That said, your stack trace is really strange: _dl_debug_initialize (ldbase=4294967292, ns=1095236752) at dl-debug. See also Thread Support in Qt, QObject::connect(), qRegisterMetaType(), and Q_DECLARE_METATYPE(). Declare new types with Q_DECLARE_METATYPE() to make them available to QVariant and other template-based functions. 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 ;. Re: Qt warning of type conversion already registered Originally. QMetaType::type () is a bit slower, but compilation succeeds if a type is not registered. uint64; If this is your first visit, be sure to check out the FAQ by clicking the link above. Re: Q_DECLARE_METATYPE vs qRegisterMetaType for non global namespace classes (QTest) The reason for this behavior might be caused by the fact that runtime signal/slot connections are checked by string manipulation - both Q_DECLARE_METATYPE, SIGNAL, SLOT macros and 'moc' are (among other things) converting type-names to text and pass it along. ) I got the hint "expected a declaration" when I tried to use qRegisterMetaType from the global scope in my cpp file. QObject::connect: Cannot queue arguments of type 'MyStruct'. qRegisterMetaType vs. Any class or struct that has a public default constructor, a public copy constructor, and a. 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. 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. @Wieland Thanks. 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. D-Bus offers an extensible type system, based on a few primitive types and associations of them. 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. I tried with and without the qRegisterMetaType<Schedule::TimePairMap>(), with and without Q_DECLARE_METATYPE(Schedule::TimePairMap). To call qRegisterMetaType (), you still need to use Q_DECLARE_METATYPE (). (Make sure 'QVector<int>' is. This function returns the Qt meta type id for the type (the same value that is returned from qRegisterMetaType()). : Q_DECLARE_METATYPE(MyClass*); That's how Qt handles it with QObject and QWidget. Q_DECLARE_METATYPE(shared_ptr<SomeClass> const &) qRegisterMetaType<shared_ptr<SomeClass> const&>(); 许多标准API都有 QString const & ，因此我认为从根本上来说是可能的，而我只是想不出语法。You actually need to do it once (i. your custom type definition. ), or any other callable, cannot declare a type for use outside of the call site. Connect and share knowledge within a single location that is structured and easy to search. Mixing doesn't work but if you always use one or the other it works. You should use Q_DECLARE_METATYPE macro for this. You may have to register before you can post: click the register link above to proceed. 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. ) summary refs log tree commit diff statsFoo and Foo* are different types and need to be registered separately. uint64; If this is your first visit, be sure to check out the FAQ by clicking the link above. To start viewing messages, select the forum that you want to visit from the selection below. 4 which does not support all C++11 features. As said in int qRegisterMetaType () documentation: To use the type T in QVariant, using Q_DECLARE_METATYPE () is sufficient. View Profile View Forum Posts View Articles Beginner Join Date Nov 2014 Posts 6 Qt products. Once they're known you can use them, but you can't create them on the QML side. Thus you need to use the runtime check QMetaType::type (). If I get AnotherQGadgetClass via getter and change it's properties, the setters are called and. 6. If you only want to store pointer to Foo with the metatype system, then use qRegisterMetaType<Foo *> ();. goocreations 12 Mar 2013, 07:22. I have a few instances of QVector<MyClass> which I want them to be exposed to QScriptEngine. The ENUM type. Normally, you would only register the pointer form if your class cannot be copied, as in the case of QObject and derivatives, but. If you want both, then register both. uint64; If this is your first visit, be sure to check out the FAQ by clicking the link above. One way to work around this is for example having a helper class (singleton or context property) with. } 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. cpp. Last updated at 2016-07-08 Posted at 2015-11-16. Any class or struct that has a public default constructor, a public copy. Declare new types with Q_DECLARE_METATYPE () to make them available. @Q_DECLARE_METATYPE (std::unique_ptr<Thing>);@. I am also using some in queued signal and slot connections. 基本理解. QMetaType registerNormalizedTypedef normalizedTypeName, type: metaType ); return. 9k 9 34 52. Q_DECLARE_METATYPE(MyObject*) somewhere in your code. Q_DECLARE_METATYPE. Using Q_ENUM () allows you to retrieve at run-time the name of an enum value: Q_GADGET makes a class member, staticMetaObject, available. There's also no need for that typedef, it only makes the code less readable. Did you also check the Q_DECLARE_METATYPE macro ? You should declare and register the types properly, lying to qRegisterMetaType will get you in trouble in the long run. Than I did read this copy constructor of derived QT class and the answer by BЈовић. 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. Q&A for work. This object can then be passed from QML to C++ via. So my first idea:. 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. Also, to use type T with the QObject::property () API, qRegisterMetaType () must be. If you ever wondered what does Q_DECLARE_META_TYPE or qRegisterMetaType do and when to use (or not to use) them, read on. Any class or struct that has a public default constructor, a public copy. c:55 This looks like some loader initialization mismatch, check debug vs release builds of your application and libraries. Declare new types with Q_DECLARE_METATYPE() to make them available to QVariant and other template-based functions. Declare new types with Q_DECLARE_METATYPE() to make them available to QVariant and other template-based functions. in a header file and call @qRegisterMetaType<std::unique_ptr<Thing>> ();@ before your signal and slots are used. Q_DECLARE_METATYPE. Detailed Description. The object it returns should also be a member of the factory class. Q_DECLARE_METATYPE(MyStruct) Q_DECLARE_METATYPE(MyList) QDBusArgument &operator<<(QDBusArgument &, const MyStruct&);. This replaces the now-deprecated Q_ENUMS and will automatically register the metatype. 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. type() typeName() PySide6. 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. It is still giving the error"QObject::connect: Cannot queue arguments of type 'quint32&' (Make sure 'quint32&' is registered using. This allows us to use the Enum as a custom-type of a QVariant, to pass it between QML and Qt, to use it in synchronous signal-slot connections, and to print the symbolic enums (instead of a magic number) with qDebug(). 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. c:55 This looks like some loader initialization mismatch, check debug vs release builds of your application and libraries that are used. QLocalSocket. See also. Without this reference, it compiles just fine. Also, this Q_DECLARE_METATYPE(SharedTestClass) shouldn't be needed. The class is used as a helper to marshall types in QVariant and in queued. 5 is compiled with GCC 4. Adding a Q_DECLARE_METATYPE() makes the type known to all template based functions, including QVariant. Now you have a valid QObject. 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). You can register a class pointer as the metatype, though. ) I have defined MyStruct in an accessible header file: myheader. qRegisterMetaType() requires also a Q_DECLARE_METATYPE() – dtech. 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. You may have to register before you can post: click the register link above to proceed. Good workaround: you may register your type with Q_DECLARE_METATYPE ( IBase * ) macro and wrap your. 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. Call qRegisterMetaType() to make type available to non-template based functions, such as the queued signal and slot connections. 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. To start viewing messages, select the forum that you want to visit from the selection below. 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. To start viewing messages, select the forum that you want to visit from the selection below. Passing across threads (queued connection) will copy the QVector in either case, but the const will remind you that you cannot alter the original QVector in. This macro is used to specialise the template class QMetaTypeId with typename TYPE, in which, a static member function qt_metatype_id () is defined. 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. Re: How to use Q_DECLARE_METATYPE. Improve this answer. 2. QLocalSocket::SocketState is not a registered metatype, so for queued connections, you will have to register it with Q_DECLARE_METATYPE() and qRegisterMetaType(). That said, your stack trace is really strange: _dl_debug_initialize (ldbase=4294967292, ns=1095236752) at dl-debug. 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. in a header file and call @qRegisterMetaType<std::unique_ptr<Thing>> ();@ before your signal and slots are used. Also, this Q_DECLARE_METATYPE(SharedTestClass) shouldn't be needed. Firstly, you shouldn't need to use Q_DECLARE_METATYPE (or qRegisterMetaType) with the enum at all, this is handled by the moc. 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. Q&A for work. 1 Answer. You don't pass around copies of QObject derived types because it is not copyable. Declare new types with Q_DECLARE_METATYPE() to make them available to QVariant and other template-based functions. Q_DECLARE_METATYPE only registers a type in meta type system. Alt. What worries me is that. c:55 This looks like some loader initialization mismatch, check debug vs release builds of your application and libraries. Hope it. Teams. This function was introduced in Qt 6. To start viewing messages, select the forum that you want to visit from the selection below. c:55 This looks like some loader initialization mismatch, check debug vs release builds of your application and libraries that are used. 3. Here you can see that the macro expands to nothing. Call qRegisterMetaType() to make types available to non-template based functions, such as the queued signal and slot connections. 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. Q_DECLARE_METATYPE (T) requires the type T to be default-constructable, copiable and destructable. The struct is declared in my worker class, which is inside a namespace. As you have already found out, you must use Q_DECLARE_METATYPE to make the type known to Qt. The Custom Type and Queued Custom Type examples show how to implement a custom type with the features outlined in this document. Specifically, the function have to be called before using the struct. [virtual] QAbstractSocket:: ~QAbstractSocket Destroys the socket. 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. It associates a type name to a type so that it can be created and destructed dynamically at run-time. 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. Note that for enum types, you no not even need to call qRegisterMetaType () in these cases. int videoSourceMetaTypeId = qRegisterMetaType< VideoSource > ();Declare new types with Q_DECLARE_METATYPE() to make them available to QVariant and other template-based functions. Custom Type Qlist and Scope. Also, this Q_DECLARE_METATYPE(SharedTestClass) shouldn't be needed. [virtual] QAbstractSocket:: ~QAbstractSocket Destroys the socket. [since 6. staticMetaObject is of type QMetaObject and provides access to the enums declared with Q_ENUMS. 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 (. 5 is compiled with GCC 4. The class is used as a helper to marshall types in QVariant and in queued signals and slots connections. 2. 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. 0. But there would be no trouble using the QMetaType class or using qRegisterMetaType before creating an instance of QCoreApplication or QApplication. In the example's Message class, a static method is included to do this. Remember that Q_DECLARE_METATYPE merely defines a specialization of QMetaTypeId for your type. e. Hello Ladies and Gentlemen. Also you may need to use qRegisterMetaType function. Note that you are technically lying to the meta type system. The reasoning is found in the. Usually it goes in a pair: Q_DECLARE_METATYPE(TypeName) goes in the header, and then in the source at runtime registration is done with: qRegisterMetaType<TypeName>();answered May 10, 2013 at 2:25. 幸哉~ Qt是支持自定义信号，且自定义信号可以发送自定义数据类型的对象。. It associates a type name to a type so that it can be created and destructed dynamically at run-time. This allows me to use this type in a Q_PROPERTY, this all. rep file extension, short for Replica. As said in int qRegisterMetaType () documentation: To use the type T in QVariant, using Q_DECLARE_METATYPE () is sufficient. 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 to send arguments over D-Bus to remote applications and to receive them back. struct StandardData { int EmpId; QString Name; }; Q_DECLARE_METATYPE (StandardData) Additionally, you might need to call qRegisterMetaType. See also state() and Creating Custom Qt Types. To use the type T in queued signal and slot connections, qRegisterMetaType () must be called before the first connection is established. 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。. The documenation of this macro gives. Q_DECLARE_METATYPE. g. That class receives a list of variants (wrapping various data) and converts those variants into a binary stream using QDataStream >. I have declared all the types with Q_DECLARE_METATYPE, Q_OBJECT and the properties with Q_PROPERTY with the proper getters and setters. Note that you are technically lying to the meta type system. without providing the Q_DECLARE_METATYPE macro in the class header, but one could provide a macro where registration is automatically performed (more or less along with meta type declaration). Sorted by: 1. Adding a Q_DECLARE_METATYPE() makes the type known to all template based functions, including QVariant. The class in Qt responsible for custom types is QMetaType . The logical equivalent of a const T &r (reference to const T) is a const T * const p (const pointer to const T). Your code should look like this: Q_ENUM (StateEnum) //note the missing 'S' here Q_PROPERTY (StateEnum state READ state NOTIFY stateChanged) Share. Consider the specific case of qRegisterMetaType. 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. I want to use drag-and-drop to drag a QTreeWidgetItem that has std::shared_ptr user data. But this is all useless if you are not using templates. 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. Q_DECLARE_METATYPE, as pointed out by @SingerOfTheFall, would register template based type into QVariant (so it can be retrieved using qvariant_cast<T>()). The default access for a class is private, so that Container* data();. It seems that for a metatype that is a QList<MyClass::MyEnum> I must. As a workaround, I'm using QVariantMap instead of std::map. 0. // This primary template calls the -Implementation, like all other specialisations should. Follow answered Jun 5, 2009 at 15:14. The class in Qt responsible for custom types is QMetaType. 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 a header file and call @qRegisterMetaType<std::unique_ptr<Thing>> ();@ before your signal and slots are used. It does not say anything about registering the type. . Q_OBJECT derived class, inheritance. This fixed the issue. Jun 13, 2021 at 19:37. Note: This function is thread-safe. It seems that for a metatype that is a QList<MyClass::MyEnum> I must. 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. To use the type T in queued signal and slot connections, qRegisterMetaType<T>() must be called before the first connection is established. Labels: meta system, Meta type, qt. If such a connection is made, and a signal triggered, the runtime warning will be shown: QObject::connect: Cannot. Step 2 (meta type Declare macro), if needed, describe your custom type/class to things like QVariant, QDebug and other "support" systems used everywhere on QObjects. Adding a Q_DECLARE_METATYPE() makes the type known to all template based functions, including QVariant. Q_DECLARE_METATYPE(Pkg) and this does not give compile errors, but in my main. 1. 2 Answers. The class is used as a helper to marshall types in QVariant and in queued signals and slots connections. I guess it's the qRegisterMetaType () call itself that's missing. Note that you are technically lying to the meta type system. The correct syntax is Q_DECLARE_METATYPE (std::string) without the ;. Sorted by: 2. Returns the internal ID used by QMetaType. uint64; If this is your first visit, be sure to check out the FAQ by clicking the link above. I read on documentation that Q_DECLARE_METATYPE makes available type to QVariant, for example (I got it from documentation): @ struct MyStruct { int i;. Returns true if convert can convert from fromType to toType. QtCore. void Message:: registerMetaType {qRegisterMetaType < Message >. Registers the type name . until today. 1、自定MyDataType 类型，在这个类型的顶部包含：#include <QMetaType>. I also don't want to use qRegisterMetaType, since it is run-time bound. You can also use QMetaEnum::fromType() to get the QMetaEnum. qRegisterMetaType vs. 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. Returns the internal ID used by QMetaType. See full list on doc. Type is not registered, please use the Q_DECLARE_METATYPE macro to make it known to Qt's meta-object system. 1）引入头文件：#include<QMetaType>. 文章目录 Q_DECLARE_METATYPE qRegisterMetaType Q_DECLARE_METATYPE 使用Q_DECLARE_METATYPE标记自定义类型，可以让QMetaType查询到类型，也可以让QVariant识别。 qRegisterMetaType 在main函数中使用qRegisterMetaType注册自定义类型到元对象系统中,可在跨线程的信号槽中进行参数传递。I'm using Qt5 and qRegisterMetaType is not documented anymore, so I'm not sure if it's deprecated. Adding a Q_DECLARE_METATYPE() makes the type known to all template based functions, including QVariant. Execute qRegisterMetaType<QItemSelection> (); before it is used as such, e. The logical equivalent of a const T &r (reference to const T) is a const T * const p (const pointer to const T). Returns the metatype of the parameter at the given index. By the way, Qt 4. 该类型必须有公有的 构造、析构、复制构造 函数. 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,. Adding a Q_DECLARE_METATYPE() makes the type known to all template based functions, including QVariant. Re: Q_DECLARE_METATYPE problem. 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 QObject { Q_OBJECT public. Accessing an enum stored in a QVariant. The third without Q_DECLARE_METATYPE. 步骤： (以自定义MyDataType类型为例）. Is your Q_DECLARE_METATYPE in a header file or an implementation file? Incidentally, there is a mistake in TreeItem. Make your own typedef and do the Q_DECLARE_METATYPE and qRegisterMetatype. . For pointer types, it also requires that the pointed to type is fully defined. But I really would like to know the correct way to solve this problem; one where it is not possible to modify. This object can then be passed from QML to C++ via Q_INVOKABLE. Then you should register your object to use it with QML. See also state() and Creating Custom Qt Types. See also state() and Creating Custom Qt Types. Connect and share knowledge within a single location that is structured and easy to search. So, whatever Q_DECLARE_METATYPE is doing cannot be done by writing a function call. It associates a type name to a type so that it can be created and destructed dynamically at run-time. QObject can't be copied and all its descendants can't be copied also. To register VideoMeta you need to call qRegisterMetaType<VideoMeta>(). 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. To enable creation of objects at run-time, call the qRegisterMetaType() template function to register it with the meta-object system. Also you may need to use qRegisterMetaType function. There's no need to call qRegisterMetaType that many times, once is enough. Obviously then you would not do registerComparator (). 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. 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。. The code compiles and runs ok. The same plugin may be loaded multiple times during the application's lifetime. Research The QMetaType class manages named types in the meta-object system. no unexpected garbage data or the like). Since Qt 5. In some cases in Qt 4, it is also necessary to use the qRegisterMetaType method. Assuming base and derived are Q_GADGETs you want to get a static member. qRegisterMetaType vs. class Test : public QWidget { Q_OBJECT public: Test(); signals: public slots: void setAppData(QList<QIcon> icons, QStringList names, QStringList versions, QStringList publishers, QString installLocation, QStringList uninstallLocations); private: }; Q_DECLARE_METATYPE(QIcon) The same issue is still present. I believe this is related to the fact that. You can't with Q_GADGETS. So using a QString as the type of a Q_PROPERTY only works because it has special built-in support in the QML engine. Creating and Destroying Custom Objects 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 class. In short, I get following error: QObject::connect: Cannot queue arguments of type 'cv::Mat' (Make sure 'cv::Mat' is registered using qRegisterMetaType (). What is(are) the good place(s) to put the qRegisterMetaType call? I obviously don't want any expllicit. See also. qRegisterMetaType usage. genC last edited by . 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. x however, the code generated by moc will call qRegisterMetaType for you if moc can determine that the type may be registered as a. 1. There's also no need for that typedef, it only makes the code less readable. This function was introduced in Qt 5. The "traditional" way of doing this is to convert each element to a QVariant, and pass collection as a QVariantList. [quote author="Andre" date="1306394817"]In that case, I think you need to register them. Read and abide by the Qt Code of Conduct. qRegisterMetaType is also called in the class constructor. 【2】使用方法（声明 和 注册自定义数据类型）. It associates a type name to a type so that it can be created and destructed dynamically at run-time. Call qRegisterMetaType() to make types available to non-template based functions, such as the queued signal and slot connections. c:55 This looks like some loader initialization mismatch, check debug vs release builds of your application and libraries. I think you need to add an explicit export/import directive to the QT_NAMESPACE macro. wysota. To start viewing messages, select the forum that you want to visit from the selection below. e. 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. Use it if you want to use it as a global enumerator and then you need to call the meta-type runtime registration from the library, not from the application. 24th July 2010, 09:54 #6. Call qRegisterMetaType() to make types available to non-template based functions, such as the queued signal and slot connections. 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. A separate point for your own benefit. M. Qt. // This primary template calls the -Implementation, like all other specialisations should. 1. I just found multiple examples showing the usage of Q_ENUM and Q_ENUMS and looking into the definition of Q_ENUM showed me that it includes Q_ENUMS and other definitions. QVariant::fromValue () returns a QVariant. The QMetaType class manages named types in the meta-object system. 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. You should use qmlRegisterType function for that. ) I got the hint "expected a declaration" when I tried to use qRegisterMetaType from the global scope in my cpp file. 2. Even though we do not intend. In Qt, you can declare a variable in two ways: 1. With Q_DECLARE_METATYPE and without qRegisterMetaType: No warning, slot is called With Q_DECLARE_METATYPE and with qRegisterMetaType: No warning, slot is called. To start viewing messages, select the forum that you want to visit from the selection below. 2. Q_DECLARE_METATYPE on the other hand is (as far as I know) preprocessor bound. @kshegunov said: you're doing it wrong. You should use qmlRegisterType function for that. 1. That would allow you to use. Using the qRegisterMetaType () function The Q_DECLARE_METATYPE () macro is the preferred way to declare a variable in Qt. 1. An alternative would be to wrap shared_ptr<int> in your own class and implement comparison the way you want. 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. Unsure if my idea would work, I created a DataPoint class marked with Q_GADGET with three properties defined using Q_PROPERTY. You may have to register before you can post: click the register link above to proceed. This function was introduced in Qt 6. 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. Using the following required me to use Q_DECLARE_METATYPE. The reasoning is found in the discussion on Identity vs Value on the Qt Object Model page. To start viewing messages, select the forum that you want to visit from the selection below. qRegisterMetaType vs. canConvert<x> (); } and. It associates a type name to a type so that it can be created and destructed dynamically at run-time.