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RealmSet — Java SDK

Atlas Device SDK 已弃用。有关详细信息，请参阅弃用页面。

版本 10.6.0 中的新增内容。

您可以使用 RealmSet数据类型来管理唯一键的集合。 RealmSet实现了 Java 的Set接口，因此它的工作方式与内置HashSet类相同，不同之处在于托管RealmSet实例将其内容持久保存到域中。包含Realm对象的RealmSet实例实际上仅存储对这些对象的引用，因此从域中删除Realm 对象也会从包含该对象的任何RealmSet实例中删除该对象。

由于RealmSet实现了RealmCollection ，因此它具有一些有用的数学方法，例如sum 、 min和max 。有关可用RealmSet方法的完整列表，请参阅： RealmSet API 参考。

方法限制

不能对包含RealmSet类型字段的对象使用以下Realm方法：

Realm.insert()
Realm.insertOrUpdate()
Realm.createAllFromJson()
Realm.createObjectFromJson()
Realm.createOrUpdateAllFromJson()
Realm.createOrUpdateObjectFromJson()

使用

要创建RealmSet 类型的字段，请定义对象类型的属性，其中RealmSet<E> E定义要存储在RealmSet 中的键。

使用RealmSet.add()将对象添加到RealmSet
使用RealmSet.addAll()添加多个对象
使用RealmSet.contains()检查集合中是否包含特定对象
使用RealmSet.containsAll()检查集合是否包含所有多个对象

import io.realm.RealmObject;
import io.realm.RealmSet;
public class Frog extends RealmObject {
    String name;
    RealmSet<Snack> favoriteSnacks;
    // realm-required empty constructor
    public Frog() {}
    public String getName() { return name; }
    public void setName(String name) { this.name = name; }
    public RealmSet<Snack> getFavoriteSnacks() { return favoriteSnacks; }
    public void setFavoriteSnacks(RealmSet<Snack> favoriteSnacks) { this.favoriteSnacks = favoriteSnacks; }
}

import io.realm.RealmObject;
public class Snack extends RealmObject {
    private String name;
    public Snack() {}
    public String getName() { return name; }
    public void setName(String name) { this.name = name; }
}

Frog frog = realm.createObject(Frog.class);
frog.setName("George Washington");
// get the RealmSet field from the object we just created
RealmSet<Snack> set = frog.getFavoriteSnacks();
// add value to the RealmSet
Snack flies = realm.createObject(Snack.class);
flies.setName("flies");
set.add(flies);
// add multiple values to the RealmSet
Snack water = realm.createObject(Snack.class);
water.setName("water");
Snack verySmallRocks = realm.createObject(Snack.class);
verySmallRocks.setName("verySmallRocks");
set.addAll(Arrays.asList(water, verySmallRocks));
// check for the presence of a key with contains
Assert.assertTrue(set.contains(flies));
// check for the presence of multiple keys with containsAll
Snack biscuits = realm.createObject(Snack.class);
biscuits.setName("biscuits");
Assert.assertTrue(set.containsAll(Arrays.asList(water, biscuits)) == false);
// remove string from a set
set.remove(verySmallRocks);
// set no longer contains that string
Assert.assertTrue(set.contains(verySmallRocks) == false);
// deleting a Realm object also removes it from any RealmSets
int sizeOfSetBeforeDelete = set.size();
flies.deleteFromRealm();
// deleting flies object reduced the size of the set by one
Assert.assertTrue(sizeOfSetBeforeDelete == set.size() + 1);

import io.realm.RealmObject
import io.realm.RealmSet
open class Frog
    : RealmObject() {
    var name: String = ""
    var favoriteSnacks: RealmSet<Snack> = RealmSet<Snack>();
}

import io.realm.RealmObject
open class Snack : RealmObject() {
    var name: String? = null
}

val frog = realm.createObject(Frog::class.java)
frog.name = "Jonathan Livingston Applesauce"
// get the RealmSet field from the object we just created
val set = frog.favoriteSnacks
// add value to the RealmSet
val flies = realm.createObject(Snack::class.java)
flies.name = "flies"
set.add(flies)
// add multiple values to the RealmSet
val water = realm.createObject(Snack::class.java)
water.name = "water"
val verySmallRocks = realm.createObject(Snack::class.java)
verySmallRocks.name = "verySmallRocks"
set.addAll(listOf(water, verySmallRocks))
// check for the presence of a key with contains
Assert.assertTrue(set.contains(flies))
// check for the presence of multiple keys with containsAll
val biscuits = realm.createObject(Snack::class.java)
biscuits.name = "biscuits"
Assert.assertTrue(set.containsAll(Arrays.asList(water, biscuits)) == false)
// remove string from a set
set.remove(verySmallRocks)
// set no longer contains that string
Assert.assertTrue(set.contains(verySmallRocks) == false)
// deleting a Realm object also removes it from any RealmSets
val sizeOfSetBeforeDelete = set.size
flies.deleteFromRealm()
// deleting flies object reduced the size of the set by one
Assert.assertTrue(sizeOfSetBeforeDelete == set.size + 1)

通知

要订阅对RealmSet的更改，请将SetChangeListener实现传递给RealmSet.addChangeListener 方法。您的SetChangeListener实现必须定义一个onChange()方法，该方法接受对已更改RealmSet的引用和一组更改作为参数。您可以通过SetChangeSet参数访问添加到集合中的项目数以及从集合中删除的项目数。

AtomicReference<Frog> frog = new AtomicReference<Frog>();
realm.executeTransaction(r -> {
    frog.set(realm.createObject(Frog.class));
    frog.get().setName("Jonathan Livingston Applesauce");
});
SetChangeListener<Snack> setChangeListener = new SetChangeListener<Snack>() {
    @Override
    public void onChange(@NotNull RealmSet<Snack> set, SetChangeSet changes) {
        Log.v("EXAMPLE", "Set changed: " +
                changes.getNumberOfInsertions() + " new items, " +
                changes.getNumberOfDeletions() + " items removed.");
    }
};
frog.get().getFavoriteSnacks().addChangeListener(setChangeListener);
realm.executeTransaction(r -> {
    // get the RealmSet field from the object we just created
    RealmSet<Snack> set = frog.get().getFavoriteSnacks();
    // add value to the RealmSet
    Snack flies = realm.createObject(Snack.class);
    flies.setName("flies");
    set.add(flies);
    // add multiple values to the RealmSet
    Snack water = realm.createObject(Snack.class);
    water.setName("water");
    Snack verySmallRocks = realm.createObject(Snack.class);
    verySmallRocks.setName("verySmallRocks");
    set.addAll(Arrays.asList(water, verySmallRocks));
});

var frog :Frog? = null
realm.executeTransaction { r: Realm? ->
    frog = realm.createObject(Frog::class.java)
    frog?.name = "Jonathan Livingston Applesauce"
}
val setChangeListener: SetChangeListener<Snack>
        = SetChangeListener<Snack> { set, changes ->
    Log.v("EXAMPLE", "Set changed: " +
            changes.numberOfInsertions + " new items, " +
            changes.numberOfDeletions + " items removed.")
}
frog?.favoriteSnacks?.addChangeListener(setChangeListener)
realm.executeTransaction { r: Realm? ->
    // get the RealmSet field from the object we just created
    val set = frog!!.favoriteSnacks
    // add value to the RealmSet
    val flies = realm.createObject(Snack::class.java)
    flies.name = "flies"
    set.add(flies)
    // add multiple values to the RealmSet
    val water = realm.createObject(Snack::class.java)
    water.name = "water"
    val verySmallRocks = realm.createObject(Snack::class.java)
    verySmallRocks.name = "verySmallRocks"
    set.addAll(Arrays.asList(water, verySmallRocks))
}

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