1万流量网站 服务器配置,短信验证码接码网站建设,5g站长工具seo综合查询,得物app公司什么是 QVariant#xff1f;
QVariant 是 Qt 中的一个类#xff0c;允许您以一种通用的方式存储和访问数据#xff0c;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#xff0c;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…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 QMetaTypeint 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. MapQVariantMap 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QVariantvar.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QVariantQVariant fromStringVar QVariant::fromValue(42);// 20. 将QVariant转为JSONQJsonObject jsonObject var.toJsonValue().toObject();// 21. 将JSON转为QVariantQVariant fromJsonVar QVariant::fromValue(jsonObject);// 22. 根据类型名创建QVariantQVariant typeVar QVariant::fromType(QMetaType::Int);// 23. 使用 QVariantList 创建 QVariantQVariantList listVar;listVar 1 2 3;// 24. 使用 QVariantMap 创建 QVariantQVariantMap mapVar;mapVar[name] John;mapVar[age] 25;// 25. QVariant的复制QVariant copyVar var;// 26. 使用 QVariantList 创建 QVariantQVariantList 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.valueCustomType();// 31. QDateQDate dateValue(2023, 11, 4);var QVariant(dateValue);// 32. QTimeQTime timeValue(14, 30);var QVariant(timeValue);// 33. QDateTimeQDateTime dateTimeValue(QDate(2023, 11, 4), QTime(14, 30));var QVariant(dateTimeValue);// 34. QByteArrayQByteArray byteArrayValue QByteArray(Hello, QVariant!);var QVariant(byteArrayValue);// 35. QStringListQStringList stringListValue;stringListValue One Two Three;var QVariant(stringListValue);// 36. QColorQColor colorValue(255, 0, 0); // 红色var QVariant(colorValue);// 37. QFontQFont fontValue(Arial, 12);var QVariant(fontValue);// 38. QPointQPoint pointValue(100, 200);var QVariant(pointValue);// 39. QSizeQSize sizeValue(300, 400);var QVariant(sizeValue);// 40. QRectQRect rectValue(100, 100, 300, 200);var QVariant(rectValue);// 41. QVariantList嵌套QVariantQVariantList nestedList;nestedList QVariant(1) QVariant(Nested) QVariant(3.0);QVariant nestedVar QVariant(nestedList);var QVariant(nestedVar);// 42. QVariantMap嵌套QVariantQVariantMap nestedMap;nestedMap[key1] QVariant(42);nestedMap[key2] QVariant(Nested);QVariant nestedMapVar QVariant(nestedMap);var QVariant(nestedMapVar);// 43. 多个类型混合的QVariantListQVariantList 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.valueQColor();QFont font var.valueQFont();QPoint point var.valueQPoint();QSize size var.valueQSize();QRect rect var.valueQRect();// 45. 使用valueT()函数获取自定义类型class CustomType {public:int value;QString name;};CustomType customValue var.valueCustomType();// 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QVariantQVariant fromJsonVar QVariant::fromValue(QJsonDocument::fromJson(jsonStr.toUtf8()).toVariant());// 51. QListQListint intList;intList 1 2 3;var QVariant::fromValue(intList);// 52. QVectorQVectorQString stringVector;stringVector One Two Three;var QVariant::fromValue(stringVector);// 53. QMapQMapQString, int stringIntMap;stringIntMap[One] 1;stringIntMap[Two] 2;var QVariant::fromValue(stringIntMap);// 54. QStringListQStringList 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QSharedPointerint sharedInt QSharedPointerint(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QListint* intListPointer new QListint();intListPointer-append(1);intListPointer-append(2);intListPointer-append(3);var QVariant::fromValue(intListPointer);// 65. QVariantListQMap指针QMapQString, int* stringIntMapPointer new QMapQString, 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;QMapQString, 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.valueCustomType();qDebug() Can convert to CustomType: custom.value custom.name;}// 74. 使用 QVariantList 遍历QVariantMapQVariantMap 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QVariantMapQVariantMap 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.dataint();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.dataCustomType();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();
}
