Detailed Description
The QPushButton widget provides a command button.
The push button, or command button, is perhaps the most commonly used widget in any graphical user interface. Push (click) a button to command the computer to perform some action, or to answer a question. Typical buttons are OK, Apply, Cancel, Close, Yes, No and Help.
A command button is rectangular and typically displays a text label describing its action. An underlined character in the label (signified by preceding it with an ampersand in the text) indicates a shortcut key, e.g.
QPushButton *pb = new QPushButton("&Download", this);
In this example the shortcut is Alt+D, and the label text will be displayed as Download.
Push buttons display a textual label, and optionally a small icon. These can be set using the constructors and changed later using setText() and setIcon(). If the button is disabled the appearance of the text and icon will be manipulated with respect to the GUI style to make the button look "disabled".
A push button emits the signal clicked() when it is activated by the mouse, the Spacebar or by a keyboard shortcut. Connect to this signal to perform the button's action. Push buttons also provide less commonly used signals, for example, pressed() and released().
Command buttons in dialogs are by default auto-default buttons, i.e. they become the default push button automatically when they receive the keyboard input focus. A default button is a push button that is activated when the user presses the Enter or Return key in a dialog. You can change this with setAutoDefault(). Note that auto-default buttons reserve a little extra space which is necessary to draw a default-button indicator. If you do not want this space around your buttons, call setAutoDefault(false).
Being so central, the button widget has grown to accommodate a great many variations in the past decade. The Microsoft style guide now shows about ten different states of Windows push buttons and the text implies that there are dozens more when all the combinations of features are taken into consideration.
The most important modes or states are:
- Available or not (grayed out, disabled).
- Standard push button, toggling push button or menu button.
- On or off (only for toggling push buttons).
- Default or normal. The default button in a dialog can generally be "clicked" using the Enter or Return key.
- Auto-repeat or not.
- Pressed down or not.
As a general rule, use a push button when the application or dialog window performs an action when the user clicks on it (such as Apply, Cancel, Close and Help) and when the widget is supposed to have a wide, rectangular shape with a text label. Small, typically square buttons that change the state of the window rather than performing an action (such as the buttons in the top-right corner of the QFileDialog) are not command buttons, but tool buttons. Qt provides a special class (QToolButton) for these buttons.
If you need toggle behavior (see setCheckable()) or a button that auto-repeats the activation signal when being pushed down like the arrows in a scroll bar (see setAutoRepeat()), a command button is probably not what you want. When in doubt, use a tool button.
A variation of a command button is a menu button. These provide not just one command, but several, since when they are clicked they pop up a menu of options. Use the method setMenu() to associate a popup menu with a push button.
Other classes of buttons are option buttons (see QRadioButton) and check boxes (see QCheckBox).
In Qt, the QAbstractButton base class provides most of the modes and other API, and QPushButton provides GUI logic. See QAbstractButton for more information about the API.
See also QToolButton, QRadioButton, QCheckBox, and GUI Design Handbook: Push Button.
Property Documentation
autoDefault : bool
This property holds whether the push button is the auto default button.
If this property is set to true then the push button is the auto default button in a dialog.
In some GUI styles a default button is drawn with an extra frame around it, up to 3 pixels or more. Qt automatically keeps this space free around auto-default buttons, i.e. auto-default buttons may have a slightly larger size hint.
This property's default is true for buttons that have a QDialog parent; otherwise it defaults to false.
See the default property for details of how default and auto-default interact.
Access functions:
- bool autoDefault () const
- void setAutoDefault ( bool )
default : bool
This property holds whether the push button is the default button.
If this property is set to true then the push button will be pressed if the user presses the Enter (or Return) key in a dialog.
Regardless of focus, if the user presses Enter: If there is a default button the default button is pressed; otherwise, if there are one or more autoDefault buttons the first autoDefault button that is next in the tab order is pressed. If there are no default or autoDefault buttons only pressing Space on a button with focus, mouse clicking, or using a shortcut will press a button.
In a dialog, only one push button at a time can be the default button. This button is then displayed with an additional frame (depending on the GUI style).
The default button behavior is provided only in dialogs. Buttons can always be clicked from the keyboard by pressing Enter (or Return) or the Spacebar when the button has focus.
This property's default is false.
Access functions:
- bool isDefault () const
- void setDefault ( bool )
flat : bool
This property holds whether the border is disabled.
This property's default is false.
Access functions:
- bool isFlat () const
- void setFlat ( bool )
Member Function Documentation
QPushButton::QPushButton ( QWidget * parent = 0 )
Constructs a push button with no text and a parent.
QPushButton::QPushButton ( const QString & text, QWidget * parent = 0 )
Constructs a push button with the parent parent and the text text.
QPushButton::QPushButton ( const QIcon & icon, const QString & text, QWidget * parent = 0 )
Constructs a push button with an icon and a text, and a parent.
Note that you can also pass a QPixmap object as an icon (thanks to the implicit type conversion provided by C++).
QPushButton::~QPushButton ()
Destroys the push button.
Returns the button's associated popup menu or 0 if no popup menu has been set.
See also setMenu().
Associates the popup menu menu with this push button. This turns the button into a menu button, which in some styles will produce a small triangle to the right of the button's text.
Ownership of the menu is not transferred to the push button.
See also menu().
Shows (pops up) the associated popup menu. If there is no such menu, this function does nothing. This function does not return until the popup menu has been closed by the user.
