CODEWITHSUNDEEP
javaandroidconstructorsingletonrealm
Calco
Calco

Reputation: 1460

Class that extends RealmObject as a singleton

I have a configuration class within my Android application that I store within a Realm database. I just edited it to follow the singleton design pattern so there is only ever once instance of the configuration.

The problem is, the class now has a private constructor to prevent instantiation without calling my 'getInstance' method. However, RealmObject seems to require a public constructor.

Is it not possible to have a class that extends RealmObject using a singleton design pattern?

Is this simply a limitation of Realm that I am going to have to account for?

Here is a snippet of code for context:

public static  AppConfiguration getInstance(){
    if(configuration == null){
        synchronized (AppConfiguration.class) {
            if (configuration == null) {
                configuration = new AppConfiguration();
            }
        }
    }
    return configuration;
}

//constructor is private to prevent instantiation without using getInstance, enforces singleton
private AppConfiguration() { //The constructor defined as private which is causing the problem
    this.isRegistered = false;
    this.isLoggedIn = false;
}

Upvotes: 0

Views: 634

Answers (1)

EpicPandaForce
EpicPandaForce

Reputation: 81588

Conceptually your singleton setup does not make sense in the context of Realm, because you synchronize an unmanaged object (thus allowing "only one thread to access it at once" via mutual exclusion / locking), which brings up the question:

  • if the object is unmanaged, then why is it a RealmObject? (Realm allows consistency with its MVCC architecture, if you use a detached copy then why use Realm at all for its persistence?)
  • if the object was managed, then how would you access it from multiple threads? (managed RealmObjects are thread-confined ~ you'd need to make it ThreadLocal, and clear it out when its Realm is closed)

But yes, you need a public constructor for RealmObject so that Realm can instantiate its proxy instances. Perhaps you can try a protected constructor, and see if the RealmProxy can be instantiated via reflection if you do that.

Upvotes: 1

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