Error when trying to update TableView

[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 : ]