Q3ProgressDialog Class Reference
^{[Qt3Support module]}

Detailed Description

The Q3ProgressDialog class provides feedback on the progress of a slow operation.

A progress dialog is used to give the user an indication of how long an operation is going to take, and to demonstrate that the application has not frozen. It can also give the user an opportunity to abort the operation.

A common problem with progress dialogs is that it is difficult to know when to use them; operations take different amounts of time on different hardware. Q3ProgressDialog offers a solution to this problem: it estimates the time the operation will take (based on time for steps), and only shows itself if that estimate is beyond minimumDuration() (4 seconds by default).

Use setTotalSteps() (or the constructor) to set the number of "steps" in the operation and call setProgress() as the operation progresses. The step value can be chosen arbitrarily. It can be the number of files copied, the number of bytes received, the number of iterations through the main loop of your algorithm, or some other suitable unit. Progress starts at 0, and the progress dialog shows that the operation has finished when you call setProgress() with totalSteps() as its argument.

The dialog automatically resets and hides itself at the end of the operation. Use setAutoReset() and setAutoClose() to change this behavior.

There are two ways of using Q3ProgressDialog: modal and modeless.

Using a modal Q3ProgressDialog is simpler for the programmer, but you must call QApplication::processEvents() or QEventLoop::processEvents(ExcludeUserInput) to keep the event loop running to ensure that the application doesn't freeze. Do the operation in a loop, call setProgress() at intervals, and check for cancellation with wasCanceled(). For example:

    Q3ProgressDialog progress("Copying files...", "Abort Copy", numFiles,
                              this, "progress", true);
    for (int i = 0; i < numFiles; i++) {
        progress.setProgress(i);
        qApp->processEvents();

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

A modeless progress dialog is suitable for operations that take place in the background, where the user is able to interact with the application. Such operations are typically based on QTimer (or QObject::timerEvent()), QSocketNotifier, or QUrlOperator; or performed in a separate thread. A Q3ProgressBar in the status bar of your main window is often an alternative to a modeless progress dialog.

You need to have an event loop to be running, connect the canceled() signal to a slot that stops the operation, and call setProgress() at intervals. For example:

    Operation::Operation(QObject *parent = 0)
        : QObject(parent), steps(0)
    {
        pd = new Q3ProgressDialog("Operation in progress.", "Cancel", 100);
        connect(pd, SIGNAL(canceled()), this, SLOT(cancel()));
        t = new QTimer(this);
        connect(t, SIGNAL(timeout()), this, SLOT(perform()));
        t->start(0);
    }

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

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

In both modes the progress dialog may be customized by replacing the child widgets with custom widgets by using setLabel(), setBar(), and setCancelButton(). The functions setLabelText() and setCancelButtonText() set the texts shown.

See also QDialog, Q3ProgressBar, and GUI Design Handbook: Progress Indicator.

Property Documentation

autoClose : bool

This property holds whether the dialog gets hidden by reset().

The default is true.

Access functions:

• bool autoClose () const
• void setAutoClose ( bool b )

See also setAutoReset().

autoReset : bool

This property holds whether the progress dialog calls reset() as soon as progress() equals totalSteps().

The default is true.

Access functions:

• bool autoReset () const
• void setAutoReset ( bool b )

See also setAutoClose().

labelText : QString

This property holds the label's text.

The default text is an empty string.

Access functions:

• QString labelText () const
• void setLabelText ( const QString & )

minimumDuration : int

This property holds the time that must pass before the dialog appears.

If the expected duration of the task is less than the minimumDuration, the dialog will not appear at all. This prevents the dialog popping up for tasks that are quickly over. For tasks that are expected to exceed the minimumDuration, the dialog will pop up after the minimumDuration time or as soon as any progress is set.

If set to 0, the dialog is always shown as soon as any progress is set. The default is 4000 milliseconds.

Access functions:

• int minimumDuration () const
• void setMinimumDuration ( int ms )

progress : int

This property holds the current amount of progress made.

For the progress dialog to work as expected, you should initially set this property to 0 and finally set it to Q3ProgressDialog::totalSteps(); you can call setProgress() any number of times in-between.

Warning: If the progress dialog is modal (see Q3ProgressDialog::Q3ProgressDialog()), this function calls QApplication::processEvents(), so take care that this does not cause undesirable re-entrancy in your code. For example, don't use a Q3ProgressDialog inside a paintEvent()!

Access functions:

• int progress () const
• void setProgress ( int progress )
• void setProgress ( int progress, int totalSteps )

See also totalSteps.

totalSteps : int

This property holds the total number of steps.

The default is 0.

Access functions:

• int totalSteps () const
• void setTotalSteps ( int totalSteps )

wasCanceled : const bool

This property holds whether the dialog was canceled.

Access functions:

• bool wasCanceled () const

See also setProgress().

Member Function Documentation

Q3ProgressDialog::Q3ProgressDialog ( QWidget * creator = 0, Qt::WFlags f = 0 )

Constructs a progress dialog.

Default settings:

• The label text is empty.
• The cancel button text is (translated) "Cancel".
• The total number of steps is 100.

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

See also setLabelText(), setLabel(), setCancelButtonText(), setCancelButton(), and setTotalSteps().

Q3ProgressDialog::Q3ProgressDialog ( const QString & labelText, const QString & cancelButtonText, int totalSteps, QWidget * creator = 0, Qt::WFlags f = 0 )

Constructs a progress dialog.

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

The cancelButtonText is the text to display on the cancel button, or 0 if no cancel button is to be shown.

The totalSteps is the total 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 would be 50. Before examining the first file, call setProgress(0). As each file is processed call setProgress(1), setProgress(2), etc., finally calling setProgress(50) after examining the last file.

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

See also setLabelText(), setLabel(), setCancelButtonText(), setCancelButton(), and setTotalSteps().

Q3ProgressDialog::~Q3ProgressDialog ()

Destroys the progress dialog.

void Q3ProgressDialog::cancel ()   [slot]

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

void Q3ProgressDialog::canceled ()   [signal]

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

See also wasCanceled().

void Q3ProgressDialog::forceShow ()   [protected slot]

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

See also setMinimumDuration().

void Q3ProgressDialog::reset ()   [slot]

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

See also setAutoClose() and setAutoReset().

void Q3ProgressDialog::setBar ( Q3ProgressBar * 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 Q3ProgressDialog::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.

See also setCancelButtonText().

void Q3ProgressDialog::setCancelButtonText ( const QString & cancelButtonText )   [slot]

Sets the cancel button's text to cancelButtonText.

See also setCancelButton().

void Q3ProgressDialog::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().

QSize Q3ProgressDialog::sizeHint () const   [virtual]

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.

Reimplemented from QWidget.