QLabel Class

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

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

Properties

Public Functions

Reimplemented Public Functions

Public Slots

Signals

Reimplemented Protected Functions

Detailed Description

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:

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.

const QPixmap *pixmapPtr = label->pixmap();
QPixmap pixmapVal = label->pixmap(Qt::ReturnByValue);

QPixmap pixmapVal = label->pixmap();

Member Function Documentation

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

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().

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

Constructs an empty label.

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

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

[slot] void QLabel::clear()

Clears any label contents.

[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().

[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(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::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::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().

[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)

Reimplements: QFrame::changeEvent(QEvent *ev).

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

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

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

Reimplements: QFrame::event(QEvent *e).

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

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

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

Reimplements: QWidget::focusNextPrevChild(bool next).

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

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

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

Reimplements: QWidget::heightForWidth(int w) const.

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

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

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

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

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

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

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

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

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

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

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 *)

Reimplements: QFrame::paintEvent(QPaintEvent *).

QPicture QLabel::picture(Qt::ReturnByValueConstant) const

Returns the label's picture.

Previously, Qt provided a version of picture() which returned the picture by-pointer. That version is now deprecated. To maintain compatibility with old code, you can explicitly differentiate between the by-pointer function and the by-value function:

const QPicture *picPtr = label->picture();
QPicture picVal = label->picture(Qt::ReturnByValue);

If you disable the deprecated version using the QT_DISABLE_DEPRECATED_BEFORE macro, then you can omit Qt::ReturnByValue as shown below:

QPicture picVal = label->picture();

This function was introduced in Qt 5.15.

QPixmap QLabel::pixmap(Qt::ReturnByValueConstant) const

Note: Getter function for property pixmap.

This function was introduced in Qt 5.15.

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().

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

Reimplements: QFrame::sizeHint() const.