Contents

• Public Types
• Public Functions
• Static Public Members
• Related Non-Members
• Detailed Description
• Standard Shortcuts
• Keyboard Layout Issues
• GNU Emacs Style Key Sequences

Detailed Description

TheQKeySequence 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 withQAction 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, astandard 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 theQt::Key andQt::Modifier enum values. Each key code consists of a singleQt::Key value and zero or more modifiers, such asQt::SHIFT,Qt::CTRL,Qt::ALT andQt::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 theShift key to activate a shortcut specified with "Ctrl+P". However, for other keys, the use ofShift 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 theKeyboard 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 aQString to obtain a human-readable translated version of the sequence. Similarly, thetoString() 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 asQt::Key_A.

Note: On Mac OS X, references to "Ctrl",Qt::CTRL, Qt::Control andQt::ControlModifier correspond to theCommand keys on the Macintosh keyboard, and references to "Meta",Qt::META, Qt::Meta andQt::MetaModifier correspond to theControl 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 manystandard 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, theCtrl value corresponds to theCommand keys on the Macintosh keyboard, and theMeta value corresponds to theControl 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 asCtrl S ("Ctrl+S") orCtrl 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 andCtrl 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 theShift key. However, users with British keyboards will need to hold down theShift 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 asCtrl plus. However, the= key needs to be accessed using theShift key on Norwegian keyboard, making the required shortcut effectivelyCtrl 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 ofstandard 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 inGNU 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 byCtrl 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: AQApplication instance must have been constructed before aQKeySequence is created; otherwise, your application may crash.

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 aQAction.

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

This enum was introduced or modified in Qt 4.2.

Member Function Documentation

QKeySequence::QKeySequence()

Constructs an empty key sequence.

QKeySequence::QKeySequence(constQString & key)

Creates a key sequence from thekey 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 (usingQObject::tr()).

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

key should be inNativeText format.

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

QMenu*file=newQMenu(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(constQString & key,SequenceFormat format)

Creates a key sequence from thekey string based onformat.

This function was introduced in Qt 4.7.

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

Constructs a key sequence with up to 4 keysk1,k2,k3 andk4.

The key codes are listed inQt::Key and can be combined with modifiers (seeQt::Modifier) such asQt::SHIFT,Qt::CTRL,Qt::ALT, orQt::META.

QKeySequence::QKeySequence(constQKeySequence & keysequence)

Copy constructor. Makes a copy ofkeysequence.

QKeySequence::QKeySequence(StandardKey key)

Constructs aQKeySequence object for the givenkey. 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 thekey.

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.

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

Return aQKeySequence from the stringstr based onformat.

This function was introduced in Qt 4.1.

See alsotoString().

bool QKeySequence::isEmpty() const

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

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

Returns a list of key bindings for the givenkey. 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 givenkey.

This function was introduced in Qt 4.2.

SequenceMatch QKeySequence::matches(constQKeySequence & seq) const

Matches the sequence withseq. ReturnsExactMatch if successful,PartialMatch ifseq matches incompletely, andNoMatch if the sequences have nothing in common. ReturnsNoMatch ifseq is shorter.

[static]QKeySequence QKeySequence::mnemonic(constQString & text)

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

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

We provide alist 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 alsoqt_set_sequence_auto_mnemonic().

void QKeySequence::swap(QKeySequence & other)

Swaps key sequenceother with this key sequence. This operation is very fast and never fails.

This function was introduced in Qt 4.8.

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

Return a string representation of the key sequence, based onformat.

For example, the valueQt::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 usingQObject::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 alsofromString().

QKeySequence::operator QVariant() const

Returns the key sequence as aQVariant

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

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

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

Provides an arbitrary comparison of this key sequence andother 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 useQKeySequence objects as keys in aQMap.

See alsooperator==(),operator!=(),operator>(),operator<=(), andoperator>=().

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

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

See alsooperator==(),operator!=(),operator<(),operator>(), andoperator>=().

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

Assignment operator. Assigns theother key sequence to this object.

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

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

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

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

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

See alsooperator==(),operator!=(),operator<(),operator<=(), andoperator>=().

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

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

See alsooperator==(),operator!=(),operator<(),operator>(), andoperator<=().

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

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

Related Non-Members

QDataStream &operator<<(QDataStream & stream, constQKeySequence & sequence)

Writes the keysequence to thestream.

See alsoFormat of the QDataStream operators.

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

Reads a key sequence from thestream into the keysequence.

See alsoFormat of the QDataStream operators.