begginers question

[JD2000]

Apologies, I misread your code and thought that maybe mdiArea->addSubwindow was being left hanging.

try

QMdiSubWindow *subWindow = mdiArea->addSubWindow(&spreadsheet);

[high_flyer]

Ok, I think that your spreadsheet parameter has an invalid pointer.
Can you show the code for MainWindowImpl::newFile ()?

[hollowhead]

Thanks for your reply....The code was above but here it is

void MainWindowImpl::newFile()
{
    Spreadsheet *spreadsheet = new Spreadsheet;
    spreadsheet->newFile();
    addSpreadsheet(spreadsheet);
    spreadsheet->show(); // possibly required?
}

void MainWindowImpl::newFile()
{
    Spreadsheet *spreadsheet = new Spreadsheet;
    spreadsheet->newFile();
    addSpreadsheet(spreadsheet);
    spreadsheet->show(); // possibly required?
}

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This calls this function in spreadsheet.cpp

void Spreadsheet::newFile()
{
    static int documentNumber = 1;
 
    curFile = tr("document%1.txt").arg(documentNumber);
    setWindowTitle(curFile + "[*]");
    action->setText(curFile);
    isUntitled = true;
    ++documentNumber;
}

void Spreadsheet::newFile()
{
    static int documentNumber = 1;

    curFile = tr("document%1.txt").arg(documentNumber);
    setWindowTitle(curFile + "[*]");
    action->setText(curFile);
    isUntitled = true;
    ++documentNumber;
}

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QMdiSubWindow *subWindow = mdiArea->addSubWindow(&spreadsheet); won't compile

[high_flyer]

Thanks for your reply....The code was above but here it is

Sorry, I missed it.

What does the Spreadsheet() constructor do?

Also you can try:

void MainWindowImpl::newFile()
{
    Spreadsheet *spreadsheet = new Spreadsheet;
    spreadsheet->newFile();
    spreadsheet->show();//to see if it gets displayed or also crashes.
   //addSpreadsheet(spreadsheet);
    //spreadsheet->show(); // possibly required? not needed here if its called in addSpreadsheet()
}

void MainWindowImpl::newFile()
{
    Spreadsheet *spreadsheet = new Spreadsheet;
    spreadsheet->newFile();
    spreadsheet->show();//to see if it gets displayed or also crashes.
   //addSpreadsheet(spreadsheet);
    //spreadsheet->show(); // possibly required? not needed here if its called in addSpreadsheet()
}

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What I also noticed in spreadsheet:

QAction *windowMenuAction() const { return action; } //added for MDI

QAction *windowMenuAction() const { return action; } //added for MDI

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When does 'action' gets initialized?

[hollowhead]

Thanks for your reply. I'm afraid your questions are starting to loose me....

I've pasted the last section of remaining code spreadsheet.cpp in the hope this will throw some light on the situation. The windowMenuAction is used in the addSpreadsheet function posted previously.
spreadsheet.cpp

#include <QtGui>
#include "spreadsheet.h"
#include "cell.h"
#include <QTextDocument>
Spreadsheet::Spreadsheet(QWidget *parent)
 : QTableWidget(parent)
{
 
	action = new QAction(this);
    action->setCheckable(true);
    connect(action, SIGNAL(triggered()), this, SLOT(show()));
    connect(action, SIGNAL(triggered()), this, SLOT(setFocus()));
 
    isUntitled = true;
 
	 autoRecalc = true;
 
    setItemPrototype(new Cell);
    setSelectionMode(ContiguousSelection);
 
    connect(this, SIGNAL(itemChanged(QTableWidgetItem *)),
            this, SLOT(somethingChanged()));
	   clear();
	   setAttribute(Qt::WA_DeleteOnClose);
}
void Spreadsheet::newFile()
{
    static int documentNumber = 1;
curFile = tr("document%1.txt").arg(documentNumber);
    setWindowTitle(curFile + "[*]");
    action->setText(curFile);
    isUntitled = true;
    ++documentNumber;
}
QString Spreadsheet::currentLocation() const
{
    return QChar('A' + currentColumn())
           + QString::number(currentRow() + 1);
}
QString Spreadsheet::currentFormula() const
{
    return formula(currentRow(), currentColumn());
}
QTableWidgetSelectionRange Spreadsheet::selectedRange() const
{
    QList<QTableWidgetSelectionRange> ranges = selectedRanges();
    if (ranges.isEmpty())
        return QTableWidgetSelectionRange();
    return ranges.first();
}
void Spreadsheet::clear()
{
    setRowCount(0);
    setColumnCount(0);
    setRowCount(RowCount);
    setColumnCount(ColumnCount);
 for (int i = 0; i < ColumnCount; ++i) {
        QTableWidgetItem *item = new QTableWidgetItem;
        item->setText(QString(QChar('A' + i)));
        setHorizontalHeaderItem(i, item);
    }
setCurrentCell(0, 0);
}
bool Spreadsheet::readFile(const QString &fileName)
{
    QFile file(fileName);
    if (!file.open(QIODevice::ReadOnly)) {
        QMessageBox::warning(this, tr("Spreadsheet"),
                             tr("Cannot read file %1:\n%2.")
                             .arg(file.fileName())
                             .arg(file.errorString()));
        return false;
    }
 
    QDataStream in(&file);
    in.setVersion(QDataStream::Qt_4_3);
 
    quint32 magic;
    in >> magic;
    if (magic != MagicNumber) {
        QMessageBox::warning(this, tr("Spreadsheet"),
                             tr("The file is not a Spreadsheet file."));
        return false;
    }
 
    clear();
 
    quint16 row;
    quint16 column;
    QString str;
 
    QApplication::setOverrideCursor(Qt::WaitCursor);
    while (!in.atEnd()) {
        in >> row >> column >> str;
        setFormula(row, column, str);
    }
    QApplication::restoreOverrideCursor();
    return true;
}
 
bool Spreadsheet::writeFile(const QString &fileName)
{
    QFile file(fileName);
    if (!file.open(QIODevice::WriteOnly)) {
        QMessageBox::warning(this, tr("Spreadsheet"),
                             tr("Cannot write file %1:\n%2.")
                             .arg(file.fileName())
                             .arg(file.errorString()));
        return false;
    }
 
    QDataStream out(&file);
    out.setVersion(QDataStream::Qt_4_3);
 
    out << quint32(MagicNumber);
 
    QApplication::setOverrideCursor(Qt::WaitCursor);
    for (int row = 0; row < RowCount; ++row) {
        for (int column = 0; column < ColumnCount; ++column) {
            QString str = formula(row, column);
            if (!str.isEmpty())
                out << quint16(row) << quint16(column) << str;
        }
    }
    QApplication::restoreOverrideCursor();
    return true;
}
void Spreadsheet::sort(const SpreadsheetCompare &compare)
{
    QList<QStringList> rows;
    QTableWidgetSelectionRange range = selectedRange();
    int i;
 
    for (i = 0; i < range.rowCount(); ++i) {
        QStringList row;
        for (int j = 0; j < range.columnCount(); ++j)
            row.append(formula(range.topRow() + i,
                               range.leftColumn() + j));
        rows.append(row);
    }
 
    qStableSort(rows.begin(), rows.end(), compare);
 
    for (i = 0; i < range.rowCount(); ++i) {
        for (int j = 0; j < range.columnCount(); ++j)
            setFormula(range.topRow() + i, range.leftColumn() + j,
                       rows[i][j]);
    }
 
    clearSelection();
    somethingChanged();
}
void Spreadsheet::cut()
{
    copy();
    del();
}
void Spreadsheet::copy()
{
    QTableWidgetSelectionRange range = selectedRange();
    QString str;
 
    for (int i = 0; i < range.rowCount(); ++i) {
        if (i > 0)
            str += "\n";
        for (int j = 0; j < range.columnCount(); ++j) {
            if (j > 0)
                str += "\t";
            str += formula(range.topRow() + i, range.leftColumn() + j);
        }
    }
    QApplication::clipboard()->setText(str);
}
void Spreadsheet::paste()
{
    QTableWidgetSelectionRange range = selectedRange();
    QString str = QApplication::clipboard()->text();
    QStringList rows = str.split('\n');
    int numRows = rows.count();
    int numColumns = rows.first().count('\t') + 1;
 
    if (range.rowCount() * range.columnCount() != 1
            && (range.rowCount() != numRows
                || range.columnCount() != numColumns)) {
        QMessageBox::information(this, tr("Spreadsheet"),
                tr("The information cannot be pasted because the copy "
                   "and paste areas aren't the same size."));
        return;
    }
 
    for (int i = 0; i < numRows; ++i) {
        QStringList columns = rows[i].split('\t');
        for (int j = 0; j < numColumns; ++j) {
            int row = range.topRow() + i;
            int column = range.leftColumn() + j;
            if (row < RowCount && column < ColumnCount)
                setFormula(row, column, columns[j]);
        }
    }
    somethingChanged();
}
void Spreadsheet::del()
{
    QList<QTableWidgetItem *> items = selectedItems();
    if (!items.isEmpty()) {
        foreach (QTableWidgetItem *item, items)
            delete item;
        somethingChanged();
    }
}
void Spreadsheet::selectCurrentRow()
{
    selectRow(currentRow());
}
 
void Spreadsheet::selectCurrentColumn()
{
    selectColumn(currentColumn());
}
 
void Spreadsheet::recalculate()
{
    for (int row = 0; row < RowCount; ++row) {
        for (int column = 0; column < ColumnCount; ++column) {
            if (cell(row, column))
                cell(row, column)->setDirty();
        }
    }
    viewport()->update();
}
void Spreadsheet::setAutoRecalculate(bool recalc)
{
    autoRecalc = recalc;
    if (autoRecalc)
        recalculate();
}
 
 
void Spreadsheet::somethingChanged()
{
    if (autoRecalc)
        recalculate();
    emit modified();
}
 
Cell *Spreadsheet::cell(int row, int column) const
{
    return static_cast<Cell *>(item(row, column));
}
 
void Spreadsheet::setFormula(int row, int column,
                             const QString &formula)
{
    Cell *c = cell(row, column);
    if (!c) {
        c = new Cell;
        setItem(row, column, c);
    }
    c->setFormula(formula);
}
 
QString Spreadsheet::formula(int row, int column) const
{
    Cell *c = cell(row, column);
    if (c) {
        return c->formula();
    } else {
        return "";
    }
}
 
QString Spreadsheet::text(int row, int column) const
{
    Cell *c = cell(row, column);
    if (c) {
        return c->text();
    } else {
        return "";
    }
}
 
bool SpreadsheetCompare::operator()(const QStringList &row1,
                                    const QStringList &row2) const
{
    for (int i = 0; i < KeyCount; ++i) {
        int column = keys[i];
        if (column != -1) {
            if (row1[column] != row2[column]) {
                if (ascending[i]) {
                    return row1[column] < row2[column];
                } else {
                    return row1[column] > row2[column];
                }
            }
        }
    }
    return false;
}
 
 
void Spreadsheet::selectFont()
{
    QList<QTableWidgetItem *> items = selectedItems();
    if (items.isEmpty()) 
return;    	
 
 
        bool ok = false;
    	QFont fnt = QFontDialog::getFont(&ok, font(), this);
 
    if (!ok)
        return;
    foreach (QTableWidgetItem *item, items)
        if(item)
            item->setFont(fnt);
        somethingChanged();
 
}
 
void::Spreadsheet::toHtml(const QString &plainText)
{
    QTableWidgetSelectionRange range = selectedRange();
    QString html= Qt::escape(plainText);
 
    for (int i = 0; i < range.rowCount(); ++i) {
        if (i > 0)
            html.replace("\n", "\n<tr><td>");
        for (int j = 0; j < range.columnCount(); ++j) {
            if (j > 0)
                html.replace("\t", "\t<tr><td>");
 
html.prepend("<table>\n<tr><td>");
html.append("\n</table>");
        }
    }
    printHtml(html);
 
}
}
Spreadsheet *Spreadsheet::openFile(const QString &fileName, QWidget *parent)
{
    Spreadsheet *spreadsheet = new Spreadsheet(parent);
    if (spreadsheet->readFile(fileName)) 
    	{
        spreadsheet->setCurrentFile(fileName);
        return spreadsheet;
        } else 
        {
        delete spreadsheet;
        return 0;
    }
}
void Spreadsheet::setCurrentFile(const QString &fileName)
{
    curFile = fileName;
    isUntitled = false;
    action->setText(strippedName(curFile));
    //document()->setModified(false);
    setWindowTitle(strippedName(curFile) + "[*]");
    setWindowModified(false);
}

#include <QtGui>
#include "spreadsheet.h"
#include "cell.h"
#include <QTextDocument>
Spreadsheet::Spreadsheet(QWidget *parent)
 : QTableWidget(parent)
{
	
	action = new QAction(this);
    action->setCheckable(true);
    connect(action, SIGNAL(triggered()), this, SLOT(show()));
    connect(action, SIGNAL(triggered()), this, SLOT(setFocus()));

    isUntitled = true;
	
	 autoRecalc = true;

    setItemPrototype(new Cell);
    setSelectionMode(ContiguousSelection);

    connect(this, SIGNAL(itemChanged(QTableWidgetItem *)),
            this, SLOT(somethingChanged()));
	   clear();
	   setAttribute(Qt::WA_DeleteOnClose);
}
void Spreadsheet::newFile()
{
    static int documentNumber = 1;
curFile = tr("document%1.txt").arg(documentNumber);
    setWindowTitle(curFile + "[*]");
    action->setText(curFile);
    isUntitled = true;
    ++documentNumber;
}
QString Spreadsheet::currentLocation() const
{
    return QChar('A' + currentColumn())
           + QString::number(currentRow() + 1);
}
QString Spreadsheet::currentFormula() const
{
    return formula(currentRow(), currentColumn());
}
QTableWidgetSelectionRange Spreadsheet::selectedRange() const
{
    QList<QTableWidgetSelectionRange> ranges = selectedRanges();
    if (ranges.isEmpty())
        return QTableWidgetSelectionRange();
    return ranges.first();
}
void Spreadsheet::clear()
{
    setRowCount(0);
    setColumnCount(0);
    setRowCount(RowCount);
    setColumnCount(ColumnCount);
 for (int i = 0; i < ColumnCount; ++i) {
        QTableWidgetItem *item = new QTableWidgetItem;
        item->setText(QString(QChar('A' + i)));
        setHorizontalHeaderItem(i, item);
    }
setCurrentCell(0, 0);
}
bool Spreadsheet::readFile(const QString &fileName)
{
    QFile file(fileName);
    if (!file.open(QIODevice::ReadOnly)) {
        QMessageBox::warning(this, tr("Spreadsheet"),
                             tr("Cannot read file %1:\n%2.")
                             .arg(file.fileName())
                             .arg(file.errorString()));
        return false;
    }

    QDataStream in(&file);
    in.setVersion(QDataStream::Qt_4_3);

    quint32 magic;
    in >> magic;
    if (magic != MagicNumber) {
        QMessageBox::warning(this, tr("Spreadsheet"),
                             tr("The file is not a Spreadsheet file."));
        return false;
    }

    clear();

    quint16 row;
    quint16 column;
    QString str;

    QApplication::setOverrideCursor(Qt::WaitCursor);
    while (!in.atEnd()) {
        in >> row >> column >> str;
        setFormula(row, column, str);
    }
    QApplication::restoreOverrideCursor();
    return true;
}

bool Spreadsheet::writeFile(const QString &fileName)
{
    QFile file(fileName);
    if (!file.open(QIODevice::WriteOnly)) {
        QMessageBox::warning(this, tr("Spreadsheet"),
                             tr("Cannot write file %1:\n%2.")
                             .arg(file.fileName())
                             .arg(file.errorString()));
        return false;
    }

    QDataStream out(&file);
    out.setVersion(QDataStream::Qt_4_3);

    out << quint32(MagicNumber);

    QApplication::setOverrideCursor(Qt::WaitCursor);
    for (int row = 0; row < RowCount; ++row) {
        for (int column = 0; column < ColumnCount; ++column) {
            QString str = formula(row, column);
            if (!str.isEmpty())
                out << quint16(row) << quint16(column) << str;
        }
    }
    QApplication::restoreOverrideCursor();
    return true;
}
void Spreadsheet::sort(const SpreadsheetCompare &compare)
{
    QList<QStringList> rows;
    QTableWidgetSelectionRange range = selectedRange();
    int i;

    for (i = 0; i < range.rowCount(); ++i) {
        QStringList row;
        for (int j = 0; j < range.columnCount(); ++j)
            row.append(formula(range.topRow() + i,
                               range.leftColumn() + j));
        rows.append(row);
    }

    qStableSort(rows.begin(), rows.end(), compare);

    for (i = 0; i < range.rowCount(); ++i) {
        for (int j = 0; j < range.columnCount(); ++j)
            setFormula(range.topRow() + i, range.leftColumn() + j,
                       rows[i][j]);
    }

    clearSelection();
    somethingChanged();
}
void Spreadsheet::cut()
{
    copy();
    del();
}
void Spreadsheet::copy()
{
    QTableWidgetSelectionRange range = selectedRange();
    QString str;

    for (int i = 0; i < range.rowCount(); ++i) {
        if (i > 0)
            str += "\n";
        for (int j = 0; j < range.columnCount(); ++j) {
            if (j > 0)
                str += "\t";
            str += formula(range.topRow() + i, range.leftColumn() + j);
        }
    }
    QApplication::clipboard()->setText(str);
}
void Spreadsheet::paste()
{
    QTableWidgetSelectionRange range = selectedRange();
    QString str = QApplication::clipboard()->text();
    QStringList rows = str.split('\n');
    int numRows = rows.count();
    int numColumns = rows.first().count('\t') + 1;

    if (range.rowCount() * range.columnCount() != 1
            && (range.rowCount() != numRows
                || range.columnCount() != numColumns)) {
        QMessageBox::information(this, tr("Spreadsheet"),
                tr("The information cannot be pasted because the copy "
                   "and paste areas aren't the same size."));
        return;
    }

    for (int i = 0; i < numRows; ++i) {
        QStringList columns = rows[i].split('\t');
        for (int j = 0; j < numColumns; ++j) {
            int row = range.topRow() + i;
            int column = range.leftColumn() + j;
            if (row < RowCount && column < ColumnCount)
                setFormula(row, column, columns[j]);
        }
    }
    somethingChanged();
}
void Spreadsheet::del()
{
    QList<QTableWidgetItem *> items = selectedItems();
    if (!items.isEmpty()) {
        foreach (QTableWidgetItem *item, items)
            delete item;
        somethingChanged();
    }
}
void Spreadsheet::selectCurrentRow()
{
    selectRow(currentRow());
}

void Spreadsheet::selectCurrentColumn()
{
    selectColumn(currentColumn());
}

void Spreadsheet::recalculate()
{
    for (int row = 0; row < RowCount; ++row) {
        for (int column = 0; column < ColumnCount; ++column) {
            if (cell(row, column))
                cell(row, column)->setDirty();
        }
    }
    viewport()->update();
}
void Spreadsheet::setAutoRecalculate(bool recalc)
{
    autoRecalc = recalc;
    if (autoRecalc)
        recalculate();
}


void Spreadsheet::somethingChanged()
{
    if (autoRecalc)
        recalculate();
    emit modified();
}

Cell *Spreadsheet::cell(int row, int column) const
{
    return static_cast<Cell *>(item(row, column));
}

void Spreadsheet::setFormula(int row, int column,
                             const QString &formula)
{
    Cell *c = cell(row, column);
    if (!c) {
        c = new Cell;
        setItem(row, column, c);
    }
    c->setFormula(formula);
}

QString Spreadsheet::formula(int row, int column) const
{
    Cell *c = cell(row, column);
    if (c) {
        return c->formula();
    } else {
        return "";
    }
}

QString Spreadsheet::text(int row, int column) const
{
    Cell *c = cell(row, column);
    if (c) {
        return c->text();
    } else {
        return "";
    }
}

bool SpreadsheetCompare::operator()(const QStringList &row1,
                                    const QStringList &row2) const
{
    for (int i = 0; i < KeyCount; ++i) {
        int column = keys[i];
        if (column != -1) {
            if (row1[column] != row2[column]) {
                if (ascending[i]) {
                    return row1[column] < row2[column];
                } else {
                    return row1[column] > row2[column];
                }
            }
        }
    }
    return false;
}


void Spreadsheet::selectFont()
{
    QList<QTableWidgetItem *> items = selectedItems();
    if (items.isEmpty()) 
return;    	
    	
    	
        bool ok = false;
    	QFont fnt = QFontDialog::getFont(&ok, font(), this);

    if (!ok)
        return;
    foreach (QTableWidgetItem *item, items)
        if(item)
            item->setFont(fnt);
        somethingChanged();
    
}

void::Spreadsheet::toHtml(const QString &plainText)
{
    QTableWidgetSelectionRange range = selectedRange();
    QString html= Qt::escape(plainText);

    for (int i = 0; i < range.rowCount(); ++i) {
        if (i > 0)
            html.replace("\n", "\n<tr><td>");
        for (int j = 0; j < range.columnCount(); ++j) {
            if (j > 0)
                html.replace("\t", "\t<tr><td>");
          
html.prepend("<table>\n<tr><td>");
html.append("\n</table>");
        }
    }
    printHtml(html);
    
}
}
Spreadsheet *Spreadsheet::openFile(const QString &fileName, QWidget *parent)
{
    Spreadsheet *spreadsheet = new Spreadsheet(parent);
    if (spreadsheet->readFile(fileName)) 
    	{
        spreadsheet->setCurrentFile(fileName);
        return spreadsheet;
        } else 
        {
        delete spreadsheet;
        return 0;
    }
}
void Spreadsheet::setCurrentFile(const QString &fileName)
{
    curFile = fileName;
    isUntitled = false;
    action->setText(strippedName(curFile));
    //document()->setModified(false);
    setWindowTitle(strippedName(curFile) + "[*]");
    setWindowModified(false);
}

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[high_flyer]

its really hard to do help you this way.
Set a break point in addSpreadSheet() first line, and step through until it crashes.
Then you know which line crashed.
Then examine the variables, and I guess you will see a bad pointer there.
It looks like you have an initialization problem somewhere in your code.

[hollowhead]

Thanks for your reply again. This has just got very strange. The results I get depend on what I debug with....
If I use KDbg and just run program from within it, it works perfectly! I cannot see all the source code to set a breakpoint it only shows the first few lines.
If I use gdb at the command line and set the break at the function you suggested (void MainWindowImpl::addSpreadsheet(Spreadsheet *spreadsheet)) it works again perfectly!

If I use QDevelop and set the breakpoint at void MainWindowImpl::addSpreadsheet(Spreadsheet *spreadsheet) it comes up with this message "
Scope for 115:
Symbol subWindow is a variable with complex or multiple locations (DWARF2), length 4.
Symbol this is a variable with complex or multiple locations (DWARF2), length 4.
Symbol spreadsheet is a variable with complex or multiple locations (DWARF2), length 4.
(gdb) "
If I then stepover it then crashes.

I tried going to the programs top level dir and running qmake just in case its a QDevelop issue but doing this then double clicking on the exe it crashes out.

[JD2000]

Well there you have it, each call to addSpreadSheet() creates a new subwindow with

QMdiSubWindow *subWindow = mdiArea->addSubWindow(spreadsheet);

QMdiSubWindow *subWindow = mdiArea->addSubWindow(spreadsheet);

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reusing the subWindow pointer and orphaning previous subWindows, thereby confusing the poor old viewport which ends up holding multiple SubWindows all with the same name.

You could try re-implementing this making subWindow an array of pointers.

I assume that the two working debuggers are only using the most recent subWindow.

Atleast that's what I think is happening!

[hollowhead]

Thanks for your post JD2000. I sort of understand but don't know how to implement it.... Are you sure you are a beginner?

[hollowhead]

Thanks for your post JD2000. I sort of understand but don't know how to implement it.... Are you sure you are a beginner?

[high_flyer]

Well there you have it, each call to addSpreadSheet() creates a new subwindow with

Very good JD200, I totally missed that one.

I sort of understand but don't know how to implement it....

You can use a QVector to manage your subWindows.

[hollowhead]

Thanks but I haven't a clue how to implement this.

[hollowhead]

Solved.

MainWindowImpl::MainWindowImpl( QWidget * parent, Qt::WFlags f) 
	: QMainWindow(parent, f)
{ // on constructor
	 setupUi(this); // required so menues appear
 
	 mdiArea = new QMdiArea;
	 mdiArea->setHorizontalScrollBarPolicy(Qt::ScrollBarAsNeeded);
     mdiArea->setVerticalScrollBarPolicy(Qt::ScrollBarAsNeeded);
    setCentralWidget(mdiArea);
    setWindowTitle(tr("Spreadsheet"))
 
 
}
void MainWindowImpl::createMdiWindow(const QString &fileName)
{
    Spreadsheet *spreadsheet = new Spreadsheet;
    QMdiSubWindow *subWindow = mdiArea->addSubWindow(spreadsheet);
    subWindow->show();
    if (!fileName.isEmpty()) {
       // spreadsheet->load(fileName);
        statusBar()->showMessage(tr("File loaded"), 2000);
    }
}
 
void MainWindowImpl::newFile()
{
    createMdiWindow();
}
 
Spreadsheet *MainWindowImpl::activeSpreadsheet()
{
    QMdiSubWindow *subWindow = mdiArea->activeSubWindow();
    if (subWindow)
       return qobject_cast<Spreadsheet*>(subWindow->widget());
    return 0;
}

MainWindowImpl::MainWindowImpl( QWidget * parent, Qt::WFlags f) 
	: QMainWindow(parent, f)
{ // on constructor
	 setupUi(this); // required so menues appear
	
	 mdiArea = new QMdiArea;
	 mdiArea->setHorizontalScrollBarPolicy(Qt::ScrollBarAsNeeded);
     mdiArea->setVerticalScrollBarPolicy(Qt::ScrollBarAsNeeded);
    setCentralWidget(mdiArea);
    setWindowTitle(tr("Spreadsheet"))


}
void MainWindowImpl::createMdiWindow(const QString &fileName)
{
    Spreadsheet *spreadsheet = new Spreadsheet;
    QMdiSubWindow *subWindow = mdiArea->addSubWindow(spreadsheet);
    subWindow->show();
    if (!fileName.isEmpty()) {
       // spreadsheet->load(fileName);
        statusBar()->showMessage(tr("File loaded"), 2000);
    }
}

void MainWindowImpl::newFile()
{
    createMdiWindow();
}

Spreadsheet *MainWindowImpl::activeSpreadsheet()
{
    QMdiSubWindow *subWindow = mdiArea->activeSubWindow();
    if (subWindow)
       return qobject_cast<Spreadsheet*>(subWindow->widget());
    return 0;
}

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[hollowhead]

Thanks for your post JD2000. I sort of understand but don't know how to implement it.... Are you sure you are a beginner?