Instantiate QTableWidget dynamically during runtime

[ouekah]

Hi guys,

I'm developing an application which carries a matrix and I would like to allow the user to display that matrix on demand. I use a QTableWidget within a QDialog to do that.

When I launch the application the QDialog is created but cannot be displayed (I don't want to...) until a first matrix is computed. At that time the QTableWidget is not instantiated yet. My idea is to instantiate the table only once the first matrix computed (because then I will know the dimensions). If the matrix or its dimension are further modified, the table will be modified accordingly (but not instantiated again for efficiency purposes).

Apparently there is a problem with my philosophy, because when I run the application, it suddenly crashes when it executes:

this->matrixTable = new QTableWidget(size, size, this);

this->matrixTable = new QTableWidget(size, size, this);

To copy to clipboard, switch view to plain text mode 

And I don't understand why... Could somebody explain me why I can't do that and hopefully also tell me how to proceed then ?

[JD2000]

I think that you want a QTableView to do this.

Base it on a model and use the dataChanged() or layoutChanged() signals to achieve what you are after.

[Lykurg]

I guess matrixTable is your original table widget. So there is no need to create a new one. just clear the existing and reuse it.

[ouekah]

I modified my dialog but my program keeps crashing and I don't find the root cause.

My application is defined as follows:

there are 3 classes:

Dummy, Coordinator and MatrixDialog

Dummy performs computation to generate the matrix I need. This matrix is then sent to the Coordinator which forwards it to the MatrixDialog.

here is the code of MatrixDialog:

matrixDialog.h

class MatrixDialog : public QDialog {
	Q_OBJECT
 
public:
	MatrixDialog(QString windowTitle, QWidget *parent = 0);
	void updateTable(QStringList& strings, SquareMatrix& matrix);
 
 
private slots:
	void ok();
 
private:
	QTableWidget *matrixTable;
};

class MatrixDialog : public QDialog {
	Q_OBJECT

public:
	MatrixDialog(QString windowTitle, QWidget *parent = 0);
	void updateTable(QStringList& strings, SquareMatrix& matrix);


private slots:
	void ok();

private:
	QTableWidget *matrixTable;
};

To copy to clipboard, switch view to plain text mode 

matrixDialog.cpp

#include "matrixDialog.h"
 
MatrixDialog::MatrixDialog(QString windowTitle, QWidget *parent) : QDialog(parent) {
	this->matrixTable = new QTableWidget(this);
	this->matrixTable->setEditTriggers(QAbstractItemView::NoEditTriggers);
	this->matrixTable->horizontalHeader()->setStretchLastSection(true);
	this->matrixTable->verticalHeader()->setStretchLastSection(true);
 
	QHBoxLayout *formatLayout = new QHBoxLayout;
	formatLayout->addWidget(mapleLabel);
	formatLayout->addWidget(mapleEdit);
 
	QPushButton *okButton = new QPushButton("OK");
	okButton->setFixedSize(okButton->size());
	connect(okButton, SIGNAL(clicked()), this, SLOT(ok()));
 
	QVBoxLayout *mainLayout = new QVBoxLayout;
	mainLayout->addWidget(matrixTable);
	mainLayout->addWidget(okButton);
 
	setLayout(mainLayout);
 
	setWindowTitle(windowTitle);
}
 
void MatrixDialog::ok() {
	this->hide();
}
 
void MatrixDialog::updateTable(QStringList& tickers, SquareMatrix& matrix) {
	int dimension = matrix.getDimension();
	double value;
 
	this->matrixTable->clear();
	this->matrixTable->setRowCount(matrix.getRows());
	this->matrixTable->setColumnCount(matrix.getColumns());
 
	for(int row = 0; row < dimension; ++row) {
		QTableWidgetItem *headerItem = new QTableWidgetItem(tickers.at(row));
		matrixTable->setHorizontalHeaderItem(row, headerItem);
		matrixTable->setVerticalHeaderItem(row, headerItem);
		for(int column = 0; column < dimension; ++column) {
			matrix.getElement(row, column, value);
			QTableWidgetItem *item = new QTableWidgetItem(QString::number(value));
			item->setTextAlignment(Qt::AlignCenter);
			this->matrixTable->setItem(row, column, item);
		}
	}
}

#include "matrixDialog.h"

MatrixDialog::MatrixDialog(QString windowTitle, QWidget *parent) : QDialog(parent) {
	this->matrixTable = new QTableWidget(this);
	this->matrixTable->setEditTriggers(QAbstractItemView::NoEditTriggers);
	this->matrixTable->horizontalHeader()->setStretchLastSection(true);
	this->matrixTable->verticalHeader()->setStretchLastSection(true);

	QHBoxLayout *formatLayout = new QHBoxLayout;
	formatLayout->addWidget(mapleLabel);
	formatLayout->addWidget(mapleEdit);

	QPushButton *okButton = new QPushButton("OK");
	okButton->setFixedSize(okButton->size());
	connect(okButton, SIGNAL(clicked()), this, SLOT(ok()));

	QVBoxLayout *mainLayout = new QVBoxLayout;
	mainLayout->addWidget(matrixTable);
	mainLayout->addWidget(okButton);

	setLayout(mainLayout);

	setWindowTitle(windowTitle);
}

void MatrixDialog::ok() {
	this->hide();
}

void MatrixDialog::updateTable(QStringList& tickers, SquareMatrix& matrix) {
	int dimension = matrix.getDimension();
	double value;

	this->matrixTable->clear();
	this->matrixTable->setRowCount(matrix.getRows());
	this->matrixTable->setColumnCount(matrix.getColumns());

	for(int row = 0; row < dimension; ++row) {
		QTableWidgetItem *headerItem = new QTableWidgetItem(tickers.at(row));
		matrixTable->setHorizontalHeaderItem(row, headerItem);
		matrixTable->setVerticalHeaderItem(row, headerItem);
		for(int column = 0; column < dimension; ++column) {
			matrix.getElement(row, column, value);
			QTableWidgetItem *item = new QTableWidgetItem(QString::number(value));
			item->setTextAlignment(Qt::AlignCenter);
			this->matrixTable->setItem(row, column, item);
		}
	}
}

To copy to clipboard, switch view to plain text mode 

When the Coordinator calls updateTable of MatrixDialog, the application crashes. I even deleted all updateTable's content, but the application still crashes !

Coordinator is defined as follows:

class Coordinator : public QObject {
	Q_OBJECT
...
};

class Coordinator : public QObject {
	Q_OBJECT
...
};

To copy to clipboard, switch view to plain text mode 

I'm lost...I just don't understand how I can do an unauthorized access... I would really appreciate some help !

Thanks guys in advance for your support

[Lykurg]

Run a debugger and see where it crashes exactly. I guess its on tickers.at(row) are you sure your string list is as long as your dimension?

[Lykurg]

matrixTable->setHorizontalHeaderItem(row, headerItem);
matrixTable->setVerticalHeaderItem(row, headerItem);

matrixTable->setHorizontalHeaderItem(row, headerItem);
matrixTable->setVerticalHeaderItem(row, headerItem);

To copy to clipboard, switch view to plain text mode 

And this is also buggy! if matrix.getRows() > matrix.getColums()

[ouekah]

I believe the issue is somewhere else because if I delete all the instructions within updateTable, the application still crashes. But If the Coordinator doesn't call updateTable, the application runs ok...

Thank you so much for your help, I really appreciate...

[Lykurg]

Then how the Coordinator is calling the member function of MatrixDialog. Have you check the pointer?

[ouekah]

I solved the issue finally ! It was not a Qt issue, but a pointer issue ...(shame on me) ^^