我是否正确实现了 EpicPandaForce 的 RealmManager？

Question

我是 Realm（和 Android 开发）的新手，我想使用 Singleton 类来简化 Realm 数据管理，以便我的朋友更容易在我们的小组项目中使用。

EpicPandaForce 编写了一个名为 RealmManager here 的单例类，但我找不到实现它的示例，所以这是我尝试过的：

public class RealmManager {
    private static RealmManager instance;
    private final ThreadLocal<Realm> localRealm = new ThreadLocal<>();

    RealmManager(){}

    public synchronized static RealmManager getInstance(){
        if(instance == null){
            instance = new RealmManager();
        }
        return instance;
    }

    public Realm openLocalInstance() {
        Realm realm = Realm.getDefaultInstance();
        if(localRealm.get() == null) {
            localRealm.set(realm);
        }
        return realm;
    }

    public Realm getLocalInstance() {
        Realm realm = localRealm.get();
        if(realm == null) {
            throw new IllegalStateException("No open Realms were found on this thread.");
        }
        return realm;
    }

    public void closeLocalInstance() {
        Realm realm = localRealm.get();
        if(realm == null) {
            throw new IllegalStateException(
                "Cannot close a Realm that is not open.");
        }
        realm.close();
        if(Realm.getLocalInstanceCount(Realm.getDefaultConfiguration()) <= 0) {
        localRealm.set(null);
        }
    }

    public void storePreferenceDao(int userID, String rank){
        final PreferenceDao preferenceDao = new PreferenceDao();
        preferenceDao.setUserID(userID);
        preferenceDao.setRank(rank);
        openLocalInstance();
        getLocalInstance().executeTransactionAsync(new Realm.Transaction() {
            @Override
            public void execute(Realm realm) {
                realm.copyToRealmOrUpdate(preferenceDao);
            }
        }, new Realm.Transaction.OnSuccess(){
            @Override
            public void onSuccess(){
                System.out.println("Data is stored successfully!");
            }
        }, new Realm.Transaction.OnError(){
            @Override
            public void onError(Throwable error){
                System.out.println("There is an error in storePreferenceDao()");
            }
        });
        closeLocalInstance();
    }

所以当我的朋友想要存储一些数据时，他们可以使用：

RealmManager.getInstance().storePreferenceDao(123, "Alpaca");

这是应该如何使用的还是多余的？如何提高效率？

Answer 1

其实在这种情况下，该方法仍然只能从UI线程调用，并且本地实例应该在事务回调中关闭（否则不会调用onSuccess/onError）

如果可以，您可以创建一个能够在 bg 线程上执行的方法，如果已经在 bg 线程上，则可以在当前线程上执行

// method in RealmManager
public final void runTransaction(Realm.Transaction transaction) {
    runTransaction(transaction, null, null);
}

public final void runTransaction(Realm.Transaction transaction, Realm.Transaction.OnSuccess onSuccess) {
    runTransaction(transaction, onSuccess, null);
}

public final void runTransaction(Realm.Transaction transaction, Realm.Transaction.OnSuccess onSuccess, Realm.Transaction.OnError onError) {
    Realm realm = openLocalInstance();
    if(realm.isAutoRefresh()) {
        realm.executeTransactionAsync(transaction, new Realm.Transaction.OnSuccess() {
            @Override
            public void onSuccess() {
                try {
                    if(onSuccess != null) {
                        onSuccess.onSuccess();
                    }
                } finally {
                    closeLocalInstance();
                }
            }
        }, new Realm.Transaction.OnError() {
            @Override
            public void onError(Throwable e) {
                try {
                    if(onError != null) {
                        onError.onError(e);
                    }
                } finally {
                    closeLocalInstance();
                }
            }
        });
    } else {
        try {
            realm.executeTransaction(transaction);
            if(onSuccess != null) {
                onSuccess.onSuccess();
            }
        } catch(Exception e) {
            if(onError != null) {
                onError.onError(e);
            }
            throw new RuntimeException(e);
        } finally {
            closeLocalInstance();
        }
    }
}

如果您添加此方法，那么您现在可以执行一个事务，该事务将在可能的情况下通过async 事务方法在后台线程上执行，如果不在循环线程上则使用synchronous 事务方法（f.ex.后台线程）

你现在可以这样做

public void storePreferenceDao(int userID, String rank) {
    final PreferenceDao preferenceDao = new PreferenceDao();
    preferenceDao.setUserID(userID);
    preferenceDao.setRank(rank);
    runTransaction(new Realm.Transaction() {
        @Override
        public void execute(Realm realm) {
            realm.copyToRealmOrUpdate(preferenceDao);
        }
    }, new Realm.Transaction.OnSuccess(){
        @Override
        public void onSuccess(){
            System.out.println("Data is stored successfully!");
        }
    }, new Realm.Transaction.OnError(){
        @Override
        public void onError(Throwable error){
            System.out.println("There is an error in storePreferenceDao()");
        }
    });
}

或者只是

public void storePreferenceDao(int userID, String rank) {
    final PreferenceDao preferenceDao = new PreferenceDao();
    preferenceDao.setUserID(userID);
    preferenceDao.setRank(rank);
    runInTransaction(new Realm.Transaction() {
        @Override
        public void execute(Realm realm) {
            realm.copyToRealmOrUpdate(preferenceDao);
        }
    });
}

你知道，我一直觉得我应该在该示例中添加一个 runTransaction() 方法。不过，是否应该默认使用executeTransactionAsync（如果可以的话）还有待商榷。

Answer 2

一个简单的单例示例，

public class MySingleton {
private static MySingleton sMySingleton;

//private constructor.
private MySingleton() {
    if (sMySingleton != null){
        throw new RuntimeException("Use getInstance() for the instance");
    }
} 

public synchronized static MySingleton getInstance() {
    if (sMySingleton == null){ 
        sMySingleton = new MySingleton();
    }
    return sMySingleton;
}
}

希望对你有帮助！

Answer 3

这可能不是最好的答案，但这里是我如何在我的应用程序中使用领域

public class BaseActivity extends AppCompatActivity {
public Realm realm;
  @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_base);
        realm = Realm.getDefaultInstance();
    }

}

根据你的使用在其他Activity中扩展BaseActivity

public class MainActivity extends BaseActivity {

       @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        //Here you can directly access realm object and perform your task
        realm.where()//just example
    }
    @Override
    protected void onDestroy() {
        super.onDestroy();
        if(realm!=null)
           realm.close();
       //Don't forget to close realm object
    }

}

我并不是说这是最好的方法，但它是最好的方法之一。使用这种方式，我可以轻松管理我的领域类，并可以减少与领域相关的错误。对于片段，您可以制作 BaseFragment 并在其他片段中扩展它。

希望这会对您有所帮助...如果您有其他更好的方法，请告诉我