QtC++与QVariant详解-CSDN博客

什么是 QVariant

QVariant 是 Qt 中的一个类允许您以一种通用的方式存储和访问数据即使这些数据具有不同的数据类型。它在许多情况下非常有用例如在模型视图编程、数据序列化、设置和配置管理等领域。QVariant 可以包含以下类型的数据

基本数据类型如整数、浮点数、布尔值、枚举等。
Qt 内置的数据类型如 QString、QByteArray、QDate、QTime、QDateTime 等。
用户自定义的数据类型只要您为其定义了 QVariant 转换函数

丰富的示例

#include <QCoreApplication>
#include <QVariant>
#include <QDebug>
#include <QDate>
#include <QTime>
#include <QDateTime>
#include <QByteArray>
#include <QStringList>
#include <QColor>
#include <QFont>
#include <QPoint>
#include <QSize>
#include <QRect>
#include <QMetaType>

int main(int argc, char *argv[])
{
    QCoreApplication a(argc, argv);

    // 创建一个QVariant对象并设置其值
    QVariant var;
     // 1. 整数
    int intValue = 42;
    var = QVariant(intValue);

    // 2. 浮点数
    double doubleValue = 3.14159;
    var = QVariant(doubleValue);

    // 3. 字符串
    QString stringValue = "Hello, QVariant!";
    var = QVariant(stringValue);

    // 4. 布尔值
    bool boolValue = true;
    var = QVariant(boolValue);

    // 5. 列表
    QVariantList list;
    list.append(1);
    list.append("Two");
    list.append(3.0);
    var = QVariant(list);

    // 6. Map
    QVariantMap map;
    map["name"] = "Alice";
    map["age"] = 30;
    map["isStudent"] = false;
    var = QVariant(map);

    // 7. 枚举
    enum Color { Red, Green, Blue };
    Color colorValue = Blue;
    var = QVariant(colorValue);

    // 8. 自定义类型
    class CustomType {
    public:
        int value;
        QString name;
    };
    CustomType customValue;
    customValue.value = 123;
    customValue.name = "Custom";
    var = QVariant::fromValue(customValue);

    // 9. 数据类型检查
    if (var.type() == QVariant::Int) {
        int intValue = var.toInt();
    }

    // 10. 数据类型转换
    QString strValue = var.toString();

    // 11. 比较
    QVariant anotherIntValue = QVariant(42);
    if (var == anotherIntValue) {
        qDebug() << "var is equal to anotherIntValue";
    }

    // 12. 访问Map中的值
    QVariantMap mapValue = var.toMap();
    QString name = mapValue["name"].toString();
    int age = mapValue["age"].toInt();

    // 13. 获取枚举值名称
    QString enumName = var.typeName();

    // 14. 清空QVariant
    var.clear();

    // 15. 判断QVariant是否为空
    if (var.isNull()) {
        qDebug() << "var is null";
    }

    // 其他高级方法

    // 16. QVariant类型的自省
    QVariant::Type type = var.type();

    // 17. QVariant的详细类型信息
    const QMetaObject *metaObject = var.metaObject();

    // 18. 类型是否可转换
    bool canConvert = var.canConvert(QVariant::Int);

    // 19. 从字符串创建QVariant
    QVariant fromStringVar = QVariant::fromValue("42");

    // 20. 将QVariant转为JSON
    QJsonObject jsonObject = var.toJsonValue().toObject();

    // 21. 将JSON转为QVariant
    QVariant fromJsonVar = QVariant::fromValue(jsonObject);

    // 22. 根据类型名创建QVariant
    QVariant typeVar = QVariant::fromType(QMetaType::Int);

    // 23. 使用 QVariantList 创建 QVariant
    QVariantList listVar;
    listVar << 1 << 2 << 3;

    // 24. 使用 QVariantMap 创建 QVariant
    QVariantMap mapVar;
    mapVar["name"] = "John";
    mapVar["age"] = 25;

    // 25. QVariant的复制
    QVariant copyVar = var;

    // 26. 使用 QVariantList 创建 QVariant
    QVariantList listVar2 = QVariantList() << 4 << 5 << 6;

    // 27. 检查是否有值
    if (var.isValid()) {
        qDebug() << "var is valid";
    }

    // 28. 获取 QVariant 内部数据指针
    const void *dataPtr = var.constData();

    // 29. 获取 QVariant 内部数据大小
    int dataSize = var.dataSize();

    // 30. 使用自定义转换函数
    QVariant customConvertedVar = var.value<CustomType>();

    // 31. QDate
    QDate dateValue(2023, 11, 4);
    var = QVariant(dateValue);

    // 32. QTime
    QTime timeValue(14, 30);
    var = QVariant(timeValue);

    // 33. QDateTime
    QDateTime dateTimeValue(QDate(2023, 11, 4), QTime(14, 30));
    var = QVariant(dateTimeValue);

    // 34. QByteArray
    QByteArray byteArrayValue = QByteArray("Hello, QVariant!");
    var = QVariant(byteArrayValue);

    // 35. QStringList
    QStringList stringListValue;
    stringListValue << "One" << "Two" << "Three";
    var = QVariant(stringListValue);

    // 36. QColor
    QColor colorValue(255, 0, 0); // 红色
    var = QVariant(colorValue);

    // 37. QFont
    QFont fontValue("Arial", 12);
    var = QVariant(fontValue);

    // 38. QPoint
    QPoint pointValue(100, 200);
    var = QVariant(pointValue);

    // 39. QSize
    QSize sizeValue(300, 400);
    var = QVariant(sizeValue);

    // 40. QRect
    QRect rectValue(100, 100, 300, 200);
    var = QVariant(rectValue);

    // 41. QVariantList嵌套QVariant
    QVariantList nestedList;
    nestedList << QVariant(1) << QVariant("Nested") << QVariant(3.0);
    QVariant nestedVar = QVariant(nestedList);
    var = QVariant(nestedVar);

    // 42. QVariantMap嵌套QVariant
    QVariantMap nestedMap;
    nestedMap["key1"] = QVariant(42);
    nestedMap["key2"] = QVariant("Nested");
    QVariant nestedMapVar = QVariant(nestedMap);
    var = QVariant(nestedMapVar);

    // 43. 多个类型混合的QVariantList
    QVariantList mixedList;
    mixedList << QVariant(42) << QVariant("Mixed") << QVariant(QDate(2023, 11, 4));
    var = QVariant(mixedList);

    // 44. 使用toXxx()函数获取值
    int intValue = var.toInt();
    double doubleValue = var.toDouble();
    QString stringValue = var.toString();
    QDate date = var.toDate();
    QTime time = var.toTime();
    QDateTime dateTime = var.toDateTime();
    QByteArray byteArray = var.toByteArray();
    QStringList stringList = var.toStringList();
    QColor color = var.value<QColor>();
    QFont font = var.value<QFont>();
    QPoint point = var.value<QPoint>();
    QSize size = var.value<QSize>();
    QRect rect = var.value<QRect>();

    // 45. 使用value<T>()函数获取自定义类型
    class CustomType {
    public:
        int value;
        QString name;
    };
    CustomType customValue = var.value<CustomType>();

    // 46. 使用constData()获取数据指针
    const void *dataPtr = var.constData();

    // 47. 检查是否为空
    if (var.isNull()) {
        qDebug() << "var is null";
    }

    // 48. 获取类型名称
    QString typeName = var.typeName();

    // 49. 将QVariant转为JSON字符串
    QString jsonStr = QVariant::fromValue(var).toJsonValue().toString();

    // 50. 从JSON字符串创建QVariant
    QVariant fromJsonVar = QVariant::fromValue(QJsonDocument::fromJson(jsonStr.toUtf8()).toVariant());

// 51. QList
    QList<int> intList;
    intList << 1 << 2 << 3;
    var = QVariant::fromValue(intList);

    // 52. QVector
    QVector<QString> stringVector;
    stringVector << "One" << "Two" << "Three";
    var = QVariant::fromValue(stringVector);

    // 53. QMap
    QMap<QString, int> stringIntMap;
    stringIntMap["One"] = 1;
    stringIntMap["Two"] = 2;
    var = QVariant::fromValue(stringIntMap);

    // 54. QStringList
    QStringList stringList;
    stringList << "Apple" << "Banana" << "Cherry";
    var = QVariant::fromValue(stringList);

    // 55. QVariantList混合数据类型
    QVariantList mixedDataList;
    mixedDataList << 42 << "Mixed" << 3.14;
    var = QVariant(mixedDataList);

    // 56. QVariantMap混合数据类型
    QVariantMap mixedDataMap;
    mixedDataMap["key1"] = 42;
    mixedDataMap["key2"] = "Mixed";
    mixedDataMap["key3"] = 3.14;
    var = QVariant(mixedDataMap);

    // 57. QVariantList深度嵌套
    QVariantList deepNestedList;
    QVariantList innerList;
    innerList << 1 << 2 << 3;
    deepNestedList << innerList << "Nested" << 3.14;
    var = QVariant(deepNestedList);

    // 58. QVariantMap深度嵌套
    QVariantMap deepNestedMap;
    QVariantMap innerMap;
    innerMap["key1"] = 42;
    innerMap["key2"] = "Nested";
    deepNestedMap["inner"] = innerMap;
    deepNestedMap["key3"] = 3.14;
    var = QVariant(deepNestedMap);

    // 59. QVariantMap枚举类型
    enum Fruit { Apple, Banana, Cherry };
    QVariantMap enumMap;
    enumMap["fruit"] = Fruit::Apple;
    var = QVariant(enumMap);

    // 60. QVariantList枚举类型
    QVariantList enumList;
    enumList << Fruit::Apple << Fruit::Banana << Fruit::Cherry;
    var = QVariant(enumList);

    // 61. QVariantList指针类型
    int* intPointer = new int(42);
    var = QVariant::fromValue(intPointer);

    // 62. QVariantListQSharedPointer类型
    QSharedPointer<int> sharedInt = QSharedPointer<int>(new int(42));
    var = QVariant::fromValue(sharedInt);

    // 63. QVariantList自定义类指针
    class CustomType {
    public:
        int value;
        QString name;
    };
    CustomType* customPointer = new CustomType();
    customPointer->value = 42;
    customPointer->name = "CustomPointer";
    var = QVariant::fromValue(customPointer);

    // 64. QVariantListQList指针
    QList<int>* intListPointer = new QList<int>();
    intListPointer->append(1);
    intListPointer->append(2);
    intListPointer->append(3);
    var = QVariant::fromValue(intListPointer);

    // 65. QVariantListQMap指针
    QMap<QString, int>* stringIntMapPointer = new QMap<QString, int>();
    stringIntMapPointer->insert("One", 1);
    stringIntMapPointer->insert("Two", 2);
    var = QVariant::fromValue(stringIntMapPointer);

    // 66. QVariantListQVariantList指针
    QVariantList* nestedListPointer = new QVariantList();
    nestedListPointer->append(1);
    nestedListPointer->append("Nested");
    var = QVariant::fromValue(nestedListPointer);

    // 67. QVariantListQVariantMap指针
    QVariantMap* nestedMapPointer = new QVariantMap();
    (*nestedMapPointer)["key1"] = 42;
    (*nestedMapPointer)["key2"] = "Nested";
    var = QVariant::fromValue(nestedMapPointer);

    // 68. QVariantList复合结构
    struct ComplexStruct {
        int intValue;
        QString stringValue;
        QMap<QString, QVariant> dataMap;
    };
    ComplexStruct complexValue = {42, "Complex", stringIntMap};
    var = QVariant::fromValue(complexValue);

    // 69. QVariantListQVariant指针
    QVariant* varPointer = new QVariant(42);
    var = QVariant::fromValue(varPointer);

    // 70. QVariantListQVariantList指针
    QVariantList* varListPointer = new QVariantList();
    varListPointer->append(1);
    varListPointer->append("Nested");
    var = QVariant::fromValue(varListPointer);

    // 71. QVariantListQVariantMap指针
    QVariantMap* varMapPointer = new QVariantMap();
    (*varMapPointer)["key1"] = 42;
    (*varMapPointer)["key2"] = "Nested";
    var = QVariant::fromValue(varMapPointer);

    // 72. 检查是否包含特定类型
    if (var.canConvert(QVariant::Int)) {
        int convertedInt = var.toInt();
        qDebug() << "Can convert to int: " << convertedInt;
    }

    // 73. 检查是否包含特定自定义类型
    bool hasCustomType = QMetaType::type("CustomType") != QMetaType::UnknownType;
    if (hasCustomType && var.canConvert(QMetaType::type("CustomType"))) {
        CustomType custom = var.value<CustomType>();
        qDebug() << "Can convert to CustomType: " << custom.value << custom.name;
    }

    // 74. 使用 QVariantList 遍历QVariantMap
    QVariantMap mapInList;
    mapInList["name"] = "John";
    mapInList["age"] = 30;
    QVariantList listInMap;
    listInMap << 1 << 2 << mapInList;
    QVariantMap mapWithList;
    mapWithList["data"] = listInMap;
    var = QVariant(mapWithList);
    QVariantList nestedDataList = var.toMap()["data"].toList();
    for (const QVariant& item : nestedDataList) {
        if (item.canConvert(QVariant::String)) {
            QString strValue = item.toString();
            qDebug() << "String in nested list: " << strValue;
        }
        else if (item.canConvert(QVariant::Map)) {
            QVariantMap mapValue = item.toMap();
            QString name = mapValue["name"].toString();
            int age = mapValue["age"].toInt();
            qDebug() << "Map in nested list: Name - " << name << ", Age - " << age;
        }
    }

    // 75. 使用 QVariantMap 遍历QVariantMap
    QVariantMap mapData;
    mapData["key1"] = 42;
    mapData["key2"] = "Value";
    mapData["key3"] = 3.14;
    var = QVariant(mapData);
    QVariantMap dataMap = var.toMap();
    for (const QString& key : dataMap.keys()) {
        QVariant value = dataMap[key];
        if (value.canConvert(QVariant::Int)) {
            int intValue = value.toInt();
            qDebug() << "Key: " << key << " - Int Value: " << intValue;
        }
        else if (value.canConvert(QVariant::String)) {
            QString strValue = value.toString();
            qDebug() << "Key: " << key << " - String Value: " << strValue;
        }
        else if (value.canConvert(QVariant::Double)) {
            double doubleValue = value.toDouble();
            qDebug() << "Key: " << key << " - Double Value: " << doubleValue;
        }
    }

    // 76. QVariantList 转换为数组
    QVariantList listToConvert;
    listToConvert << 1 << 2 << 3 << 4 << 5;
    int* intArray = listToConvert.data<int>();
    for (int i = 0; i < listToConvert.size(); ++i) {
        qDebug() << "Array Value: " << intArray[i];
    }

    // 77. QVariantList 转换为自定义类数组
    class CustomType {
    public:
        int value;
        QString name;
    };
    QVariantList customList;
    CustomType custom1 = {1, "One"};
    CustomType custom2 = {2, "Two"};
    CustomType custom3 = {3, "Three"};
    customList << QVariant::fromValue(custom1) << QVariant::fromValue(custom2) << QVariant::fromValue(custom3);
    CustomType* customArray = customList.data<CustomType>();
    for (int i = 0; i < customList.size(); ++i) {
        qDebug() << "Custom Array Value: " << customArray[i].value << customArray[i].name;
    }

    // 78. 使用 QVariantList 进行排序
    QVariantList sortList;
    sortList << 5 << 2 << 1 << 4 << 3;
    std::sort(sortList.begin(), sortList.end(), [](const QVariant& a, const QVariant& b) {
        return a.toInt() < b.toInt();
    });
    qDebug() << "Sorted List: " << sortList;

    // 79. 使用 QVariantList 进行过滤
    QVariantList filterList;
    filterList << 1 << 2 << 3 << 4 << 5;
    QVariantList filtered = filterList.filter([](const QVariant& value) {
        return value.toInt() % 2 == 0;
    });
    qDebug() << "Filtered List: " << filtered;

    // 80. 使用 QVariantList 进行映射
    QVariantList mapList;
    mapList << 1 << 2 << 3;
    QVariantList mapped = mapList.map([](const QVariant& value) {
        return value.toInt() * 2;
    });
    qDebug() << "Mapped List: " << mapped;

    // 81. 使用 QVariantList 进行折叠
    QVariantList foldList;
    foldList << 1 << 2 << 3 << 4 << 5;
    int sum = foldList.fold(0, [](int accumulator, const QVariant& value) {
        return accumulator + value.toInt();
    });
    qDebug() << "Folded Sum: " << sum;

    // 82. 使用 QVariantList 进行查找
    QVariantList findList;
    findList << 10 << 20 << 30 << 40 << 50;
    QVariant found = findList.find([](const QVariant& value) {
        return value.toInt() == 30;
    });
    qDebug() << "Found Value: " << found;

    // 83. 使用 QVariantList 进行去重
    QVariantList duplicateList;
    duplicateList << 1 << 2 << 3 << 2 << 1;
    QVariantList unique = duplicateList.unique();
    qDebug() << "Unique List: " << unique;

    // 84. 使用 QVariantMap 进行排序
    QVariantMap sortMap;
    sortMap["one"] = 5;
    sortMap["two"] = 2;
    sortMap["three"] = 1;
    QVariantMap sortedMap = sortMap.sortedKeys();
    qDebug() << "Sorted Map: " << sortedMap;

    // 85. 使用 QVariantMap 进行过滤
    QVariantMap filterMap;
    filterMap["one"] = 1;
    filterMap["two"] = 2;
    filterMap["three"] = 3;
    QVariantMap filteredMap = filterMap.filter([](const QVariant& key, const QVariant& value) {
        return value.toInt() % 2 == 0;
    });
    qDebug() << "Filtered Map: " << filteredMap;

    // 86. 使用 QVariantMap 进行映射
    QVariantMap mapMap;
    mapMap["one"] = 1;
    mapMap["two"] = 2;
    mapMap["three"] = 3;
    QVariantMap mappedMap = mapMap.map([](const QVariant& key, const QVariant& value) {
        return QVariant(key.toString() + "Squared", value.toInt() * value.toInt());
    });
    qDebug() << "Mapped Map: " << mappedMap;

    // 87. 使用 QVariantMap 进行折叠
    QVariantMap foldMap;
    foldMap["one"] = 1;
    foldMap["two"] = 2;
    foldMap["three"] = 3;
    int sumMap = foldMap.fold(0, [](int accumulator, const QVariant& key, const QVariant& value) {
        return accumulator + value.toInt();
    });
    qDebug() << "Folded Sum in Map: " << sumMap;



    return a.exec();
}