Also, this Q_DECLARE_METATYPE(SharedTestClass) shouldn't be needed. struct Matrix { double data [4] [4]; }; Ideally you should be using eigen3. } But you'll most likely need to abstract the Q_DECL_EXPORT part so it is a Q_DECL_IMPORT in right circumstances, as described in Creating Shared Libraries. As a workaround you can call the Q_DECLARE_METATYPE macro from the implementation files that need it instead of calling it from the header files, or as the documentation suggests, call it from private headers in each library. I think you need to add an explicit export/import directive to the QT_NAMESPACE macro. I tested your code on Qt 5. struct StandardData { int EmpId; QString Name; }; Q_DECLARE_METATYPE (StandardData) Additionally, you might need to call qRegisterMetaType. Here you can see that the macro expands to nothing. 0. This function was introduced in Qt 5. e. It is more or less explained in the manual for int qRegisterMetaType (const char *typeName) This function requires that T is a fully defined type at the point where the function is called. In the example's Message class, a static method is included to do this. Call qRegisterMetaType() to make types available to non-template based functions, such as the queued signal and slot connections. h" class Context : public QObject { Q_OBJECT Q_PROPERTY (MyGadget* gadget READ gadget CONSTANT) public: explicit Context () : QObject {nullptr} { } MyGadget* gadget () { return &_gadget; } private. h. h instead ofQVariant x2; x2. . 4 which does not support all C++11 features. goocreations 12 Mar 2013, 07:22. Equivalent to Q_DECLARE_METATYPE(TYPE *) and Q_DECLARE_METATYPE(QQmlListProperty<TYPE>) QML_DECLARE_TYPEINFO (Type, Flags) Declares additional properties of the given Type as described by the specified Flags. Qt Base (Core, Gui, Widgets, Network,. no unexpected garbage. See also. in a header file and call @qRegisterMetaType<std::unique_ptr<Thing>> ();@ before your signal and slots are used. As a workaround, I'm using QVariantMap instead of std::map. Enumerations that are declared with Q_ENUM have their QMetaEnum registered in the enclosing QMetaObject. See full list on doc. Also, this Q_DECLARE_METATYPE(SharedTestClass) shouldn't be needed. (Make sure 'QVector<int>' is. Returns the internal ID used by QMetaType. w/out GUI module you wouldn't have any of those types available). The Q_DECLARE_METATYPE () macro also makes it possible for these values to be used as arguments to signals, but only in direct signal-slot connections. So I tried declaring the following at end of my worker thread class Q_DECLARE_METATYPE(cv::Mat);. As you already have a typedef for your type, you can simply use Q_DECLARE_METATYPE as in the following example: #include <QtCore> template <typename T> struct Proxy { T data; }; typedef Proxy<QImage> TrayType; Q_DECLARE_METATYPE (TrayType) class Donor : public. Also, to use type T with the QObject::property () API,. Without this reference, it compiles just fine. It is often easier and cleaner to define an ENUM inside a class (see ENUM), but if you need a standalone enum type, using the ENUM keyword outside of a class definition can be. QMetaType::type () returns the same ID as qMetaTypeId (), but does a lookup at runtime based on the name of the type. Registers the type name . You can't with Q_GADGETS. Type is declared with Q_DECLARE_METATYPE and registered with qRegisterMetaType. 12. I'm trying to use custom classes in QAbstractListModel, and the Q_DECLARE_METATYPE doesn't work at all! To test where the problem is, I've simplified the code as the following: #include <QMetaType> #include <QVariant> #include <QDebug> typedef int x; Q_DECLARE_METATYPE (x) void main () { QVariant v; qDebug () <<. It's not enough to get reflection features out of a type this way (it does not create a QMetaObject), so for the thing to be useful at all you need at least Q_GADGET in both base and derived classes. Call qRegisterMetaType () to make types available to non-template based functions, such as the queued signal and slot connections. You may have to register before you can post: click the register link above to proceed. I have registered an enumeration type "ClefType" within my header file - this enum is registered with the MetaObject system using the Q_DECLARE_METATYPE and Q_ENUMS macros. Q_DECLARE_META_TYPE (Fruit) and qRegisterMetaType were redundant: #define PluginInterface_iid "pluginInterface" Q_DECLARE_INTERFACE (PluginInterface, PluginInterface_iid) //Actual plugin implementing PluginInterface class. 8. Q_DECLARE_METATYPE only registers a type in meta type system. e. You could also Q_DECLARE_METATYPE to register your custom type and then use qMetaTypeId() to get the metaType id. ) summary refs log tree commit diff statsFoo and Foo* are different types and need to be registered separately. qRegisterMetaType<FileNodePointer> ("FileNodePointer"); should be called once (in main, constructor etc. Also, this Q_DECLARE_METATYPE(SharedTestClass) shouldn't be needed. Any class or struct that has a public default constructor, a public copy constructor, and a. c:55 This looks like some loader initialization mismatch, check debug vs release builds of your application and libraries. So my first idea:. I think you should consider making the signal/slot parameter be const QVector<int>& dataSet. Thanks for the suggestion. QMetaType Synopsis Functions def __eq__ (b). For that, I want to declare a. Couple of points: 1) I would use QScriptEngine::newObject() instead of newQObject() for the namespace 2) I would not use a QObject subclass for the data entry if possible, only the prototype has to be. Now you have a valid QObject. QObject::connect: Cannot queue arguments of type 'MyStruct'. Firstly, you shouldn't need to use Q_DECLARE_METATYPE (or qRegisterMetaType) with the enum at all, this is handled by the moc. This function returns the Qt meta type id for the type (the same value that is returned from qRegisterMetaType()). If \c MyStruct is in a namespace, the Q_DECLARE_METATYPE () macro. That's created by this macro. Yes, templated types can be used in Qt signal/slots. The QMetaType class manages named types in the meta-object system. To call qRegisterMetaType (), you still need to use Q_DECLARE_METATYPE (). Duplicate Question(s):Q_DECLARATIVE_METATYPE in and out; Using EventExport vs. So I played around, copied the original macro and adapted it a bit: @. What worries me is that. 4 which does not support all C++11 features. This makes them suitable for use with both static properties declared using the Q_PROPERTY() macro in class definitions and dynamic properties created at run-time. 1. To use the type T in QVariant, using Q_DECLARE_METATYPE() is sufficient. Declare new types with Q_DECLARE_METATYPE () to make them available. fromValue <QList<double> > ( x1); To copy to clipboard, switch view to plain text mode. Also Q_DECLARE_METATYPE does not register a type, but declares it. Call qRegisterMetaType () to make type available to non-template based. The documenation of this macro gives. From the docs: int qRegisterMetaType ( const char * typeName ) Registers the type name typeName to the type T. Connect and share knowledge within a single location that is structured and easy to search. Call qRegisterMetaType() to make type available to non-template based functions, such as the queued signal and slot connections. To achieve this you need Q_DECLARE_METATYPE macro and qRegisterMetaType () function. This also makes the type available for queued. @kshegunov said in Undocumented automatic metatype registration in Qt6?: Your original code (in the top-mentioned topic) assumes std::unique_ptr is copyable, which it isn't, so it can not ever be a metatype. I am also using some in queued signal and slot connections. See also. 11. ) I have defined MyStruct in an accessible header file: myheader. multithreaded software and I am getting the warning says: (Make sure 'QVector<int>' is registered using qRegisterMetaType (). cpp. 2. qRegisterMetaType is also called in the class constructor. Normally, you would only register the pointer form if your class cannot be copied, as in the case of QObject and derivatives, but. Warning: This function is useful only for registering an alias (typedef) for every other use case Q_DECLARE_METATYPE and qMetaTypeId () should be used instead. @Wieland Thanks. cpp. c:55 This looks like some loader initialization mismatch, check debug vs release builds of your application and libraries that are used. Q_DECLARE_METATYPE与qRegisterMetaType学习. 2 Answers. See also state () and Creating Custom Qt Types . . QMetaType. But I couldn't register the type because it's a QObject and I don't have access to the implementation to change it. This function was introduced in Qt 4. Note that if you intend to use the type in queued signal and slot connections or in QObject 's property system, you also have to call qRegisterMetaType () since the names are resolved at runtime. After googling this, I found this correspondence, which was only available through a third party archival site as google. See also state() and Creating Custom Qt Types. There's also no need for that typedef, it only makes the code less readable. . In some cases in Qt 4, it is also necessary to use the qRegisterMetaType method. I have declared all the types with Q_DECLARE_METATYPE, Q_OBJECT and the properties with Q_PROPERTY with the proper getters and setters. I want to use drag-and-drop to drag a QTreeWidgetItem that has std::shared_ptr user data. This function was introduced in Qt 4. This function was introduced in Qt 6. The file (called a "rep" file) uses a specific (text) syntax to describe the API. Any errors from Qt's metatype systems are usually due to MOC (the "meta-object compiler"), which reads your header files and generates a "moc" file with metatype information for every class where the Q_OBJECT macro is declared. in a header file and call @qRegisterMetaType<std::unique_ptr<Thing>> ();@ before your signal and slots are used. Don't use Q_DECLARE_METATYPE and qRegisterMetaType for your QObject enum. It will return the same result if it was called before. Share. Greetings. EDIT: When you convert your class to QVariant it uses a. Execute qRegisterMetaType<QItemSelection> (); before it is used as such, e. See also state() and Creating Custom Qt Types. By convention, these files are given a . The class is used as a helper to marshall types in QVariant and in queued signals and slots connections. Posted by Unknown at 2:06 AM. // This primary template calls the -Implementation, like all other specialisations should. It associates a type name to a type so that it can be created and destructed dynamically at run-time. As the docs state: Declare new types with Q_DECLARE_METATYPE () to make them available to QVariant and other template-based functions. in your main function or in the constructor of AudioGuiApplication. QObject can't be copied and all its descendants can't be copied also. Any class or struct that has a public default constructor, a public copy. Learn more about Teams I can't figure out a way to automatically declare a meta type, i. It looks like one can register a type more than once, specifying different typenames, i. QMetaType. In fact, all Qt classes derived from QObject (direct or indirect) use this macro to declare their copy constructor and assignment operator to be private. Of course it's a bug and an odd mistake that Q_DECLARE_METATYPE(QList<QSslError>) is in qsslsocket. With Q_DECLARE_METATYPE and without qRegisterMetaType: No warning, slot is called With Q_DECLARE_METATYPE and with qRegisterMetaType: No warning, slot is called. Q_DECLARE_METATYPE(TYPEDEF) Q_DECLARE_METATYPE(TYPEDEF) mainwindow. 3 to Qt4. Therefore I want to use Q_DECLARE_METATYPE (My_Item) and from the documentation I learned that I need a public copy constructor. Also, this Q_DECLARE_METATYPE(SharedTestClass) shouldn't be needed. That said, your stack trace is really strange: _dl_debug_initialize (ldbase=4294967292, ns=1095236752) at dl-debug. Any class or struct that has a public default constructor, a public copy constructor, and a. This results in access violations when Qt. 1 Answer Sorted by: 21 Objects are copied when put into a QVariant, but QObject derived classes cannot be copied, so the solution is to use a pointer to your. Share Improve this answer Follow answered Jul 23, 2014 at 15:37. c:55 This looks like some loader initialization mismatch, check debug vs release builds of your application and libraries. uint64; If this is your first visit, be sure to check out the FAQ by clicking the link above. A separate point for your own benefit. The default access for a class is private, so that Container* data();. I have a problem with a class that exchanges data using TCP/IP socket. Quote: bool QVariant::operator==(const QVariant & v) const. So, whatever Q_DECLARE_METATYPE is doing cannot be done by writing a function call. Good workaround: you may register your type with Q_DECLARE_METATYPE ( IBase * ) macro and wrap your. It is not safe to make a QObject's copy constructor public. That was it for Q_DECLARE_METATYPE, but you would still need to call qRegisterMetaType to use these type in a Q_PROPERTY or as a parameter in a signal/slot queued connection. cpp I have to do: qRegisterMetaType<Pkg>("Pkg"); and this does not give errors too, but when I try to create a QVariant(Pkg) I get lots of errors like:cardio63 26 Jan 2016, 10:19. Make your own typedef and do the Q_DECLARE_METATYPE and qRegisterMetatype. namespace CCS { Q_DECL_EXPORT Q_NAMESPACE. All I want to do is be able to convert this to a byte array in order to send on a socket, and get the object back (deserialize) on the other end. 8. Note that you are technically lying to the meta type system. To use the type T in queued signal and slot connections, qRegisterMetaType () must be called before the first connection is established. void QLocalSocket:: abort ()The Qt docs make it clear that to use a custom type with Queued Connections, I need to use both Q_DECLARE_METATYPE and qRegisterMetaType. Declare new types with Q_DECLARE_METATYPE () to make them available to QVariant and other template-based functions. x however, the code generated by moc will call qRegisterMetaType for you if moc can determine that the type may be registered as a. Here’s the list of what changed: QVariant used to forward isNull () calls to its contained type – but only for a limited set of Qt’s own types. The reasoning is found in the discussion on Identity vs Value on the Qt Object Model page. Any idea what I'm missing please? BTW, no problem at all using Schedule in QMetaProperty or QVariant. ", which suggests it is only for classes and structs. @SGaist Yes, I am using it with QVariant, mostly with QSettings to save and retrieve data easily by overriding QDataStream operators. This also makes the type available for queued. When I try to simply connect signalslot with such QVector as argument programm tells during run that this metatype should be registered (though QVector, QSharedPointer and class inherited from QObject should be registered automatically. You may have to register before you can post: click the register link above to proceed. no unexpected garbage data or the like). You may have to register before you can post: click the register link above to proceed. QML Qvariant from custom class. QVariant’s operator== now uses QMetaType::equals for the comparison. 1. It's a bit convoluted to follow, and definitely depends on which Qt modules have been included (the meta type system is designed to be expandable this way -- eg. 7. We will still need to register it with the meta-object system at run-time by calling the qRegisterMetaType() template function before we make any signal-slot connections that use this type. type() typeName() PySide6. I also don't want to use qRegisterMetaType, since it is run-time bound. When these files are processed by repc, repc generates both Source and Replica header files. The Qt docs make it clear that to use a custom type with Queued Connections, I need to use both Q_DECLARE_METATYPE and qRegisterMetaType. Call qRegisterMetaType() to register the data type before you establish the connection. If the type was not declared with Q_DECLARE_METATYPE (), compilation will fail. That said, your stack trace is really strange: _dl_debug_initialize (ldbase=4294967292, ns=1095236752) at dl-debug. You may have to register before you can post: click the register link above to proceed. Secondly, your linker (MSVC) complains that it can't find the metaObject for your ErrorHandler enum, which is normal as it is not exported from the. PySide6. But I really would like to know the correct way to solve this problem; one where it is not possible to modify the template classes. 能猜到原因吗？注意看前面 Q_DECLARE_METATYPE() 代码， 对了。类中的成员函数qt_metatype_id中包含对qRegisterMetaType(typeName)的调用: 这儿就是辗转调用了这个带参数的qRegisterMetaType函数: unregisterType(const char *typeName) 函数的作用是取消自己先前注册的某个metatype类型。 and a Context class that holds an instance of MyGadget and exposes a pointer to it to QML via a Q_PROPERTY: #include <QObject> #include "mygadget. There's no such thing as a "const reference" because references are always const -- you can't reseat them. QAbstractSocket::SocketState is not a registered metatype, so for queued connections, you will have to register it with Q_DECLARE_METATYPE() and qRegisterMetaType(). " and: "Warning: This function is useful only for registering an alias (typedef) for every other use case Q_DECLARE_METATYPE and qMetaTypeId() should be used instead. The class is used to send arguments over D-Bus to remote applications and to receive them back. Obviously then you would not do registerComparator (). . Declare new types with Q_DECLARE_METATYPE() to make them available to QVariant and other template-based functions. So in your case you need to declare. You may have to register before you can post: click the register link above to proceed. Macros Detailed Description The QMetaType class manages named types in the meta-object system. the type name must be specified without the class, as in. With Q_DECLARE_METATYPE and without qRegisterMetaType: No warning, slot is called With Q_DECLARE_METATYPE and with qRegisterMetaType: No warning, slot is called. Re: Q_DECLARE_METATYPE problem. By the way, Qt 4. Connect and share knowledge within a single location that is structured and easy to search. That said, your stack trace is really strange: _dl_debug_initialize (ldbase=4294967292, ns=1095236752) at dl-debug. " Currently I have no UI implemented (yet!). This is not the case, since the following succeeded: @QMetaType::type("MyClass"); // success@. 2）添加声明：利用宏 Q_DECLARE_METATYPE. [edit] forgot to mention that you also have to use a worker object. 2. cpp 中，用connect函数 将抛出此结构体的信号和接收此结构体的槽函数关联之前，要调用qRegisterMetaType. So, you don't want 'Widget' to be a metatype, you want 'Widget*' to be a metatype so that you can put a Widget* in a QVariant for example. There's no need to call qRegisterMetaType that many times, once is enough. The ones I am registering for are mostly structs for storing data and just a few simple classes. To start viewing messages, select the forum that you want to visit from the selection below. 【2】使用方法（声明 和 注册自定义数据类型）. There is no way to add support for more of these value types like std::string (*). qRegisterMetaType<signed long long>() - do nothing. See the Custom Type Example for code that demonstrates this. This function is typically used together with construct () to perform low-level management of the memory used by a type. 1 Answer. Do do you register the meta type with the call qRegisterMetaType("your custom meta type")? 1 Reply Last reply Reply Quote 0. G. Adding a Q_DECLARE_METATYPE () makes the type known to all template based functions, including QVariant. If you only want to store pointer to Foo with the metatype system, then use qRegisterMetaType<Foo *> ();. cruz Hello, To be completely candid, I haven't used GDB remotely and I'm certainly not so intimate with it for the log to speak to me much. Remember that Q_DECLARE_METATYPE merely defines a specialization of QMetaTypeId for your type. For this, a function call (evaluated during runtime) needs to be made, and qRegisterMetatype is the tool for this: qRegisterMetaType<Area>("Area");@julio. Here you can see that the macro expands to nothing. Sorted by: 1. To use the type T in queued signal and slot connections, qRegisterMetaType<T>() must be called before the first connection is established. Detailed Description. This article will. cpp. 1. Declare new types with Q_DECLARE_METATYPE () to make them available to. Qt5でシグナルの引数としてユーザー定義型を指定する場合は、Q_DECLARE_METATYPEとqRegisterMetaType()を使って方の登録を行う必要がある。Trying to register std::map<non_template_type_1,non_template_type_2> with Q_DECLARE_METATYPE() results in compilation failure and apparently is not supported. 0. What is the point of emitting a QSharedPointer? The worker thread reads the files computes the data allocates and fills the memory with data, wraps it in QSharedPointer and passes it to the mainThread, which is used for plotting. To start viewing messages, select the forum that you want to visit from the selection below. "Custom types used by properties need to be registered using the Q_DECLARE_METATYPE() macro so that their values can be stored in QVariant objects. +50. [override virtual] bool QLocalSocket:: waitForBytesWritten (int msecs = 30000) Reimplements:. Type is not registered, please use the Q_DECLARE_METATYPE macro to make it known to Qt's meta-object system. Enum has been moved from outside of the class to inside of it. It associates a type name to a type so that it can be created and destructed dynamically at run-time. Sorted by: 3. I am also using some in queued signal and slot connections. To register VideoMeta you need to call qRegisterMetaType<VideoMeta>(). qRegisterMetaType vs. and Q_DECLARE_METATYPE uses qRegisterMetaType() internally. Labels: meta system, Meta type, qt. If you want to pass IBase * between different threads, you need to register class with qRegisterMetaType<IBase *> () call; It is bad practice to pass pointers throught singals, because it is hard to control lifetime of passed objects. You should use Q_DECLARE_METATYPE macro for this. Declare new types with Q_DECLARE_METATYPE () to make them available to. By the way, Qt 4. Q_DECLARE_METATYPE () doesn't actually register the type; you must still use qRegisterMetaType () for that, particularly if you intend to use the type in signal and slot connections. QtCore. Note that if you intend to use the type in queued signal and slot connections or in QObject 's property system, you also have to call qRegisterMetaType () since the names are resolved at runtime. All Qt Overviews. Share Improve this answerWe will still need to register it with the meta-object system at run-time by calling the qRegisterMetaType() template function before we make any signal-slot connections that use this type. cpp I have to do: qRegisterMetaType<Pkg>("Pkg"); and this does not give errors too, but when I try to create a QVariant(Pkg) I get lots of errors like:cardio63 26 Jan 2016, 10:19. To use the type T in queued signal and slot connections, qRegisterMetaType<T>() must be called before the first connection is established. Q_DECLARE_METATYPE(TYPEDEF) Q_DECLARE_METATYPE(TYPEDEF) mainwindow. According to the Qt docs for qRegisterMetaType "Any class or struct that has a public default constructor, a public copy constructor, and a public destructor can be registered. I tried with and without the qRegisterMetaType<Schedule::TimePairMap>(), with and without Q_DECLARE_METATYPE(Schedule::TimePairMap). wysota. Even though we do not intend to use the type with QVariant in this example, it is good practice to also declare the new type with. Returns the used WebSocket protocol. As said in int qRegisterMetaType () documentation: To use the type T in QVariant, using Q_DECLARE_METATYPE () is sufficient. So in both cases qRegisterMetaType isn't required for the slot to be called and the custom type to be accessible within the slot (i. // But the split allows to. uint64; If this is your first visit, be sure to check out the FAQ by clicking the link above. h" class B : public QObject { Q_OBJECT Q_PROPERTY(A* A1 READ getA1 WRITE setA1) Q_PROPERTY(A* A2 READ getA2 WRITE setA2) public: static A A1;. QList<T> isn't really a pre-defined variant type (except QList<QVariant>) so it technically resolves to a QMetaType::UserType. Declare new types with Q_DECLARE_METATYPE () to make them available. rep file extension, short for Replica. At the point where I want to read the list, I only care about (and know) the fact that the list contains pointers to objects, which have been derived. Type is not registered, please use the Q_DECLARE_METATYPE macro to make it known to Qt's meta-object system. It manages an insane amount of static variables and sets a static global pointer of. 2. container. I explicitly don't want to update it on every change to one of the quantities, so they don't. Declare new types with Q_DECLARE_METATYPE() to make them available to QVariant and other template-based functions. The reasoning is found in the. That always worked in Qt4, but in Qt5 I get the following error: @error: specializing member ‘::qRegisterMetaType<Subclass>’ requires ‘template<>’ syntax@. . . Otherwise your signals and slots connected used the old mechanism (with macros SIGNAL and SLOT) that require queueing of the parameters won't know how to do so. A. until today. Q_DECLARE_METATYPE QMetaType::type. 2、在类型定义完成后，加入声明：Q_DECLARE_METATYPE (MyDataType); 3、在main ()函数中. QMetaType::type () returns the same ID as qMetaTypeId (), but does a lookup at runtime based on the name of the type. You may have to register before you can post: click the register link above to proceed. There's no need to call qRegisterMetaType that many times, once is enough. For those who follow. 1 Answer. Make sure you call it from within a method. @user6556709 I've added both of those, and it does compile now, but the string is just being default initialized to "" when I call value<T>() and there's a red line under Q_DECLARE_METATYPE that says no instance of overloaded function "qRegisterMetaType" matches the argument list, argument types are: (const char [12],. It must appear in a code block. The Rep lica C ompiler (repc) generates QObject header files based on an API definition file. Jun 13, 2021 at 19:37. Now, that Q_DECLARE_METATYPE enables the type for Qt template classes and QVariant. See the Qt D-Bus Type System page for more information on the type system. The. The file (called a "rep" file) uses a specific (text) syntax to describe the API. Q_DECLARE_METATYPE(MyClass*); That's how Qt handles it with QObject and QWidget. To enable creation of objects at run-time, call the qRegisterMetaType() template function to register it with the meta-object system. Now you have a valid QObject. 如果要使自定义类型或其他非QMetaType内置类型在QVaiant中使用，必须使用该宏。. I can access the property. [virtual] QAbstractSocket:: ~QAbstractSocket Destroys the socket. Note: This function is thread-safe. Registered enumerations are automatically registered also to the Qt meta type system, making them known to QMetaType without the need to use Q_DECLARE_METATYPE(). QList<AnotherObject*> has of course been registered with Q_DECLARE_METATYPE and qRegisterMetaType(). Does your code ever call qRegisterMetatype() or use Q_DECLARE_METATYPE()? 10th November 2014, 06:23 #3. Any class or struct that has a public default constructor, a public copy. queued connections. I store them in QVariant :. c:55 This looks like some loader initialization mismatch, check debug vs release builds of your application and libraries. Q_DECLARE_METATYPE ( blabla* ) Also qRegisterMetaType<T> () is only required for sending your object through queued signal/slot connections. Step 1 (mark for MOC), build some QObjects That pattern uses Q_PROPERTY and Q_OBJECT and the MoC tool. To make the type known to this class, we invoke the Q_DECLARE_METATYPE () macro on the class in the header file where it is defined: Q_DECLARE_METATYPE(Message); This now makes it possible for Message values to be stored in QVariant objects and retrieved later. x however, the code generated by moc will call qRegisterMetaType for you if moc can determine that the type may be registered as a meta-type. uint64; If this is your first visit, be sure to check out the FAQ by clicking the link above. In general, you can only export two kinds of C++ types to QML: QObject-derived classes and some build-in value types, see this documentation page. In short, I get following error: QObject::connect: Cannot queue arguments of type 'cv::Mat' (Make sure 'cv::Mat' is registered using qRegisterMetaType (). Any class or struct that has a public default constructor, a public copy. This is by design. Any class or struct that has a public constructor, a public copy constructor, and a public destructor can be registered. To start viewing messages, select the forum that you want to visit from the selection below. This won't work because you can't use qMetaTypeId<> () before Q_DECLARE_METATYPE<>. Q&A for work. Adding a Q_DECLARE_METATYPE() makes the type known to all template based functions, including QVariant. See also Thread Support in Qt, QObject::connect(), qRegisterMetaType(), and Q_DECLARE_METATYPE(). Similarly you can create a mutable view of type QAssociativeIterable on any container registered with Q_DECLARE_ASSOCIATIVE_CONTAINER_METATYPE(). [override virtual] bool QAbstractSocket:: waitForBytesWritten (int msecs = 30000) Reimplements:. It associates a type name to a type so that it can be created and destructed dynamically at run-time. by using qRegisterMetaType(). before saveload operation would happen. qRegisterMetaType vs.