Xamarin Realm - when to close Realm

Question

I have a Shared Project where I have changed the database to Realm instead of SQLite.

My problem is, if I close the Realm in my DatabaseManager, the result is removed. Therefore i have created a static singelton instance of the Realm, which all my DatabaseManager use. Now my app crash after short time on memory, and if i remove all my database-functions, it works.

I create my Realm-instance here:

public class RealmDatabase
{
    private Realm mRealmDB;
    public Realm RealmDB
    {
        get
        {
            if (mRealmDB == null || mRealmDB.IsClosed)
            {
                SetRealm ();
            }
            return mRealmDB;  
        }
    }

    static RealmDatabase cCurrentInstance;
    public static RealmDatabase Current
    {
        get
        {
            if (cCurrentInstance == null)
                cCurrentInstance = new RealmDatabase ();

            return cCurrentInstance;
        }
    }

    public RealmDatabase ()
    {
    }

    private void SetRealm ()
    {
        var config = new RealmConfiguration ("DBName.realm", true);
        mRealmDB = Realm.GetInstance (config);
    }

    public Transaction BeginTransaction ()
    {
        return RealmDB.BeginWrite ();
    }
}

The I have my DatabaseManagler looking like this:

public class NewFreeUserManager
{
    internal Realm RealmDB = RealmDatabase.Current.RealmDB;
    static NewFreeUserManager cCurrentInstance;
    public static NewFreeUserManager Current
    {
        get
        {
            if (cCurrentInstance == null)
                cCurrentInstance = new NewFreeUserManager ();

            return cCurrentInstance;
        }
    }

    private NewFreeUserManager ()
    {
    }

    internal bool Save (FreeUser freeuser)
    {
        try
        {
            using (var trans = RealmDB.BeginWrite ())
            {
                RealmDB.RemoveAll<FreeUser> ();
                var fu = RealmDB.CreateObject<FreeUser> ();
                fu = freeuser;
                trans.Commit ();
            }
            return true;
        }
        catch (Exception e)
        {
            Console.WriteLine ("FreeUser save: " + e.ToString ());
            return false;
        }
    }

    internal FreeUser Get ()
    {
        return RealmDB.All<FreeUser> ().FirstOrDefault ();
    }
}

Can anyone help me?

Answer 1

there are a few issues with your current setup that prevent you from persisting objects properly.

The first and very important one is that Realm instances are not thread-safe. That is, using them as singletons is strongly discouraged, unless you are certain that you'll never access them from another thread.

The second is more subtle, but in your save method you are calling:

var fu = RealmDB.CreateObject<FreeUser>();
fu = freeuser;

What it does is, effectively, you are creating an object in the Realm, and then assigning the variable to another object. This will not assign freeuser's properties to fu, it just replaces one reference with another. What you're looking for is Realm.Manage so your code should look like this:

using (var trans = RealmDB.BeginWrite())
{
    RealmDB.Manage(freeuser);
    trans.Commit();
}

Once you fix the second bug, you should be able to go back and close Realm instances when you don't need them anymore.