How can I cast a QVariant to custom class?

You could try using qvariant_cast and qobject_cast.

QObject *object = qvariant_cast<QObject*>(selectItem);
Category *category = qobject_cast<Category*>(object);

Also, never put any persistent statement into Q_ASSERT. It will not be used when the assert is not enabled.

EDIT: works for non QObject derived type (see Final Contest's answer for this case)

First of all, you need to register your type to be part of QVariant managed types

//customtype.h
class CustomType {
};

Q_DECLARE_METATYPE(CustomType)

Then you can retrieve your custom type from QVariant in this way :

CustomType ct = myVariant.value<CustomType>();

which is equivalent to:

CustomType ct = qvariant_cast<CustomType>(myVariant);

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