path: root/src/qml/doc/src/qmlfunctions.qdoc

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/*!
  \macro QML_DECLARE_TYPE()
  \relates QQmlEngine

  Equivalent to \c Q_DECLARE_METATYPE(TYPE *) and \c Q_DECLARE_METATYPE(QQmlListProperty<TYPE>)

  #include <QtQml> to use this macro.
*/

/*!
  \macro QML_DECLARE_TYPEINFO(Type,Flags)
  \relates QQmlEngine

  Declares additional properties of the given \a Type as described by the
  specified \a Flags.

  Current the only supported type info is \c QML_HAS_ATTACHED_PROPERTIES which
  declares that the \a Type supports \l {Attached Properties}.

  #include <QtQml> to use this macro.
*/

/*!
  \fn void qmlClearTypeRegistrations()
  \relates QQmlEngine

  Clears all stored type registrations, such as those produced with \l qmlRegisterType.

  Do not call this function while a QQmlEngine exists or behavior will be undefined.
  Any existing QQmlEngines must be deleted before calling this function.  This function
  only affects the application global cache. Delete the QQmlEngine to clear all cached
  data relating to that engine.

  #include <QtQml> to use this method.
*/


/*!
  \fn int qmlRegisterType(const char *uri, int versionMajor, int versionMinor, const char *qmlName)
  \relates QQmlEngine

  This template function registers the C++ type in the QML system with
  the name \a qmlName, in the library imported from \a uri having the
  version number composed from \a versionMajor and \a versionMinor.

  Returns the QML type id.

  There are two forms of this template function:

  \code
  template<typename T>
  int qmlRegisterType(const char *uri, int versionMajor, int versionMinor, const char *qmlName);

  template<typename T, int metaObjectRevision>
  int qmlRegisterType(const char *uri, int versionMajor, int versionMinor, const char *qmlName);
  \endcode

  The former is the standard form which registers the type \e T as a new type.
  The latter allows a particular revision of a class to be registered in
  a specified version (see \l {Type Revisions and Versions}).


  For example, this registers a C++ class \c MySliderItem as a QML type
  named \c Slider for version 1.0 of a type namespace called
  "com.mycompany.qmlcomponents":

  \code
  #include <QtQml>

  ...

  qmlRegisterType<MySliderItem>("com.mycompany.qmlcomponents", 1, 0, "Slider");
  \endcode

  Once this is registered, the type can be used in QML by importing the
  specified type namespace and version number:

  \qml
  import com.mycompany.qmlcomponents 1.0

  Slider {
      // ...
  }
  \endqml

  Note that it's perfectly reasonable for a library to register types to older versions
  than the actual version of the library. Indeed, it is normal for the new library to allow
  QML written to previous versions to continue to work, even if more advanced versions of
  some of its types are available.
*/

/*!
  \fn int qmlRegisterRevision(const char *uri, int versionMajor, int versionMinor)
  \relates QQmlEngine

  This template function registers the specified revision of a C++ type in the QML system with
  the library imported from \a uri having the version number composed
  from \a versionMajor and \a versionMinor.

  Returns the QML type id.

  \code
  template<typename T, int metaObjectRevision>
  int qmlRegisterRevision(const char *uri, int versionMajor, int versionMinor);
  \endcode

  This function is typically used to register the revision of a base class to
  use for the specified version of the type (see \l {Type Revisions and Versions}).
*/

/*!
  \fn int qmlRegisterUncreatableType(const char *uri, int versionMajor, int versionMinor, const char *qmlName, const QString& message)
  \relates QQmlEngine

  This template function registers the C++ type in the QML system with
  the name \a qmlName, in the library imported from \a uri having the
  version number composed from \a versionMajor and \a versionMinor.

  While the type has a name and a type, it cannot be created, and the
  given error \a message will result if creation is attempted.

  This is useful where the type is only intended for providing attached properties or enum values.

  Returns the QML type id.

  #include <QtQml> to use this function.

  \sa qmlRegisterTypeNotAvailable()
*/

/*!
  \fn int qmlRegisterTypeNotAvailable(const char *uri, int versionMajor, int versionMinor, const char *qmlName, const QString& message)
  \relates QQmlEngine

  This function registers a type in the QML system with the name \a qmlName, in the type namespace imported from \a uri having the
  version number composed from \a versionMajor and \a versionMinor, but any attempt to instantiate the type
  will produce the given error \a message.

  Normally, the types exported by a plugin should be fixed. However, if a C++ type is not available, you should
  at least "reserve" the QML type name, and give the user of the unavailable type a meaningful error message.

  Returns the QML type id.

  Example:

  \code
  #ifdef NO_GAMES_ALLOWED
  qmlRegisterTypeNotAvailable("MinehuntCore", 0, 1, "Game", "Get back to work, slacker!");
  #else
  qmlRegisterType<MinehuntGame>("MinehuntCore", 0, 1, "Game");
  #endif
  \endcode

  This will cause any QML which imports the "MinehuntCore" type namespace and attempts to use the type to produce an error message:
  \code
  fun.qml: Get back to work, slacker!
     Game {
     ^
  \endcode

  Without this, a generic "Game is not a type" message would be given.

  #include <QtQml> to use this function.

  \sa qmlRegisterUncreatableType()
*/

/*!
  \fn int qmlRegisterType()
  \relates QQmlEngine
  \overload

  This template function registers the C++ type in the QML
  system. Instances of this type cannot be created from the QML
  system.

  #include <QtQml> to use this function.

  Returns the QML type id.
*/

/*!
  \fn int qmlRegisterInterface(const char *typeName)
  \relates QQmlEngine

  This template function registers the C++ type in the QML system
  under the name \a typeName.

  #include <QtQml> to use this function.

  Returns the QML type id.
*/

/*!
   \fn int qmlRegisterSingletonType(const char *uri, int versionMajor, int versionMinor, const char *typeName, QJSValue (*callback)(QQmlEngine *, QJSEngine *))
   \relates QQmlEngine

   This function may be used to register a singleton type provider \a callback in a particular \a uri
   and \a typeName with a version specified in \a versionMajor and \a versionMinor.

   Installing a singleton type allows developers to provide arbitrary functionality
   (methods and properties) to a client without requiring individual instances of the type to
   be instantiated by the client.

   A singleton type may be either a QObject or a QJSValue.
   This function should be used to register a singleton type provider function which returns a QJSValue as a singleton type.

   \b{NOTE:} QJSValue singleton type properties will \b{not} trigger binding re-evaluation if changed.

   Usage:
   \code
   // First, define the singleton type provider function (callback).
   static QJSValue *example_qjsvalue_singletontype_provider(QQmlEngine *engine, QJSEngine *scriptEngine)
   {
       Q_UNUSED(engine)

       static int seedValue = 5;
       QJSValue example = scriptEngine->newObject();
       example.setProperty("someProperty", seedValue++);
       return example;
   }

   // Second, register the singleton type provider with QML by calling this function in an initialization function.
   #include <QtQml>
   ...
   qmlRegisterSingletonType("Qt.example.qjsvalueApi", 1, 0, "MyApi", example_qjsvalue_singletontype_provider);
   ...
   \endcode

   In order to use the registered singleton type in QML, you must import the singleton type.
   \qml
   import QtQuick 2.0
   import Qt.example.qjsvalueApi 1.0 as ExampleApi
   Item {
       id: root
       property int someValue: ExampleApi.MyApi.someProperty
   }
   \endqml
  */

/*!
    \fn Object *qmlAttachedPropertiesObject(const QObject *attachee, bool create = true)
    \relates QQmlEngine

    The form of this template function is:

    \code
    template<typename T> QObject *qmlAttachedPropertiesObject(const QObject *attachee, bool create = true)
    \endcode

    This returns the attached object instance that has been attached to the specified
    \a attachee by the attaching type \e T.

    If \a create is true and type \e T is a valid attaching type, this creates and returns a new
    attached object instance.

    Returns 0 if type \e T is not a valid attaching type, or if \a create is false and no
    attachment object instance has previously been created for \a attachee.

    \sa {Providing Attached Objects for Data Annotations}

*/

/*!
   \fn int qmlRegisterSingletonType(const char *uri, int versionMajor, int versionMinor, const char *typeName, QObject *(*callback)(QQmlEngine *, QJSEngine *))
   \relates QQmlEngine

   This function may be used to register a singleton type provider \a callback in a particular \a uri
   and \a typeName with a version specified in \a versionMajor and \a versionMinor.

   Installing a singleton type into a uri allows developers to provide arbitrary functionality
   (methods and properties) to clients without requiring individual instances ot the type to be
   instantiated by the client.

   A singleton type may be either a QObject or a QJSValue.
   This function should be used to register a singleton type provider function which returns a QObject
   of the given type T as a singleton type.

   A QObject singleton type may be referenced via the type name with which it was registered, and this
   typename may be used as the target in a \l Connections type or otherwise used as any other type id would.
   One exception to this is that a QObject singleton type property may not be aliased (because the
   singleton type name does not identify an object within the same component as any other item).

   \b{NOTE:} A QObject singleton type instance returned from a singleton type provider is owned by the QML
   engine.  For this reason, the singleton type provider function should \b{not} be implemented as a
   singleton factory.

   Usage:
   \code
   // First, define your QObject which provides the functionality.
   class SingletonTypeExample : public QObject
   {
       Q_OBJECT
       Q_PROPERTY (int someProperty READ someProperty WRITE setSomeProperty NOTIFY somePropertyChanged)

   public:
       SingletonTypeExample(QObject* parent = 0)
           : QObject(parent), m_someProperty(0)
       {
       }

       ~SingletonTypeExample() {}

       Q_INVOKABLE int doSomething() { setSomeProperty(5); return m_someProperty; }

       int someProperty() const { return m_someProperty; }
       void setSomeProperty(int val) { m_someProperty = val; emit somePropertyChanged(val); }

   signals:
       void somePropertyChanged(int newValue);

   private:
       int m_someProperty;
   };

   // Second, define the singleton type provider function (callback).
   static QObject *example_qobject_singletontype_provider(QQmlEngine *engine, QJSEngine *scriptEngine)
   {
       Q_UNUSED(engine)
       Q_UNUSED(scriptEngine)

       SingletonTypeExample *example = new SingletonTypeExample();
       return example;
   }

   // Third, register the singleton type provider with QML by calling this function in an initialization function.
   #include <QtQml>
   ...
   qmlRegisterSingletonType<SingletonTypeExample>("Qt.example.qobjectSingleton", 1, 0, "MyApi", example_qobject_singletontype_provider);
   ...
   \endcode

   In order to use the registered singleton type in QML, you must import the singleton type.
   \qml
   import QtQuick 2.0
   import Qt.example.qobjectSingleton 1.0
   Item {
       id: root
       property int someValue: MyApi.someProperty

       Component.onCompleted: {
           someValue = MyApi.doSomething()
       }
   }
   \endqml

   Since singleton types do not have an associated QQmlContext object, then within the functions of a QObject-derived
   type that is registered as a singleton type implementation the QML context and engine information is not available.
   The QQmlEngine::contextForObject() function returns NULL when supplied with a pointer to an QObject that
   implements a singleton type.

   Extending the above example:

   \code
   class SingletonTypeExample : public QObject
   {
       ...

       Q_INVOKABLE void doSomethingElse()
       {
           // QML Engine/Context information is not accessible here:
           Q_ASSERT(QQmlEngine::contextForObject(this) == 0);
           Q_ASSERT(qmlContext(this) == 0);
           Q_ASSERT(qmlEngine(this) == 0);
       }

       ...
   }
   \endcode

  */

/*!
  \fn int qmlRegisterType(const QUrl &url, const char *uri, int versionMajor, int versionMinor, const char *qmlName);
  \relates QQmlEngine

  This function registers a type in the QML system with the name \a qmlName, in the library imported from \a uri having the
  version number composed from \a versionMajor and \a versionMinor. The type is defined by the QML file located at \a url. The
  url must be an absolute URL, i.e. url.isRelative() == false.

  Normally QML files can be loaded as types directly from other QML files, or using a qmldir file. This function allows
  registration of files to types from C++ code, such as when the type mapping needs to be procedurally determined at startup.

  #include <QtQml> to use this function.

  Returns non-zero if the registration was sucessful.
*/