QProgressDialog progress("Copying files...", "Abort Copy", 0, numFiles, this);
    progress.setWindowModality(Qt::WindowModal);

    for (int i = 0; i < numFiles; i++) {
        progress.setValue(i);

        if (progress.wasCanceled())
            break;
        //... copy one file
    }
    progress.setValue(numFiles);

// Operation constructor
Operation::Operation(QObject *parent)
    : QObject(parent), steps(0)
{
    pd = new QProgressDialog("Operation in progress.", "Cancel", 0, 100);
    connect(pd, &QProgressDialog::canceled, this, &Operation::cancel);
    t = new QTimer(this);
    connect(t, &QTimer::timeout, this, &Operation::perform);
    t->start(0);
}

void Operation::perform()
{
    pd->setValue(steps);
    //... perform one percent of the operation
    steps++;
    if (steps > pd->maximum())
        t->stop();
}

void Operation::cancel()
{
    t->stop();
    //... cleanup
}

Member Function Documentation

QProgressDialog::QProgressDialog(const QString &labelText, const QString &cancelButtonText, int minimum, int maximum, QWidget *parent = nullptr, Qt::WindowFlags f = Qt::WindowFlags())

Constructs a progress dialog.

The labelText is the text used to remind the user what is progressing.

The cancelButtonText is the text to display on the cancel button. If QString() is passed then no cancel button is shown.

The minimum and maximum is the number of steps in the operation for which this progress dialog shows progress. For example, if the operation is to examine 50 files, this value minimum value would be 0, and the maximum would be 50. Before examining the first file, call setValue(0). As each file is processed call setValue(1), setValue(2), etc., finally calling setValue(50) after examining the last file.

The parent argument is the dialog's parent widget. The parent, parent, and widget flags, f, are passed to the QDialog::QDialog() constructor.

See also setLabelText(), setLabel(), setCancelButtonText(), setCancelButton(), setMinimum(), and setMaximum().

QProgressDialog::QProgressDialog(QWidget *parent = nullptr, Qt::WindowFlags f = Qt::WindowFlags())

Constructs a progress dialog.

Default settings:

• The label text is empty.
• The cancel button text is (translated) "Cancel".
• minimum is 0;
• maximum is 100

The parent argument is dialog's parent widget. The widget flags, f, are passed to the QDialog::QDialog() constructor.

See also setLabelText(), setCancelButtonText(), setCancelButton(), setMinimum(), and setMaximum().

[slot] void QProgressDialog::cancel()

Resets the progress dialog. wasCanceled() becomes true until the progress dialog is reset. The progress dialog becomes hidden.

[signal] void QProgressDialog::canceled()

This signal is emitted when the cancel button is clicked. It is connected to the cancel() slot by default.

See also wasCanceled().

[protected slot] void QProgressDialog::forceShow()

Shows the dialog if it is still hidden after the algorithm has been started and minimumDuration milliseconds have passed.

See also setMinimumDuration().

[slot] void QProgressDialog::reset()

Resets the progress dialog. The progress dialog becomes hidden if autoClose() is true.

See also setAutoClose() and setAutoReset().

[slot] void QProgressDialog::setCancelButtonText(const QString &cancelButtonText)

Sets the cancel button's text to cancelButtonText. If the text is set to QString() then it will cause the cancel button to be hidden and deleted.

See also setCancelButton().

[slot] void QProgressDialog::setRange(int minimum, int maximum)

Sets the progress dialog's minimum and maximum values to minimum and maximum, respectively.

If maximum is smaller than minimum, minimum becomes the only legal value.

If the current value falls outside the new range, the progress dialog is reset with reset().

See also minimum and maximum.

[virtual] QProgressDialog::~QProgressDialog()

Destroys the progress dialog.

[override virtual protected] void QProgressDialog::changeEvent(QEvent *ev)

Reimplements: QWidget::changeEvent(QEvent *event).

[override virtual protected] void QProgressDialog::closeEvent(QCloseEvent *e)

Reimplements: QDialog::closeEvent(QCloseEvent *e).

void QProgressDialog::open(QObject *receiver, const char *member)

Opens the dialog and connects its canceled() signal to the slot specified by receiver and member.

The signal will be disconnected from the slot when the dialog is closed.

This function was introduced in Qt 4.5.

[override virtual protected] void QProgressDialog::resizeEvent(QResizeEvent *event)

Reimplements: QDialog::resizeEvent(QResizeEvent *).

void QProgressDialog::setBar(QProgressBar *bar)

Sets the progress bar widget to bar. The progress dialog resizes to fit. The progress dialog takes ownership of the progress bar which will be deleted when necessary, so do not use a progress bar allocated on the stack.

void QProgressDialog::setCancelButton(QPushButton *cancelButton)

Sets the cancel button to the push button, cancelButton. The progress dialog takes ownership of this button which will be deleted when necessary, so do not pass the address of an object that is on the stack, i.e. use new() to create the button. If nullptr is passed, no cancel button will be shown.

See also setCancelButtonText().

void QProgressDialog::setLabel(QLabel *label)

Sets the label to label. The progress dialog resizes to fit. The label becomes owned by the progress dialog and will be deleted when necessary, so do not pass the address of an object on the stack.

See also setLabelText().

[override virtual protected] void QProgressDialog::showEvent(QShowEvent *e)

Reimplements: QDialog::showEvent(QShowEvent *event).

[override virtual] QSize QProgressDialog::sizeHint() const

Reimplements: QDialog::sizeHint() const.

Returns a size that fits the contents of the progress dialog. The progress dialog resizes itself as required, so you should not need to call this yourself.