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I have a problem with enum classes, QVariants and the QSettings class. There are enum class values that I want to store within a QVariant which goes into a QSettings instance. So, my code actually looks something like this:
enum class Foo
{
Bar1, Bar2
}
Q_ENUMS(Foo)
Q_DECLARE_METATYPE(Foo)
...
Foo value = Bar2;
QSettings settings;
settings.setValue(QString("Foo"), QVariant::fromValue(value));
At this point in executing the code, an assertion jumps in and complains:
ASSERT failure in QVariant::save: "Invalid type to save", file kernel\qvariant.cpp
Searching the internet, I found out that the class is missing a fitting << and >> operator. But that is not an option for enum classes. I even tried to use
qRegisterMetaType<Foo>("Foo");
but it did not help. Maybe you have some other suggestions/solutions for me. Thanks!
663
Yes, we can define an enumeration inside a class. You can retrieve the values in an enumeration using the values() method.
Although enumerations are probably the most common type that is nested inside a class, C++ will let you define other types within a class, such as typedefs, type aliases, and even other classes!
Description. The java.lang.Enum.name() method returns the name of this enum constant, exactly as declared in its enum declaration.
An enum just spills its contents into the enclosing scope, and is basically a const static integer. This means that the first element of any default enum is the same using the == operator. Enum classes have their own scope, and don't pollute the namespace that they are in.
Enums, which are masked unsigned ints, seem to be a problem, see
Qt4 QSettings save enumeration value (for example Qt::CheckState)
The solution there and probably here would be to convert it an unsigned. To check if the static_cast-result back to the enum is valid you might add Foo_lowest and Foo_highest values to the beginning and end of the enum range.
55
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