Problem to access QStandardItemModel object

Combas · wrote on 30 Aug 2019, 18:51

I have built a class which contains an object "QTreeView" linked to an object "QStandardItemModel".
Inside this class, a button is linked to a "slot function" which inserts lines in the "QTreeView" and it works very well.
But if I call this function from outside this object, it crashes because the functions of the object "QStandardItemModel" are not accessible anymore. And I don't understand why...

The image below shows the very simple interface:

The object "QTreeView" with 2 columns
The left button "Insert Line" which belongs to the same class as the "QStandardItemModel" and the "QTreeView". This button is linked to a function "void InsertLine()" with QObject::connect process. This button works.
The button at the bottom "Test" does not belong to this class: it is connected to an intermediate function which calls the method "InsertLine()". This button does not work.

The line which causes the crash is:

nbColumns = SIM_table.columnCount();

The header file of the main class "mainwindow.h" is:

#ifndef MAINWINDOW_H
#define MAINWINDOW_H

#include "blocktablefields.h"

#include <QMainWindow>
#include <QPushButton>
#include <QStandardItemModel>
#include <QTreeView>

QT_BEGIN_NAMESPACE
class QAction;
class QLabel;
class QMenu;
QT_END_NAMESPACE

class MainWindow : public QMainWindow
{
    Q_OBJECT

public:
    MainWindow();

private slots:
    void Test();


private:
    QWidget *centralWidget;
    QVBoxLayout *vertLayout_Main;

    BlockTableFields *BTF_test;
    QPushButton *BT_test;

};

#endif

The corresponding .cpp file:


#include <QtWidgets>

#include "mainwindow.h"

MainWindow::MainWindow()
{

    QString titleTest;
    QList<QString> *listHeaders;

    // Initializations
    titleTest = QString("Tests");
    listHeaders = new QList<QString>;
    listHeaders->push_back("Field 1");
    listHeaders->push_back("Field 2");

    vertLayout_Main = new QVBoxLayout();
    BlockTableFields *BTF_test = new BlockTableFields(this, &titleTest, listHeaders);
    vertLayout_Main->addWidget(BTF_test);

    BT_test = new QPushButton("Test");
    QObject::connect(BT_test, SIGNAL(clicked()), this, SLOT(Test()));
    vertLayout_Main->addWidget(BT_test);

    centralWidget = new QWidget;
    setCentralWidget(centralWidget);
    centralWidget->setLayout(vertLayout_Main);

    setWindowTitle(tr("Test"));
    resize(400, 200);
}

void MainWindow::Test()
{
    BTF_test->InsertLine();
}

The header file of the class which contains the objects "QTreeView" and "QStandardItemModel" is:

#ifndef BLOCKTABLEFIELDS_H
#define BLOCKTABLEFIELDS_H

#include <QWidget>
#include <QLabel>
#include <QBoxLayout>
#include <QPushButton>
#include <QStandardItemModel>
#include <QTreeView>

class BlockTableFields : public QWidget
{
    Q_OBJECT
public:
    explicit BlockTableFields(QWidget *parent = nullptr, QString *blockTitle = nullptr, QList<QString> *listHeaders = nullptr);

signals:


public slots:
    void InitTable();
    void InsertLine();

private:
    QLabel *LB_title;
    QStandardItemModel SIM_table;
    QTreeView *TV_table;

    QPushButton *BT_AddLineBefore;

    // Layouts
    QHBoxLayout *horizLayout_All;
    QVBoxLayout *vertLayout_Text;
    QVBoxLayout *vertLayout_Buttons;
};

#endif // BLOCKTABLEFIELDS_H

The corresponding .cpp file:

#include "blocktablefields.h"

BlockTableFields::BlockTableFields(QWidget *parent, QString *blockTitle, QList<QString> *listHeaders) : QWidget(parent)
{
    int numHeader;

    // Title
    LB_title = new QLabel();
    if (blockTitle != nullptr)
    {
        LB_title->setText(*blockTitle);
    }

    // Headers
    // if no header is given, a table with only 1 column is built, with an empty header
    // else, the number of columns is fixed by the number of headers
    if ((listHeaders != nullptr) && (listHeaders->size() > 0))
    {
        SIM_table.setColumnCount(int(listHeaders->size()));
        for (numHeader = 0; numHeader < int(listHeaders->size()); numHeader++)
        {
            SIM_table.setHeaderData(numHeader, Qt::Horizontal, listHeaders->at(numHeader));
        }
    }
    else
    {
        SIM_table.setColumnCount(1);
        SIM_table.setHeaderData(0, Qt::Horizontal, QObject::tr(""));
    }

    // Creation of the first line
    InitTable();

    // Creation of the link between SIM_table and TV_table
    TV_table = new QTreeView;
    TV_table->setRootIsDecorated(false);
    TV_table->setAlternatingRowColors(true);
    TV_table->setModel(&SIM_table);

    // Buttons
    vertLayout_Buttons = new QVBoxLayout();
    // Add new line before the current line
    BT_AddLineBefore = new QPushButton("Insert Line");
    QObject::connect(BT_AddLineBefore, SIGNAL(clicked()), this, SLOT(InsertLine()));
    vertLayout_Buttons->addWidget(BT_AddLineBefore);

    // Spaces at the beginning and the end
    vertLayout_Buttons->insertStretch(0);
    vertLayout_Buttons->addStretch();

    // Vertical Layout (Title and field for text)
    vertLayout_Text = new QVBoxLayout();
    vertLayout_Text->addWidget(LB_title);
    vertLayout_Text->addWidget(TV_table);

    // Main Layout
    horizLayout_All = new QHBoxLayout();
    this->setLayout(horizLayout_All);
    horizLayout_All->addLayout(vertLayout_Buttons);
    horizLayout_All->addLayout(vertLayout_Text);

}

void BlockTableFields::InitTable()
{
    int numColumn;
    QStandardItem *defaultItem = new QStandardItem(QString(""));
    QList<QStandardItem *> defaultLine;
    for (numColumn = 0; numColumn < SIM_table.columnCount(); numColumn++){ defaultLine.push_back(defaultItem); }
    SIM_table.insertRow(0, defaultLine);
}

void BlockTableFields::InsertLine()
{
    QModelIndex tableIndex;
    int numLine = 0, numColumn, nbColumns;
    QStandardItem *defaultItem = new QStandardItem(QString(""));
    QList<QStandardItem *> defaultLine;
    nbColumns = SIM_table.columnCount();
    for (numColumn = 0; numColumn < nbColumns; numColumn++){ defaultLine.push_back(defaultItem); }

    tableIndex = TV_table->currentIndex();
    if (tableIndex.isValid())
    {
        numLine = tableIndex.row();
        SIM_table.insertRow(numLine, defaultLine);
        tableIndex = SIM_table.index(numLine, tableIndex.column());
        TV_table->setCurrentIndex(tableIndex);
    }
    else
    {
        numLine = 0;
        SIM_table.insertRow(numLine, defaultLine);
        tableIndex = SIM_table.index(numLine, 0);
        TV_table->setCurrentIndex(tableIndex);
    }
}

The complete project (very light) can be downloaded here:
Complete_project

If someone can tell me why it does not work, it would be very usefull for me!
Thank you in advance for your help!
Laurent

Christian Ehrlicher · 30 Aug 2019, 20:36

Your member MainWindow ::BTF_test is not initialized.
Apart from this you're leaking listHeaders (don't know why you need a pointer here) and your InitTable does not set anything correct since you're setting the same item on more than one cell which is not allowed.

Combas · wrote on 30 Aug 2019, 20:36

@christian-ehrlicher
Thank you very much for your answer !
Indeed, there was a double declaration of "BTF_test" which was the cause of my problem.
I will check the other points you mentionned to avoid new bugs.