- Qt 6.4
- Qt Help
- C++ Classes
- QHelpEngineCore
- Qt 6.4.2 Reference Documentation

# QHelpEngineCore Class

The QHelpEngineCore class provides the core functionality of the help system. More...

Header: | #include <QHelpEngineCore>
CMake: | find_package(Qt6 REQUIRED COMPONENTS Help) target_link_libraries(mytarget PRIVATE Qt6::Help)
qmake: | QT += help
Inherited By: | QHelpEngine

- List of all members, including inherited members
- Deprecated members

## Properties

- autoSaveFilter : bool
- collectionFile : QString
- readOnly : bool

## Public Functions

| QHelpEngineCore(const QString &collectionFile, QObject *parent = nullptr)
virtual | ~QHelpEngineCore()
bool | autoSaveFilter() const
QString | collectionFile() const
bool | copyCollectionFile(const QString &fileName)
QVariant | customValue(const QString &key, const QVariant &defaultValue = QVariant()) const
QString | documentationFileName(const QString &namespaceName)
QList<QHelpLink> | documentsForIdentifier(const QString &id) const
QList<QHelpLink> | documentsForIdentifier(const QString &id, const QString &filterName) const
QList<QHelpLink> | documentsForKeyword(const QString &keyword) const
QList<QHelpLink> | documentsForKeyword(const QString &keyword, const QString &filterName) const
QString | error() const
QByteArray | fileData(const QUrl &url) const
QList<QUrl> | files(const QString namespaceName, const QString &filterName, const QString &extensionFilter = QString())
QHelpFilterEngine * | filterEngine() const
QUrl | findFile(const QUrl &url) const
bool | isReadOnly() const
bool | registerDocumentation(const QString &documentationFileName)
QStringList | registeredDocumentations() const
bool | removeCustomValue(const QString &key)
void | setAutoSaveFilter(bool save)
void | setCollectionFile(const QString &fileName)
bool | setCustomValue(const QString &key, const QVariant &value)
void | setReadOnly(bool enable)
void | setUsesFilterEngine(bool uses)
bool | setupData()
bool | unregisterDocumentation(const QString &namespaceName)
bool | usesFilterEngine() const

## Signals

void | setupFinished()
void | setupStarted()
void | warning(const QString &msg)

## Static Public Members

QVariant | metaData(const QString &documentationFileName, const QString &name)
QString | namespaceName(const QString &documentationFileName)

## Detailed Description

Before the help engine can be used, it must be initialized by calling setupData(). At the beginning of the setup process the signal setupStarted() is emitted. From this point on until the signal setupFinished() is emitted, is the help data in an undefined meaning unusable state.

The core help engine can be used to perform different tasks. By calling documentsForIdentifier() the engine returns URLs specifying the file locations inside the help system. The actual file data can then be retrieved by calling fileData().

The help engine can contain any number of custom filters. The management of the filters, including adding new filters, changing filter definitions, or removing existing filters, is done through the QHelpFilterEngine class, which can be accessed by the filterEngine() method.

Note: QHelpFilterEngine replaces the older filter API that is deprecated since Qt 5.13. Call setUsesFilterEngine() with `true` to enable the new functionality.

The core help engine has two modes:

- Read-only mode, where the help collection file is not changed unless explicitly requested. This also works if the collection file is in a read-only location, and is the default.
- Fully writable mode, which requires the help collection file to be writable.

The mode can be changed by calling setReadOnly() method, prior to calling setupData().

The help engine also offers the possibility to set and read values in a persistent way comparable to ini files or Windows registry entries. For more information see setValue() or value().

This class does not offer any GUI components or functionality for indices or contents. If you need one of those use QHelpEngine instead.

## Property Documentation

### autoSaveFilter : bool

This property holds whether QHelpEngineCore is in auto save filter mode or not.

If QHelpEngineCore is in auto save filter mode, the current filter is automatically saved when it is changed by the QHelpFilterEngine::setActiveFilter() function. The filter is saved persistently in the help collection file.

By default, this mode is on.

Access functions:

bool | autoSaveFilter() const
void | setAutoSaveFilter(bool save)

### collectionFile : QString

This property holds the absolute file name of the collection file currently used.

Setting this property leaves the help engine in an invalid state. It is important to invoke setupData() or any getter function in order to setup the help engine again.

Access functions:

QString | collectionFile() const
void | setCollectionFile(const QString &fileName)

### `[since 6.0]` readOnly : bool

This property holds whether the help engine is read-only.

In read-only mode, the user can use the help engine with a collection file installed in a read-only location. In this case, some functionality won't be accessible, like registering additional documentation, filter editing, or any action that would require changes to the collection file. Setting it to `false` enables the full functionality of the help engine.

By default, this property is `true`.

This property was introduced in Qt 6.0.

Access functions:

bool | isReadOnly() const
void | setReadOnly(bool enable)

## Member Function Documentation

### QHelpEngineCore::QHelpEngineCore(const QString &collectionFile, QObject *parent = nullptr)

Constructs a new core help engine with a parent. The help engine uses the information stored in the collectionFile to provide help. If the collection file does not exist yet, it'll be created.

### `[signal]` void QHelpEngineCore::setupFinished()

This signal is emitted when the setup is complete.

### `[signal]` void QHelpEngineCore::setupStarted()

This signal is emitted when setup is started.

### `[signal]` void QHelpEngineCore::warning(const QString &msg)

This signal is emitted when a non critical error occurs. The warning message is stored in msg.

### `[virtual]` QHelpEngineCore::~QHelpEngineCore()

Destructs the help engine.

### bool QHelpEngineCore::copyCollectionFile(const QString &fileName)

Creates the file fileName and copies all contents from the current collection file into the newly created file, and returns true if successful; otherwise returns false.

The copying process makes sure that file references to Qt Collection files (`.qch`) files are updated accordingly.

### QVariant QHelpEngineCore::customValue(const QString &key, const QVariant &defaultValue = QVariant()) const

Returns the value assigned to the key. If the requested key does not exist, the specified defaultValue is returned.

See also setCustomValue() and removeCustomValue().

### QString QHelpEngineCore::documentationFileName(const QString &namespaceName)

Returns the absolute file name of the Qt compressed help file (.qch) identified by the namespaceName. If there is no Qt compressed help file with the specified namespace registered, an empty string is returned.

See also namespaceName().

### `[since 5.15]` QList<QHelpLink> QHelpEngineCore::documentsForIdentifier(const QString &id) const

Returns a list of all the document links found for the id. The returned list contents depend on the current filter, and therefore only the keywords registered for the current filter will be returned.

This function was introduced in Qt 5.15.

### `[since 5.15]` QList<QHelpLink> QHelpEngineCore::documentsForIdentifier(const QString &id, const QString &filterName) const

Returns a list of the document links found for the id, filtered by filterName. The returned list contents depend on the passed filter, and therefore only the keywords registered for this filter will be returned. If you want to get all results unfiltered, pass empty string as filterName.

This function was introduced in Qt 5.15.

### `[since 5.15]` QList<QHelpLink> QHelpEngineCore::documentsForKeyword(const QString &keyword) const

Returns a list of all the document links found for the keyword. The returned list contents depend on the current filter, and therefore only the keywords registered for the current filter will be returned.

This function was introduced in Qt 5.15.

### `[since 5.15]` QList<QHelpLink> QHelpEngineCore::documentsForKeyword(const QString &keyword, const QString &filterName) const

Returns a list of the document links found for the keyword, filtered by filterName. The returned list contents depend on the passed filter, and therefore only the keywords registered for this filter will be returned. If you want to get all results unfiltered, pass empty string as filterName.

This function was introduced in Qt 5.15.

### QString QHelpEngineCore::error() const

Returns a description of the last error that occurred.

### QByteArray QHelpEngineCore::fileData(const QUrl &url) const

Returns the data of the file specified by url. If the file does not exist, an empty QByteArray is returned.

See also findFile().

### QList<QUrl> QHelpEngineCore::files(const QString namespaceName, const QString &filterName, const QString &extensionFilter = QString())

Returns a list of files contained in the Qt compressed help file for namespaceName. The files can be filtered by filterName as well as by their extension extensionFilter (for example, 'html').

### `[since 5.13]` QHelpFilterEngine *QHelpEngineCore::filterEngine() const

Returns the filter engine associated with this help engine. The filter engine allows for adding, changing, and removing existing filters for this help engine. To use the engine you also have to call setUsesFilterEngine() set to `true`.

This function was introduced in Qt 5.13.

### QUrl QHelpEngineCore::findFile(const QUrl &url) const

Returns the corrected URL for the url that may refer to a different namespace defined by the virtual folder defined as a part of the url. If the virtual folder matches the namespace of the url, the method just checks if the file exists and returns the same url. When the virtual folder doesn't match the namespace of the url, it tries to find the best matching namespace according to the active filter. When the namespace is found, it returns the corrected URL if the file exists, otherwise it returns an invalid URL.

### `[static]` QVariant QHelpEngineCore::metaData(const QString &documentationFileName, const QString &name)

Returns the meta data for the Qt compressed help file documentationFileName. If there is no data available for name, an invalid QVariant() is returned. The meta data is defined when creating the Qt compressed help file and cannot be modified later. Common meta data includes e.g. the author of the documentation.

### `[static]` QString QHelpEngineCore::namespaceName(const QString &documentationFileName)

Returns the namespace name defined for the Qt compressed help file (.qch) specified by its documentationFileName. If the file is not valid, an empty string is returned.

See also documentationFileName().

### bool QHelpEngineCore::registerDocumentation(const QString &documentationFileName)

Registers the Qt compressed help file (.qch) contained in the file documentationFileName. One compressed help file, uniquely identified by its namespace can only be registered once. True is returned if the registration was successful, otherwise false.

See also unregisterDocumentation() and error().

### QStringList QHelpEngineCore::registeredDocumentations() const

Returns a list of all registered Qt compressed help files of the current collection file. The returned names are the namespaces of the registered Qt compressed help files (.qch).

### bool QHelpEngineCore::removeCustomValue(const QString &key)

Removes the key from the settings section in the collection file. Returns true if the value was removed successfully, otherwise false.

See also customValue() and setCustomValue().

### bool QHelpEngineCore::setCustomValue(const QString &key, const QVariant &value)

Save the value under the key. If the key already exist, the value will be overwritten. Returns true if the value was saved successfully, otherwise false.

See also customValue() and removeCustomValue().

### `[since 5.13]` void QHelpEngineCore::setUsesFilterEngine(bool uses)

Enables or disables the new filter engine functionality inside the help engine, according to the passed uses parameter.

This function was introduced in Qt 5.13.

See also usesFilterEngine() and filterEngine().

### bool QHelpEngineCore::setupData()

Sets up the help engine by processing the information found in the collection file and returns true if successful; otherwise returns false.

By calling the function, the help engine is forced to initialize itself immediately. Most of the times, this function does not have to be called explicitly because getter functions which depend on a correctly set up help engine do that themselves.

Note: `qsqlite4.dll` needs to be deployed with the application as the help system uses the sqlite driver when loading help collections.

### bool QHelpEngineCore::unregisterDocumentation(const QString &namespaceName)

Unregisters the Qt compressed help file (.qch) identified by its namespaceName from the help collection. Returns true on success, otherwise false.

See also registerDocumentation() and error().

### `[since 5.13]` bool QHelpEngineCore::usesFilterEngine() const

Returns whether the help engine uses the new filter functionality.

This function was introduced in Qt 5.13.

See also setUsesFilterEngine() and filterEngine().