Also, Q_DECLARE_METATYPE(MyNamespace::MyType) should be in the header declaring MyType so that you don't have to repeat it all over again and again. It associates a type name to a type so that it can be created and destructed dynamically at run-time. So I played around, copied the original macro and adapted it a bit: @. When these files are processed by repc, repc generates both. Obviously then you would not do registerComparator (). c:55 This looks like some loader initialization mismatch, check debug vs release builds of your application and libraries. const EventExport& in signal and slot profiles; Sending empty EventExport in prepareExport() so emit has no/low data amount; Checking connect statement (always returns true) Having qDebug() in prepareExport() and signal always appears to be emitted; Calling emit right. 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. rep file extension, short for Replica. 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 Q_DECLARE_METATYPE(). 该类型必须有公有的 构造、析构、复制构造 函数. The reasoning is found in the discussion on Identity vs Value on the Qt Object Model page. Obviously then you would not do registerComparator (). The QMetaType class manages named types in the meta-object system. That said, your stack trace is really strange: _dl_debug_initialize (ldbase=4294967292, ns=1095236752) at dl-debug. You should use qmlRegisterType function for that. To use the type T in queued signal and slot connections, qRegisterMetaType () must be called before the first connection is established. +50. 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. To start viewing messages, select the forum that you want to visit from the selection below. Franzk 26 May 2011, 06:59. To register VideoMeta you need to call qRegisterMetaType<VideoMeta>(). A. Call qRegisterMetaType() to make types available to non-template based functions, such as the queued signal and slot connections. The following should work: Note that you also have to call qRegisterMetaType<MyMpiMessage> (); before you use the function the first time. 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. Q_DECLARE_METATYPE(MyObject*) somewhere in your code. 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. namespace CCS { Q_DECL_EXPORT Q_NAMESPACE. You'll need Q_DECLARE_METATYPE () if you want to store your type within a QVariant and you will additionally need qRegisterMetaType<> () if you want to dynamically create and destroy objects of that type at runtime, mostly for queued signal and slots connections or the QObject property system. Returns the metatype of the parameter at the given index. The docs only talk about class or struct with public default constructor, copy constructor and. But this is all useless if you are not using templates. There's no such thing as a "const reference" because references are always const -- you can't reseat them. I only care about runtime. The third without Q_DECLARE_METATYPE. I store them in QVariant :. uint64; If this is your first visit, be sure to check out the FAQ by clicking the link above. To use the type T in QVariant, using Q_DECLARE_METATYPE() is sufficient. SocketState is not a registered metatype, so for queued connections, you will have to register it with Q_DECLARE_METATYPE() and qRegisterMetaType(). 7. Consider the specific case of qRegisterMetaType. G. canConvert<x> (); } and. Adding a Q_DECLARE_METATYPE() makes the type known to all template based functions, including QVariant. If I get AnotherQGadgetClass via getter and change it's properties, the setters are called and. One of the overloads is a function template that can be used to create an alias for a type and the form is: qRegisterMetaType<Type> ("alias"); That is, it wants to know the type for which you are declaring something. Step 1 (mark for MOC), build some QObjects That pattern uses Q_PROPERTY and Q_OBJECT and the MoC tool. Using the following required me to use Q_DECLARE_METATYPE. Additionally Qt5 always refers to Q_DECLARE_METATYPE, saying that qRegisterMetaType is only when you want to. qRegisterMetaType 必须使用该函数的两种情况. By convention, these files are given a . Call qRegisterMetaType() to make types available to non-template based functions, such as the queued signal and slot connections. // But the split allows to. See also Q_DECLARE_METATYPE() and. To start viewing messages, select the forum that you want to visit from the selection below. See also Thread Support in Qt, QObject::connect(), qRegisterMetaType(), and Q_DECLARE_METATYPE(). " Currently I have no UI implemented (yet!). uint64; If this is your first visit, be sure to check out the FAQ by clicking the link above. hpp and qRegisterMetaType<quint32>("quint32"); in both the Constructors of Class1 and Class2. Unsure if my idea would work, I created a DataPoint class marked with Q_GADGET with three properties defined using Q_PROPERTY. private: AnotherQGadgetClass test_; } Q_DECLARE_METATYPE(QGadgetClass) I am trying to access Q_GADGET from QML classic way like accessing a Q_OBJECT , but the setters are not called. The correct syntax is Q_DECLARE_METATYPE (std::string) without the ;. By the way, Qt 4. qRegisterMetaType vs. This worked very well. As G. In short, I get following error: QObject::connect: Cannot queue arguments of type 'cv::Mat' (Make sure 'cv::Mat' is registered using qRegisterMetaType (). complains that the metatype isn't registered. 如果是指针类型他需要有完整的定义。使用Q_DECLARE_OPAQUE_POINTER()去注册指针用于转发数据类型。 使用Q_DECLARE_METATYPE()可以让这个数据类型T放到QVariant里面。如果想以队列的方式让T使用信号与槽，当第一次连接的时候就要调用qRegisterMetaType<T>()。Detailed Description. Without this reference, it compiles just fine. Can it be Done for a Custom Type? If you really need the qMetatypeId<Type>() to be constexpr, you have to take the responsibility for making it so by specializing struct QMetaTypeId<Type> (or. このケースでも、Q_DECLARE_METATYPE(QSharedPointer<MyObject>)の宣言と、qRegisterMetatype<QSharedPointer<MyObject>>()の呼び出しが必要になる。 上のサンプルでは、同じsignalに対して2回connectを実行している。The same plugin may be loaded multiple times during the application's lifetime. There's no need to call qRegisterMetaType that many times, once is enough. 该类型必须有公有的 构造、析构、复制构造 函数. ), or any other callable, cannot declare a type for use outside of the call site. With Q_DECLARE_METATYPE and without qRegisterMetaType: No warning, slot is called With Q_DECLARE_METATYPE and with qRegisterMetaType: No warning, slot is called. 0. If you are using queued connections, you need to register std::string as meta type. QML_DECLARE_TYPE. io Please note that I do not use Q_DECLARE_METATYPE on purpose because I don't actually need its features (QVariant expansion) right now. Q_DECLARE_METATYPE(NSP::MyStruct) qRegisterMetaTypeIt associates a type name to a type so that it can be created and destructed dynamically at run-time. 23k 10 10 gold. 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. ", which suggests it is only for classes and structs. If the type was not declared with Q_DECLARE_METATYPE (), compilation will fail. See also state(). Labels: meta system, Meta type, qt. Qt is throwing an exception because it doesn't know how to store the shared_ptr onto a QDataStream. qRegisterMetaType vs. e. ) I have defined MyStruct in an accessible header file: myheader. It seems that for a metatype that is a QList<MyClass::MyEnum> I must. Returns the internal ID used by QMetaType. " –If I declare Class B as follows, it works fine, despite the fact that I haven't done Q_DECLARE_METATYPE for the pointer: #include <QObject> #include <QMetaType> #include "a. I have a const pointer to a class derived from qobject and want to put into QVariant like below: QVariant::fromValue(objectPointer) I have declared the meta type of derived class using: Q_DECLARE_METATYPE(const QDrivedClass *) in the header file (. That said, your stack trace is really strange: _dl_debug_initialize (ldbase=4294967292, ns=1095236752) at dl-debug. To enable using the type in queued signals and such, there also needs to be a corresponding call: qRegisterMetaType<foo::FooState>(); Question. But there would be no trouble using the QMetaType class or using qRegisterMetaType before creating an instance of QCoreApplication or QApplication. Re: Q_DECLARE_METATYPE problem. Type is not registered, please use the Q_DECLARE_METATYPE macro to make it known to Qt's meta-object system. enum Qt:: ContextMenuPolicycall qRegisterMetaType() to register the data type before you call QMetaMethod::invoke(). Re: How to use Q_DECLARE_METATYPE. QMetaType registerNormalizedTypedef normalizedTypeName, type: metaType ); return. : Q_DECLARE_METATYPE(MyClass*); That's how Qt handles it with QObject and QWidget. For that, I want to declare a. Hello, Can someone tell me about how to register a metatype in pyqt5. } 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. Your code should look like this: Q_ENUM (StateEnum) //note the missing 'S' here Q_PROPERTY (StateEnum state READ state NOTIFY stateChanged) Share. 4. QLocalSocket::SocketState is not a registered metatype, so for queued connections, you will have to register it with Q_DECLARE_METATYPE() and qRegisterMetaType(). Call qRegisterMetaType() to make types available to non-template based functions, such as the queued signal and slot connections. pro file, several errors appear referencing the QMouseEvent and QWheelEvent classes. One of the overloads is a function template that can be used to create an alias for a type and the form is: qRegisterMetaType<Type> ("alias"); That is, it wants to know the type for which you are declaring something. If the type was not declared with Q_DECLARE_METATYPE (), compilation will fail. I tried and it looks like it's possible to register an enum type with Q_DECLARE_METATYPE or qRegisterMetaType and use it the same way. You can also use QMetaEnum::fromType() to get the QMetaEnum. Email This BlogThis! Share to Twitter Share to Facebook Share to Pinterest. 1. The default access for a class is private, so that Container* data(); declares a private member function, but it looks like you expect it to be public. The class is used as a helper to marshall types in QVariant and in queued signals and slots connections. qRegisterMetaType vs. 2. This won't work because you can't use qMetaTypeId<> () before Q_DECLARE_METATYPE<>. uint64; If this is your first visit, be sure to check out the FAQ by clicking the link above. 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. QAbstractSocket::SocketState is not a registered metatype, so for queued connections, you will have to register it with Q_REGISTER_METATYPE() and qRegisterMetaType(). See also. If \c MyStruct is in a namespace, the Q_DECLARE_METATYPE () macro. The ones I am registering for are mostly structs for storing data and just a few simple classes. 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. // But the split allows to. There's no need to call qRegisterMetaType that many times, once is enough. qRegisterMetaType vs. Detailed Description. Qt Base (Core, Gui, Widgets, Network,. Once they're known you can use them, but you can't create them on the QML side. ) I got the hint "expected a declaration" when I tried to use qRegisterMetaType from the global scope in my cpp file. " Yet types like QVariantMap are themself typedefs. I my real world application Context holds a large number of physical quantities (masses, forces, velocities,. Qt has to stay free or it will die. Note that you are technically lying to the meta type system. The QMetaType class manages named types in the meta-object system. Connect and share knowledge within a single location that is structured and easy to search. QVariant’s operator== now uses QMetaType::equals for the comparison. Returns the internal ID used by QMetaType. See also. 2 Answers. I simplified the code quite a bit and the problem went away. QAbstractSocket::SocketState is not a registered metatype, so for queued connections, you will have to register it with Q_DECLARE_METATYPE() and qRegisterMetaType(). Normally, you would only register the pointer form if your class cannot be copied, as in the case of QObject and derivatives, but. Declare new types with Q_DECLARE_METATYPE () to make them available to QVariant and other template-based functions. QLocalSocket. 被 Q_DECLARE_METATYPEQ 标记的类型可以让Q MetaType 查询到类型，也可以让QVariant识别到。 struct MyStruct { QString name; }; Q_DECLARE_METATYPE(MyStruct) 若对象包含在自定义的命名空间中时，注册时要带上完整的命令空间. When I emit a signal, then I get next error to the output stream:. 0. cpp. このケースでも、Q_DECLARE_METATYPE(QSharedPointer<MyObject>)の宣言と、qRegisterMetatype<QSharedPointer<MyObject>>()の呼び出しが必要になる。 上のサンプルでは、同じsignalに対して2回connectを実行している。 The correct syntax is Q_DECLARE_METATYPE (std::string) without the ;. qRegisterMetaType vs. Detailed Description The QMetaType class manages named types in the meta-object system. uint64; If this is your first visit, be sure to check out the FAQ by clicking the link above. ", which suggests it is only for classes and structs. It looks like one can register a type more than once, specifying different typenames, i. To call qRegisterMetaType (), you still need to use Q_DECLARE_METATYPE (). If you want both, then register both. 5 is compiled with GCC 4. 用qRegisterMetaType对自定义的类型进行注册，就是为了告诉Qt如何去做这些事情。. staticMetaObject is of type QMetaObject and provides access to the enums declared with Q_ENUMS. I tested your code on Qt 5. 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. However Q_DECLARE_METATYPE () is a bit more complicated. There is no contradiction, because you can't register QObject descendants with Q_DECLARE_METATYPE. This function is typically used together with construct () to perform low-level management of the memory used by a type. 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. To use the type T in queued signal and slot connections, qRegisterMetaType () must be called before the first connection is established. After googling this, I found this correspondence, which was only available through a third party archival site as google. Here you can see that the macro expands to nothing. Learn more about Teams Declaring a meta type. But I couldn't register the type because it's a QObject and I don't have access to the implementation to change it. 如果非QMetaType内置类型要. 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. You may have to register before you can post: click the register link above to proceed. With Q_DECLARE_METATYPE and without qRegisterMetaType: No warning, slot is called With Q_DECLARE_METATYPE and with qRegisterMetaType: No warning, slot is called. I need to call the Q_DECLARE_METATYPE() to pass the smart pointer. 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. void QAbstractSocket:: abort ()Declare new types with Q_DECLARE_METATYPE() to make them available to QVariant and other template-based functions. 基本理解. }; Q_DECLARE_METATYPE (MyCustomType); Then in my application, I have a signal "void sendMsg (MyCustomType)" and I qRegisterMetaType (). In practice, both the Q_DECLARE_METATYPE() macro and the qRegisterMetaType() template function can be used to register custom types, but qRegisterMetaType() is only required if you need to perform signal-slot communication or need to create and destroy objects of the custom type at run-time. To enable using the type in queued signals and such, there also needs to be a corresponding call: qRegisterMetaType<foo::FooState>(); Question. I have a problem with a class that exchanges data using TCP/IP socket. There's no compile time error, but when I run. Then you should register your object to use it with QML. qRegisterMetaType() docs say: Any class or struct that has a public constructor, a public copy constructor, and a public destructor can be registered. The same plugin may be loaded multiple times during the application's lifetime. ) is supported. 12. c:55 This looks like some loader initialization mismatch, check debug vs release builds of your application and libraries that are used. Follow answered Jun 5, 2009 at 15:14. 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. To start viewing messages, select the forum that you want to visit from the selection below. If such a connection is made, and a signal triggered, the runtime warning will be shown: QObject::connect: Cannot. Sorted by: 3. From the docs: int qRegisterMetaType ( const char * typeName ) Registers the type name typeName to the type T. 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. See also state() and Creating Custom Qt Types. Firstly, you shouldn't need to use Q_DECLARE_METATYPE (or qRegisterMetaType) with the enum at all, this is handled by the moc. This macro is used to specialise the template class QMetaTypeId with typename TYPE, in which, a static member function qt_metatype_id () is defined. qRegisterMetaType<FileNodePointer> ("FileNodePointer"); should be called once (in main, constructor etc. Greetings. @Q_DECLARE_METATYPE (std::unique_ptr<Thing>);@. wysota. This example is meant to declare and register only the pointer type of a given class: In conclusion: Don't use Q_DECLARE_METATYPE and qRegisterMetaType for your QObject enum. This also makes the type available for queued. Even though we do not intend. 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. The object it returns should also be a member of the factory class. This function returns the Qt meta type id for the type (the same value that is returned from qRegisterMetaType()). c:55 This looks like some loader initialization mismatch, check debug vs release builds of your application and libraries that are used. To start viewing messages, select the forum that you want to visit from the selection below. You can't with Q_GADGETS. Accessing an enum stored in a QVariant. That said, your stack trace is really strange: _dl_debug_initialize (ldbase=4294967292, ns=1095236752) at dl-debug. QVariant v = QVariant::fromValue<cMyClass>(MyObject); However, as soon as I use Q_DECLARE_METATYPE, I get errors about using a deleted function. To use the type T in queued signal and slot connections,. e. 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. Basically, I created a library containing a type: struct MyCustomType {. D-Bus offers an extensible type system, based on a few primitive types and associations of them. There's also no need for that typedef, it only makes the code less readable. Also, this Q_DECLARE_METATYPE(SharedTestClass) shouldn't be needed. So in your case you need to declare. Any class or struct that has a public default constructor, a public copy. See the Custom Type Example for code that demonstrates this. When the plugin is reloaded later, the old declaration still points to the original memory space of the now-unloaded library. In my module tests, I turn the card up and down, and can verify that the number of signals are increasing using QSignalSpy. void QLocalSocket:: abort ()The signal "orientationChanged" includes an enum of type "Orientation" to indicate if the card has been turned up or down. Q_DECLARE_METATYPE (std::string) Quoting Qt Doc. 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. 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. Than I did read this copy constructor of derived QT class and the answer by BЈовић. Has anyone else encountered this?See also qRegisterMetaType(). Share. QtCore. Connect and share knowledge within a single location that is structured and easy to search. In the example's Message class, a static method is included to do this. QMetaType::type () is a bit slower, but compilation succeeds if a type is not registered. It is a static method, it does not (cannot) change x2. The documentation for exposing C++ properties to QML says that: "Note: Do not use typedef or using for Q_PROPERTY types as these will confuse moc. The Custom Type, Custom Type Sending and Queued Custom Type examples show how to implement a custom type with the features outlined in this document. 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. 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. 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. 4 and it seems to work. 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 () << v. Declare new types with Q_DECLARE_METATYPE () to make them available. Call qRegisterMetaType () to make type available to non-template based. c:55 This looks like some loader initialization mismatch, check debug vs release builds of your application and libraries that are used. Avoid having to qRegisterMetaType (pointer. Specifically, the function have to be called before using the struct. 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. See also. That. c:55 This looks like some loader initialization mismatch, check debug vs release builds of your application and libraries. I tried with and without the qRegisterMetaType<Schedule::TimePairMap>(), with and without Q_DECLARE_METATYPE(Schedule::TimePairMap). There's also no need for that typedef, it only makes the code less readable. c:55 This looks like some loader initialization mismatch, check debug vs release builds of your application and libraries. By the way, Qt 4. If you ever wondered what does Q_DECLARE_META_TYPE or qRegisterMetaType do and when to use (or not to use) them, read on. You may have to register before you can post: click the register link above to proceed. Declare new types with Q_DECLARE_METATYPE() to make them available to QVariant and other template-based functions. # In the class MainWindow declaration #ifndef Q_MOC_RUN # define the tag text as empty,. Also you may need to use qRegisterMetaType function. Now, that Q_DECLARE_METATYPE enables the type for Qt template classes and QVariant. You can also use QMetaEnum::fromType() to get the QMetaEnum. e. {. I need to call the Q_DECLARE_METATYPE() to pass the smart pointer. . Adding a Q_DECLARE_METATYPE() makes the type known to all template based functions, including QVariant. You could try using registerConverter () to allow implicit conversion of the shared_ptr<int> to a regular int, and compare them that way. I have an application that requires use of both Qt 3D and the QCustomPlot library. 1）引入头文件：#include<QMetaType>. waitForConnected ([msecs=30000]) # Parameters: msecs – int. Any class or struct that has a public default constructor, a public copy. 3. That said, your stack trace is really strange: _dl_debug_initialize (ldbase=4294967292, ns=1095236752) at dl-debug. uint64; If this is your first visit, be sure to check out the FAQ by clicking the link above. That said, your stack trace is really strange: _dl_debug_initialize (ldbase=4294967292, ns=1095236752) at dl-debug. The other overload around has almost the same form but for the fact that it. Step 1 (mark for MOC), build some QObjects That pattern uses Q_PROPERTY and Q_OBJECT and the MoC tool. If you have to use Q_DECLARE_METATYPE yourself, the id is not constexpr. by using qRegisterMetaType(). 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. The class is used as a helper to marshall types in QVariant and in queued signals and slots connections. I thought there was a bug with QMetaType or Q_DECLARE_METATYPE. This has been changed, and isNull () now only returns true if the QVariant is empty or contains a nullptr. There's no need to call qRegisterMetaType that many times, once is enough. It is not safe to make a QObject's copy constructor public. 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. until today. QLocalSocket::SocketState is not a registered metatype, so for queued connections, you will have to register it with Q_DECLARE_METATYPE() and qRegisterMetaType(). The logical equivalent of a const T &r (reference to const T) is a const T * const p (const pointer to const T). Mixing doesn't work but if you always use one or the other it works. You can make them known ( Q_DECLARE_METATYPE ), however you can't register them as QML type. The ENUM type. The default access for a class is private, so that Container* data();. Also you may need to use qRegisterMetaType function. So you can call it from your constructor. From the QVariant::value documentation: If the QVariant contains a pointer to a type derived from QObject then T may be any QObject type. However, I cannot figure out how to verify that the included parameter is FACE_UP or FACE_DOWN. What you made is a const pointer to a non-const T; but top-level consts in function signatures are not part of the function. 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). c:55 This looks like some loader initialization mismatch, check debug vs release builds of your application and libraries that are used. The fix is probably to include qsslsocket. void Message:: registerMetaType {qRegisterMetaType < Message >. But because QUuid stores its content as a QByteArray which is already supported by QVariant, you. 4. Note that you are technically lying to the meta type system. You don't pass around copies of QObject derived types because it is not copyable. 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. EDIT: When you convert your class to QVariant it uses a. // to be declared somewhere Q_DECLARE_METATYPE(std::string); // to be invoked at the beginning of program qRegisterMetaType<std::string>(); Without type registration Qt doesn't know how to do. Update. 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. Q_DECLARE_METATYPE(Pkg) and this does not give compile errors, but in my main. Adding a Q_DECLARE_METATYPE() makes the type known to all template based functions, including QVariant. Adding a Q_DECLARE_METATYPE() makes the type known to all template based functions, including QVariant. 0. So using qRegisterMetaType () you will just trade Q_ENUM () for Q_DECLARE_METATYPE (). See also isRegistered () and Q_DECLARE_METATYPE (). QObject::connect: Cannot queue arguments of type 'MyStruct'. I think you need to add an explicit export/import directive to the QT_NAMESPACE macro. To make the custom type. This is not the case, since the following succeeded: @QMetaType::type("MyClass"); // success@. Detailed Description. qRegisterMetaType 必须使用该函数的两种情况. Normally, you would only register the pointer form if your class cannot be copied, as in the case of QObject and derivatives, but. Add qRegisterMetaType and qDBusRegisterMetaType calls to enable the framework to work with the custom type. Also Q_DECLARE_METATYPE does not register a type, but declares it. @Q_DECLARE_METATYPE (std::unique_ptr<Thing>);@. Qt Base (Core, Gui, Widgets, Network,. Since Qt 5. Q_DECLARE_METATYPE(TYPEDEF) Q_DECLARE_METATYPE(TYPEDEF) mainwindow. and Q_DECLARE_METATYPE uses qRegisterMetaType() internally. The class is used as a helper to marshall types in QVariant and in queued signals and slots connections. This function was introduced in Qt 4. So I tried declaring the following at end of my worker thread class Q_DECLARE_METATYPE(cv::Mat);. . h. Enumerations that are declared with Q_ENUM have their QMetaEnum registered in the enclosing QMetaObject. I can access the property. your custom type definition. Also, this Q_DECLARE_METATYPE(SharedTestClass) shouldn't be needed. Declare new types with Q_DECLARE_METATYPE() to make them available to QVariant and other template-based functions. The class is used to send arguments over D-Bus to remote applications and to receive them back. Also, this Q_DECLARE_METATYPE(SharedTestClass) shouldn't be needed. For pointer types, it also requires that the pointed to type is fully defined. That would allow you to use.