Last updated at 2016-07-08 Posted at 2015-11-16. You should use qmlRegisterType function for that. If you ever wondered what does Q_DECLARE_META_TYPE or qRegisterMetaType do and when to use (or not to use) them, read on. The Q_DECLARE_METATYPE() macro and qRegisterMetaType() function documentation contain more detailed information about their uses and limitations. There is no way to add support for more of these value types like std::string (*). 0. However, as you need the type to be. You can create Q_GADGETS in QML using a C++ factory object registered to be accessible in QML, and a Q_INVOKABLE function in this factory which returns an instance of the Q_GADGET object. void QAbstractSocket:: abort ()2 Answers. There's no such thing as a "const reference" because references are always const -- you can't reseat them. Q&A for work. As a workaround, I'm using QVariantMap instead of std::map. 16. Returns the used WebSocket protocol. namespace CCS { Q_DECL_EXPORT Q_NAMESPACE. You can register a class pointer as the metatype, though. Update. See also state(). Declare new types with Q_DECLARE_METATYPE () to make them available to. Also, to use type T with the QObject::property () API,. 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. You may have to register before you can post: click the register link above to proceed. @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],. qRegisterMetaTypeしているにもかかわらずQObject::connectでランタイムエラーが出る場合の回避策. struct Matrix { double data [4] [4]; }; Ideally you should be using eigen3. QVariantList , QString (if the list contains exactly one item) Casting between primitive type (int, float, bool etc. Also you may need to use qRegisterMetaType function. Q_DECLARE_METATYPE(MyObject*) somewhere in your code. To use the type T in queued signal and slot connections,. Also, to use type T with the QObject::property () API, qRegisterMetaType () must be. 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. You can make them known ( Q_DECLARE_METATYPE ), however you can't register them as QML type. QMetaType::type () returns the same ID as qMetaTypeId (), but does a lookup at runtime based on the name of the type. 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。. Detailed Description. qRegisterMetaType vs. Now I want to read this property with Qt's meta object system. The Q_DECLARE_METATYPE() macro and qRegisterMetaType() function documentation contain more detailed information about their uses and limitations. It is meant to be put in a header where the given type is declared. staticMetaObject is of type QMetaObject and provides access to the enums declared with Q_ENUMS. Call qRegisterMetaType() to make types available to non-template based functions, such as the queued signal and slot connections. Actually, they are declared, but in a private section with the macro Q_DISABLE_COPY(). Note that you are technically lying to the meta type system. Thus you need to use the runtime check QMetaType::type (). You are looking for the Q_ENUM () macro. The QMetaType class manages named types in the meta-object system. Well, I certainly overplayed this particular point, but the statement I believe is valid in principle. Than I did read this copy constructor of derived QT class and the answer by BЈовић. Quote: bool QVariant::operator==(const QVariant & v) const. 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 (). Sorted by: 3. Q_DECLARE_METATYPE is required to store type with QVariant, those two are required to register object's "big three" to manage it as resource and its serialization methods. (Make sure 'QVector<int>' is. by using qRegisterMetaType(). g. See the Qt D-Bus Type System page for more information on the type system. Q_DECLARE_METATYPE only registers a type in meta type system. There's no need to call qRegisterMetaType that many times, once is enough. Do do you register the meta type with the call qRegisterMetaType("your custom meta type")? 1 Reply Last reply Reply Quote 0. 如果非QMetaType内置类型要. QAbstractSocket::SocketState is not a registered metatype, so for queued connections, you will have to register it with Q_DECLARE_METATYPE() and qRegisterMetaType(). Call qRegisterMetaType<std::string> (); in the initialization of your code. Sorted by: 1. Enum has been moved from outside of the class to inside of it. Sorted by: 2. However, it does appear (at least to me) that you're trying to debug a release build of the application. 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. Now, in your registerTypes function, it should be registered like this: qRegisterMetaType<AccReal > ("data::AccReal"); In other words, the typeName string must match exactly the type of the signal argument as it is written there. Tried proposed solution using QVariant::fromValue, but kept getting compiler errors of type: . This worked very well. Ah, sorry, I didn't noticed that part. }; Q_DECLARE_METATYPE (MyCustomType); Then in my application, I have a signal "void sendMsg (MyCustomType)" and I qRegisterMetaType (). From the QVariant::value documentation: If the QVariant contains a pointer to a type derived from QObject then T may be any QObject type. You should use Q_DECLARE_METATYPE macro for this. 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. in a header file and call @qRegisterMetaType<std::unique_ptr<Thing>> ();@ before your signal and slots are used. state() Creating Custom Qt Types. in your main function or in the constructor of AudioGuiApplication. // copiable, C++98 brace-initializable, etc. Also, this Q_DECLARE_METATYPE(SharedTestClass) shouldn't be needed. For this, a function call (evaluated during runtime) needs to be made, and qRegisterMetatype is the tool for this: qRegisterMetaType<Area>("Area");@julio. in a header file and call @qRegisterMetaType<std::unique_ptr<Thing>> ();@ before your signal and slots are used. Jun 13, 2021 at 19:37. 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: This now makes it possible for Message values to be stored in QVariant objects and retrieved later. This has been changed, and isNull () now only returns true if the QVariant is empty or contains a nullptr. QLocalSocket::SocketState is not a registered metatype, so for queued connections, you will have to register it with Q_DECLARE_METATYPE() and qRegisterMetaType(). M. Adding a Q_DECLARE_METATYPE() makes the type known to all template based functions, including QVariant. So I played around, copied the original macro and adapted it a bit: @. Avoid having to qRegisterMetaType (pointer. If I get AnotherQGadgetClass via getter and change it's properties, the setters are called and. After googling this, I found this correspondence, which was only available through a third party archival site as google. 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(NSP::MyStruct) qRegisterMetaTypeIt associates a type name to a type so that it can be created and destructed dynamically at run-time. I want to use drag-and-drop to drag a QTreeWidgetItem that has std::shared_ptr user data. Q_DECLARE_METATYPE(MyClass); qRegisterMetaType<MyClass>(); I can use the type in queued connection with signals like this one: void MySignal(MyType o); Now I also would like to use the type with signals like this: void MyVectorSignal(QVector<MyType> v);Qt 5. qRegisterMetaType is also called in the class constructor. Q_DECLARE_METATYPE, as pointed out by @SingerOfTheFall, would register template based type into QVariant (so it can be retrieved using qvariant_cast<T>()). Re: Qt warning of type conversion already registered Originally. This function returns the Qt meta type id for the type (the same value that is returned from qRegisterMetaType()). In short, I get following error: QObject::connect: Cannot queue arguments of type 'cv::Mat' (Make sure 'cv::Mat' is registered using qRegisterMetaType (). This fixed the issue. Type is not registered, please use the Q_DECLARE_METATYPE macro to make it known to Qt's meta-object system. c:55 This looks like some loader initialization mismatch, check debug vs release builds of your application and libraries that are used. void Message:: registerMetaType {qRegisterMetaType < Message >. Using the Q_DECLARE_METATYPE () macro 2. 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. I haven't used that module yet but one thing you should do is remove the string argument from your qRegisterMetaType calls. Adding a Q_DECLARE_METATYPE () makes the type known to all template based functions, including QVariant. The Problem: I want to create an object instance at runtime using QMetaType by the type name. Make a typedef for QSharedPointer<UserDataType>, and use both Q_DECLARE_METATYPE as well as qRegisterMetaType () to register it for use. type() typeName() PySide6. That. uint64; If this is your first visit, be sure to check out the FAQ by clicking the link above. 2. on top of main. See full list on doc. You may have to register before you can post: click the register link above to proceed. QtNetwork. " 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. Make your own typedef and do the Q_DECLARE_METATYPE and qRegisterMetatype. Sorted by: 5. typedef QVector<QSharedPointer<Tester> > TestPointerVector;. See also Q_DECLARE_METATYPE() and. 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. The QMetaType class manages named types in the meta-object system. Q_DECLARE_METATYPE(MyClass*); That's how Qt handles it with QObject and QWidget. There's no need to call qRegisterMetaType that many times, once is enough. 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. The QML engine provides built-in support for a. QtCore. QVariant x2 = QVariant::fromValue( x1); To copy to clipboard, switch view to plain text mode. The. I my real world application Context holds a large number of physical quantities (masses, forces, velocities,. QMetaType::type () is a bit slower, but compilation succeeds if a type is not registered. [virtual] QAbstractSocket:: ~QAbstractSocket Destroys the socket. It associates a type name to a type so that it can be created and destructed dynamically at run-time. QtCore. qRegisterMetaType vs. 1. 1. ) I got the hint "expected a declaration" when I tried to use qRegisterMetaType from the global scope in my cpp file. You may have to register before you can post: click the register link above to proceed. 【2】使用方法（声明 和 注册自定义数据类型）. The ENUM type. 1 Answer. Call qRegisterMetaType() to make types available to non-template based functions, such as the queued signal and slot connections. Q_DECLARE_METATYPE. // This primary template calls the -Implementation, like all other specialisations should. Q_DECLARE_METATYPE. 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. By the way, Qt 4. 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. Current the only supported type info is QML_HAS_ATTACHED_PROPERTIES. Q_DECLARE_METATYPE QMetaType::type. 1. " –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 however have a scenario where I want to declare such an object in qml and transmit it to the c++. 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. ) QObject::connect: Cannot queue arguments of type 'QVector<int>'. So my first idea:. Posted by Unknown at 2:06 AM. By convention, these files are given a . This object can then be passed from QML to C++ via Q_INVOKABLE. This replaces the now-deprecated Q_ENUMS and will automatically register the metatype. You may have to register before you can post: click the register link above to proceed. @Q_DECLARE_METATYPE (std::unique_ptr<Thing>);@. nyaruko. [virtual] QLocalSocket:: ~QLocalSocket Destroys the socket, closing the connection if necessary. ) What I'm trying to do is send a signal containing two cv::Mat images from a QThread to the main thread, so that I can display the output. no unexpected garbage. That said, your stack trace is really strange: _dl_debug_initialize (ldbase=4294967292, ns=1095236752) at dl-debug. 8. Enumerations that are declared with Q_ENUM have their QMetaEnum registered in the enclosing QMetaObject. That said, your stack trace is really strange: _dl_debug_initialize (ldbase=4294967292, ns=1095236752) at dl-debug. cpp. QLocalSocket. You may have to register before you can post: click the register link above to proceed. The struct is declared in my worker class, which is inside a namespace. The file (called a "rep" file) uses a specific (text) syntax to describe the API. Using the qRegisterMetaType () function The Q_DECLARE_METATYPE () macro is the preferred way to declare a variable in Qt. See also state() and Creating Custom Qt Types. 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. 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. If you are using queued connections, you need to register std::string as meta 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(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. 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 () <<. . So, whatever Q_DECLARE_METATYPE is doing cannot be done by writing a function call. G. When the plugin is reloaded later, the old declaration still points to the original memory space of the now-unloaded library. Now, that Q_DECLARE_METATYPE enables the type for Qt template classes and QVariant. multithreaded software and I am getting the warning says: (Make sure 'QVector<int>' is registered using qRegisterMetaType (). h. Declare new types with Q_DECLARE_METATYPE() to make them available to QVariant and other template-based functions. [since 6. QAbstractSocket::SocketState is not a registered metatype, so for queued connections, you will have to register it with Q_REGISTER_METATYPE() and qRegisterMetaType(). In my module tests, I turn the card up and down, and can verify that the number of signals are increasing using QSignalSpy. Re: Qt warning of type conversion already registered Originally. 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. Also, this Q_DECLARE_METATYPE(SharedTestClass) shouldn't be needed. 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. 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. Duplicate Question(s):Q_DECLARATIVE_METATYPE in and out; Using EventExport vs. 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. So, if you had a custom type FooType, you'd put the Q_DECLARE_METATYPE directly after the declaration, and in. To use the type T in QVariant, using Q_DECLARE_METATYPE() is sufficient. ) summary refs log tree commit diff stats Foo and Foo* are different types and need to be registered separately. So I am doing this: Qt Code: Switch view. Is your feature request related to a problem? No, it's an improvement Please describe. To enable using the type in queued signals and such, there also needs to be a corresponding call: qRegisterMetaType<foo::FooState>(); Question. uint64; If this is your first visit, be sure to check out the FAQ by clicking the link above. I read a bit and it seems that Q_DECLARE_SMART_POINTER_METATYPE is supposed to allow this to work. 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. A. Don't use Q_DECLARE_METATYPE and qRegisterMetaType for your QObject enum. . 2. 8. Then you should register your object to use it with QML. ompiler (repc) generates header files based on an API definition file. namespace CCS { Q_DECL_EXPORT Q_NAMESPACE. e. The other overload around has almost the same form but for the. until today. 3. It seems that for a metatype that is a QList<MyClass::MyEnum> I must. 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. @SGaist Yes, I am using it with QVariant, mostly with QSettings to save and retrieve data easily by overriding QDataStream operators. To start viewing messages, select the forum that you want to visit from the selection below. Data Type Conversion Between QML and C++. qRegisterMetaType 必须使用该函数的两种情况. It is not safe to make a QObject's copy constructor public. Execute qRegisterMetaType<QItemSelection> (); before it is used as such, e. Call qRegisterMetaType() to make type available to non-template based functions, such as the queued signal and slot connections. See also state(). S 1 Reply Last reply Reply Quote 0. Note that for enum types, you no not even need to call qRegisterMetaType () in these cases. "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. uint64; If this is your first visit, be sure to check out the FAQ by clicking the link above. int videoSourceMetaTypeId = qRegisterMetaType< VideoSource > ();QAbstractSocket::SocketState is not a registered metatype, so for queued connections, you will have to register it with Q_DECLARE_METATYPE() and qRegisterMetaType(). An alternative would be to wrap shared_ptr<int> in your own class and implement comparison the way you want. This function was introduced in Qt 6. To start viewing messages, select the forum that you want to visit from the selection below. QMetaType registerNormalizedTypedef normalizedTypeName, type: metaType ); return. In some cases in Qt 4, it is also necessary to use the qRegisterMetaType method. 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. So using qRegisterMetaType () you will just trade Q_ENUM () for Q_DECLARE_METATYPE (). You may have to register before you can post: click the register link above to proceed. Assuming base and derived are Q_GADGETs you want to get a static member. The code compiles and runs ok. Using the following required me to use Q_DECLARE_METATYPE. The logical equivalent of a const T &r (reference to const T) is a const T * const p (const pointer to const T). :) QApplication is the root QObject of the program and its full initialization is required before anything can practically be done with anything else. The object it returns should also be a member of the factory class. By convention, these files are given a . 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. Note: it's also safe to call qRegisterMetaType () multiple times. Does your code ever call qRegisterMetatype() or use Q_DECLARE_METATYPE()? 10th November 2014, 06:23 #3. But I couldn't register the type because it's a QObject and I don't have access to the implementation to change it. qRegisterMetaType usage. 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. To use the type T in queued signal and slot connections, qRegisterMetaType<T>() must be called before the first connection is established. Q_OBJECT derived class, inheritance. goocreations 12 Mar 2013, 07:22. i. 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. 如果非QMetaType内置类型要. The id is constexpr in the special case of Qt built-in types only. 4 and it seems to work. This macro is used to specialise the template class QMetaTypeId with typename TYPE, in which, a static member function qt_metatype_id () is defined. 2. Call qRegisterMetaType() to register the data type before you establish the connection. no unexpected garbage. e. However, I cannot figure out how to verify that the included parameter is FACE_UP or FACE_DOWN. 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. I have declared all the types with Q_DECLARE_METATYPE, Q_OBJECT and the properties with Q_PROPERTY with the proper getters and setters. There's no need to call qRegisterMetaType that many times, once is enough. 8. Note that you are technically lying to the meta type system. I placed Q_DECLARE_METATYPE (DataPoint) after the class definition. Of course it's a bug and an odd mistake that Q_DECLARE_METATYPE(QList<QSslError>) is in qsslsocket. 7. [edit] forgot to mention that you also have to use a worker object. 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. This also makes the type available for queued. However, if you want to use a type in a pure runtime context, for example in a QML document, the Qt runtime doesn't know the type declared with Q_DECLARE_METATYPE. I want to use drag-and-drop to drag a QTreeWidgetItem that has std::shared_ptr user data. Any class or struct that has a public default constructor, a public copy. Yes I tried with qRegisterMetaType, it. See also. . In the header, after the class declaration, outside the namespace, I've included. Some structure need to be registered to be queued in asynchronous signals using qRegisterMetaType<T>(name), such as signal which passes QVector<int>. As said in int qRegisterMetaType () documentation: To use the type T in QVariant, using Q_DECLARE_METATYPE () is sufficient. QAbstractSocket::SocketState is not a registered metatype, so for queued connections, you will have to register it with Q_DECLARE_METATYPE() and qRegisterMetaType(). I read a bit and it seems that Q_DECLARE_SMART_POINTER_METATYPE is supposed to allow this to work. 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. Q&A for work. 2）添加声明：利用宏 Q_DECLARE_METATYPE. The Q_DECLARE_METATYPE() macro and qRegisterMetaType() function documentation contain more detailed information about their uses and limitations. For that, I want to declare a. qRegisterMetaType vs. See also. The following code will work as well: using namespace foo; Q_DECLARE_METATYPE (MyClass) Teams. Declare new types with Q_DECLARE_METATYPE() to make them available to QVariant and other template-based functions. Thank you Volker, I had a couple of problems I forgot about the Q_DECLARE_METATYPE(myType); and I don't' think I was never consistent with the global scope specifier. The application using it does this: typedef QMap<int, int> MyOtherType; Q_DECLARE_METATYPE (MyOtherType) qRegisterMetaType<MyOtherType> (); Now the D-Bus marshaller and demarshaller get registered with the wrong type id. That said, your stack trace is really strange: _dl_debug_initialize (ldbase=4294967292, ns=1095236752) at dl-debug. Declare new types with Q_DECLARE_METATYPE() to make them available to QVariant and other template-based functions. @SGaist Yes, I am using it with QVariant, mostly with QSettings to save and retrieve data easily by overriding QDataStream operators. c:55 This looks like some loader initialization mismatch, check debug vs release builds of your application and libraries that are used. 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. @Mark81 Actually you'll probably need only Q_DECLARE_METATYPE as this is done at compile time - exposing the type to the metatype system (I know it is an enum but it's needed for the QVariant and the like). This results in access violations. QML Qvariant from custom class. It is only useful to the code that follows it, in the same file. 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. 1. You can't with Q_GADGETS. Also, this Q_DECLARE_METATYPE(SharedTestClass) shouldn't be needed. Is your Q_DECLARE_METATYPE in a header file or an implementation file? Incidentally, there is a mistake in TreeItem. But there would be no trouble using the QMetaType class or using qRegisterMetaType before creating an instance of QCoreApplication or QApplication. There's no compile time error, but when I run. After googling this, I found this correspondence, which was only available through a third party archival site as google. qRegisterMetaType vs. struct StandardData { int EmpId; QString Name; }; Q_DECLARE_METATYPE (StandardData) Additionally, you might need to call qRegisterMetaType. When using signals and slots with multiple threads, see Signals and Slots Across Threads. 该类型必须有公有的 构造、析构、复制构造 函数. c:55 This looks like some loader initialization mismatch, check debug vs release builds of your application and libraries. 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. Q_DECLARE_METATYPE. Returns true if convert can convert from fromType to toType. I just tried. It associates a type name to a type so that it can be created and destructed dynamically at run-time. Also, this Q_DECLARE_METATYPE(SharedTestClass) shouldn't be needed. " Yet types like QVariantMap are themself typedefs. See also state() and Creating Custom Qt Types. 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. Inheritance diagram of PySide6. What worries me is that. What worries me is that. QVariant v = QVariant::fromValue<cMyClass>(MyObject); However, as soon as I use Q_DECLARE_METATYPE, I get errors about using a deleted function. c:55 This looks like some loader initialization mismatch, check debug vs release builds of your application and libraries. The reasoning is found in the. 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. Share. More. I think you need to add an explicit export/import directive to the QT_NAMESPACE macro. First of all you need to declare your custom object for Qt metatype system. See also state () and Creating Custom Qt Types . 1. 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. See the Custom Type Example for code that demonstrates this. Also, this Q_DECLARE_METATYPE(SharedTestClass) shouldn't be needed. To use the type T in queued signal and slot connections, qRegisterMetaType () must be called before the first connection is established. This function was introduced in Qt 4. Declare new types with Q_DECLARE_METATYPE () to make them available. Declare new types with Q_DECLARE_METATYPE() to make them available to QVariant and other template-based functions. Any class or struct that has a public default constructor, a public copy. ) I got the hint "expected a declaration" when I tried to use qRegisterMetaType from the global scope in my cpp file. 2. Adding a Q_DECLARE_METATYPE() makes the type known to all template based functions, including QVariant. : Q_DECLARE_METATYPE(MyClass*); That's how Qt handles it with QObject and QWidget. You pass around pointers instead. The class is used as a helper to marshall types in QVariant and in queued signals and slots connections.