QAbstractButton Class Reference

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

Inherits: QWidget.

Inherited by: Q3Button, QCheckBox, QPushButton, QRadioButton, and QToolButton.

Detailed Description

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

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:

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, because they have no automatic shortcut.

All of 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 are provided by 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.
• 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.