How to verify QVariant of type QVariant::UserType is expected type?

问题

I'm writing testing code that will automatically iterate thru all Q_PROPERTY's of widgets and some properties are using types that are registered via qRegisterMetaType. If i want to read/write these into QVariant i need to use QVariant::UserType when storing them into variant. So far so good.

But when i want to test reads and writes of these properties, i need to also know their type. For stuff that are already standard qt types, i can do this via QVariant::type() but as i have alot of usertypes, how would this be accomplished ?

From the api of QVariant, i spotted this:

bool QVariant::canConvert ( Type t ) const

But i'm slightly doubtful if this will lead to wrong types in case of enums?

So, what would be the foolproof way to verify what type of usertype is stored in QVariant ?

回答1:

For user defined types there is QVariant::userType(). It works like QVariant::type() but returns the type id integer of the user defined type whereas QVariant::type() always return QVariant::UserType.

There is also QVariant::typeName() which returns the name of the type as a string.

EDIT :

It probably depends on how you set the QVariant. Directly using QVariant::QVariant(int type, const void * copy) is discouraged.

Say I have three types like this :

class MyFirstType
{ 
    public:
        MyFirstType();
        MyFirstType(const MyFirstType &other);
        ~MyFirstType();

        MyFirstType(const QString &content);

        QString content() const;

    private:
        QString m_content;
};
Q_DECLARE_METATYPE(MyFirstType);

The third without Q_DECLARE_METATYPE

I store them in QVariant :

 QString content = "Test";

 MyFirstType first(content);

 MySecondType second(content);

 MyThirdType third(content);

 QVariant firstVariant;
 firstVariant.setValue(first);

 QVariant secondVariant = QVariant::fromValue(second);

 int myType = qRegisterMetaType<MyThirdType>("MyThirdType");

 QVariant thirdVariant(myType, &third); // Here the type isn't checked against the data passed

 qDebug() << "typeName for first :" << firstVariant.typeName();
 qDebug() << "UserType :" << firstVariant.userType();
 qDebug() << "Type : " << firstVariant.type();

 [...]

I get :

typeName for first : MyFirstType 
UserType : 256 
Type :  QVariant::UserType 

typeName for second : MySecondType 
UserType : 257 
Type :  QVariant::UserType 

typeName for third : MyThirdType 
UserType : 258 
Type :  QVariant::UserType

来源：https://stackoverflow.com/questions/3193275/how-to-verify-qvariant-of-type-qvariantusertype-is-expected-type

标签

qvariant