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. no I didn't, do I need to put in the file generated by repc or I can put it anywhere ? – Houss_gc. 2. To call qRegisterMetaType (), you still need to use Q_DECLARE_METATYPE (). To start viewing messages, select the forum that you want to visit from the selection below. qRegisterMetaType 必须使用该函数的两种情况. This worked very well. uint64; If this is your first visit, be sure to check out the FAQ by clicking the link above. This allows me to use this type in a Q_PROPERTY, this all. Any class or struct that has a public constructor, a public copy constructor, and a public destructor can be registered. Q_DECLARE_META_TYPE (Fruit) and qRegisterMetaType were redundant: #define PluginInterface_iid "pluginInterface" Q_DECLARE_INTERFACE (PluginInterface, PluginInterface_iid) //Actual plugin implementing PluginInterface class. 3 to Qt4. . I need to call the Q_DECLARE_METATYPE() to pass the smart pointer. However, it does appear (at least to me) that you're trying to debug a release build of the application. The class is used as a helper to marshall types in QVariant and in queued signals and slots connections. I my real world application Context holds a large number of physical quantities (masses, forces, velocities,. 4. Note that if you intend to use the type in queued signal and slot connections or in QObject's property system, you also have to call qRegisterMetaType() since the names are resolved at runtime. Q_DECLARE_METATYPE (std::string) Quoting Qt Doc. . See the Custom Type Example for code that demonstrates this. 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. 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. The following should work: Note that you also have to call qRegisterMetaType<MyMpiMessage> (); before you use the function the first time. Q_DECLARE_METATYPE only registers a type in meta type system. typedef QVector<QSharedPointer<Tester> > TestPointerVector;. qRegisterMetaType vs. From the docs: int qRegisterMetaType ( const char * typeName ) Registers the type name typeName to the type T. But because QUuid stores its content as a QByteArray which is already supported by QVariant, you. That said, your stack trace is really strange: _dl_debug_initialize (ldbase=4294967292, ns=1095236752) at dl-debug. . cpp. Using Qt 3D with QCustomPlot. e. In the header, after the class declaration, outside the namespace, I've included. As said in int qRegisterMetaType () documentation: To use the type T in QVariant, using Q_DECLARE_METATYPE () is sufficient. 3. To use the type T in queued signal and slot connections, qRegisterMetaType () must be called before the first connection is established. Remember that Q_DECLARE_METATYPE merely defines a specialization of QMetaTypeId for your type. The QMetaType class manages named types in the meta-object system. Obviously then you would not do registerComparator (). To start viewing messages, select the forum that you want to visit from the selection below. 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. Ah, sorry, I didn't noticed that part. hpp and qRegisterMetaType<quint32>("quint32"); in both the Constructors of Class1 and Class2. }; Q_DECLARE_METATYPE (MyCustomType); Then in my application, I have a signal "void sendMsg (MyCustomType)" and I qRegisterMetaType (). Therefore I want to use Q_DECLARE_METATYPE (My_Item) and from the documentation I learned that I need a public copy constructor. When data values are exchanged between QML and C++, they are converted by the QML engine to have the correct data types as appropriate for use in QML or C++. 1 Answer. Returns the used WebSocket protocol. Registers the type name . I pass the MyClass pointer to the streaming operator and only stream things like QString, QPointF, etc. See also Thread Support in Qt, QObject::connect(), qRegisterMetaType(), and Q_DECLARE_METATYPE(). After googling this, I found this correspondence, which was only available through a third party archival site as google. This object can then be passed from QML to C++ via. View Profile View Forum Posts View Articles Beginner Join Date Nov 2014 Posts 6 Qt products. 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. There's no need to call qRegisterMetaType that many times, once is enough. 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. As said in int qRegisterMetaType () documentation: To use the type T in QVariant, using Q_DECLARE_METATYPE () is sufficient. Note that you are technically lying to the meta type system. hpp which is included in Class1. You should use Q_DECLARE_METATYPE macro for this. With Q_DECLARE_METATYPE and without qRegisterMetaType: No warning, slot is called With Q_DECLARE_METATYPE and with qRegisterMetaType: No warning, slot is called. Q_OBJECT derived class, inheritance. " Currently I have no UI implemented (yet!). You should use qmlRegisterType function for that. 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. . in a header file and call @qRegisterMetaType<std::unique_ptr<Thing>> ();@ before your signal and slots are used. Qt5でシグナルの引数としてユーザー定義型を指定する場合は、Q_DECLARE_METATYPEとqRegisterMetaType()を使って方の登録を行う必要がある。Trying to register std::map<non_template_type_1,non_template_type_2> with Q_DECLARE_METATYPE() results in compilation failure and apparently is not supported. 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. You may have to register before you can post: click the register link above to proceed. There is no way to add support for more of these value types like std::string (*). QVariantList , QString (if the list contains exactly one item) Casting between primitive type (int, float, bool etc. [virtual] QAbstractSocket:: ~QAbstractSocket Destroys the socket. Q_DECLARE_METATYPE. Make sure you call it from within a method. 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. statement to the header file containing. w/out GUI module you wouldn't have any of those types available). qRegisterMetaType vs. 16. I read on documentation that Q_DECLARE_METATYPE makes available type to QVariant, for example (I got it from documentation): @ struct MyStruct { int i;. c:55 This looks like some loader initialization mismatch, check debug vs release builds of your application and libraries. Similarly you can create a mutable view of type QAssociativeIterable on any container registered with Q_DECLARE_ASSOCIATIVE_CONTAINER_METATYPE(). append (QVariant::fromValue (l)); } return list; } The metatype system declaration and registration you have. I meet a qt metatype issue. Actually, they are declared, but in a private section with the macro Q_DISABLE_COPY(). Call qRegisterMetaType() to make types available to non-template based functions, such as the queued signal and slot connections. Q_DECLARE_METATYPE(TYPEDEF) Q_DECLARE_METATYPE(TYPEDEF) mainwindow. 5 is compiled with GCC 4. 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. 2 Answers. It associates a type name to a type so that it can be created and destructed dynamically at run-time. If you want both, then register both. It associates a type name to a type so that it can be created and destructed dynamically at run-time. To start viewing messages, select the forum that you want to visit from the selection below. Teams. 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. I've registered my class with: @Q_DECLARE_METATYPE(MyClass);@ and. } 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. Then you should register your object to use it with QML. What is(are) the good place(s) to put the qRegisterMetaType call? I obviously don't want any expllicit. // But the split allows to. Call qRegisterMetaType() to make types available to non-template based functions, such as the queued signal and slot connections. e. I guess it's the qRegisterMetaType () call itself that's missing. e. Note: This function is thread-safe. Using the macro directly turned out to be impossible. Any class or struct that has a public constructor, a public copy constructor, and a public destructor can be registered. i. As the docs state: Declare new types with Q_DECLARE_METATYPE () to make them available to QVariant and other template-based functions. To call qRegisterMetaType (), you still need to use Q_DECLARE_METATYPE (). Greetings. 0. @Q_DECLARE_METATYPE (std::unique_ptr<Thing>);@. Q_DECLARE_METATYPE(TYPEDEF) Q_DECLARE_METATYPE(TYPEDEF) mainwindow. Q_DECLARE_METATYPE only registers a type in meta type system. QtCore. See also. cpp. e. I am also using some in queued signal and slot connections. Email This BlogThis! Share to Twitter Share to Facebook Share to Pinterest. 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. Good workaround: you may register your type with Q_DECLARE_METATYPE ( IBase * ) macro and wrap your. 1. QMetaType::type () is a bit slower, but compilation succeeds if a type is not registered. :) QApplication is the root QObject of the program and its full initialization is required before anything can practically be done with anything else. In the example's Message class, a static method is included to do this. 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 make the custom type. 4 which does not support all C++11 features. Declare new types with Q_DECLARE_METATYPE() to make them available to QVariant and other template-based functions. 0. Duplicate Question(s):Q_DECLARATIVE_METATYPE in and out; Using EventExport vs. Yes I tried with qRegisterMetaType, it. Adding a Q_DECLARE_METATYPE() makes the type known to all template based functions, including QVariant. View Profile View Forum Posts View Articles Beginner Join Date Nov 2014 Posts 6 Qt products. 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. Any idea what I'm missing please? BTW, no problem at all using Schedule in QMetaProperty or QVariant. Also you may need to use qRegisterMetaType function. Your code should look like this: Q_ENUM (StateEnum) //note the missing 'S' here Q_PROPERTY (StateEnum state READ state NOTIFY stateChanged) Share. The QMetaType class manages named types in the meta-object system. struct StandardData { int EmpId; QString Name; }; Q_DECLARE_METATYPE (StandardData) Additionally, you might need to call qRegisterMetaType. @SGaist Yes, I am using it with QVariant, mostly with QSettings to save and retrieve data easily by overriding QDataStream operators. I'm confused by this error, as the documentation states (emphasis mine): Returns the meta type id of type T at compile time. Call qRegisterMetaType() to make types available to non-template based functions, such as the queued signal and slot connections. It will return the same result if it was called before. @Q_DECLARE_METATYPE (std::unique_ptr<Thing>);@. 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. There's also no need for that typedef, it only makes the code less readable. Since Qt 5. To use the type T in queued signal and slot connections, qRegisterMetaType () must be called before the first connection is established. Your Matrix type is not copiable, thus you can't use Q_DECLARE_METATYPE on it. For pointer types, it also requires that the pointed to type is fully defined. 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. Also, this Q_DECLARE_METATYPE(SharedTestClass) shouldn't be needed. : Q_DECLARE_METATYPE(MyClass*); That's how Qt handles it with QObject and QWidget. 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. 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. I tried to write one, but I failed. Re: How to use Q_DECLARE_METATYPE. ompiler (repc) generates header files based on an API definition file. uint64; If this is your first visit, be sure to check out the FAQ by clicking the link above. That's created by this macro. See the Qt D-Bus Type System page for more information on the type system. 1. Consider the specific case of qRegisterMetaType. But this is all useless if you are not using templates. It does not say anything about registering the type. 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. Last updated at 2016-07-08 Posted at 2015-11-16. I'd understood if i want to pass my custom type like struct or so, but it is essential type. After googling this, I found this correspondence, which was only available through a third party archival site as google. Well, I certainly overplayed this particular point, but the statement I believe is valid in principle. It must appear in a code block. The same plugin may be loaded multiple times during the application's lifetime. 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. // 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. Any class or struct that has a public default constructor, a public copy constructor, and a. In the header, after the class declaration, outside the namespace, I've included. e. QML_DECLARE_TYPE. The class is used as a helper to marshall types in QVariant and in queued signals and slots connections. Question: Is there a way to check at compile-time if qRegisterMetaType<T> () was called for a custom type T? The custom type T needs to be registered in Qt meta-type system in order to be used in e. Here you can see that the macro expands to nothing. You can also use QMetaEnum::fromType() to get the QMetaEnum. There's also no need for that typedef, it only makes the code less readable. 5 is compiled with GCC 4. The following code will work as well: using namespace foo; Q_DECLARE_METATYPE (MyClass) Teams. Make sure you call it from within a method. QLocalSocket::SocketState is not a registered metatype, so for queued connections, you will have to register it with Q_DECLARE_METATYPE() and qRegisterMetaType(). Is your Q_DECLARE_METATYPE in a header file or an implementation file? Incidentally, there is a mistake in TreeItem. See also state() and Creating Custom Qt Types. So in your case you need to declare. It associates a type name to a type so that it can be created and destructed dynamically at run-time. That said, your stack trace is really strange: _dl_debug_initialize (ldbase=4294967292, ns=1095236752) at dl-debug. Note that for enum types, you no not even need to call qRegisterMetaType () in these cases. 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. 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. 1）引入头文件：#include<QMetaType>. From the docs: int qRegisterMetaType ( const char * typeName ) Registers the type name typeName to the type T. To start viewing messages, select the forum that you want to visit from the selection below. Q_DECLARE_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. To use the type T in queued signal and slot connections, qRegisterMetaType<T>() must be called before the first connection is established. Call qRegisterMetaType() to make type available to non-template based functions, such as the queued signal and slot connections. 1 Answer. struct Matrix { double data [4] [4]; }; Ideally you should be using eigen3. The Custom Type and Queued Custom Type examples show how to implement a custom type with the features outlined in this document. Connect and share knowledge within a single location that is structured and easy to search. In short, I get following error: QObject::connect: Cannot queue arguments of type 'cv::Mat' (Make sure 'cv::Mat' is registered using qRegisterMetaType (). Hello Ladies and Gentlemen. Qt is throwing an exception because it doesn't know how to store the shared_ptr onto a QDataStream. The QMetaType class manages named types in the meta-object system. . 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. That's created by this macro. The class is used as a helper to marshall types in QVariant and in queued signals and slots connections. If you are using queued connections, you need to register std::string as meta type. My workround was to explicitly cast the enum values to int when passing them onto a function requiring a QVariant type, in my case. 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. This is by design. @Wieland Thanks. Gerald Gerald. In my project, MyClass is a cache for multi-dimensional data "point", and it looks like: class MyClass { public: MyClass(); /* Some functions */ private: int m_index; double m_time; QList<int> *m_data; };Firstly, you shouldn't need to use Q_DECLARE_METATYPE (or qRegisterMetaType) with the enum at all, this is handled by the moc. +50. 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(). It associates a type name to a type so that it can be created and destructed dynamically at run-time. uint64; If this is your first visit, be sure to check out the FAQ by clicking the link above. [edit] forgot to mention that you also have to use a worker object. But there would be no trouble using the QMetaType class or using qRegisterMetaType before creating an instance of QCoreApplication or QApplication. Then you should register your object to use it with QML. A. Using the Q_DECLARE_METATYPE () macro 2. QAbstractSocket::SocketState is not a registered metatype, so for queued connections, you will have to register it with Q_DECLARE_METATYPE() and qRegisterMetaType(). 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. rep file extension, short for Replica. Join Date Mar 2010 Posts 69 Thanks 8 Thanked 1 Time in 1 Post Qt products Platforms} Q_DECLARE_METATYPE(Topic) In main, I have included this: qRegisterMetaType<Topic>("Topic"); When propagating these elements from c++ to QML, everything is working. Call qRegisterMetaType() to make types available to non-template based functions, such as the queued signal and slot connections. 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. canConvert<x> (); } and. See full list on doc. 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. c:55 This looks like some loader initialization mismatch, check debug vs release builds of your application and libraries that are used. Q_DECLARE_METATYPE与qRegisterMetaType学习. 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. Sorted by: 5. 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. since it is a runtime registration. You may have to register before you can post: click the register link above to proceed. e. 2 Answers. I however have a scenario where I want to declare such an object in qml and transmit it to the c++. Situation. [since 6. It does not say anything about registering the type. " and: "Warning: This function is useful only for registering an alias (typedef) for every other use case Q_DECLARE_METATYPE and qMetaTypeId() should be used instead. The QMetaType class manages named types in the meta-object system. A separate point for your own benefit. 2）添加声明：利用宏 Q_DECLARE_METATYPE. This function is useful to register typedefs so they can be used by QMetaProperty, or in QueuedConnections. Step 1 (mark for MOC), build some QObjects That pattern uses Q_PROPERTY and Q_OBJECT and the MoC tool. 1. Because Foo is not derived from QObject and QVariant only supports polymorphism for QObject -derived types. To copy to clipboard, switch view to plain text mode. @kshegunov said: you're doing it wrong. But this is all useless if you are not using templates. This replaces the now-deprecated Q_ENUMS and will automatically register the metatype. Jun 13, 2021 at 19:37. 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. by using qRegisterMetaType(). Returns the used WebSocket protocol. That said, your stack trace is really strange: _dl_debug_initialize (ldbase=4294967292, ns=1095236752) at dl-debug. QList of Custom Objects. qRegisterMetaType is also called in the class constructor. 2. 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(). Note: This function is thread-safe. Detailed Description. Use Q_DECLARE_OPAQUE_POINTER () to be able to register pointers to forward. Declare new types with Q_DECLARE_METATYPE () to make them available to. qRegisterMetaType<FileNodePointer> ("FileNodePointer"); should be called once (in main, constructor etc. To enable using the type in queued signals and such, there also needs to be a corresponding call: qRegisterMetaType<foo::FooState>(); Question. [since 6. 14. Share. Re: Q_DECLARE_METATYPE problem. However Q_DECLARE_METATYPE () is a bit more complicated. The. QML Qvariant from custom class. @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). the type name must be specified without the class, as in. So you can call it from your constructor. The class is used as a helper to marshall types in QVariant and in queued signals and slots connections. Declare new types with Q_DECLARE_METATYPE() to make them available to QVariant and other template-based functions. Also, this Q_DECLARE_METATYPE(SharedTestClass) shouldn't be needed. Sorted by: 1. 手册中告诉我们，执行这个的时候，模板参数T必须用 Q_DECLARE_METATYPE() 声明过 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. Q_DECLARE_METATYPE QMetaType::type. [virtual] QAbstractSocket:: ~QAbstractSocket Destroys the socket. For those who follow. 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. I tested your code on Qt 5. 24th July 2010, 09:54 #6. Normally, you would only register the pointer form if your class cannot be copied, as in the case of QObject and derivatives, but. qRegisterMetaType 必须使用该函数的两种情况. I have an application that requires use of both Qt 3D and the QCustomPlot library. e. This results in access violations. However, as you need the type to be. 14 vs 5. Consider the specific case of qRegisterMetaType. It associates a type name to a type so that it can be created and destructed dynamically at run-time. Q_DECLARE_METATYPE ( blabla* ) Also qRegisterMetaType<T> () is only required for sending your object through queued signal/slot connections. 手册中告诉我们，执行这个的时候，模板参数T必须用 Q_DECLARE_METATYPE() 声明过 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. When these files are processed by repc, repc generates both Source and Replica header files. QMetaType. @Q_DECLARE_METATYPE (std::unique_ptr<Thing>);@. I store them in QVariant :. Registered enumerations are automatically registered also to the Qt meta type system, making them known to QMetaType without the need to use. Update. Additional types can be registered using qRegisterMetaType() or by calling registerType(). qRegisterMetaType vs. 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. Declare new types with Q_DECLARE_METATYPE() to make them available to QVariant and other template-based functions. QList<T> isn't really a pre-defined variant type (except QList<QVariant>) so it technically resolves to a QMetaType::UserType. ) I got the hint "expected a declaration" when I tried to use qRegisterMetaType from the global scope in my cpp file. Adding a Q_DECLARE_METATYPE() makes the type known to all template based functions, including QVariant. Then the TYPE ID is saved in local static vairable metatype_id. Any class or struct that has a public default constructor, a public copy. 4. First of all you need to declare your custom object for Qt metatype system. @SGaist Yes, I am using it with QVariant, mostly with QSettings to save and retrieve data easily by overriding QDataStream operators. Accessing an enum stored in a QVariant. Q_DECLARE_METATYPE(MyObject*) somewhere in your code. You may have to register before you can post: click the register link above to proceed. Yes, templated types can be used in Qt signal/slots. qRegisterMetaType () is called to register the TYPE and generate a TYPE ID. 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. 1. ) I got the hint "expected a declaration" when I tried to use qRegisterMetaType from the global scope in my cpp file. 步骤： (以自定义MyDataType类型为例）. This function returns the Qt meta type id for the type (the same value that is returned from qRegisterMetaType()). 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. e. You may have to register before you can post: click the register link above to proceed. 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 () <<. Any class or struct that has a public default constructor, a public copy. {. QMetaType::type () is a bit slower, but compilation succeeds if a type is not registered. Adding a Q_DECLARE_METATYPE () makes the type known to all template based functions, including QVariant. g. 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。. qRegisterMetaType<cv::Mat>(); Modified: qRegisterMetaType< Mat >("Mat");The code generated by repc creates a Q_GADGET class for each POD, with corresponding Q_PROPERTY members for each type defined for the POD. So using qRegisterMetaType () you will just trade Q_ENUM () for Q_DECLARE_METATYPE (). Any class or struct that has a public default constructor, a public copy. Declare new types with Q_DECLARE_METATYPE() to make them available to QVariant and other template-based functions. call qRegisterMetaType() to register the data type before you establish the connection. 23k 10 10 gold. Our first stop for registrations always is the macro Q_DECLARE_METATYPE. If I get AnotherQGadgetClass via getter and change it's properties, the setters are called and. 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.