QLabel Class

The QLabel widget provides a text or image display. More...

Header:	#include <QLabel>
qmake:	QT += widgets
Inherits:	QFrame

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

Properties

alignment : Qt::Alignment hasSelectedText : const bool indent : int margin : int openExternalLinks : bool pixmap : QPixmap

scaledContents : bool selectedText : const QString text : QString textFormat : Qt::TextFormat textInteractionFlags : Qt::TextInteractionFlags wordWrap : bool

• 6 properties inherited from QFrame
• 59 properties inherited from QWidget
• 1 property inherited from QObject

Public Functions

	QLabel(QWidget *parent = nullptr, Qt::WindowFlags f = ...)
	QLabel(const QString &text, QWidget *parent = nullptr, Qt::WindowFlags f = ...)
virtual	~QLabel()
Qt::Alignment	alignment() const
QWidget *	buddy() const
bool	hasScaledContents() const
bool	hasSelectedText() const
int	indent() const
int	margin() const
QMovie *	movie() const
bool	openExternalLinks() const
const QPicture *	picture() const
const QPixmap *	pixmap() const
QString	selectedText() const
int	selectionStart() const
void	setAlignment(Qt::Alignment)
void	setBuddy(QWidget *buddy)
void	setIndent(int)
void	setMargin(int)
void	setOpenExternalLinks(bool open)
void	setScaledContents(bool)
void	setSelection(int start, int length)
void	setTextFormat(Qt::TextFormat)
void	setTextInteractionFlags(Qt::TextInteractionFlags flags)
void	setWordWrap(bool on)
QString	text() const
Qt::TextFormat	textFormat() const
Qt::TextInteractionFlags	textInteractionFlags() const
bool	wordWrap() const

Reimplemented Public Functions

virtual int	heightForWidth(int w) const override
virtual QSize	minimumSizeHint() const override
virtual QSize	sizeHint() const override

• 14 public functions inherited from QFrame
• 214 public functions inherited from QWidget
• 31 public functions inherited from QObject
• 14 public functions inherited from QPaintDevice

Public Slots

void	clear()
void	setMovie(QMovie *movie)
void	setNum(int num)
void	setNum(double num)
void	setPicture(const QPicture &picture)
void	setPixmap(const QPixmap &)
void	setText(const QString &)

• 19 public slots inherited from QWidget
• 1 public slot inherited from QObject

Signals

void	linkActivated(const QString &link)
void	linkHovered(const QString &link)

• 3 signals inherited from QWidget
• 2 signals inherited from QObject

Static Public Members

const QMetaObject

staticMetaObject

• 5 static public members inherited from QWidget
• 9 static public members inherited from QObject

Reimplemented Protected Functions

virtual void	changeEvent(QEvent *ev) override
virtual void	contextMenuEvent(QContextMenuEvent *ev) override
virtual bool	event(QEvent *e) override
virtual void	focusInEvent(QFocusEvent *ev) override
virtual bool	focusNextPrevChild(bool next) override
virtual void	focusOutEvent(QFocusEvent *ev) override
virtual void	keyPressEvent(QKeyEvent *ev) override
virtual void	mouseMoveEvent(QMouseEvent *ev) override
virtual void	mousePressEvent(QMouseEvent *ev) override
virtual void	mouseReleaseEvent(QMouseEvent *ev) override
virtual void	paintEvent(QPaintEvent *) override

• 4 protected functions inherited from QFrame
• 35 protected functions inherited from QWidget
• 9 protected functions inherited from QObject
• 1 protected function inherited from QPaintDevice

Additional Inherited Members

• 4 protected functions inherited from QFrame
• 35 protected functions inherited from QWidget
• 9 protected functions inherited from QObject
• 1 protected function inherited from QPaintDevice
• 1 protected slot inherited from QWidget

Detailed Description

The QLabel widget provides a text or image display.

QLabel is used for displaying text or an image. No user interaction functionality is provided. The visual appearance of the label can be configured in various ways, and it can be used for specifying a focus mnemonic key for another widget.

A QLabel can contain any of the following content types:

Content	Setting
Plain text	Pass a QString to setText().
Rich text	Pass a QString that contains rich text to setText().
A pixmap	Pass a QPixmap to setPixmap().
A movie	Pass a QMovie to setMovie().
A number	Pass an int or a double to setNum(), which converts the number to plain text.
Nothing	The same as an empty plain text. This is the default. Set by clear().

Warning: When passing a QString to the constructor or calling setText(), make sure to sanitize your input, as QLabel tries to guess whether it displays the text as plain text or as rich text, a subset of HTML 4 markup. You may want to call setTextFormat() explicitly, e.g. in case you expect the text to be in plain format but cannot control the text source (for instance when displaying data loaded from the Web).

When the content is changed using any of these functions, any previous content is cleared.

By default, labels display left-aligned, vertically-centered text and images, where any tabs in the text to be displayed are automatically expanded. However, the look of a QLabel can be adjusted and fine-tuned in several ways.

The positioning of the content within the QLabel widget area can be tuned with setAlignment() and setIndent(). Text content can also wrap lines along word boundaries with setWordWrap(). For example, this code sets up a sunken panel with a two-line text in the bottom right corner (both lines being flush with the right side of the label):

QLabel *label = new QLabel(this);
label->setFrameStyle(QFrame::Panel | QFrame::Sunken);
label->setText("first line\nsecond line");
label->setAlignment(Qt::AlignBottom | Qt::AlignRight);

The properties and functions QLabel inherits from QFrame can also be used to specify the widget frame to be used for any given label.

A QLabel is often used as a label for an interactive widget. For this use QLabel provides a useful mechanism for adding an mnemonic (see QKeySequence) that will set the keyboard focus to the other widget (called the QLabel's "buddy"). For example:

QLineEdit *phoneEdit = new QLineEdit(this);
QLabel *phoneLabel = new QLabel("&Phone:", this);
phoneLabel->setBuddy(phoneEdit);

In this example, keyboard focus is transferred to the label's buddy (the QLineEdit) when the user presses Alt+P. If the buddy was a button (inheriting from QAbstractButton), triggering the mnemonic would emulate a button click.

See also QLineEdit, QTextEdit, QPixmap, QMovie, and GUI Design Handbook: Label.

Member Function Documentation

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

Constructs an empty label.

The parent and widget flag f, arguments are passed to the QFrame constructor.

See also setAlignment(), setFrameStyle(), and setIndent().

QLabel::QLabel(const QString &text, QWidget *parent = nullptr, Qt::WindowFlags f = ...)

Constructs a label that displays the text, text.

The parent and widget flag f, arguments are passed to the QFrame constructor.

See also setText(), setAlignment(), setFrameStyle(), and setIndent().

[virtual] QLabel::~QLabel()

Destroys the label.

QWidget *QLabel::buddy() const

Returns this label's buddy, or nullptr if no buddy is currently set.

See also setBuddy().

[override virtual protected] void QLabel::changeEvent(QEvent *ev)

Reimplemented from QFrame::changeEvent().

[slot] void QLabel::clear()

Clears any label contents.

[override virtual protected] void QLabel::contextMenuEvent(QContextMenuEvent *ev)

Reimplemented from QWidget::contextMenuEvent().

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

Reimplemented from QFrame::event().

[override virtual protected] void QLabel::focusInEvent(QFocusEvent *ev)

Reimplemented from QWidget::focusInEvent().

[override virtual protected] bool QLabel::focusNextPrevChild(bool next)

Reimplemented from QWidget::focusNextPrevChild().

[override virtual protected] void QLabel::focusOutEvent(QFocusEvent *ev)

Reimplemented from QWidget::focusOutEvent().

[override virtual] int QLabel::heightForWidth(int w) const

Reimplemented from QWidget::heightForWidth().

[override virtual protected] void QLabel::keyPressEvent(QKeyEvent *ev)

Reimplemented from QWidget::keyPressEvent().

[signal] void QLabel::linkActivated(const QString &link)

This signal is emitted when the user clicks a link. The URL referred to by the anchor is passed in link.

This function was introduced in Qt 4.2.

See also linkHovered().

[signal] void QLabel::linkHovered(const QString &link)

This signal is emitted when the user hovers over a link. The URL referred to by the anchor is passed in link.

This function was introduced in Qt 4.2.

See also linkActivated().

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

Reimplemented from QWidget::minimumSizeHint().

[override virtual protected] void QLabel::mouseMoveEvent(QMouseEvent *ev)

Reimplemented from QWidget::mouseMoveEvent().

[override virtual protected] void QLabel::mousePressEvent(QMouseEvent *ev)

Reimplemented from QWidget::mousePressEvent().

[override virtual protected] void QLabel::mouseReleaseEvent(QMouseEvent *ev)

Reimplemented from QWidget::mouseReleaseEvent().

QMovie *QLabel::movie() const

Returns a pointer to the label's movie, or nullptr if no movie has been set.

See also setMovie().

[override virtual protected] void QLabel::paintEvent(QPaintEvent *)

Reimplemented from QFrame::paintEvent().

const QPicture *QLabel::picture() const

Returns the label's picture or nullptr if the label doesn't have a picture.

See also setPicture().

int QLabel::selectionStart() const

selectionStart() returns the index of the first selected character in the label or -1 if no text is selected.

Note: The textInteractionFlags set on the label need to include either TextSelectableByMouse or TextSelectableByKeyboard.

This function was introduced in Qt 4.7.

See also selectedText().

void QLabel::setBuddy(QWidget *buddy)

Sets this label's buddy to buddy.

When the user presses the shortcut key indicated by this label, the keyboard focus is transferred to the label's buddy widget.

The buddy mechanism is only available for QLabels that contain text in which one character is prefixed with an ampersand, '&'. This character is set as the shortcut key. See the QKeySequence::mnemonic() documentation for details (to display an actual ampersand, use '&&').

In a dialog, you might create two data entry widgets and a label for each, and set up the geometry layout so each label is just to the left of its data entry widget (its "buddy"), for example:

QLineEdit *nameEdit  = new QLineEdit(this);
QLabel    *nameLabel = new QLabel("&Name:", this);
nameLabel->setBuddy(nameEdit);
QLineEdit *phoneEdit  = new QLineEdit(this);
QLabel    *phoneLabel = new QLabel("&Phone:", this);
phoneLabel->setBuddy(phoneEdit);
// (layout setup not shown)

With the code above, the focus jumps to the Name field when the user presses Alt+N, and to the Phone field when the user presses Alt+P.

To unset a previously set buddy, call this function with buddy set to nullptr.

See also buddy(), setText(), QShortcut, and setAlignment().

[slot] void QLabel::setMovie(QMovie *movie)

Sets the label contents to movie. Any previous content is cleared. The label does NOT take ownership of the movie.

The buddy shortcut, if any, is disabled.

See also movie() and setBuddy().

[slot] void QLabel::setNum(int num)

Sets the label contents to plain text containing the textual representation of integer num. Any previous content is cleared. Does nothing if the integer's string representation is the same as the current contents of the label.

The buddy shortcut, if any, is disabled.

See also setText(), QString::setNum(), and setBuddy().

[slot] void QLabel::setNum(double num)

This is an overloaded function.

Sets the label contents to plain text containing the textual representation of double num. Any previous content is cleared. Does nothing if the double's string representation is the same as the current contents of the label.

The buddy shortcut, if any, is disabled.

See also setText(), QString::setNum(), and setBuddy().

[slot] void QLabel::setPicture(const QPicture &picture)

Sets the label contents to picture. Any previous content is cleared.

The buddy shortcut, if any, is disabled.

See also picture() and setBuddy().

void QLabel::setSelection(int start, int length)

Selects text from position start and for length characters.

Note: The textInteractionFlags set on the label need to include either TextSelectableByMouse or TextSelectableByKeyboard.

This function was introduced in Qt 4.7.

See also selectedText().

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

Reimplemented from QFrame::sizeHint().