QTableWidget and the setHorizontalHeaderItem/setVerticalHeaderItem functions

[ouekah]

Hi,

I use a QTableWidget to display a matrix. This matrix is subject to change over time and consequently so is the display.

I always use the same function to update the display: "updateTable"

The latter takes a list of names and a SquareMatrix object (that I created my self) as arguments.

My problem is the following:

everything goes fine when the display is updated for the first time, but the application crashes on subsequent updates. I checked my function and the problems seems to come from the setHorizontalHeaderItem/setVerticalHeaderItem functions.

Here is the code of "updateTable":

void MatrixDialog::updateTable(QStringList& names, SquareMatrix& matrix) {
	int dimension = matrix.getDimension();
	double value;
 
	this->mapleEdit->setText(matrix.toMapleFormat());
	this->mapleEdit->setCursorPosition(0);
	this->matlabEdit->setText(matrix.toMatlabFormat());
	this->matlabEdit->setCursorPosition(0);
 
	this->matrixTable->clear();
	this->matrixTable->setRowCount(matrix.getRows());
	this->matrixTable->setColumnCount(matrix.getColumns());
 
	for(int row = 0; row < dimension; ++row) {
		QTableWidgetItem *headerItem = new QTableWidgetItem(names.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);
		}
	}
}

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

	this->mapleEdit->setText(matrix.toMapleFormat());
	this->mapleEdit->setCursorPosition(0);
	this->matlabEdit->setText(matrix.toMatlabFormat());
	this->matlabEdit->setCursorPosition(0);

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

	for(int row = 0; row < dimension; ++row) {
		QTableWidgetItem *headerItem = new QTableWidgetItem(names.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);
		}
	}
}

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If I comment the calls to these functions, the application doesn't crash anymore and the values are correctly updated.

void MatrixDialog::updateTable(QStringList& names, SquareMatrix& matrix) {
	int dimension = matrix.getDimension();
	double value;
 
	this->mapleEdit->setText(matrix.toMapleFormat());
	this->mapleEdit->setCursorPosition(0);
	this->matlabEdit->setText(matrix.toMatlabFormat());
	this->matlabEdit->setCursorPosition(0);
 
	this->matrixTable->clear();
	this->matrixTable->setRowCount(matrix.getRows());
	this->matrixTable->setColumnCount(matrix.getColumns());
 
	for(int row = 0; row < dimension; ++row) {
		QTableWidgetItem *headerItem = new QTableWidgetItem(names.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);
		}
	}
}

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

	this->mapleEdit->setText(matrix.toMapleFormat());
	this->mapleEdit->setCursorPosition(0);
	this->matlabEdit->setText(matrix.toMatlabFormat());
	this->matlabEdit->setCursorPosition(0);

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

	for(int row = 0; row < dimension; ++row) {
		QTableWidgetItem *headerItem = new QTableWidgetItem(names.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);
		}
	}
}

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This might be related to

this->matrixTable->clear();

this->matrixTable->clear();

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but I'm not sure. Could someone explain to me what's going on and what should I do to prevent these crashes from happening ?

[Lykurg]

If your matrix don't have different sizes and names you could use QTableWidget::clearContents().

What crashes your app is that if dimension is lesser than matrix.getColumns() or matrix.getRows(). That the only reason I can see right now.

[ouekah]

Unfortunately the matrix's size may vary over time... And dimension points to the same value as rows and columns in SquareMatrix... I feel sad

[Lykurg]

And dimension points to the same value as rows and columns in SquareMatrix...

I thought so because of the name. But you never know here... So only thing I can guess of (without proving it) is, that you cant reuse one item for vertical and horizontal header. So try:

matrixTable->setHorizontalHeaderItem(row, new QTableWidgetItem(names.at(row)));
matrixTable->setVerticalHeaderItem(row, new QTableWidgetItem(names.at(row)));

matrixTable->setHorizontalHeaderItem(row, new QTableWidgetItem(names.at(row)));
matrixTable->setVerticalHeaderItem(row, new QTableWidgetItem(names.at(row)));

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If that is also not helping, debug and backtrace to see where it exactly crashes.

[ouekah]

I read the documentation again and I noticed this function: "QTableWidget::setHorizontalHeaderLabels".

It's even easier with that one and there is no more crash...

[borzh62]

I read the documentation again and I noticed this function: "QTableWidget::setHorizontalHeaderLabels".

It's even easier with that one and there is no more crash...

Row/column indexes start from 1. You should use next code:

matrixTable->setHorizontalHeaderItem(row+1, headerItem);
matrixTable->setVerticalHeaderItem(row+1, headerItem);

matrixTable->setHorizontalHeaderItem(row+1, headerItem);
matrixTable->setVerticalHeaderItem(row+1, headerItem);

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[ChrisW67]

Row/column indexes start from 1.

No, no they don't.

I also note that if the names list ever contains fewer names than the dimension of the matrix, deliberately or by accident, then the calls to QStringList::at() will fail.