QLabel Class Reference
^{[QtGui module]}

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:

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

The look of a QLabel can be tuned in several ways. All the settings of QFrame are available for specifying a widget frame. 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 bounderies 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);

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.

Property Documentation

alignment : Qt::Alignment

This property holds the alignment of the label's contents.

Access functions:

• Qt::Alignment alignment () const
• void setAlignment ( Qt::Alignment )

See also text.

indent : int

This property holds the label's text indent in pixels.

If a label displays text, the indent applies to the left edge if alignment() is Qt::AlignLeft, to the right edge if alignment() is Qt::AlignRight, to the top edge if alignment() is Qt::AlignTop, and to to the bottom edge if alignment() is Qt::AlignBottom.

If indent is negative, or if no indent has been set, the label computes the effective indent as follows: If frameWidth() is 0, the effective indent becomes 0. If frameWidth() is greater than 0, the effective indent becomes half the width of the "x" character of the widget's current font().

Access functions:

• int indent () const
• void setIndent ( int )

See also alignment, margin, frameWidth(), and font().

margin : int

This property holds the width of the margin.

The margin is the distance between the innermost pixel of the frame and the outermost pixel of contents.

The default margin is 0.

Access functions:

• int margin () const
• void setMargin ( int )

See also indent.

pixmap : QPixmap

This property holds the label's pixmap.

If no pixmap has been set this will return an invalid pixmap.

Setting the pixmap clears any previous content. The buddy shortcut, if any, is disabled.

Access functions:

• const QPixmap * pixmap () const
• void setPixmap ( const QPixmap & )

scaledContents : bool

This property holds whether the label will scale its contents to fill all available space.

When enabled and the label shows a pixmap, it will scale the pixmap to fill the available space.

This property's default is false.

Access functions:

• bool hasScaledContents () const
• void setScaledContents ( bool )

text : QString

This property holds the label's text.

If no text has been set this will return an empty string. Setting the text clears any previous content, unless they are the same.

The text will be interpreted either as a plain text or as a rich text, depending on the text format setting; see setTextFormat(). The default setting is Qt::AutoText, i.e. QLabel will try to auto-detect the format of the text set.

If the text is interpreted as a plain text and a buddy has been set, the buddy mnemonic key is updated from the new text.

The label resizes itself if auto-resizing is enabled.

Note that Qlabel is well-suited to display small rich text documents, i.e. those small documents that get their document specific settings (font, text color, link color) from the label's palette and font properties. For large documents, use QTextEdit in read-only mode instead. QTextEdit will flicker less on resize and can also provide a scrollbar when necessary.

Access functions:

• QString text () const
• void setText ( const QString & )

See also setTextFormat(), setBuddy(), and alignment.

textFormat : Qt::TextFormat

This property holds the label's text format.

See the Qt::TextFormat enum for an explanation of the possible options.

The default format is Qt::AutoText.

Access functions:

• Qt::TextFormat textFormat () const
• void setTextFormat ( Qt::TextFormat )

See also text().

wordWrap : bool

This property holds the label's word-wrapping policy.

If this property is true then label text is wrapped where necessary at word-breaks; otherwise it is not wrapped at all.

Access functions:

• bool wordWrap () const
• void setWordWrap ( bool on )

Member Function Documentation

QLabel::QLabel ( QWidget * parent = 0, Qt::WFlags f = 0 )

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 = 0, Qt::WFlags f = 0 )

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 ()

Destroys the label.

QWidget * QLabel::buddy () const

Returns this label's buddy, or 0 if no buddy is currently set.

See also setBuddy().

void QLabel::clear ()   [slot]

Clears any label contents.

QMovie * QLabel::movie () const

Returns a pointer to the label's movie, or 0 if no movie has been set.

See also setMovie().

const QPicture * QLabel::picture () const

Returns the label's picture or 0 if the label doesn't have a picture.

See also setPicture().

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 plain text in which one letter is prefixed with an ampersand, &. This letter is set as the shortcut key. The letter is displayed underlined, and the '&' is not displayed (i.e. the Qt::TextShowMnemonic alignment flag is turned on; see setAlignment()).

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 *nameEd  = new QLineEdit(this);
    QLabel    *nameLb  = new QLabel("&Name:", this);
    nameLb->setBuddy(nameEd);
    QLineEdit *phoneEd = new QLineEdit(this);
    QLabel    *phoneLb = new QLabel("&Phone:", this);
    phoneLb->setBuddy(phoneEd);
    // (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 0.

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

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

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

The buddy shortcut, if any, is disabled.

The label resizes itself if auto-resizing is enabled.

See also movie() and setBuddy().

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

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.

The label resizes itself if auto-resizing is enabled.

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

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

This is an overloaded member function, provided for convenience. It behaves essentially like the above 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.

The label resizes itself if auto-resizing is enabled.

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

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

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

The buddy shortcut, if any, is disabled.

See also picture() and setBuddy().