郑州网站设计制作哪家好,火狐浏览器下载,梵克雅宝官网报价,手机网站设计公司优选亿企邦Map简介 键值对的集合#xff0c;您可以使用其关联的键从中检索值。 普通的 HashMap是无序的#xff08;不保证顺序#xff09;#xff0c;LinkedHashMap 按键插入顺序迭代#xff0c;而像 SplayTreeMap 这样的排序映射按排序顺序迭代键。 1#xff0c;添加元素 addEntri…Map简介 键值对的集合您可以使用其关联的键从中检索值。 普通的 HashMap是无序的不保证顺序LinkedHashMap 按键插入顺序迭代而像 SplayTreeMap 这样的排序映射按排序顺序迭代键。 1添加元素 addEntries()
final planets int, String{1: Mercury, 2: Venus,3: Earth, 4: Mars};
final gasGiants int, String{5: Jupiter, 6: Saturn};
final iceGiants int, String{7: Uranus, 8: Neptune};
planets.addEntries(gasGiants.entries);
planets.addEntries(iceGiants.entries);
print(planets);
// {1: Mercury, 2: Venus, 3: Earth, 4: Mars, 5: Jupiter, 6: Saturn,
// 7: Uranus, 8: Neptune}2更新组元素 update()
final planetsFromSun int, String{1: Mercury, 2: unknown,3: Earth};
// Update value for known key value 2.
planetsFromSun.update(2, (value) Venus);
print(planetsFromSun); // {1: Mercury, 2: Venus, 3: Earth}final largestPlanets int, String{1: Jupiter, 2: Saturn,3: Neptune};
// Key value 8 is missing from list, add it using [ifAbsent].
largestPlanets.update(8, (value) New, ifAbsent: () Mercury);
print(largestPlanets); // {1: Jupiter, 2: Saturn, 3: Neptune, 8: Mercury}3更新所有元素的值 updateAll()
final terrestrial int, String{1: Mercury, 2: Venus, 3: Earth};
terrestrial.updateAll((key, value) value.toUpperCase());
print(terrestrial); // {1: MERCURY, 2: VENUS, 3: EARTH}4删除指定的元素 removeWhere
final terrestrial int, String{1: Mercury, 2: Venus, 3: Earth};
terrestrial.removeWhere((key, value) value.startsWith(E));
print(terrestrial); // {1: Mercury, 2: Venus}5查找 [key] 的值如果不存在则添加新条目。 putIfAbsent
final diameters num, String{1.0: Earth};
final otherDiameters double, String{0.383: Mercury, 0.949: Venus};for (final item in otherDiameters.entries) {diameters.putIfAbsent(item.key, () item.value);
}
print(diameters); // {1.0: Earth, 0.383: Mercury, 0.949: Venus}// If the key already exists, the current value is returned.
final result diameters.putIfAbsent(0.383, () Random);
print(result); // Mercury
print(diameters); // {1.0: Earth, 0.383: Mercury, 0.949: Venus}6将所有键值对添加到此映射中。 addAll
final planets int, String{1: Mercury, 2: Earth};
planets.addAll({5: Jupiter, 6: Saturn});
print(planets); // {1: Mercury, 2: Earth, 5: Jupiter, 6: Saturn}7从映射中删除 [key] 及其关联值如果存在。 remove
final terrestrial int, String{1: Mercury, 2: Venus, 3: Earth};
final removedValue terrestrial.remove(2); // Venus
print(terrestrial); // {1: Mercury, 3: Earth}8从映射中移除所有条目。 clear
final planets int, String{1: Mercury, 2: Venus, 3: Earth};
planets.clear(); // {}9循环应用于映射的每个键值对。 forEach
final planetsByMass num, String{0.81: Venus, 1: Earth,0.11: Mars, 17.15: Neptune};planetsByMass.forEach((key, value) {print($key: $value);// 0.81: Venus// 1: Earth// 0.11: Mars// 17.15: Neptune
});10此映射是否包含给定的 [key]。 containsKey
final moonCount String, int{Mercury: 0, Venus: 0, Earth: 1,Mars: 2, Jupiter: 79, Saturn: 82, Uranus: 27, Neptune: 14 };
final containsUranus moonCount.containsKey(Uranus); // true
final containsPluto moonCount.containsKey(Pluto); // false11此映射是否包含给定的 [value]。 containsValue
final moonCount String, int{Mercury: 0, Venus: 0, Earth: 1,Mars: 2, Jupiter: 79, Saturn: 82, Uranus: 27, Neptune: 14 };
final moons3 moonCount.containsValue(3); // false
final moons82 moonCount.containsValue(82); // true12创建一个 Map 实例其中键和值是从 [iterable] 计算的。 fromIterable
final numbers int[1, 2, 3];
final map MapString, int.fromIterable(numbers,key: (item) item.toString(),value: (item) item * item);
print(map); // {1: 1, 2: 4, 3: 9}final numbers int[1, 2, 3];
final map Map.fromIterable(numbers);
print(map); // {1: 1, 2: 2, 3: 3}13创建一个映射将给定的 [键] 与给定的 [值] 相关联。 fromIterables
final rings bool[false, false, true, true];
final planets String{Earth, Mars, Jupiter, Saturn};
final map MapString, bool.fromIterables(planets, rings);
print(map); // {Earth: false, Mars: false, Jupiter: true, Saturn: true}14创建一个映射将给定的 [键] 与给定的 [值] 相关联。 unmodifiable
final planets int, String{1: Mercury, 2: Venus, 3: Earth};
final unmodifiableMap Map.unmodifiable(planets);
unmodifiableMap[4] Mars; // Throws
