QDialog Class

The QDialog class is the base class of dialog windows. More...

Header:	#include <QDialog>
qmake:	QT += widgets
Inherits:	QWidget
Inherited By:	QColorDialog, QErrorMessage, QFileDialog, QFontDialog, QInputDialog, QMessageBox, QProgressDialog, and QWizard

• List of all members, including inherited members
• Obsolete members

Public Types

enum	DialogCode { Accepted, Rejected }

Properties

• modal : bool
• sizeGripEnabled : bool

Public Functions

	QDialog(QWidget *parent = nullptr, Qt::WindowFlags f = Qt::WindowFlags())
virtual	~QDialog()
bool	isSizeGripEnabled() const
int	result() const
void	setModal(bool modal)
void	setResult(int i)
void	setSizeGripEnabled(bool)

Reimplemented Public Functions

virtual QSize	minimumSizeHint() const override
virtual void	setVisible(bool visible) override
virtual QSize	sizeHint() const override

Public Slots

virtual void	accept()
virtual void	done(int r)
virtual int	exec()
virtual void	open()
virtual void	reject()

Signals

void	accepted()
void	finished(int result)
void	rejected()

Reimplemented Protected Functions

virtual void	closeEvent(QCloseEvent *e) override
virtual void	contextMenuEvent(QContextMenuEvent *e) override
virtual bool	eventFilter(QObject *o, QEvent *e) override
virtual void	keyPressEvent(QKeyEvent *e) override
virtual void	resizeEvent(QResizeEvent *) override
virtual void	showEvent(QShowEvent *event) override

Detailed Description

A dialog window is a top-level window mostly used for short-term tasks and brief communications with the user. QDialogs may be modal or modeless. QDialogs can provide a return value, and they can have default buttons. QDialogs can also have a QSizeGrip in their lower-right corner, using setSizeGripEnabled().

Note that QDialog (and any other widget that has type Qt::Dialog) uses the parent widget slightly differently from other classes in Qt. A dialog is always a top-level widget, but if it has a parent, its default location is centered on top of the parent's top-level widget (if it is not top-level itself). It will also share the parent's taskbar entry.

Use the overload of the QWidget::setParent() function to change the ownership of a QDialog widget. This function allows you to explicitly set the window flags of the reparented widget; using the overloaded function will clear the window flags specifying the window-system properties for the widget (in particular it will reset the Qt::Dialog flag).

Note: The parent relationship of the dialog does not imply that the dialog will always be stacked on top of the parent window. To ensure that the dialog is always on top, make the dialog modal. This also applies for child windows of the dialog itself. To ensure that child windows of the dialog stay on top of the dialog, make the child windows modal as well.

Modal Dialogs

A modal dialog is a dialog that blocks input to other visible windows in the same application. Dialogs that are used to request a file name from the user or that are used to set application preferences are usually modal. Dialogs can be application modal (the default) or window modal.

When an application modal dialog is opened, the user must finish interacting with the dialog and close it before they can access any other window in the application. Window modal dialogs only block access to the window associated with the dialog, allowing the user to continue to use other windows in an application.

The most common way to display a modal dialog is to call its exec() function. When the user closes the dialog, exec() will provide a useful return value. To close the dialog and return the appropriate value, you must connect a default button, e.g. an OK button to the accept() slot and a Cancel button to the reject() slot. Alternatively, you can call the done() slot with Accepted or Rejected.

An alternative is to call setModal(true) or setWindowModality(), then show(). Unlike exec(), show() returns control to the caller immediately. Calling setModal(true) is especially useful for progress dialogs, where the user must have the ability to interact with the dialog, e.g. to cancel a long running operation. If you use show() and setModal(true) together to perform a long operation, you must call QCoreApplication::processEvents() periodically during processing to enable the user to interact with the dialog. (See QProgressDialog.)

Modeless Dialogs

A modeless dialog is a dialog that operates independently of other windows in the same application. Find and replace dialogs in word-processors are often modeless to allow the user to interact with both the application's main window and with the dialog.

Modeless dialogs are displayed using show(), which returns control to the caller immediately.

If you invoke the show() function after hiding a dialog, the dialog will be displayed in its original position. This is because the window manager decides the position for windows that have not been explicitly placed by the programmer. To preserve the position of a dialog that has been moved by the user, save its position in your closeEvent() handler and then move the dialog to that position, before showing it again.

Default Button

A dialog's default button is the button that's pressed when the user presses Enter (Return). This button is used to signify that the user accepts the dialog's settings and wants to close the dialog. Use QPushButton::setDefault(), QPushButton::isDefault() and QPushButton::autoDefault() to set and control the dialog's default button.

Escape Key

If the user presses the Esc key in a dialog, QDialog::reject() will be called. This will cause the window to close: The close event cannot be ignored.

Extensibility

Extensibility is the ability to show the dialog in two ways: a partial dialog that shows the most commonly used options, and a full dialog that shows all the options. Typically an extensible dialog will initially appear as a partial dialog, but with a More toggle button. If the user presses the More button down, the dialog is expanded. The Extension Example shows how to achieve extensible dialogs using Qt.

Return Value (Modal Dialogs)

Modal dialogs are often used in situations where a return value is required, e.g. to indicate whether the user pressed OK or Cancel. A dialog can be closed by calling the accept() or the reject() slots, and exec() will return Accepted or Rejected as appropriate. The exec() call returns the result of the dialog. The result is also available from result() if the dialog has not been destroyed.

In order to modify your dialog's close behavior, you can reimplement the functions accept(), reject() or done(). The closeEvent() function should only be reimplemented to preserve the dialog's position or to override the standard close or reject behavior.

Code Examples

A modal dialog:

void EditorWindow::countWords()
{
    WordCountDialog dialog(this);
    dialog.setWordCount(document().wordCount());
    dialog.exec();
}

A modeless dialog:

void EditorWindow::find()
{
    if (!findDialog) {
        findDialog = new FindDialog(this);
        connect(findDialog, &FindDialog::findNext,
                this, &EditorWindow::findNext);
    }

    findDialog->show();
    findDialog->raise();
    findDialog->activateWindow();
}

See also QDialogButtonBox, QTabWidget, QWidget, QProgressDialog, GUI Design Handbook: Dialogs, Standard, Extension Example, and Standard Dialogs Example.

Member Type Documentation

enum QDialog::DialogCode

The value returned by a modal dialog.

Constant	Value
QDialog::Accepted	1
QDialog::Rejected	0

Member Function Documentation

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

Constructs a dialog with parent parent.

A dialog is always a top-level widget, but if it has a parent, its default location is centered on top of the parent. It will also share the parent's taskbar entry.

The widget flags f are passed on to the QWidget constructor. If, for example, you don't want a What's This button in the title bar of the dialog, pass Qt::WindowTitleHint | Qt::WindowSystemMenuHint in f.

See also QWidget::setWindowFlags().

[virtual slot] void QDialog::accept()

Hides the modal dialog and sets the result code to Accepted.

See also reject() and done().

[signal] void QDialog::accepted()

This signal is emitted when the dialog has been accepted either by the user or by calling accept() or done() with the QDialog::Accepted argument.

Note that this signal is not emitted when hiding the dialog with hide() or setVisible(false). This includes deleting the dialog while it is visible.

This function was introduced in Qt 4.1.

See also finished() and rejected().

[virtual slot] void QDialog::done(int r)

Closes the dialog and sets its result code to r. The finished() signal will emit r; if r is QDialog::Accepted or QDialog::Rejected, the accepted() or the rejected() signals will also be emitted, respectively.

If this dialog is shown with exec(), done() also causes the local event loop to finish, and exec() to return r.

As with QWidget::close(), done() deletes the dialog if the Qt::WA_DeleteOnClose flag is set. If the dialog is the application's main widget, the application terminates. If the dialog is the last window closed, the QApplication::lastWindowClosed() signal is emitted.

See also accept(), reject(), QApplication::activeWindow(), and QCoreApplication::quit().

[virtual slot] int QDialog::exec()

Shows the dialog as a modal dialog, blocking until the user closes it. The function returns a DialogCode result.

If the dialog is application modal, users cannot interact with any other window in the same application until they close the dialog. If the dialog is window modal, only interaction with the parent window is blocked while the dialog is open. By default, the dialog is application modal.

Note: Avoid using this function; instead, use open(). Unlike exec(), open() is asynchronous, and does not spin an additional event loop. This prevents a series of dangerous bugs from happening (e.g. deleting the dialog's parent while the dialog is open via exec()). When using open() you can connect to the finished() signal of QDialog to be notified when the dialog is closed.

See also open(), show(), result(), and setWindowModality().

[signal] void QDialog::finished(int result)

This signal is emitted when the dialog's result code has been set, either by the user or by calling done(), accept(), or reject().

Note that this signal is not emitted when hiding the dialog with hide() or setVisible(false). This includes deleting the dialog while it is visible.

This function was introduced in Qt 4.1.

See also accepted() and rejected().

[virtual slot] void QDialog::open()

Shows the dialog as a window modal dialog, returning immediately.

This function was introduced in Qt 4.5.

See also exec(), show(), result(), and setWindowModality().

[virtual slot] void QDialog::reject()

Hides the modal dialog and sets the result code to Rejected.

See also accept() and done().

[signal] void QDialog::rejected()

This signal is emitted when the dialog has been rejected either by the user or by calling reject() or done() with the QDialog::Rejected argument.

Note that this signal is not emitted when hiding the dialog with hide() or setVisible(false). This includes deleting the dialog while it is visible.

This function was introduced in Qt 4.1.

See also finished() and accepted().

[virtual] QDialog::~QDialog()

Destroys the QDialog, deleting all its children.

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

Reimplements: QWidget::closeEvent(QCloseEvent *event).

[override virtual protected] void QDialog::contextMenuEvent(QContextMenuEvent *e)

Reimplements: QWidget::contextMenuEvent(QContextMenuEvent *event).

[override virtual protected] bool QDialog::eventFilter(QObject *o, QEvent *e)

Reimplements: QObject::eventFilter(QObject *watched, QEvent *event).

[override virtual protected] void QDialog::keyPressEvent(QKeyEvent *e)

Reimplements: QWidget::keyPressEvent(QKeyEvent *event).

[override virtual] QSize QDialog::minimumSizeHint() const

Reimplements an access function for property: QWidget::minimumSizeHint.

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

Reimplements: QWidget::resizeEvent(QResizeEvent *event).

int QDialog::result() const

In general returns the modal dialog's result code, Accepted or Rejected.

Note: When called on a QMessageBox instance, the returned value is a value of the QMessageBox::StandardButton enum.

Do not call this function if the dialog was constructed with the Qt::WA_DeleteOnClose attribute.

See also setResult().

void QDialog::setResult(int i)

Sets the modal dialog's result code to i.

Note: We recommend that you use one of the values defined by QDialog::DialogCode.

See also result().

[override virtual] void QDialog::setVisible(bool visible)

Reimplements an access function for property: QWidget::visible.

[override virtual protected] void QDialog::showEvent(QShowEvent *event)

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

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

Reimplements an access function for property: QWidget::sizeHint.