Qvariant custom type. If you have a problem, CUT and PASTE your code.

Qvariant custom type In other words, QVariant::fromValue() doesn't know what to do with your cclass type and simply create a null QVariant, which is then serialized accordingly in the QJsonDocument. Hot Network Questions QVariant variantList = QVariant::fromValue(defaultList); // here list will contain N SomeClass instances, everything’s fine: SomeClassList list = variantList. Please read the doc carefully to understand how it works. For QPair though it's quite straightforward: #include <QPair> #include <QDebug> typedef QPair<int,int> MyType; // typedef for your type Q_DECLARE_METATYPE(MyType); // makes Hello, I am trying to add a custom class object to my QVariantList but I get an error: error: 'QVariant::QVariant(void*)' is private e. proto file using the protoc compiler and added them to my project in QtCreator. h. canConvert<int>(); // returns true v. By sudheer168 in forum Qt Programming Using canConvert() and convert() Consecutively. For instance: QColor colr; QVariant colorv = QVariant::fromValue(colr); qDebug() << colorv; generates such output: QVariant(QColor, QColor(Invalid)) My type generates such: I receive data in JSON using a QJsonObject. I'm writing a lexical scanner that generates a stream of tokens from some input. QLineF. You can provide two functions for packing QVariant with custom type inside to QByteArray and vise versa. The code created for such type has to be very generic to work for different kind of data. Invalid parameter passed to C runtime function. Custom QVariant troubles. Class1 inherits QObject, Class2 inherits Class1. If this is the case, then it's way better to have a constructor (AND getter + setter) that takes the custom type directly, without having to do QVariant conversion: class MyItem : public QStandardItem { public: // NICE: Constructor for your custom type MyItem(MyData *value); // NICE: Getter and setter for your custom type. The class is used as a helper to marshall types in QVariant and in queued signals and slots connections. Q_DECLARE_METATYPE (Type) This macro makes the type Type known to QMetaType as long as it provides a public default constructor, a public copy constructor and a public destructor. For pointer types, it also requires that QVariant doesn’t have the fromPyObject function by the looks of it - so either its been deprecated/superseded or maybe in the thread was a custom method created for the purpose: doc. QList<T> isn't really a pre-defined variant type (except QList<QVariant>) so it technically resolves to a QMetaType::UserType. So if QSettings can recreate the QVariant without relying upon QVariant::UserType(), God knows how, then it should in principle, be sent over to other machine too. How do I sort a QList of QDateTime*? 3. This now makes it possible for Message values to be stored in QVariant objects and retrieved later. The QVariant::type() is always the same. h: I have my ModelObject derived from QObject, some custom types subclasses of ModelObject, some of them have properties as pointers to other custom classes. For QPair though it's quite straightforward: #include <QPair> #include <QDebug> typedef QPair<int,int> MyType; // typedef for your type Q_DECLARE_METATYPE(MyType); // makes Template:ArticleMetaData. I don't even get the value from that QVariant anywhere in the code, and still have the crash. When I try to work with them as QVariant (using properties) them unexpectedly crashes. However, for source compatibility reasons the return type could not be changed. . Qt provides a range of standard value types that are used to provide rich and meaningful APIs. So I tried to convert to QObject* both with QVariant::value<QObject*> and qvariant_cast but it seems to hold a void pointer: My attempt: Somehow, for Qt types like QSize and QColor streaming the QVariant into QDebug works just fine. zshrc be modified automatically? Polynomial. In QML im getting @QVariant(CustomTypeList*)@ by MyMapObject["KEY"]. Ask Question Asked 7 years, 10 months ago. Chaining the necessary conversions, we end up with: qDebug() << myVar. 2 How to cast QVariant to custom class? 2 convert function return from ‘std::vector<QString>’ to ‘QVariant’ 1 qvariant_cast with custom type Template:ArticleMetaData. 2. So all you need to do is use None wherever QVariant. Convert custom type to QVariant. A custom type represented by a structure, like QDateTime, QPoint, etc. So, the signal definition inside the qml description of Setting has to be replaced with var. You can check on runtime if it can be converted to one type you need. Now I want to verify that I can send the custom class as a QVariant through the dbus API. To make the custom type I have implemented a custom QVariant type by registering the class with Q_DECLARE_METATYPE(Vector) and defining the stream operators. What I want is to attach an actual object to each node represented using QStandardItem. Xander84. From the Qt docs, Note: If you are working with custom types, you should use the Q_DECLARE_METATYPE() macro to register your custom type. Assume that your T typename is included in QVariant union types (otherwise you cannot). But I can't debug the problem because under debugger everything is 100% working! ModelObject: @ Re: Casting a custom class to QVariant. But i want to return a custom type std::vector<QString> Came to know about Q_DECLARE_METATYPE(); It makes new types available to QVariant. For example here is how QColor packer and unpacker looks like: 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. Because Foo is not derived from QObject and QVariant only supports polymorphism for QObject-derived types. But I can't debug the problem because under debugger everything is 100% working! ModelObject: @ In order to use it with custom types registered QVariant::setValue has to be used instead. Use delegate to draw different type of items. In fact, I would go even further and convert your data into table form, rather than squeeze it all into a single cell as a BLOB. Given QVariant, get reference to variable with some type. Recover user-defined type stored in QVariant. Is it worth raising as a bug/suggestion? I can imagine a lot of people running into this. These types are integrated with the meta-object system, enabling them to be stored in See Creating Custom Qt Types for details. [quote author="genC" date="1311851619"]Oh, one last thing: why can't the QVariant of type QObject* be converted to a Class1* (using QVariant::convert(Type t))?[/quote]Because QVariant::type() returns 2 different type ids for Class1* and QObject*, and you can see in the source code of QVariant::canConvert(Type) that if the two type ids are different the functions I am having a custom type which I use with QVariant. Return custom user type from QAbstractItemModel. The order of items in QTreeWidget. first(). This QVariant can hold a wide range of standard C++ and Qt types, including integers, floating-point numbers, strings, dates, times, and custom types registered with the Qt Meta-Object System That looks like an unusual use of QVariant. QList in QVariant, QVariant::type() returns weird type. For pointer types, it also requires that I'm trying to save multiple models automatically, and I would like to avoid checking in foreachs the QVariant types, if it's a custom type then call toByteArray() on it. and since you declared what type you will pass, qt accept it (because when i was just apssing void * or other pointer Of course you can use QVariant::canConvert() with your custom data types. you can consider this class as my custom type (T). I would like to find out what needs to be done for custom types in order for QVariant to actually call the custom stream handler. The QVariant class acts like a union for the most common Qt data types. From the QVariant::value documentation: If the QVariant contains a pointer to a type derived from QObject then T may be any QObject type. Community Bot. For pointer types, it also requires that the Standard types such as QSize, QColor and QString can all be stored in QVariant objects, used as the types of properties in QObject -based classes, and emitted in signal-slot communication. 27. By nifei in forum Qt Programming And here it is. By nifei in forum Qt Programming Eidt: misread your post. How to sort QList<MyClass*> using Qt library (maybe qSort())? 3. To do this, you can register an interpolator function for a given type. 1 1 1 silver badge. Sorting a column alphabetically in QStandardItemModel: QSortFilterProxyModel. ASSERT failure in QVariant::save: "Invalid type to save", file kernel\qvariant. – Standard types such as QSize, QColor and QString can all be stored in QVariant objects, used as the types of properties in QObject-based classes, and emitted in signal-slot communication. Sort QStandardItemModel in c++ Qt. It associates a type name to a type so that it can be created and destructed dynamically at run-time. I know does exists QVariant::value<XXX>() but since i don't know a-priori what XXX is I cannot do that. Viewed 646 times The header of the custom meta type: class QSong : public QObject { private: Q_OBJECT Q_PROPERTY( QString artist READ artist CONSTANT ) Q_PROPERTY( QString album READ album Variable return type with QVariant and templates. In In Qt/QML, it is possible to define custom types from C++ and use them in QML by using: qmlRegisterType<CustomType>("ImportName",1,0,"TypeName"); Qt also has support I'm trying to provide a way to convert a custom (QObject derived) class to a QVariant using a custom method. QStringListModel sorting. Here is my custom Money class: class Money { public: Money(double value = 0. h: Given that Qvariant has constructors from int and bool, these constructors will be used to perform the implicit conversion. Just added simple code snipped in MouseArray onClicked function: Standard types such as QSize, QColor and QString can all be stored in QVariant objects, used as the types of properties in QObject-based classes, and emitted in signal-slot communication. Improve this answer. It is possible, but at a price - and QVariant doesn't do it. One solution could be to extend QString to create a custom type. 1 class MyClass : public QObject { Q_OBJECT } Q_DECLARE_METATYPE(MyClass) class MyClass2 : public QObject { Q_OBJECT } Q_DECLARE_METATYPE(MyClass2) 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. 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. 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(). 2 How to cast QVariant to custom class? 2 convert function return from ‘std::vector<QString>’ to ‘QVariant’ 1 qvariant_cast with custom type Qt QMetaType serialization of custom types and QVariant. Long story, I'm new to Qt/C++ so I'm trying to do everything very carefully, but I'm almost sure it's some rookie mistake in my code. Instead, just create a QHash<QString, QVariant> or QMap<QString, QVariant> for storing the properties Inside the QVariant I can store custom class declared and registered in meta-system. java - a Java class for dealing with polynomials with BigDecimal coefficients Can this strong directional blur at wide apertures still be explained by the usual arguments? A roulette wheel? An AC Milan kit? Qt also has support for the QVariant type which acts as an union for common datatypes. Instead, I would try deriving from QListWidgetItem in order to add custom data, something like this:. It's not done because it is hard to do it in a sufficiently general way, but if you had a few types in mind - you certainly Short story is: I'm trying to put custom type into QVariant and it doesn't work, on debug I see QVariant with value <not accessible> and trying to read it I'm getting segfault. qRegisterMetaType usage. You have to use the special macro Q_DECLARE_METATYPE() to make custom types available to QVariant system. Polymorphism with QVariant. 3. int value = 1; QString s = QVariant(value). QVariant types support for custom properties Below is a list of currently supported QVariant types: Int. QObject has neither a copy constructor nor an assignment operator. Since custom types are involved, you will need to specify some extra includes, so the Adaptor and Interface classes can find all the type information. Here's the documentation for qRegisterMetaTypeStreamOperators(). The main purpose of this would be outputting data about the QVariant custom type. QLine. speed of setdata - lots of items in treeview. If the pointer stored in the QVariant can be qobject_cast to T, then that result is returned. " I created a Qt provides a range of standard value types that are used to provide rich and meaningful APIs. It is I am having a custom type which I use with QVariant. , here is the code I use: items. Returns the storage type of the value stored in the variant. By Big Duck in forum Qt Programming Replies: 4 Last Post: 6th July 2006, 13:53. Is there any way to use a user-defined operator< for a struct to sort QVariants of that struct in a QSortFilterProxyModel? 9. Related questions. This works pretty well for token data that is of a non-custom type. The only caveat is you must register the type with the type system. Why does QVariant::type() return a QVariant::Type when it should be interpreted as a QMetaType::Type? 2. For instance: QColor colr; QVariant colorv = QVariant::fromValue(colr); qDebug() << colorv; generates such output: QVariant(QColor, QColor(Invalid)) My type generates such: Q_DECLARE_METATYPE(driver_status_receipt_data_type); // Q_DECLARE_METATYPE(driver_id_receipt_data_type); To copy to clipboard, switch view to plain text mode The following user says thank you to shentian for this useful post: I am having a custom type which I use with QVariant. Unless my understanding of terminology is wrong, that shouldn't be a problem (and was not up to this point). QVariant and std::size_t. ini file with an invalid QVariant type while debugging the output QVariant::load: unknown user type with name CustomDataType, is this behavior normal? J I have implemented a custom QVariant type by registering the class with Q_DECLARE_METATYPE(Vector) and defining the stream operators. And I think you can write a custom type in QSettings. There are two related approaches: QVariant could dispatch all operators to the type-specific ones at runtime, e. How to sort QList<MyClass*> using Qt library (maybe qSort())? 5. How to support comparisons for QVariant objects containing a custom type? 17. typedef QVariantMap. The type may not even be a class, no methods of the type are exposed to QVariant. 00) { _val = value; } ~Money() { } These types are integrated with the meta-object system, enabling them to be stored in QVariant objects, written out in debugging information and sent between components in signal-slot communication. As to your question: you can just use Q_DECLARE_METATYPE and you You have to use the special macro Q_DECLARE_METATYPE() to make custom types available to QVariant system. Hello, as the Qt docs state QVariant does not call the "operator==" when you compare two variants with custom types. I'm using a custom data type in the items of a QStandardItemModel, but setting item data for different roles seems to affect the data of all roles, and setting the text for the items seems to overwrite the data as well. Not only better type-checking, they expose properties and invokable methods while packing the type to QVariant implies your C++ function supposed to first recognize the type and cast the variant value to it. Note that this only works for QObject subclasses which use the Q_OBJECT macro. The datatypes used in the object typically are one of the following but not limited to Convert custom type to QVariant. qvariant_cast with custom type. qRegisterMetaType is also called in the class constructor. g. Because QVariant is part of the Qt Core module, it cannot provide conversion functions to data types defined in Qt GUI, such as QColor, QImage, It is needed to use the type Type as a custom type in QVariant. See the list of supported types in the documentation. QPoint. I can set items within a list, check to see if canConvert, but when I try to actually make an item of type Foo things fail at compile time. It is ok but i have to reach an invokable method (insert Method) in order to manupulate this model object. At least if you expose it to QML or use in any kind of subclasses from QAbstractListModel( all values there returned by data function and return type is QVariant). I don't want to use QVariantList or any list creating a QVariant, as I'd like to preserve the custom objects structure and also allow using the signals from it (CItem). wrote on last edited by #4. Sorting algorithm with Qt/C++ - sort a QList of struct. toString(); Share. 1. This function is equivalent to QVariant::canConvert(value). I could not figure out how to do the opposite operation: extract a value to a pointer without knowing the actual definition of the type. QVariantList append. When I take out the ->setData line it works without problem. UInt. I would expect something like Only if you use custom classes it won't work. QVariant Class The QVariant class acts like a union for the most common Qt data types. 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. QSizeF. You need to pass yor ModelId object as Qbject*, but your method objId() returns copy of ModelId which is inherited from QObject. You can change your function to return pointer to your member and then use something like return QVariant::fromValue(qobject_cast<QObject*>(ur_ptr)); in your model. Those tokens have a type and a value. One thing I seem not be able to do though is to properly serialize it to debug output. Custom types registered using qRegisterMetaType() and qRegisterMetaTypeStreamOperators() can be stored using Sorting and displaying a custom QVariant type. So I tried to convert to QObject* both with QVariant::value<QObject*> and qvariant_cast but it seems to hold a void pointer: My attempt: Use QObject-derived types for interacting with QML when possible. Re: QVariant with Custom Type I dont see how casting is relevant since you cannot use simple casts to recover 'proper' types from a QVariant. Instead, everything is automatically converted to an equivalent python type. QSize. Start there to fix your streaming operators, i. why you don't convert every T object in QVariant, put all this converted in QList<QVariant> and finally convert it to QVariant ? Qt Note: If you are working with custom types, you should use the Q_DECLARE_METATYPE() macro to register your custom type Clearly as a user, we cannot determine the order in which it gets created. I understand since I want to use custom data, I need to make QVariant understand my class, and for this I need my class to have a default constructor, a copy constructor , a destructor, and 2 operator overlord << and >>. Synonym for QList<QVariant>. By hickscorp in forum Qt Programming Replies: 0 Last Post: 3rd May 2010, 15:23. Their streaming operators are called. io QVariant Class | Qt Core 6. qt sorting of container of Type* elements. Convert QVector<char*> list into a QStringList. From its help: From its help: QVariant v = 42; v. Generate Adaptor and Interface classes. I am having a custom type which I use with QVariant. QVariant::toString and custom data types. why you don't convert every T object in QVariant, put all this converted in QList<QVariant> and finally convert it to QVariant ? Qt Note: If you are working with custom types, you should use the Q_DECLARE_METATYPE() macro to register your custom type Overview¶. Example: class MyClass{ int item1; int item2; QString string1; AnotherClass subc Custom QVariant ¶. toString(); Variable s ends up being a null string During the startup, before the custom data type is registered using qRegisterMetaType, I call QSettings::setValue() to set a normal integer value (completely For QVariant to store a custom type, you need the type to be registered with the qt meta object system. This here describes a similar issue with no answer as of posting date: Qt QDbus Sending Custom Types with QVariant; c++; qt5; dbus; Share. I can see no-reason why QVariant cannot call custom operators. Therefore, you must use QMap as the property type instead of QMap<QString,QVariant>. Custom types registered using qRegisterMetaType() and qRegisterMetaTypeStreamOperators() can be stored using @Matthew11 said in Passing custom type pointers between threads via signals and slots cause app to crash:. If you have a problem, CUT and PASTE your code. I've created the class from the . Once they're known you can use them, but you can't create them on the QML side. I'm guessing that crash is caused by accessing the shared resource (my custom class instance). 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. I'm not even sure if QVariant would support holding a QObject or QObject* that way. This macro requires that Type is a fully defined type at the point where it is used. class CTest : public QObject Q_INVOKABLE QVector<CItemWrapper> getAllItems You're trying to register float and QString types that are already registered hence the error: static assertion failed: QMetaType::registerConverter: At least one of the types must be a custom type. Now that the XML contains all the information qdbusxml2cpp needs, it's time to generate the Adaptor and Interface classes. For pointer types, it also requires that Hi I have a custom QAbstractItemModel with drag and drop support. Problem regaridng Type casting QVariant. If you do not, you'll get a friendly reminder via a static_assert, error: static assertion failed: Type is not registered, please use the Q_DECLARE_METATYPE macro to make it known to Qt's meta-object system For custom types, the data is stored internally as a void* pointer treating the data itself as a black box. In this document, we take a custom type and describe how to integrate it into Qt’s object model so that it can be stored in the same way as standard Qt types. Converting QVariant to QVector<int> 5. Hi, I'm having problem getting custom type name from a QVariant using a QtQuick project on Qt 5. Ask Question Asked 7 years, 9 months ago. Custom types can also be integrated with the meta-object system Standard types such as QSize, QColor and QString can all be stored in QVariant objects, used as the types of properties in QObject-based classes, and emitted in signal-slot communication. QVariant custom type. 12. According to the documentation, the class must provide a default constructor, destructor and a copy constructor. By KK in forum Qt Programming Replies: 4 Last Post: 27th February 2009, 05:54. Although this function is declared as returning QVariant::Type, the return value should be interpreted as QMetaType::Type. The map has a key name of type QVariant holding a QString. Span contains the following declaration for the QMETATYPE QVariant registration in the class header file: Contents: Overview. I have found that QVariant::value<QString>() or QVariant::convert(QVariant::QString) seem to be more helpful, because they return the actual value in the QVariant. Custom types can also be integrated with the meta-object system QVariant::canConvert() is a templated method that returns true or false, whether the variant can be converted to a particular type. First there was QVariant with a type enum for supported types. According to the docs, the classes that inherit from QObject can not have a copy constructor or assignment operator:. So QVariant was changed, the types aligned, so that its own type enum could be deprecated and it would depend on QMetaType for type information. It is the model for my repeater. 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. Convert QstringList to Qstring in PyQt. I reimplemented methods like mimeData() and itemData() to serialize informations I want to drag from a view to another. It may be possible to partially specialize qvariant_cast for your type, but that's not a documented supported use case, and I'd be reluctant to rely on it. Declare new types with Q_DECLARE_METATYPE() to make them available to QVariant and other template-based functions. toMap(). 1639: 1640 \section 1 A Note on GUI Types: 1641: 1642: Because QVariant is part of the Qt Core module, it cannot provide: 1643: conversion functions to data types defined The data function has a return type of QVariant(Union). Hot Network Questions Please help to adjust the landscape-mode table How to re-orientate a mesh with messed up world co-ordinates Is my transaction in a single or multiple block candidate? Convincing the contrapositive is equivalent QVariant custom type. 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. CTest. More Header: #include <QVariant> CMake: find_package(Qt6 COMPONENTS Core REQUIRED) target_link_libraries(mytarget PRIVATE Qt6::Core) qmake: QT += core List of all members, including inherited members Obsolete members Public Functions QVariant(QVariant &&other) Qt 5. Standard types such as QSize, QColor and QString can all be stored in QVariant objects, used as the types of properties in QObject-based classes, and emitted in signal-slot communication. For instance: QColor colr; QVariant colorv = QVariant::fromValue(colr); qDebug() << colorv; generates such output: QVariant(QColor, QColor(Invalid)) My type generates such: @dissidia By custom you mean its been implemented by you (or your company)? Or are there any public resources (documentation, download) available? TypeError: PyQt4. AFAIK, JavaScript will not understand your custom type, so it cannot convert. How deserialize the output from a QVariant without Qt. 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. For instance: QColor colr; QVariant colorv = QVariant::fromValue(colr); qDebug() << colorv; generates such output: QVariant(QColor, QColor(Invalid)) My type generates such:. 4. append(¤tItem); where items is of type QVariantList and currentItem is of Type CMyClass. Now when I drag an item from a view, a Qt debug @sykac said in Comparing QVariant::Type with custom registered types: one method for passing multiple datatypes in one argument. I also have a QObject-based object holding properties, using Q_PROPERTY(), for the keys in the JSON. Vector. Since you seem to have registered everything correctly, you might be encounting a bug that sometimes happen with QML where objects seem to be stuck in a QVariant wrapping. QVariant represents a mapped type and cannot be instantiated I would suggest moving away from using QVariant in this way. QDBusArgument &QDBusArgument:: operator<< (const QString &arg) This is an overloaded function. 2 (to have standard Qt libs on linux x86_64). If you need to interpolate other variant types, including custom types, you have to implement interpolation for these yourself. It's not done because it is hard to do it in a sufficiently general way, but if you had a few types in mind - you certainly You're trying to register float and QString types that are already registered hence the error: static assertion failed: QMetaType::registerConverter: At least one of the types must be a custom type. For built-ins types in QtCore, each meta-type function is basically a switch that has special code for each type. Using canConvert() and convert() Consecutively. otherwise a String value using the returned QString. How can I convert QVariant to QString and vice versa in Qt? 3. w/out GUI module you wouldn't have any of those types available). I then want to take that QVariant and convert it to and from a QVariant of type double. Hot Network Questions Can . class ImageListItem : public QListWidgetItem { // (Not a Q_OBJECT) public: ImageListItem(const QIcon & icon, const When a QML object type is used as a signal parameter, the parameter should use var as the type, and the value should be received in C++ using the QVariant type. The implementation Q_DECLARE_METATYPE(Type) This macro makes the type Type known to QMetaType as long as it provides a public default constructor, a public copy constructor and a public destructor. One way to work around this is for example having a helper class (singleton or context property) with a (static) member function I'd like to send a custom c++ class through the Qt DBUS API. cpp, line 2124 Invalid parameter passed to C runtime function. 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. QStandardItem *child = new QStandardItem(s); child->setFlags(child->flags() & ~Qt::ItemIsEditable); child->setData(QVariant(QVariant::UserType, i), Qt::UserRole + 10); QVariant Class The QVariant class acts like a union for the most common Qt data types. Serializing QVariant through QDataStream. Add a comment | 2 Answers Sorted by: Reset to default 16 You can use QVariant You can use QVariant::toString for types listed in the method documentation. Modified 7 years, 8 months ago. value<SomeClassList>(); // But, if there’s nothing to read from "somelist", anotherList gets empty, // toString() does NOT return the value in the QVariant as a QString but rather describes the QVariant in a way that might be more suitable for debugging. Using QVariant with custom data type. It works fine with Qt 4. – Elcan. Next message: [Qt-interest] QVariant comparisons and custom types? Messages sorted by: This is really crap. It is needed to use the type Type as a custom type in QVariant. I have a receiver and sender program and can send a simple test string so Dbus works. 7. Convert a QVariant of a custom type to a QString. Howto serialize and deserialize between unknown typedef struct and QByteArray. QDataStream won’t work with custom crafted char array. So I think you need to find a way to convert your custom type to QString to be able to see it For QMap, QList, and QValueList properties, the property value is a QVariant whose value is the entire list or map. @Mozzie said in How to create a QJsonValue from custom type?: I am trying to find is there any way to serializes a custom type to json by QVariant or Qt meta object system. Commented Dec 15, 2016 at 14:27. Note that you do have to be responsible with the parameters, as there is no type safety, in fact it has implicit analog to ListModel's dynamicRoles - that is, it will accept and work with any QVariant compatible value on every role slot. 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. Improve this question. Viewed 747 times 0 I am trying to c++ function pointer used to convert a QVariant to {a custom type. When using canConvert() and convert() consecutively, it is possible for canConvert() to return true, but convert() to return false. Everything works fine here. >-----Original Message----- As a whole you have a QVariant holding a QVariantList with a single QVariant value, which in turn is a QMap. Looks like you really want a template method instead "La mort n'est rien, mais vivre vaincu et sans gloire, c'est mourir tous les jours" ~Napoleon Bonaparte. Modified 7 years, 10 months ago. In particular, QVariant::UserType is returned here only if the value is equal or greater than QMetaType::User. Share Follow QVariant can be extended to support other types than those: 1637: mentioned in the \l Type enum. h class CustomType { }; Q_DECLARE_METATYPE(CustomType) Then you can retrieve your custom type from QVariant in this way : CustomType ct = In all the tutorials I've found, it is mentioned that "you must use Q_DECLARE_METATYPE to declare custom types to the Qt meta-system. 8. Overview [edit | edit source]. QRect. Conversion from QList<QListWidgetItem *> to QStringList? 4. 6. How to verify QVariant of type QVariant::UserType is expected type? 4. i also save the class name (here "Measurement") along with serialized data for furthur uses, because as you know we can get the registered type with QMetaType::type(char*) but with that type i can only construct a QVariant with QVariant(int typeId, const void *copy) but here i want to construct Stack Overflow for Teams Where developers & technologists share private knowledge with coworkers; Advertising & Talent Reach devs & technologists worldwide about your product, service or employer brand; OverflowAI GenAI features for Teams; OverflowAPI Train & fine-tune LLMs; Labs The future of collective knowledge sharing; About the company It enables things such as QVariant wrapping of custom types, copy of queued connection arguments, and more. The problem is, it seems like it creates an object with the default constructor when I thought it would use the copy constructor Qt QMetaType serialization of custom types and QVariant. adding two QVariants that hold integers could invoke int operator+(int,int). QVariant can hold a wide range of standard C++ and Qt types, including integers, floating-point numbers, strings, dates, times, and custom types registered with the Qt Meta-Object System @Onyx said in Casting a custom class to QVariant:. Is there any way to define a comparison method for these types? I want to put a custom type (boost::smart_ptr) into the QComboBox data which works well for enum's when you cast them to int, otherwise not - and the smart_ptr can't be Re: Casting a custom class to QVariant. Step 3, register with more systems at runtime. For pointer types Custom type in QVariant converts to empty string. it should look like this: QDataStream &operator Convert custom type to QVariant. QDBusArgument::MapType: 4: An associative container, like QMap<Key, Value> or QHash<Key, Value> It is similar to the Qt QVariant type. This would allow me to register the following class for example: With QML2 we now allow (via an undocumented interface) modules to provide their own value-types. Not directly, because JSON has a very limited number of types it supports (there isn't even integers). Hot Network Questions A widower with 3 children wins a female android at a football game Low-budget fantasy movie scene where a sorcerer's apprentice creates a banana but has no idea what it is Why is there a difference between the ma-def2-tzvp basis set used in ORCA and downloaded from official website? In QtScript there's the qScriptRegisterMetaType() function that registers custom types using custom conversion functions. I looked the forum but the solutions are mainly related to defining stream operators, but that is the case when object is used as custom QVariant type, not pointer. cpp, line 2144 Debug Error! What is the problem? How can i (de)serialize a custom class with QDataStream which is "wrapped" into a QVariant? Thanks in advance, It should be a big help for me, BR, Peter Span is a simple class that contains 2 double type properties. -Test Case Code- Convert a QVariant of a custom type to a QString. See the Custom Type Example for code that demonstrates this. Reply Quote 0. QtCore. value<QVariantList>(). Sorting a QListWidget using sortItems() 2. Here's a minimal example: #include <QObject> #include <QVariant> #include <QVariantMap> #include <QDebug> class MyQObjectClass : public QObject { Q_OBJECT public: explicit MyQObjectClass(QObject *parent = nullptr) : QObject(parent) {} void greet() { As you've found out, by default, QVariant does not exist in PyQt4 when used with Python3. For historical reason, there is a big difference between built-in types and custom types. canConvert<QString>(); // returns true That looks like an unusual use of QVariant. asked Jul 19, 2013 at 18:07. Hot Network Questions Custom QVariant ¶. A custom type can be used with QVariant by using: Q_DECLARE_METATYPE(CustomType); Recently, I was doing implementations with listviews and treeviews where the model inherits from QAbstractItemModel and where this function is A QVariant is holding a QMap object that is to be converted into a custom type, MyClass or MyClass2. Hot Network Questions Why does this official Arduino book recommend to use an LED with no resistor? Which thin replacements for recessed light bulbs do I need? Has there been a clarification regarding whether the use of 'Get Real' move is encouraged or discouraged? In a life-and-death emergency, could an I'm trying to save multiple models automatically, and I would like to avoid checking in foreachs the QVariant types, if it's a custom type then call toByteArray() on it. identify if QVariant is String or Int. Hello Everyone, I Have a custom type, let say MyClassA class MyClassA { function a (); function b (); . More Header: #include <QVariant> CMake: find_package(Qt6 COMPONENTS Core REQUIRED) target_link_libraries(mytarget PRIVATE Qt6::Core) qmake: QT += core List of all members, including inherited members Obsolete members Public Functions QVariant(QVariant &&other) A custom type represented by a structure, like QDateTime, QPoint, etc. QRectF. 4. To make the custom type Custom type in QVariant converts to empty string. You can't with Q_GADGETS. I tried to add some serialization using QMutex, with and without QMutexLocker, QReadWriteLocker but the result was the same - crash. This macro makes the type Type known to QMetaType as long as it provides a public default constructor, a public copy constructor and a public destructor. Create a QVariant from a metatype id. I want to use a QVariantMap with a custom class (based upon QObject). How to get data back from QVariant for a usertype? 4. Float. See the QItemEditorFactory documentation. Follow edited May 23, 2017 at 12:06. I have just run my app throught debugger with breakpoints to see what happens with Q_PROPERTY variables. I would expect something like toString() does NOT return the value in the QVariant as a QString but rather describes the QVariant in a way that might be more suitable for debugging. Custom types can also be integrated with the meta-object system as long as they are written to conform to some simple guidelines. What is a QVariant and when should it be used? 3. 1 class MyClass : public QObject { Q_OBJECT } Q_DECLARE_METATYPE(MyClass) class MyClass2 : public QObject { Q_OBJECT } Q_DECLARE_METATYPE(MyClass2) This macro makes the type Type known to QMetaType as long as it provides a public default constructor, a public copy constructor and a public destructor. 7 - C++ Signal / QML Slot - Custom Meta type wrapped in QVariant. I have successfully sent and recovered a QVariant containing just a QString across the dbus interface in the same manner I am trying to do below with a QVariant of a custom class. 16. Recently I had to downgrade Qt to Qt 4. See also convert(). QVariant to QList with unkown list template parameter. Custom type in QVariant converts to empty string. Qt QMetaType serialization of custom types and QVariant. I don't have multiple inheritance though. You can make them known (Q_DECLARE_METATYPE), however you can't register them as QML type. Unfortunately, I have several custom types that are stored inside of tokens as well. 6. These types are "QVariant-storable types which have sub From the Qt docs, Note: If you are working with custom types, you should use the Q_DECLARE_METATYPE() macro to register your custom type. 39. Type QVariant:: type const. Q_ENUM or Q_ENUM_NS in the header of the type; qRegisterMetaType<MyType>() called sometime before you try to use the type with QVariant (usually setup somewhere that is called when your app starts) QVariant::save: unable to save type 'TreeItem*' (type id: 1037). Sorting: You can't rely on the comparison operator for QVariant as it doesn't work with custom types, so you'll need to implement QSortFilterProxyModel::lessThan to have custom Inside the QVariant I can store custom class declared and registered in meta-system. Here's an example: If you want to edit items of that type, you'll need to call registerEditor so you can associate your custom type to an editor. bool qVariantCanConvert ( const QVariant & value) Returns true if the given value can be converted to the template type specified; otherwise returns false. class ImageListItem : public QListWidgetItem { // (Not a Q_OBJECT) public: ImageListItem(const QIcon & icon, const But doing this makes the QSettings replace all the custom types currently in the settings. The good thing on QVariant is that you don't have to tell, which type it stores. Using QVariant passed in from a QModelIndex &index: Check out this article and this article about how to create custom types in Qt/QML. void QVariant:: clear (). QColor. I would use the variant if I need to pass different types of parameter to the function. This is helpful, but not "necessary" and depends on how you plan to use your object. QPointF. I'm using QTreeView to show some data to the user. To save the object reference into QStandardItem:. Hot Network Questions Where can I find an up-to-date map of Stockholm Central Station that shows the platform layout? Is there definitive confirmation that the This macro makes the type Type known to QMetaType as long as it provides a public default constructor, a public copy constructor and a public destructor. ini file with an invalid QVariant type while debugging the output QVariant::load: unknown user type with name CustomDataType, is this behavior normal? J Somehow, for Qt types like QSize and QColor streaming the QVariant into QDebug works just fine. Since Qt now has some more datatypes than JSON how can one check if they are convertible. See \l {Creating Custom Qt Types}{Creating Custom Qt Types} 1638: for details. Qt cast with inheritance. Deserialize QByteArray to Java data types. if you have any suggestions, i would be pretty appreciate. X Offline. Converting QList to QVariant. Oh sorry I noticed that befre but thought it would also work, I guess you can't use the QVariant constructor for custom types, so replace @ @QVariant::QVariant(int typeId, const void * copy)@ to create a QVariant of specific type with specific value, without knowing the actual definition of the type. 2. You can store custom classes inside a QVariant object if you register these classes with Q_DECLARE_METATYPE. value("name"). 0 Button { signal settingChanged(string, var) // Convert custom type to QVariant. According to the Qt documentation, QVariant::operator== does not work as one might expect if the variant contains a custom type: bool QVariant::operator== ( const QVariant I’ve got a class (pubic default and copy constructors and destructor are implemented) named, say, SomeClass and SomeClassList that is a typedef for I store that in a QVariant and I want to convert it to a QString: QVariant v = QVariant::fromValue(m); QString s = v. Mathematical union of a QList<int>? 1. But keep in mind that For all other QVariant types a conversion to a QString will be attempted. Your earlier answers to a similar thread said to use this. Here's an example: I am discovering Custom Types with QVariant and tried to implement it in my project. toString(); assuming the whole These types are integrated with the meta-object system, enabling them to be stored in QVariant objects, written out in debugging information and sent between components in signal-slot communication. e. Convert this variant to type QMetaType::UnknownType and free up any resources used. Qt QDbus Sending Custom Types with QVariant. By QAlex in forum Qt Programming Replies: 3 Last Post: 4th December 2009, 13:04. This will make the conversion possible from Media to QVariant in your C++ code, but the Media class will not be usable in QML as you would like. Call qRegisterMetaType Related Non-Members typedef QVariantList. No Copy Constructor or Assignment Operator. 0. Since I'm using Qt I chose to store the token data as a QVariant. First of all, you need to register your type to be part of QVariant managed types //customtype. No, i think you don't. 10. 1 Reply Last reply . But doing this makes the QSettings replace all the custom types currently in the settings. Other qt systems (Qml engine) maintain their own Sorting and displaying a custom QVariant type. import Setting 1. Output: Qt QMetaType serialization of custom types and QVariant. For instance: QColor colr; QVariant colorv = QVariant::fromValue(colr); qDebug() << colorv; generates such output: QVariant(QColor, QColor(Invalid)) My type generates such: I am having a custom type which I use with QVariant. – I have my ModelObject derived from QObject, some custom types subclasses of ModelObject, some of them have properties as pointers to other custom classes. @QVariant::QVariant(int typeId, const void * copy)@ to create a QVariant of specific type with specific value, without knowing the actual definition of the type. How to use a union of two types. Hot Network Questions A widower with 3 children wins a female android at a football game Low-budget fantasy movie scene where a sorcerer's apprentice creates a banana but has no idea what it is Why is there a difference between the ma-def2-tzvp basis set used in ORCA and downloaded from official website? Type QVariant:: type const. This is typically because canConvert() only reports the general ability of QVariant to convert between types given suitable data; it is still possible to supply data which cannot actually be converted. For pointer types, it also requires that So I have a custom class Foo which has been registered as a metatype using the Q_DECLARE_METATYPE(Foo) macro at the end of the class definition. For example here is how QColor packer and unpacker looks like: After days of experimenting I surrender returning a list of custom objects to QML. As far as creating your own primitive types (int, bool, double, etc) I don't think this is a possibility without digging into the source code of the Qt language itself and I don't think that's a good idea. Secrets are power. Then there came QMetaType with its own type enum for supported types. Synonym for QMap<QString, QVariant>. These types are integrated with the meta-object system, enabling them to be stored in QVariant objects, written out in debugging information and sent between components in signal-slot communication. qt. I'm trying to save multiple models automatically, and I would like to avoid checking in foreachs the QVariant types, if it's a custom type then call toByteArray() on it. Share. Handling QMetaType registration in Qt5 with dynamic plug-ins. Note that the Q_PROPERTY string cannot contain commas, because commas separate macro arguments. To make the custom type generally usable with the signals and slots mechanism, we need to perform some extra work. Is there any way to define a comparison method for these types? I want to put a custom type (boost::smart_ptr) into the QComboBox data which works well for enum's when you cast them to int, otherwise not - and the smart_ptr can't be Just try to use QVariant::value and see if the value in a QVariant can be converted to your target class. null would normally be expected, and avoid attempting to use any QVariant methods (such as toPyObject, which is obviously redundant anyway). By Vladimir in forum Qt Programming Replies: 2 Last Post: 16th January 2007, 16:36. QVariant v = QVariant::fromValue<cMyClass>(MyObject); When I do this the compiler complains that I need to use Q_DECLARE_METATYPE(cMyClass). Double. If the returned string is empty, a Null QJsonValue will be stored, otherwise a String value using the returned QString. This is by design. 5. I have a custom class called Money that I want stored in a QVariant. How to sort QList<QVariant> in Qt? 0. As for memory efficiency, consider that QVariant has 8 bytes for data, plus 4 bytes for type id, plus another 4 bytes of padding, for a Properties and Custom Types. I'm afraid you cannot avoid these checks. mjyfl tmxay trtdw yrax kxrqjuu qjip ubtsfs pyen dxumv cqo