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// Copyright (C) 2016 The Qt Company Ltd.
// SPDX-License-Identifier: LicenseRef-Qt-Commercial OR BSD-3-Clause
#undef QT_NO_FOREACH // this file contains unported legacy Q_FOREACH uses
//! [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<QColor>();
//! [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<MyCustomStruct>();
//! [4]
//! [5]
QVariant v;
MyCustomStruct c;
if (v.canConvert<MyCustomStruct>())
c = v.value<MyCustomStruct>();
v = 7;
int i = v.value<int>(); // same as v.toInt()
QString s = v.value<QString>(); // same as v.toString(), s is now "7"
MyCustomStruct c2 = v.value<MyCustomStruct>(); // conversion failed, c2 is empty
//! [5]
//! [6]
QVariant v = 42;
v.canConvert<int>(); // returns true
v.canConvert<QString>(); // returns true
MyCustomStruct s;
v.setValue(s);
v.canConvert<int>(); // returns false
v.canConvert<MyCustomStruct>(); // returns true
//! [6]
//! [7]
MyCustomStruct s;
return QVariant::fromValue(s);
//! [7]
//! [9]
QList<int> intList = {7, 11, 42};
QVariant variant = QVariant::fromValue(intList);
if (variant.canConvert<QVariantList>()) {
QSequentialIterable iterable = variant.value<QSequentialIterable>();
// 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<int, QString> mapping;
mapping.insert(7, "Seven");
mapping.insert(11, "Eleven");
mapping.insert(42, "Forty-two");
QVariant variant = QVariant::fromValue(mapping);
if (variant.canConvert<QVariantHash>()) {
QAssociativeIterable iterable = variant.value<QAssociativeIterable>();
// 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]
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