// Copyright (C) 2016 The Qt Company Ltd. // SPDX-License-Identifier: LicenseRef-Qt-Commercial OR BSD-3-Clause //! [0] QDataStream out(...); QVariant v(123); // The variant now contains an int int x = v.toInt(); // x = 123 out << v; // Writes a type tag and an int to out v = QVariant(tr("hello")); // The variant now contains a QString int y = v.toInt(); // y = 0 since v cannot be converted to an int QString s = v.toString(); // s = tr("hello") (see QObject::tr()) out << v; // Writes a type tag and a QString to out ... QDataStream in(...); // (opening the previously written stream) in >> v; // Reads an Int variant int z = v.toInt(); // z = 123 qDebug("Type is %s", // prints "Type is int" v.typeName()); v = v.toInt() + 100; // The variant now holds the value 223 v = QVariant(QStringList()); // The variant now holds a QStringList //! [0] //! [1] QVariant x; // x.isNull() == true QVariant y = QVariant::fromValue(nullptr); // y.isNull() == true //! [1] //! [2] QVariant variant; ... QColor color = variant.value(); //! [2] //! [3] QColor color = palette().background().color(); QVariant variant = color; //! [3] //! [4] QVariant v; v.setValue(5); int i = v.toInt(); // i is now 5 QString s = v.toString(); // s is now "5" MyCustomStruct c; v.setValue(c); ... MyCustomStruct c2 = v.value(); //! [4] //! [5] QVariant v; MyCustomStruct c; if (v.canConvert()) c = v.value(); v = 7; int i = v.value(); // same as v.toInt() QString s = v.value(); // same as v.toString(), s is now "7" MyCustomStruct c2 = v.value(); // conversion failed, c2 is empty //! [5] //! [6] QVariant v = 42; v.canConvert(); // returns true v.canConvert(); // returns true MyCustomStruct s; v.setValue(s); v.canConvert(); // returns false v.canConvert(); // returns true //! [6] //! [7] MyCustomStruct s; return QVariant::fromValue(s); //! [7] //! [8] QObject *object = getObjectFromSomewhere(); QVariant data = QVariant::fromValue(object); //! [8] //! [9] QList intList = {7, 11, 42}; QVariant variant = QVariant::fromValue(intList); if (variant.canConvert()) { QSequentialIterable iterable = variant.value(); // Can use foreach: foreach (const QVariant &v, iterable) { qDebug() << v; } // Can use C++11 range-for: for (const QVariant &v : iterable) { qDebug() << v; } // Can use iterators: QSequentialIterable::const_iterator it = iterable.begin(); const QSequentialIterable::const_iterator end = iterable.end(); for ( ; it != end; ++it) { qDebug() << *it; } } //! [9] //! [10] QHash mapping; mapping.insert(7, "Seven"); mapping.insert(11, "Eleven"); mapping.insert(42, "Forty-two"); QVariant variant = QVariant::fromValue(mapping); if (variant.canConvert()) { QAssociativeIterable iterable = variant.value(); // Can use foreach over the values: foreach (const QVariant &v, iterable) { qDebug() << v; } // Can use C++11 range-for over the values: for (const QVariant &v : iterable) { qDebug() << v; } // Can use iterators: QAssociativeIterable::const_iterator it = iterable.begin(); const QAssociativeIterable::const_iterator end = iterable.end(); for ( ; it != end; ++it) { qDebug() << *it; // The current value qDebug() << it.key(); qDebug() << it.value(); } } //! [10]