QAbstractButton Class

The QAbstractButton class is the abstract base class of button widgets, providing functionality common to buttons. More...

Header:	#include <QAbstractButton>
qmake:	QT += widgets
Inherits:	QWidget
Inherited By:	QCheckBox, QPushButton, QRadioButton, and QToolButton

• List of all members, including inherited members

Properties

autoExclusive : bool autoRepeat : bool autoRepeatDelay : int autoRepeatInterval : int checkable : bool checked : bool

down : bool icon : QIcon iconSize : QSize shortcut : QKeySequence text : QString

Public Functions

	QAbstractButton(QWidget *parent = nullptr)
virtual	~QAbstractButton()
bool	autoExclusive() const
bool	autoRepeat() const
int	autoRepeatDelay() const
int	autoRepeatInterval() const
QButtonGroup *	group() const
QIcon	icon() const
QSize	iconSize() const
bool	isCheckable() const
bool	isChecked() const
bool	isDown() const
void	setAutoExclusive(bool)
void	setAutoRepeat(bool)
void	setAutoRepeatDelay(int)
void	setAutoRepeatInterval(int)
void	setCheckable(bool)
void	setDown(bool)
void	setIcon(const QIcon &icon)
void	setShortcut(const QKeySequence &key)
void	setText(const QString &text)
QKeySequence	shortcut() const
QString	text() const

Public Slots

void	animateClick(int msec = 100)
void	click()
void	setChecked(bool)
void	setIconSize(const QSize &size)
void	toggle()

Signals

void	clicked(bool checked = false)
void	pressed()
void	released()
void	toggled(bool checked)

Protected Functions

virtual void	checkStateSet()
virtual bool	hitButton(const QPoint &pos) const
virtual void	nextCheckState()

Reimplemented Protected Functions

virtual void	changeEvent(QEvent *e) override
virtual bool	event(QEvent *e) override
virtual void	focusInEvent(QFocusEvent *e) override
virtual void	focusOutEvent(QFocusEvent *e) override
virtual void	keyPressEvent(QKeyEvent *e) override
virtual void	keyReleaseEvent(QKeyEvent *e) override
virtual void	mouseMoveEvent(QMouseEvent *e) override
virtual void	mousePressEvent(QMouseEvent *e) override
virtual void	mouseReleaseEvent(QMouseEvent *e) override
virtual void	paintEvent(QPaintEvent *e) override = 0
virtual void	timerEvent(QTimerEvent *e) override

Detailed Description

This class implements an abstract button. Subclasses of this class handle user actions, and specify how the button is drawn.

QAbstractButton provides support for both push buttons and checkable (toggle) buttons. Checkable buttons are implemented in the QRadioButton and QCheckBox classes. Push buttons are implemented in the QPushButton and QToolButton classes; these also provide toggle behavior if required.

Any button can display a label containing text and an icon. setText() sets the text; setIcon() sets the icon. If a button is disabled, its label is changed to give the button a "disabled" appearance.

If the button is a text button with a string containing an ampersand ('&'), QAbstractButton automatically creates a shortcut key. For example:

QPushButton *button = new QPushButton(tr("Ro&ck && Roll"), this);

The Alt+C shortcut is assigned to the button, i.e., when the user presses Alt+C the button will call animateClick(). See the QShortcut documentation for details. To display an actual ampersand, use '&&'.

You can also set a custom shortcut key using the setShortcut() function. This is useful mostly for buttons that do not have any text, and therefore can't have any automatic shortcut.

button->setIcon(QIcon(":/images/print.png"));
button->setShortcut(tr("Alt+F7"));

All the buttons provided by Qt (QPushButton, QToolButton, QCheckBox, and QRadioButton) can display both text and icons.

A button can be made the default button in a dialog by means of QPushButton::setDefault() and QPushButton::setAutoDefault().

QAbstractButton provides most of the states used for buttons:

• isDown() indicates whether the button is pressed down.
• isChecked() indicates whether the button is checked. Only checkable buttons can be checked and unchecked (see below).
• isEnabled() indicates whether the button can be pressed by the user.

  Note: As opposed to other widgets, buttons derived from QAbstractButton accept mouse and context menu events when disabled.

• setAutoRepeat() sets whether the button will auto-repeat if the user holds it down. autoRepeatDelay and autoRepeatInterval define how auto-repetition is done.
• setCheckable() sets whether the button is a toggle button or not.

The difference between isDown() and isChecked() is as follows. When the user clicks a toggle button to check it, the button is first pressed then released into the checked state. When the user clicks it again (to uncheck it), the button moves first to the pressed state, then to the unchecked state (isChecked() and isDown() are both false).

QAbstractButton provides four signals:

1. pressed() is emitted when the left mouse button is pressed while the mouse cursor is inside the button.
2. released() is emitted when the left mouse button is released.
3. clicked() is emitted when the button is first pressed and then released, when the shortcut key is typed, or when click() or animateClick() is called.
4. toggled() is emitted when the state of a toggle button changes.

To subclass QAbstractButton, you must reimplement at least paintEvent() to draw the button's outline and its text or pixmap. It is generally advisable to reimplement sizeHint() as well, and sometimes hitButton() (to determine whether a button press is within the button). For buttons with more than two states (like tri-state buttons), you will also have to reimplement checkStateSet() and nextCheckState().

See also QButtonGroup.

Member Function Documentation

QAbstractButton::QAbstractButton(QWidget *parent = nullptr)

Constructs an abstract button with a parent.

[slot] void QAbstractButton::animateClick(int msec = 100)

Performs an animated click: the button is pressed immediately, and released msec milliseconds later (the default is 100 ms).

Calling this function again before the button is released resets the release timer.

All signals associated with a click are emitted as appropriate.

This function does nothing if the button is disabled.

See also click().

[slot] void QAbstractButton::click()

Performs a click.

All the usual signals associated with a click are emitted as appropriate. If the button is checkable, the state of the button is toggled.

This function does nothing if the button is disabled.

See also animateClick().

[signal] void QAbstractButton::clicked(bool checked = false)

This signal is emitted when the button is activated (i.e., pressed down then released while the mouse cursor is inside the button), when the shortcut key is typed, or when click() or animateClick() is called. Notably, this signal is not emitted if you call setDown(), setChecked() or toggle().

If the button is checkable, checked is true if the button is checked, or false if the button is unchecked.

See also pressed(), released(), and toggled().

[signal] void QAbstractButton::pressed()

This signal is emitted when the button is pressed down.

See also released() and clicked().

[signal] void QAbstractButton::released()

This signal is emitted when the button is released.

See also pressed(), clicked(), and toggled().

[slot] void QAbstractButton::toggle()

Toggles the state of a checkable button.

See also checked.

[signal] void QAbstractButton::toggled(bool checked)

This signal is emitted whenever a checkable button changes its state. checked is true if the button is checked, or false if the button is unchecked.

This may be the result of a user action, click() slot activation, or because setChecked() is called.

The states of buttons in exclusive button groups are updated before this signal is emitted. This means that slots can act on either the "off" signal or the "on" signal emitted by the buttons in the group whose states have changed.

For example, a slot that reacts to signals emitted by newly checked buttons but which ignores signals from buttons that have been unchecked can be implemented using the following pattern:

void MyWidget::reactToToggle(bool checked)
{
   if (checked) {
      // Examine the new button states.
      ...
   }
}

Button groups can be created using the QButtonGroup class, and updates to the button states monitored with the QButtonGroup::buttonClicked() signal.

Note: Notifier signal for property checked.

See also checked and clicked().

[virtual] QAbstractButton::~QAbstractButton()

Destroys the button.

[override virtual protected] void QAbstractButton::changeEvent(QEvent *e)

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

[virtual protected] void QAbstractButton::checkStateSet()

This virtual handler is called when setChecked() is used, unless it is called from within nextCheckState(). It allows subclasses to reset their intermediate button states.

See also nextCheckState().

[override virtual protected] bool QAbstractButton::event(QEvent *e)

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

[override virtual protected] void QAbstractButton::focusInEvent(QFocusEvent *e)

Reimplements: QWidget::focusInEvent(QFocusEvent *event).

[override virtual protected] void QAbstractButton::focusOutEvent(QFocusEvent *e)

Reimplements: QWidget::focusOutEvent(QFocusEvent *event).

QButtonGroup *QAbstractButton::group() const

Returns the group that this button belongs to.

If the button is not a member of any QButtonGroup, this function returns nullptr.

See also QButtonGroup.

[virtual protected] bool QAbstractButton::hitButton(const QPoint &pos) const

Returns true if pos is inside the clickable button rectangle; otherwise returns false.

By default, the clickable area is the entire widget. Subclasses may reimplement this function to provide support for clickable areas of different shapes and sizes.

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

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

[override virtual protected] void QAbstractButton::keyReleaseEvent(QKeyEvent *e)

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

[override virtual protected] void QAbstractButton::mouseMoveEvent(QMouseEvent *e)

Reimplements: QWidget::mouseMoveEvent(QMouseEvent *event).

[override virtual protected] void QAbstractButton::mousePressEvent(QMouseEvent *e)

Reimplements: QWidget::mousePressEvent(QMouseEvent *event).

[override virtual protected] void QAbstractButton::mouseReleaseEvent(QMouseEvent *e)

Reimplements: QWidget::mouseReleaseEvent(QMouseEvent *event).

[virtual protected] void QAbstractButton::nextCheckState()

This virtual handler is called when a button is clicked. The default implementation calls setChecked(!isChecked()) if the button isCheckable(). It allows subclasses to implement intermediate button states.

See also checkStateSet().

[override pure virtual protected] void QAbstractButton::paintEvent(QPaintEvent *e)

Reimplements: QWidget::paintEvent(QPaintEvent *event).

[override virtual protected] void QAbstractButton::timerEvent(QTimerEvent *e)

Reimplements: QObject::timerEvent(QTimerEvent *event).