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枚举 — Java SDK

Atlas Device SDK 已弃用。有关详细信息，请参阅弃用页面。

枚举在 Java SDK 中不是原生支持的。不过，如果按照以下步骤操作，您可以在 Realm 对象中使用 Java 和 Kotlin 枚举。

使用

要在Realm 对象类中使用枚举，请定义一个字段与您的枚举的根本的数据类型相匹配的字段。为字段创建 getter 和 setter，以在根本的值和枚举类型之间转换字段值。您可以使用 Java 的内置 Enum.valueOf() 方法从根本的类型转换为枚举类型。

Enum 类

public enum FrogState {
    TADPOLE("Tadpole"),
    FROG("Frog"),
    OLD_FROG("Old Frog");
    private String state;
    FrogState(String state) {
        this.state = state;
    }
    public String getState() {
        return state;
    }
}

Realm 对象

import io.realm.RealmObject;
public class Frog extends RealmObject {
    String name;
    String state = FrogState.TADPOLE.getState();
    // realm-required empty constructor
    public Frog() {}
    public String getName() { return name; }
    public void setName(String name) { this.name = name; }
    public FrogState getState() {
        // because state is actually a String and another client could assign an invalid value,
        // default the state to "TADPOLE" if the state is unreadable
        FrogState currentState = null;
        try {
            // fetches the FrogState enum value associated with the current internal string value
            currentState = FrogState.valueOf(state);
        } catch (IllegalArgumentException e) {
            currentState = FrogState.TADPOLE;
        }
        return currentState;
    }
    public void setState(FrogState value) {
        // users set state using a FrogState, but it is saved as a string internally
        this.state = value.getState();
    }
}

使用

Frog frog = realm.createObject(Frog.class);
frog.setName("Jonathan Livingston Applesauce");
// set the state using the enum
frog.setState(FrogState.FROG);
// fetching the state returns an enum
FrogState currentJonathanState = frog.getState();

Enum 类

enum class FrogState(val state: String) {
    TADPOLE("Tadpole"),
    FROG("Frog"),
    OLD_FROG("Old Frog");
}

Realm 对象

import io.realm.RealmObject
import java.lang.IllegalArgumentException
open class Frog  // realm-required empty constructor
    : RealmObject() {
    var name: String? = null
    private var state: String = FrogState.TADPOLE.state
    var stateEnum: FrogState
        get() {
            // because state is actually a String and another client could assign an invalid value,
            // default the state to "TADPOLE" if the state is unreadable
            return try {
                // fetches the FrogState enum value associated with the current internal string value
                FrogState.valueOf(state)
            } catch (e: IllegalArgumentException) {
                FrogState.TADPOLE
            }
        }
        set(value) {
            // users set state using a FrogState, but it is saved as a string internally
            state = value.state
        }
}

使用

val frog = realm.createObject(Frog::class.java)
frog.name = "Jonathan Livingston Applesauce"
// set the state using the enum
frog.stateEnum = FrogState.FROG
// fetching the state returns an enum
val currentJonathanState: FrogState = frog.stateEnum

后退

混合

来年

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