Q_INVOKABLE method returning custom C++ type

问题

I have a C++ method made Q_INVOKABLE. I can call this method from QML and it works when it returns basic types (like QString). But I can't with a custom type. How should I do this? Should I return a QVariant instead? Ideally, I would like to return a pointer to my custom type if possible.

EDIT I do:

qmlRegisterType<MyType>("Mine", 1, 0, "MyType");
qmlEngine->rootContext()->setContextProperty("testObj", new MyType());

I can use testObj global object or create MyType QML component. But I cannot use it in some javascript code as a return type from a Q_INVOKABLE C++ method.

回答1:

Yes, QVariant is the way to go for your custom class in that construction. Make sure you register your class.

That being said, you may wish to consider using Q_PROPERTY instead, for your custom type and then you can access that even without a function call. If you need custom parameters to the method and you cannot rearrange the code, this is obviously not an option.

回答2:

This is possible but you need to define your custom type as an interface.

First of all in your main() function:

qmlRegisterInterface<MyType>("MyType");

Now you can proceed to create an object and return a pointer in a Q_INVOKABLE:

MyType* example = new MyType(parent);
return example;

Note: it might be beneficial to pass the parent to your custom QObject to ensure that this object is deleted together with his parent (to avoid memory leaks).

回答3:

Note that the target of this answer are people with a similar problem, rather than the original asker.

The described method should work, at least in recent versions of Qt (I'm using Qt 5.12, but it should work in older versions too). Maybe it was a bug in one of the first QML releases.

Checklist: Verify you have done the following:

• Registered your type qmlRegisterType<MyType>("Mine", 1, 0, "MyType"); (or use qmlRegisterUncreatableType)
• Imported your custom types in qml: import Mine 1.0
• Derived your class from QObject.
• Added Q_OBJECT to your class definition.

When returning pointers from a Q_INVOKABLE method, please take object ownership into account.

回答4:

I think Dimitri's answer only applies when your type is copyable (so it wouldn't work for QObject). My understanding is that when you have a type that is being manipulated by Qt, for example if it is being returned by an invokable, the type has to be registered as a metatype:

• Non-copyable types like any QObject derived model cannot be metatypes
• A pointer type is a different type, therefore it needs to register separately from the classes it points to
• For pointer type Foo* you can register it with metatype system: qRegisterMetaType<Foo*>("Foo*");

来源：https://stackoverflow.com/questions/24414873/q-invokable-method-returning-custom-c-type