默认会发送给主线程即默认的连接Qt::AutoConnection ，如果是多线程的话就是Qt::QueuedConnection了，所以要明确指定。. QtGui. ) QObject::connect: Cannot queue arguments of type 'QTextCursor' (Make sure 'QTextCursor' is registered using qRegisterMetaType(). I'm getting this message in the application output pane in Qt Creator running Qt 5. The syntax gets especially interesting when specializing a template function of a. show(); int functionIndex = win. Add a comment | 5 I believe the following is state is not defined in your MyThread class. Attention: Answers. . If I save it just at the beginning of. 2. Reproducible Example Of The. For example, this registers a Python class ‘MySliderItem’ as a QML type named ‘Slider’ for version ‘1. Convert this variant to type QMetaType::UnknownType and free up any. FollowQObject::connect: Cannot queue arguments of type 'QProcess::ProcessError' (Make sure 'QProcess::ProcessError' is registered using qRegisterMetaType(). You could wrap the used functions and classes into custom widgets or plain py-files and in your main frame class only import those custom widgets. It will look for the signature of methods using string matching. I get the following listed in the Application Output pane in QtCreator: QObject::connect: Cannot queue arguments of type 'QQmlChangeSet' (Make sure 'QQmlChangeSet' is registered using qRegisterMetaType (). In this case, PyQt will just create a new signal type for you on the fly when you emit the signal. (Make sure 'QVector<int>' is registered using qRegisterMetaType (). #pragma once #include <QObject> class MyClass : public QObject { Q_OBJECT public: static void initQML (); MyClass (); MyClass (const MyClass &myClass. When the Citizen object is moved to the new thread the QNetworkAccessmanager still has its thread affinity set to. OTOH, passing it by value in lambdas too is dangerous and can cause memory leaks. You always need to inform the compiler that you are specializing a template by placing template<> in front of it. goocreations 12 Mar 2013, 07:22. QML has a signal and handler mechanism, where the signal is the event and the signal is responded to through a signal handler. 1 Answer. QDBusArgument is the central class in the Qt D-Bus type system, providing functions to marshall and demarshall the primitive types. pro file: CONFIG += qmltypes. Debugging signals and slots connections. So using qRegisterMetaType () you will just trade Q_ENUM () for Q_DECLARE_METATYPE (). I provide a minimal working example for int reference arguments. A QItemSelection describes the items in a model that have been selected by the user. 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. 11. func2. multithreaded software and I am getting the warning says: (Make sure 'QVector<int>' is registered using qRegisterMetaType (). In this __init__ we create the QPlainTextEdit that will contain the logs. 就是说 类实列化一次，QML中可以直接使用这个类。. metaObject()->indexOfSlot("testFunc ()"); QMetaMethod mm = win. ); RealTimeHistogram: the main widget, a user interface; DataGeneratorThread class DataGeneratorThread. g. 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++. iv. main. There are two versions of each of these: one that accepts the SIGNAL () / SLOT () syntax and one that accepts the (recommended) function pointers. The difference between Qt::QueuedConnection and Qt::AutoConnection is due to a difference in the. Hello, Can someone tell me about how to register a metatype in pyqt5. QObject::connect: Cannot queue arguments of type 'QVector<int>' (Make sure 'QVector<int>' is registered using qRegisterMetaType(). The physical memory sizes returned include the memory from all nodes. Learn more about TeamsAh I found the problem, which was a logic problem. 它的作用是将自定义的数据类型转换为Qt元对象系统中的类型，使得这些类型可以在不同线程之间进行信号槽的传递。. 二者的联系： QMetaTypeId<TYPE>的类中的成员包含对qRegisterMetaType的调用. [override virtual noexcept] QQmlEngine:: ~QQmlEngine Destroys the QQmlEngine. flush ( self) This function writes as much as possible from the internal write buffer to the socket, without blocking. Maybe qRegisterMetaType is what you missed. ) I got the hint "expected a declaration" when I tried to use qRegisterMetaType from the global scope in my cpp file. It provides a safer and easier way to manage dynamic memory allocation and deallocation by automatically managing the reference counting of a shared object. f. Oct 17, 2020 at 11:47. ) 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. karensantana. connect(self. The Windows registry and INI files use case-insensitive keys, whereas the CFPreferences API on macOS and iOS uses case. ", which suggests it is only for classes and structs. Sep 21, 2015 at 14:17. 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. e. Returns true if the write succeeded; otherwise returns false. The SplitBehavior type is a typedef for QFlags <SplitBehaviorFlags>. ui. @reddy9pp said in QObject::connect: Cannot queue arguments of type 'std::string' (Make sure 'std::string' is registered using qRegisterMetaType(). Handler. program exits if. A connection defines an interface for sending/receiving data independent of the protocol. karensantana. I created a. See also qRegisterMetaType(). Detailed Description#. It associates a type name to a type so that it can be created and destructed dynamically at run-time. ). @SGaist if you see the original question I posted the contents of the devicepresence. Hello, Can someone tell me about how to register a metatype in pyqt5. I realize that this actually works when more than one signal of different types is sent, e. Here how connect looks in main constructor: connect (w1, SIGNAL (sentInt (int)), this, SLOT (receiveInt (int))); Such simple app works, but if i change parameters from int to "signed long long" it will give message during runtime and signal won't be emitted: QObject::connect: Cannot queue arguments of type 'signed long long'. I don't really know what I have to do in addition. (Parent is QTcpSocket (0x24a6ce8), parent's thread is ServiceSlots. adam-iris added a commit that referenced this issue Oct 10, 2017. 这两个东西真难理清，不妨看看源码吧。. Re: How to use Q_DECLARE_METATYPE. 12. (Make sure 'MyStruct' is registered using qRegisterMetaType (). Data Type Conversion Between QML and C++. close file : AnaEx01. 如果要使用单个全局类来访问QML或从QML访问. One or many threads can block waiting for a QWaitCondition to set a condition with wakeOne() or wakeAll(). qRegisterMetaType 将某类型注册中 MetaType 系统中. Nov 30, 2012 at 8:31. But with the shared_ptr object, not a pointer to the shared pointer! You will have to register std::shared_ptr<yourclass> with the Qt meta object system before this can work, i. MEMORYSTATUSEX reflects the state of memory at the time of the call. 3. queued connections. This fully updated, classroom-tested book teaches C++ “The Qt Way,” emphasizing design patterns and efficient reuse. Any QQmlContext's created on this engine will be invalidated, but not destroyed (unless they are parented to the. As the docs state: Declare new types with Q_DECLARE_METATYPE () to make them available to QVariant and other template-based functions. This function was introduced in Qt 6. 3. Share. I'm running the livox horizon lidar on one PC and running the loam on a different PC. You can use the tags to annotate your methods. void QVariant:: clear (). 13. [override virtual noexcept] QQmlEngine:: ~QQmlEngine Destroys the QQmlEngine. Your uint8_t is atomic and you don't need to register it, just use. If _message is a string then the slot must have the argument: foo_text = "Foo" self. The related type must provide a public default constructor, a public copy constructor and a public destructor to be eligible to be declared as a metatype. 2 Answers Sorted by: 3 You do not need to call qRegisterMetaType () to use a type with QVariant. 1. See also insertColumns (), insertRow (), and removeColumn (). Someone may be able to correct me here, but I don't think you should be needing to register the type int&. QTextCursor contains information about both the cursor's position within a QTextDocument and any selection that it has made. ) ^C[rviz-2] killing on exit [laserMapping-1] killing on exit Hello guys, i have the following message when i run the launch file. Any ideas? Nope, registering with qRegisterMetaType<std::vector<int>>() has same effect as not registering at all (using QVector<int> works without registration, but does not expose length, either). • Posting events with QApplication::postEvent(), or using queued signal/slot connections, are both safe mechanisms for communicating across threads but require the receiving thread. QObject::connect: Cannot queue arguments of type 'ProcessHandle*const' (Make sure 'ProcessHandle*const' is registered using qRegisterMetaType(). But Q_OBJECT macro handles this automatically. Without this binding click will result in no action. However, you shouldn't rely on Qt::QueuedConnection without registering the arguments types using qRegisterMetaType. can include digits and underscore). All the resources I found online point to a C++ syntax/documentation. I searched the Doc but I could not find a documentation to. Section and Key Syntax. ) It plans for a new trajectory just Okay, but when I try to execute the planned trajectory it gives me the following errors:your struct or simple class must have Q_GADGET as minimum; you should declare properties in order to access from qml; you must declare your struct/class by Q_DECLARE_METATYPE(); you must register it using qRegisterMetaType<>() somewhere before loading qml file by engine such as main. rep file extension, short for Replica. After about 20 seconds of running LOAM, the laserOdometry module crashes with [laserOdometry-2] process has died [pid 6983, exit code -11, cmd /home/ab. qRe gisterMetaType 的函数原型为： ```c++ template < type name T> int. I also have to implement for cv::Mat type data. 16. Teams. new children are appended at. Improve this answer. You can use the tags to annotate your methods. ;. Currently, on Linux and Android it is used for specifying connection to a server listening to a socket bound to an abstract address. ) I register my class like this after it's declaration: Q_DECLARE_METATYPE(taservices::ProcessHandle*); I also added this static method which I call from constructor: QObject::connect: Cannot queue arguments of type 'QProcess::ProcessError' (Make sure 'QProcess::ProcessError' is registered using qRegisterMetaType(). 10, enumerations are directly supported in QML. See also disconnect(), sender(), qRegisterMetaType(), Q_DECLARE_METATYPE(), and Differences between String-Based and Functor-Based Connections. The following code: self. Notice that with this approach you will only be able to check the value of the passed. Compares the objects at lhs and rhsfor ordering. It is. 则QML中可直接使用 MainController。. template<class T> QMetaObject::Connection connect_from_pointer ( const QSharedPointer<T>& sender,. (Make sure 'QVector<int>' is. ) From what I've read, this should totally work. PySide2. Make sure 'QTextCursor' is registered using qRegisterMetaType(). I guess it's the qRegisterMetaType () call itself that's missing. 错误原因. I have gave you below the basic process for a deletion for example. {. 子线程中：QMap<QString, QString> testMap; emit testSignal(testMap);Call qRegisterMetaType() to make type available to non-template based functions, such as the queued signal and slot connections. ) I read on some forum, that this may be caused by calling qt-functions from another Thread, and that using signals & slots instead of plain function calling may fix the issue, but i have tried signals aswell, and i. 2、使用 qRegisterMetaType，将对象注册为元类型 使用qRegisterMetaType对自. 4. Only users with topic management privileges can see it. 2] enum QLocalSocket:: SocketOption flags QLocalSocket:: SocketOptions This enum describes the possible options that can be used to connect to a server. That always worked in Qt4, but in Qt5 I get the following error: @error: specializing member ‘::qRegisterMetaType’ requires ‘template<>’ syntax@ qRegisterMetaType("Subclass") also doesn't workI am using ubuntu 16. I'm using Qt 5. clicked. qRegisterMetaType<QAbstractSocket::SocketState>(); Share. The object it returns should also be a member of the factory class. (Make sure 'QVector<int>' is registered using qRegisterMetaType(). As soon as the first event arrives I got the errormessage: @QObject::connect: Cannot queue arguments of type 'QQuickChangeSet'. To register VideoMeta you need to call qRegisterMetaType<VideoMeta>(). 31. The QML engine provides built-in support for a large number. launch" and then "roslaunch velo2cam_calibration laser_pattern. Call qRegisterMetaType() to make types available to non-template based functions, such as the queued signal and slot connections. I'm writing python library for very simple text output to Qt's QTextBrowser window (stored in window. rows += self. This function requires that T is a fully defined type at the point where the function is called. Normally, you would only register the pointer form if your class cannot be copied, as in the case of QObject and derivatives, but. The QItemSelection class is one of the Model/View Classes and is part of Qt's model/view framework. QtCore. This property holds the state (high or low) of the line signal DTR. #include <QObject> #include <QVariant> class Record : public QPair<qreal, qreal> {. ; Create a native socket descriptor, instantiate QAbstractSocket, and call setSocketDescriptor() to wrap the native socket. My Thread is as. )Note: If the setting is set before opening the port, the actual serial port setting is done automatically in the QSerialPort::open () method right after that the opening of the port succeeds. 2 Answers. And this should be used for each exe/dll instance. This maybe is not the nicest solution, but it works just fine: Add a property to the wizardpage which contains the QListView and let it return the pointer to the selectionmodel. Note: If you want to use your custom metatypes also in queued slot connections or with QMetaMethod, you have to call qRegisterMetaType<QPushButton*>() Share. For pointer types, it also requires that the pointed to type is fully defined. Use Q_DECLARE_METATYPE (std::string) in one of your headers. By implementing a factory it is possible to create custom QNetworkAccessManager with specialized caching, proxy and cookie support. Kind Regards, Sy. show(); int functionIndex = win. ) QObject::connect: Cannot queue arguments of type 'QVector<int>'. ) The text was updated successfully, but these errors were encountered: QObject::connect: Cannot queue arguments of type 'object' (Make sure 'object is registered using qRegisterMetaType(). QObject::connect: Cannot queue arguments of type 'my_enum' (Make sure 'my_enum' is registered using qRegisterMetaType(). QObject::connect: Cannot queue arguments of type 'QVector<int>' (Make sure 'QVector<int>' is registered using qRegisterMetaType(). ) So it seems to be a multi-threading issue caused by this instruction connect (process,&QProcess::started, [this. 4 and it seems to work. A QVariant containing a pointer to a type derived from QObject will also return true for this function if a qobject_cast to the template type T would succeed. QtWidgets import * Er. call qRegisterMetaType() to register the data type before you establish the connection. 使用此连接类型在同一线程中的对象之间进行. Returns true if the column is inserted; otherwise returns false. I have a class that is a subclass of QObject that I would like to register as a meta-type. Share. Returns QPartialOrdering::Unordered if comparison is not supported or the values are unordered. Variant 3: use MACRO instead of std::invoke in variant 2. qRegisterMetaType() since the names are resolved at runtime. That always worked in Qt4, but in Qt5 I get the following error: @error: specializing member ‘::qRegisterMetaType<Subclass>’ requires ‘template<>’ syntax@. The habit of passing shared_ptr by ref should not be followed in lambdas. Before emitting a signal across a thread boundary with a non-trivial argument type (like QModelIndex ), you must first call this: qRegisterMetaType<QModelIndex> ("QModelIndex"); That prepares Qt to be able to emit the signal across a thread boundary. The following example records all signal emissions for the clicked () signal of a QCheckBox:Step 1 (mark for MOC), build some QObjects That pattern uses Q_PROPERTY and Q_OBJECT and the MoC tool. The. However, you should verify its validity after construction. QtGui import * from PyQt5. QPushButton(self. ) このような場合は以下の通り qRegisterMetaType() の引数を設定することで回避できることがある。You can safely remove the const, even if the real signature of SendData and ReceiveData is const u_char*. The stretch factor changes the width of all characters in the font by factor percent. QVariants are important in QML because they used to store the arguments from signals and slots, and also get values from the QMetaProperty system. 5 and Qt Version 5. Detailed Description. 1. ) 1 stopped. qRegisterMetaType<QSqlDatabase>("QSqlDatabase"); Just changing the signal to this form: void dbConnected(QSqlDatabase *db); And, in the slot side I'll use something like this: void onDBConnected(QSqlDatabase * const db); I'm concerned with the usage of db (as in the beginning I've made the reference const), so I make it const here. 9k 13 13 gold badges 106 106 silver badges 138 138 bronze badges. QObject::connect: Cannot queue arguments of type 'uint32_t' (Make sure 'uint32_t' is registered using qRegisterMetaType(). main. ) but I do not think that relates with the phenomena. The following code allocates and destructs an instance of MyClass: The Q_DECLARE_METATYPE() macro and qRegisterMetaType() function documentation contain more detailed information about their uses and limitations. If a field is empty, don't include it in the result. There's no compile time error, but when I run. QObject::connect: Cannot queue arguments of type 'QVector<int>' (Make sure 'QVector<int>' is registered using qRegisterMetaType(). (Make sure 'QVector<int>' is. Use wakeOne() to wake one randomly selected thread or wakeAll() to wake them all. qRegisterMetaType<FileNodePointer> ("FileNodePointer"); should be called once (in main, constructor etc. 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. ) I read on some forum, that this may be caused by calling qt-functions from another Thread, and that using signals & slots instead of plain function calling may fix the issue, but i have tried signals aswell, and i. Object::connect: No such slot main_application::input_handler(button_back) Of course, there is, because signature is main_application::input_handler(button_type), and button_back is a value, not type. 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。. Even if it works now, it may fail with new Qt versions. しかし、Qtを使っている場合は、わざわざ自分でMutexの管理をしなくても、スレッドとのデータのやり取りを全て signal/slotでやってしまい、共有データを. I am trying to learn Qt and I am attempting to do so by making a little titres game. Use Q_DECLARE_METATYPE (std::string) in one of your headers. How to properly use qRegisterMetaType on a class derived from QObject? I couldn't understand from the answer to where I have to define the specialization of qMetaTypeConstructHelper. This is the same as indexOfMethod (), except that it will return -1 if the method exists but isn't a signal. Any class or struct that has a public default constructor, a public copy constructor, and a public destructor can be registered. Instead, the enum should be registered as soon as the shared library is loaded. 8 data bits. The following code allocates and destructs an instance of MyClass:使用Q_DECLARE_METATYPE()可以让这个数据类型T放到QVariant里面。如果想以队列的方式让T使用信号与槽，当第一次连接的时候就要调用qRegisterMetaType<T>()。 QObject::property()要和类型T一起使用，这个时候qRegisterMetaType<T>()要提前调用。This enum specifies how the split () functions should behave with respect to empty strings. A. The file (called a "rep" file) uses a specific (text) syntax to describe the API. An "ugly solution" would be to hack the fairly simple QSignalSpy code in order to handle the reference passed arguments. 2. Even though qRegisterMetaType(). It is part of QMetaType, which is not implemented by PySide. self. Following this logic, the following code may not work: connect (senderObject. The application may need to relay this clicking event to other applications. 0. Q_DECLARE_METATYPE is only needed for template-based functions. If I register QVector I can't dissconnect this signal and the signal is emited. Here's the twist: this class is contained in a shared library, and therefore I want to avoid instructing anyone using my library to call qRegisterMetaType. 048771190]: Out drawPath [ INFO] [1432901455. But the problem comes up when I try to send it to C++ slot, that have my enum as parameter. The errors you are getting are making it clear that it wouldn't work with const anyway you twist it, because that's not how the API is designed, because while you can pass non-const objects to const functions, you cannot do the opposite for reasons that should be obvious. QSignalSpy itself is a list of QVariant lists. h file. These are syntactically atrocious, but that’s templates for you. This function was introduced in Qt 5. If you are using a version of PySide that somehow exposes qRegisterMetaType, it's a bug. All. Returns a list of child objects. Note: it's also safe to call qRegisterMetaType () multiple times. connect(self. The following example illustrates how a structure containing an integer and a string. ) QObject::connect: Cannot queue arguments of type 'QModelIndex' (Make sure 'QModelIndex' is registed using qRegisterMetaType(). QT 信号和槽传递自定义对象问题. Note: This function is thread-safe. e. Any class or struct that has a public default. 12. hskoglund last edited by . Put a <code>static MetaTypeRegistration<YourType> registration;</code> in the <code>. 0 BY-SA 版权协议，转载请附上原文出处链接和本声. QtCore import QObject works. import executer class Window(QtWidegets. Share. qRegisterMetaType 将某类型注册中 MetaType 系统中. Detailed Description. I read on documentation that Q_DECLARE_METATYPE makes available type to QVariant, for example (I got it from documentation): @ struct MyStruct { int i;. You can connect a signal to a slot with connect (). QObject::connect: Cannot queue arguments of type 'QVector<QVector<int> >'. Call qRegisterMetaType() to make types available to non-template based functions, such as the queued signal and slot connections. @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 connect () call returns true, but when the signal is emitted, Qt outputs this: QObject::connect: Cannot queue arguments of type 'uint64'. 12. 052592317]: Writing. new children are appended at. cpp; so you will have. a copy of a cv::Mat object will point to the same data as the copied from item). Q_DECLARE_METATYPE (QSqlRecord) has to be outside any classes and namespaces. If you need a socket, you have two options: Instantiate QTcpSocket or QUdpSocket. QtのAPIのドキュメントに、thread-safeと書いてない限りは、QMutex等を使って自分で排他をする必要がある。. As explained in this thread you can try using a typedef, including the QMetaType header and then using both Q_DECLARE_METATYPE macro and the qRegisterMetaType function (as implied by this thread on a similar issue). iii. bool QMetaProperty:: writeOnGadget ( void * gadget, const QVariant & value) const. open(wsUrl); without threading the connection works fine. When a signal is emitted, the corresponding signal handler is invoked. 原因：当_qregistermetatype qRegisterMetaType的使用-程序员宅基地 - 程序员宅基地 程序员宅基地 程序员宅基地，技术文章由你所想念有所思See also QLocalSocket::state(). QObject: Cannot create children for a parent that is in a different thread. Otherwise you might be adding duplicate entries to the metatype database each time. launch" i got. ) Nothing special is printed to the execution log. QVariant’s operator== now uses QMetaType::equals for the comparison. すべてのソケットで読み書きができるようになりました。しかし、これらすべてのインスタンスをオーケストレーションするためのサーバがまだ必要です。4. ;. The operating system can enlarge the paging file up to the maximum size set by the administrator. 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. Variant 2: use std::invoke inside a lambda, which is passed to QMetaObject::invoke. But the thing is, I have. Any class or struct that has a public constructor, a public copy constructor, and a public destructor can be registered. Your code should look like this: Q_ENUM (StateEnum) //note the missing 'S' here Q_PROPERTY (StateEnum state READ state NOTIFY stateChanged) Share. Although you can just create QBluetoothDeviceInfo objects on your own and fill them with data, the easier way is to use the QBluetoothDeviceDiscoveryAgent to start an automated search for visible Bluetooth devices within the connectable range. If a field is empty, keep it in the result. You are looking for the Q_ENUM () macro. It works only in this case int qmlTypeId = qRegisterMetaType<namespace::MenuModel*> ("MenuModel*"); You return a pointer in the property, so Qt Meta Object system needs to know about it. If such a connection is made, and a signal triggered, the runtime warning will be shown: QObject::connect: Cannot queue arguments of type 'T' (Make sure 'T' is registered using qRegisterMetaType (). ) Bug is reproducable only if a queued connection is used (when objects are in different threads or explicit Qt::QueuedConnection is used) and MyType is declared inside a namespace. By convention, these files are given a . The QObjectList class is defined in the <QObject> header file as the following: typedefQList<QObject*>QObjectList; The first child added is the first object in the list and the last child added is the last object in the list, i. This event handler can be reimplemented in a subclass to receive child events. (Make sure 'QTextCursor' is registered using qRegisterMetaType(). If you need a socket, you have two options: Instantiate QTcpSocket or QUdpSocket. 9 under OSX 10. Please visit robotics. Follow. You can call this function in a subclass of QAbstractSocket to change the return value of the localPort () function after a connection has been established. Just installing it did not work for me. This function was introduced in Qt 5. It associates a type name to a type so that it can be created and destructed dynamically at run-time. ", which suggests it is only for classes and structs. ) So it seems to be a multi-threading issue caused by this instruction connect (process,&QProcess::started, [this. ) QObject: Cannot create children for a parent that is in a different thread. Solution 1: somewhere. Connect and share knowledge within a single location that is structured and easy to search. Placing logic such as a script or other operations in the handler. If it gets destroyed elsewhere (passing by ref doesn't bump the ref count), your callback/lambda may crash. QMetaType:: Q_DECLARE_OPAQUE_POINTER (PointerType) This macro enables pointers to forward-declared types (PointerType) to be registered with QMetaType using either Q_DECLARE_METATYPE() or qRegisterMetaType(). You have to register your custom type for queued signals because by registering it, Qt can make a copy of it in its event loop (which certainly uses QVariant) and pass it as argument later (when the original passed value is long since out. 3. The actual values () are either single bit or. Any class or struct that has a. class QtGuiApplication : public QWidget { Q_OBJECT public: explicit QtGuiApplication (QWidget *parent = 0. ) It still works but point to the fact that I am doing something wrong, and I am not sure that I will keep working when more threads are active. This class can tell the outside world that its state has changed by emitting a signal, valueChanged(), and it has a slot which other objects can send signals to. The following code allocates and destructs an instance of MyClass: 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. Follow answered Sep 16, 2014 at 4:21. From Qt documentation: Ideally, this macro should be placed below the declaration of the class or struct. Each emission of the signal will append one item to the list, containing the arguments of the signal. A single QMetaObject instance is created for each QObject subclass that is used in an application, and this instance stores all the meta-information for the QObject subclass. What worries me is that. M. QObject is the heart of the Qt Object Model . It provides functions for creating and manipulating selections, and selecting a range of items from a model. Detailed Description. ) 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.