Question

我对领域不熟悉。我试图在领域插入一个对象：我的模特是：

public class Citizen extends RealmObject implements Serializable {
    private static final long serialVersionUID = 1L;
    @PrimaryKey
    @SerializedName("idCitizen")
    private long id;
    private String postalSection;
    private int localityId;
    private int stateId;
    private int age;
    private String gender;
    private Evaluation evaluation;
    private User user;
    @SerializedName("degree")
    private Grade grade;
    .... // getters and setters
}

成绩模型：

public class Grade extends RealmObject implements Serializable {
    private static final long serialVersionUID = 1L;
    @SerializedName("idDegreeGrade")
    private int gradeId;
    @SerializedName("gradedsc")
    private String grade;
    // ... getters and setters
}

这是我尝试插入对象时的操作：

Realm realm = Realm.getInstance(ctx);
realm.beginTransaction();
Citizen citizen = realm.createObject(Citizen.class);
citizen.setAge(age); // This is OK
citizen.setGender(gender); // This is OK

Grade grade = new Grade();
grade.setGradeId(gradeId);
citizen.setGrade(grade); // This generate NPE

事情就是当我调试时，公民和年级都不为空。我明白了：

java.lang.NullPointerException
at io.realm.CitizenRealmProxy.setGrade(CitizenRealmProxy.java:180)
at com.myapp.action.CreateCitizenTask.onPostExecute(CreateCitizenTask.java:109)

当我尝试设置用户时也会发生这种情况：

citizen.setUser(myuser);

知道为什么???

Answer 1

必须通过以下方式创建组合对象：

 Grade grade = realm.createObject(Grade.class);

而不是：

 Grade grade = new Grade()

NPE在组合领域对象中设置对象值

1 个答案: