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QKeySequence Class Reference
[QtGui module]

The QKeySequence class encapsulates a key sequence as used by shortcuts. More...

 #include <QKeySequence>

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

Public Types

• enum SequenceFormat { NativeText, PortableText }
• enum SequenceMatch { NoMatch, PartialMatch, ExactMatch }
• enum StandardKey { UnknownKey, HelpContents, WhatsThis, Open, ..., DeleteEndOfLine }

Public Functions

• QKeySequence ()
• QKeySequence ( const QString & key )
• QKeySequence ( int k1, int k2 = 0, int k3 = 0, int k4 = 0 )
• QKeySequence ( const QKeySequence & keysequence )
• QKeySequence ( StandardKey key )
• ~QKeySequence ()
• uint count () const
• bool isEmpty () const
• SequenceMatch matches ( const QKeySequence & seq ) const
• QString toString ( SequenceFormat format = PortableText ) const
• operator QVariant () const
• bool operator!= ( const QKeySequence & other ) const
• bool operator< ( const QKeySequence & other ) const
• bool operator<= ( const QKeySequence & other ) const
• QKeySequence & operator= ( const QKeySequence & other )
• bool operator== ( const QKeySequence & other ) const
• bool operator> ( const QKeySequence & other ) const
• bool operator>= ( const QKeySequence & other ) const
• int operator[] ( uint index ) const

Static Public Members

• QKeySequence fromString ( const QString & str, SequenceFormat format = PortableText )
• QList<QKeySequence> keyBindings ( StandardKey key )
• QKeySequence mnemonic ( const QString & text )

Related Non-Members

• QDataStream & operator<< ( QDataStream & stream, const QKeySequence & sequence )
• QDataStream & operator>> ( QDataStream & stream, QKeySequence & sequence )

Detailed Description

The QKeySequence class encapsulates a key sequence as used by shortcuts.

In its most common form, a key sequence describes a combination of keys that must be used together to perform some action. Key sequences are used with QAction objects to specify which keyboard shortcuts can be used to trigger actions.

Key sequences can be constructed for use as keyboard shortcuts in three different ways:

• For standard shortcuts, a standard key can be used to request the platform-specific key sequence associated with each shortcut.
• For custom shortcuts, human-readable strings such as "Ctrl+X" can be used, and these can be translated into the appropriate shortcuts for users of different languages. Translations are made in the "QShortcut" context.
• For hard-coded shortcuts, integer key codes can be specified with a combination of values defined by the Qt::Key and Qt::Modifier enum values. Each key code consists of a single Qt::Key value and zero or more modifiers, such as Qt::SHIFT, Qt::CTRL, Qt::ALT and Qt::META.

For example, Ctrl P might be a sequence used as a shortcut for printing a document, and can be specified in any of the following ways:

 QKeySequence(QKeySequence::Print}
 QKeySequence(tr("Ctrl+P"))
 QKeySequence(tr("Ctrl+p"))
 QKeySequence(Qt::CTRL + Qt::Key_P)

Note that, for letters, the case used in the specification string does not matter. In the above examples, the user does not need to hold down the Shift key to activate a shortcut specified with "Ctrl+P". However, for other keys, the use of Shift as an unspecified extra modifier key can lead to confusion for users of an application whose keyboards have different layouts to those used by the developers. See the Keyboard Layout Issues section below for more details.

It is preferable to use standard shortcuts where possible. When creating key sequences for non-standard shortcuts, you should use human-readable strings in preference to hard-coded integer values.

QKeySequence objects can be cast to a QString to obtain a human-readable translated version of the sequence. Similarly, the toString() function produces human-readable strings for use in menus. On Mac OS X, the appropriate symbols are used to describe keyboard shortcuts using special keys on the Macintosh keyboard.

An alternative way to specify hard-coded key codes is to use the Unicode code point of the character; for example, 'A' gives the same key sequence as Qt::Key_A.

Note: On Mac OS X, references to "Ctrl", Qt::CTRL, Qt::Control and Qt::ControlModifier correspond to the Command keys on the Macintosh keyboard, and references to "Meta", Qt::META, Qt::Meta and Qt::MetaModifier correspond to the Control keys. Developers on Mac OS X can use the same shortcut descriptions across all platforms, and their applications will automatically work as expected on Mac OS X.

Standard Shortcuts

QKeySequence defines many StandardKey standard keyboard shortcuts to reduce the amount of effort required when setting up actions in a typical application. The table below shows some common key sequences that are often used for these standard shortcuts by applications on four widely-used platforms. Note that on Mac OS X, the Ctrl value corresponds to the Command keys on the Macintosh keyboard, and the Meta value corresponds to the Control keys.

Note that, since the key sequences used for the standard shortcuts differ between platforms, you still need to test your shortcuts on each platform to ensure that you do not unintentionally assign the same key sequence to many actions.

Keyboard Layout Issues

Many key sequence specifications are chosen by developers based on the layout of certain types of keyboard, rather than choosing keys that represent the first letter of an action's name, such as Ctrl S ("Ctrl+S") or Ctrl C ("Ctrl+C"). Additionally, because certain symbols can only be entered with the help of modifier keys on certain keyboard layouts, key sequences intended for use with one keyboard layout may map to a different key, map to no keys at all, or require an additional modifier key to be used on different keyboard layouts.

For example, the shortcuts, Ctrl plus and Ctrl minus, are often used as shortcuts for zoom operations in graphics applications, and these may be specified as "Ctrl++" and "Ctrl+-" respectively. However, the way these shortcuts are specified and interpreted depends on the keyboard layout. Users of Norwegian keyboards will note that the + and - keys are not adjacent on the keyboard, but will still be able to activate both shortcuts without needing to press the Shift key. However, users with British keyboards will need to hold down the Shift key to enter the + symbol, making the shortcut effectively the same as "Ctrl+Shift+=".

Although some developers might resort to fully specifying all the modifiers they use on their keyboards to activate a shortcut, this will also result in unexpected behavior for users of different keyboard layouts.

For example, a developer using a British keyboard may decide to specify "Ctrl+Shift+=" as the key sequence in order to create a shortcut that coincidentally behaves in the same way as Ctrl plus. However, the = key needs to be accessed using the Shift key on Norwegian keyboard, making the required shortcut effectively Ctrl Shift Shift = (an impossible key combination).

As a result, both human-readable strings and hard-coded key codes can both be problematic to use when specifying a key sequence that can be used on a variety of different keyboard layouts. Only the use of standard shortcuts guarantees that the user will be able to use the shortcuts that the developer intended.

Despite this, we can address this issue by ensuring that human-readable strings are used, making it possible for translations of key sequences to be made for users of different languages. This approach will be successful for users whose keyboards have the most typical layout for the language they are using.

GNU Emacs Style Key Sequences

Key sequences similar to those used in GNU Emacs, allowing up to four key codes, can be created by using the multiple argument constructor, or by passing a human-readable string of comma-separated key sequences.

For example, the key sequence, Ctrl X followed by Ctrl C, can be specified using either of the following ways:

 QKeySequence(tr("Ctrl+X, Ctrl+C"))
 QKeySequence(Qt::CTRL + Qt::Key_X, Qt::CTRL + Qt::Key_C)

Warning: A QApplication instance must have been constructed before a QKeySequence is created; otherwise, your application may crash.

See also QShortcut.

Member Type Documentation

enum QKeySequence::SequenceFormat

enum QKeySequence::SequenceMatch

enum QKeySequence::StandardKey

This enum represent standard key bindings. They can be used to assign platform dependent keyboard shortcuts to a QAction. QKeyEvent also provides the function QKeyEvent::standardKey() to query if it matches an existing key binding.

Note that the key bindings are platform dependent. The currently bound shortcuts can be queried using keyBindings().

This enum was introduced in Qt 4.2.

Member Function Documentation

QKeySequence::QKeySequence ()

Constructs an empty key sequence.

QKeySequence::QKeySequence ( const QString & key )

Creates a key sequence from the key string. For example "Ctrl+O" gives CTRL+'O'. The strings "Ctrl", "Shift", "Alt" and "Meta" are recognized, as well as their translated equivalents in the "QShortcut" context (using QObject::tr()).

Up to four key codes may be entered by separating them with commas, e.g. "Alt+X,Ctrl+S,Q".

This constructor is typically used with tr(), so that shortcut keys can be replaced in translations:

 QMenu *file = new QMenu(this);
 file->addAction(tr("&Open..."), this, SLOT(open()),
                   QKeySequence(tr("Ctrl+O", "File|Open")));

Note the "File|Open" translator comment. It is by no means necessary, but it provides some context for the human translator.

QKeySequence::QKeySequence ( int k1, int k2 = 0, int k3 = 0, int k4 = 0 )

Constructs a key sequence with up to 4 keys k1, k2, k3 and k4.

The key codes are listed in Qt::Key and can be combined with modifiers (see Qt::Modifier) such as Qt::SHIFT, Qt::CTRL, Qt::ALT, or Qt::META.

QKeySequence::QKeySequence ( const QKeySequence & keysequence )

Copy constructor. Makes a copy of keysequence.

QKeySequence::QKeySequence ( StandardKey key )

Constructs a QKeySequence object for the given key. The result will depend on the currently running platform.

The resulting object will be based on the first element in the list of key bindings for the key.

This function was introduced in Qt 4.2.

QKeySequence::~QKeySequence ()

Destroys the key sequence.

uint QKeySequence::count () const

Returns the number of keys in the key sequence. The maximum is 4.

QKeySequence QKeySequence::fromString ( const QString & str, SequenceFormat format = PortableText )   [static]

Return a QKeySequence from the string str based on format.

This function was introduced in Qt 4.1.

See also toString().

bool QKeySequence::isEmpty () const

Returns true if the key sequence is empty; otherwise returns false.

QList<QKeySequence> QKeySequence::keyBindings ( StandardKey key )   [static]

Returns a list of key bindings for the given key. The result of calling this function will vary based on the target platform. The first element of the list indicates the primary shortcut for the given platform. If the result contains more than one result, these can be considered alternative shortcuts on the same platform for the given key.

This function was introduced in Qt 4.2.

SequenceMatch QKeySequence::matches ( const QKeySequence & seq ) const

Matches the sequence with seq. Returns ExactMatch if successful, PartialMatch if seq matches incompletely, and NoMatch if the sequences have nothing in common. Returns NoMatch if seq is shorter.

QKeySequence QKeySequence::mnemonic ( const QString & text )   [static]

Returns the shortcut key sequence for the mnemonic in text, or an empty key sequence if no mnemonics are found.

For example, mnemonic("E&xit") returns Qt::ALT+Qt::Key_X, mnemonic("&Quit") returns ALT+Key_Q, and mnemonic("Quit") returns an empty QKeySequence.

We provide a list of common mnemonics in English. At the time of writing, Microsoft and Open Group do not appear to have issued equivalent recommendations for other languages.

See also qt_set_sequence_auto_mnemonic().

QString QKeySequence::toString ( SequenceFormat format = PortableText ) const

Return a string representation of the key sequence, based on format.

For example, the value Qt::CTRL+Qt::Key_O results in "Ctrl+O". If the key sequence has multiple key codes, each is separated by commas in the string returned, such as "Alt+X, Ctrl+Y, Z". The strings, "Ctrl", "Shift", etc. are translated using QObject::tr() in the "QShortcut" context.

If the key sequence has no keys, an empty string is returned.

On Mac OS X, the string returned resembles the sequence that is shown in the menu bar.

This function was introduced in Qt 4.1.

See also fromString().

QKeySequence::operator QVariant () const

Returns the key sequence as a QVariant

bool QKeySequence::operator!= ( const QKeySequence & other ) const

Returns true if this key sequence is not equal to the other key sequence; otherwise returns false.

bool QKeySequence::operator< ( const QKeySequence & other ) const

Provides an arbitrary comparison of this key sequence and other key sequence. All that is guaranteed is that the operator returns false if both key sequences are equal and that (ks1 < ks2) == !( ks2 < ks1) if the key sequences are not equal.

This function is useful in some circumstances, for example if you want to use QKeySequence objects as keys in a QMap.

See also operator==(), operator!=(), operator>(), operator<=(), and operator>=().

bool QKeySequence::operator<= ( const QKeySequence & other ) const

Returns true if this key sequence is smaller or equal to the other key sequence; otherwise returns false.

See also operator==(), operator!=(), operator<(), operator>(), and operator>=().

QKeySequence & QKeySequence::operator= ( const QKeySequence & other )

Assignment operator. Assigns the other key sequence to this object.

bool QKeySequence::operator== ( const QKeySequence & other ) const

Returns true if this key sequence is equal to the other key sequence; otherwise returns false.

bool QKeySequence::operator> ( const QKeySequence & other ) const

Returns true if this key sequence is larger than the other key sequence; otherwise returns false.

See also operator==(), operator!=(), operator<(), operator<=(), and operator>=().

bool QKeySequence::operator>= ( const QKeySequence & other ) const

Returns true if this key sequence is larger or equal to the other key sequence; otherwise returns false.

See also operator==(), operator!=(), operator<(), operator>(), and operator<=().

int QKeySequence::operator[] ( uint index ) const

Returns a reference to the element at position index in the key sequence. This can only be used to read an element.

Related Non-Members

QDataStream & operator<< ( QDataStream & stream, const QKeySequence & sequence )

This is an overloaded member function, provided for convenience.

Writes the key sequence to the stream.

See also Format of the QDataStream operators.

QDataStream & operator>> ( QDataStream & stream, QKeySequence & sequence )

This is an overloaded member function, provided for convenience.

Reads a key sequence from the stream into the key sequence.

See also Format of the QDataStream operators.