cloningLabel);
     thirdLayout->addWidget(cloningEnabled);
 
     QGridLayout *mainLayout = new QGridLayout;
     mainLayout->addWidget(titleLabel, 0, 1);   //The title widget (WInDows GadgET) is situated at row 0, column 1, in the grid layout.
     mainLayout->addWidget(descriptionLabel, 1, 1, Qt::AlignTop);
     mainLayout->addWidget(netNameLabel, 4, 0);
     mainLayout->addWidget(netNameLine, 4, 1);
     mainLayout->addLayout(thirdLayout,5,1);
     mainLayout->addWidget(addChannelButton, 6, 1);
     mainLayout->addWidget(removeChannelButton, 7, 1);
     mainLayout->addWidget(channelsView, 8, 1);
     mainLayout->addWidget(currentChannelsLabel, 8, 0, Qt::AlignTop);
     mainLayout->addLayout(secondLayout,9,1);
     setLayout(mainLayout);
     setWindowTitle(tr("Unit Loader"));
 
     QObject::connect(quitButton, SIGNAL(clicked()),
                          this,  SLOT(close()));
 
     QObject::connect(uploadButton, SIGNAL(clicked()),
                          this,  SLOT(calculateRandomCode()));
 
     QObject::connect(uploadButton, SIGNAL(clicked()),
                          this,  SLOT(send()));
 
     QObject::connect(addChannelButton, SIGNAL(clicked()),      // So I click the addChannel button and the addChannel Dialog opens
                      this,  SLOT(addChannelDialog()));         // So I click the addChannel button and the addChannel Dialog opens
 }
 
 
void Loader::addChannelDialog() // the addChannelDialog SLOT or Function..
{
    AddDialog *dialog = new AddDialog(this);    // Creates a new object; *dialog of class AddDialog
    dialog->show();                             //Shows the dialog..
 
    QObject::connect(dialog, SIGNAL(addThisChannel()),
             this, SLOT(addChannelToTable()));
}
 
void Loader::addChannelToTable()  // I want this SLOT to be activated when the addButton (from the AddDialog::dialog object) is clicked.
 
{
    QMessageBox::information(
    this,
    tr("Yes,"),
    tr("It works.") );
 
               for (int row = 0; row < 4; ++row) {
                 for (int column = 0; column < 2; ++column) {
                     QStandardItem *item = new QStandardItem(QString("%0, %1").arg(row).arg(column));
                     model->setItem(row, column, item); //This item is put in the model by using the setItem(int, int, QStandardItem*) method.
                }
            }                 // I think my problem is in the line above or below.
 
             channelsView->setModel(model);
}
 
 
 
void Loader::send()
 
 
{
 }
 
 
 
void Loader::calculateRandomCode()
{
 
}

#include <QtGui>
#include "loader.h"
#include <QString>
#include <QTextStream>
#include "qextserialport.h"
#include "addDialog.h"
#include <QtGui/QApplication>
#include <QCoreApplication>
#include <QString>
#include <QTextStream>
#include <QThread>
#include <QTime>
#include <QtGlobal>
#include <qdatetime.h>
#include <QByteArray>
#include <QBitArray> // probably shouldnt use as RS232 works with bytes.
#include <QStandardItem>
#include <QStandardItemModel>
#include <QVariant>
#include <QModelIndex>


Loader::Loader(QWidget *parent)
    : QWidget(parent)
 {


    QTableView *channelsView = new QTableView();
            QStandardItemModel *model = new QStandardItemModel(4,2);

//               for (int row = 0; row < 4; ++row) {
//                 for (int column = 0; column < 2; ++column) {
//                     QStandardItem *item = new QStandardItem(QString("%0, %1").arg(row).arg(column));
//                     //QStandardItem *item = new QStandardItem(QString("row %0, column %1").arg(row).arg(column));
//                    model->setItem(row, column, item); //This item is put in the model by using the setItem(int, int, QStandardItem*) method.
//                }
//             }                                      //When I uncomment this section the Table is updated

     channelsView->setModel(model);


     QLabel *titleLabel = new QLabel(tr("COMMUNICATIONS"));
     QLabel *descriptionLabel = new QLabel(tr("Determines Distribution"));
     QLabel *netNameLabel = new QLabel(tr("Net Name:"));
     QLabel *currentChannelsLabel = new QLabel(tr("Descriptionfor Net:"));
     QLabel *cloningLabel = new QLabel(tr("Enable Cloning"));
     netNameLine = new QLineEdit;
     currentChannelsText = new QTextEdit;
     QPushButton *saveButton = new QPushButton(tr("Save Configuration Data As..."));
     QPushButton *uploadButton = new QPushButton(tr("Upload Configuration "));
     QPushButton *quitButton = new QPushButton(tr("Quit"));
     QPushButton *addChannelButton = new QPushButton(tr("Add Channel")); // the 'tr' is for translate...
     QPushButton *removeChannelButton = new QPushButton(tr("Remove Channel"));
     QCheckBox *cloningEnabled = new QCheckBox();
     QHBoxLayout *secondLayout = new QHBoxLayout();
     secondLayout->addWidget(saveButton);
     secondLayout->addWidget(uploadButton);
     secondLayout->addWidget(quitButton);

     QHBoxLayout *thirdLayout = new QHBoxLayout();
     thirdLayout->addWidget(cloningLabel);
     thirdLayout->addWidget(cloningEnabled);

     QGridLayout *mainLayout = new QGridLayout;
     mainLayout->addWidget(titleLabel, 0, 1);   //The title widget (WInDows GadgET) is situated at row 0, column 1, in the grid layout.
     mainLayout->addWidget(descriptionLabel, 1, 1, Qt::AlignTop);
     mainLayout->addWidget(netNameLabel, 4, 0);
     mainLayout->addWidget(netNameLine, 4, 1);
     mainLayout->addLayout(thirdLayout,5,1);
     mainLayout->addWidget(addChannelButton, 6, 1);
     mainLayout->addWidget(removeChannelButton, 7, 1);
     mainLayout->addWidget(channelsView, 8, 1);
     mainLayout->addWidget(currentChannelsLabel, 8, 0, Qt::AlignTop);
     mainLayout->addLayout(secondLayout,9,1);
     setLayout(mainLayout);
     setWindowTitle(tr("Unit Loader"));

     QObject::connect(quitButton, SIGNAL(clicked()),
                          this,  SLOT(close()));

     QObject::connect(uploadButton, SIGNAL(clicked()),
                          this,  SLOT(calculateRandomCode()));

     QObject::connect(uploadButton, SIGNAL(clicked()),
                          this,  SLOT(send()));

     QObject::connect(addChannelButton, SIGNAL(clicked()),      // So I click the addChannel button and the addChannel Dialog opens
                      this,  SLOT(addChannelDialog()));         // So I click the addChannel button and the addChannel Dialog opens
 }


void Loader::addChannelDialog() // the addChannelDialog SLOT or Function..
{
    AddDialog *dialog = new AddDialog(this);    // Creates a new object; *dialog of class AddDialog
    dialog->show();                             //Shows the dialog..

    QObject::connect(dialog, SIGNAL(addThisChannel()),
             this, SLOT(addChannelToTable()));
}

void Loader::addChannelToTable()  // I want this SLOT to be activated when the addButton (from the AddDialog::dialog object) is clicked.

{
    QMessageBox::information(
    this,
    tr("Yes,"),
    tr("It works.") );

               for (int row = 0; row < 4; ++row) {
                 for (int column = 0; column < 2; ++column) {
                     QStandardItem *item = new QStandardItem(QString("%0, %1").arg(row).arg(column));
                     model->setItem(row, column, item); //This item is put in the model by using the setItem(int, int, QStandardItem*) method.
                }
            }                 // I think my problem is in the line above or below.

             channelsView->setModel(model);
}



void Loader::send()


{
 }



void Loader::calculateRandomCode()
{

}

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My code compiles and runs, but as soon as I get to the part where I can run "void Loader::addChannelToTable() " the information box "yes it works" is displayed, then windows shows and error screen and I am forced to close my program.


When I update the table from within the

Loader::Loader(QWidget *parent)
    : QWidget(parent)
 {
//
}

Loader::Loader(QWidget *parent)
    : QWidget(parent)
 {
//
}

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section it works fine.



Thanks for reading, any help would be greatly appreciated

[kichi]

In addChannelToTable(), you are using variables model and channelsView.
but in Loader(), you are defined model and channelsView as local pointer.

I'm sorry in poor English.

[Ferric]

Ah, I think I understand what you mean, I need to define model and channelsView as a global pointer maybe? or something else?

[kichi]

Ah, I think I understand what you mean, I need to define model and channelsView as a global pointer maybe? or something else?

Yes. I think you should declare model and channelsView as class member.

// Loader.h
class Loader {
    Q_OBJECT
public:
    Loader::Loader(QWidget *parent = 0);
 
    // ...
 
private:
    QTableView *channelsView;	// pointer data member
    QStandardItemModel *model;
};

// Loader.h
class Loader {
    Q_OBJECT
public:
    Loader::Loader(QWidget *parent = 0);

    // ...

private:
    QTableView *channelsView;	// pointer data member
    QStandardItemModel *model;
};

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// Loader.cpp
Loader::Loader(QWidget *parent)
    : QWidget(parent), channelsView(0), model(0) // initialization.
 {
 
 
    channelsView = new QTableView();		// constraction
    model = new QStandardItemModel(4,2);
 
    // ....
 
};
 
void Loader::addChannelToTable()  // I want this SLOT to be activated when the addButton (from the AddDialog::dialog object) is clicked.
{
    QMessageBox::information(
    this,
    tr("Yes,"),
    tr("It works.") );
 
    if (!channelsView || !model) {    // check whether pointers are not 0.
        return;
    }
 
    for (int row = 0; row < 4; ++row) {
        for (int column = 0; column < 2; ++column) {
            QStandardItem *item = new QStandardItem(QString("%0, %1").arg(row).arg(column));
            model->setItem(row, column, item); //This item is put in the model by using the setItem(int, int, QStandardItem*) method.
        }
    }                 // I think my problem is in the line above or below.
 
    //channelsView->setModel(model);    // This is not necessary, because setModel() has been called in Loader().
                                        // channelsView has already referred to the model.
}

// Loader.cpp
Loader::Loader(QWidget *parent)
    : QWidget(parent), channelsView(0), model(0) // initialization.
 {
 
 
    channelsView = new QTableView();		// constraction
    model = new QStandardItemModel(4,2);

    // ....

};

void Loader::addChannelToTable()  // I want this SLOT to be activated when the addButton (from the AddDialog::dialog object) is clicked.
{
    QMessageBox::information(
    this,
    tr("Yes,"),
    tr("It works.") );

    if (!channelsView || !model) {    // check whether pointers are not 0.
        return;
    }

    for (int row = 0; row < 4; ++row) {
        for (int column = 0; column < 2; ++column) {
            QStandardItem *item = new QStandardItem(QString("%0, %1").arg(row).arg(column));
            model->setItem(row, column, item); //This item is put in the model by using the setItem(int, int, QStandardItem*) method.
        }
    }                 // I think my problem is in the line above or below.
 
    //channelsView->setModel(model);    // This is not necessary, because setModel() has been called in Loader().
                                        // channelsView has already referred to the model.
}

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[Ferric]

Thanks a lot, it works now, if you have time could you please tell me the reasoning behind the following lines of code:

[code]
if (!channelsView || !model) { // check whether pointers are not 0.
return;
}

Thanks

[kichi]

Thanks a lot, it works now, if you have time could you please tell me the reasoning behind the following lines of code:

[code]
if (!channelsView || !model) { // check whether pointers are not 0.
return;
}

I apologize you annoying.
In this case, the code is not necessary.

This check is necessary, in the following case.

• Always initialize the pointer with 0, before using the pointer.
• Always assign 0 to the pointer which is referring to nothing.
• Make the pointer refer to object with "new", when it becomes necessary.
• Delete the pointer to object, when it becomes unnecessary, and assign 0 to the pointer.
• "new" may throw std::bad_alloc when the memory becomes insufficient. so always use "try" keyword, and "catch" the exception. In particular, never throw any exceptions out of constractor.
• Always check the pointer whether it is not 0, before which is used.

If you don't need std::bad_exception, you can write the following code.

QTableView *channelsView = new(nothrow) QTableView();

QTableView *channelsView = new(nothrow) QTableView();

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"new(nothrow)" does not throw std::bad_exec, and if there is not enough memory, it returns 0.
but I have rarely seen this using up to now, on the Web.

I'm sorry in poor English.

[Ferric]

Ah I think I understand what you are saying, Thanks once again : ]