Question

我使用Dagger 2为整个应用提供单例Realm实例（所有数据访问对象都使用单个域）。但是，据我所知，Realm可以使用@NgModule({ declarations: [ MyApp, ExpansivoComponent ], imports: [ BrowserModule, IonicModule.forRoot(MyApp) ], bootstrap: [IonicApp], entryComponents: [ MyApp, ExpansivoComponent ],进行多实例，我们必须关闭每个实例，当我们完成它时，由Realm docs提供：

Realm.getInstance()

我的问题是：我应该像我一样使用单身Realm实例，还是为每个Activity / Fragment创建一个realm实例，然后在/** * Closes the Realm instance and all its resources. * <p> * It's important to always remember to close Realm instances when you're done with it in order not to leak memory, * file descriptors or grow the size of Realm file out of measure. * * @throws IllegalStateException if attempting to close from another thread. */ @Override public void close() { if (this.threadId != Thread.currentThread().getId()) { throw new IllegalStateException(INCORRECT_THREAD_CLOSE_MESSAGE); } if (realmCache != null) { realmCache.release(this); } else { doClose(); } }使用realm.close()关闭它？

Answer 1

只有在给定线程上至少有1个Realm实例打开时，才能访问Managed RealmObjects（它们访问时延迟加载），但是在非looper后台线程上关闭Realm实例是非常严重的问题。 / p>

如果您从Dagger模块提供线程本地单例Realm，则该Realm实例只能在创建它的线程上访问。并且会导致从其他地方访问崩溃。

一种可能性是提供一个可以打开Realm实例的单例类，例如this：

@Singleton
public class RealmManager {
    private final ThreadLocal<Realm> localRealms = new ThreadLocal<>();

    @Inject
    public RealmManager() {
    }

    /**
     * Opens a reference-counted local Realm instance.
     *
     * @return the open Realm instance
     */
    public Realm openLocalInstance() {
        checkDefaultConfiguration();
        Realm realm = Realm.getDefaultInstance(); // <-- maybe this should be configurable
        if(localRealms.get() == null) {
            localRealms.set(realm);
        }
        return realm;
    }

    /**
     * Returns the local Realm instance without adding to the reference count.
     *
     * @return the local Realm instance
     * @throws IllegalStateException when no Realm is open
     */
    public Realm getLocalInstance() {
        Realm realm = localRealms.get();
        if(realm == null) {
            throw new IllegalStateException(
                    "No open Realms were found on this thread.");
        }
        return realm;
    }

    /**
     * Closes local Realm instance, decrementing the reference count.
     *
     * @throws IllegalStateException if there is no open Realm.
     */
    public void closeLocalInstance() {
        checkDefaultConfiguration();
        Realm realm = localRealms.get();
        if(realm == null) {
            throw new IllegalStateException(
                    "Cannot close a Realm that is not open.");
        }
        realm.close();
        // noinspection ConstantConditions
        if(Realm.getLocalInstanceCount(Realm.getDefaultConfiguration()) <= 0) {
            localRealms.set(null);
        }
    }

    private void checkDefaultConfiguration() {
        if(Realm.getDefaultConfiguration() == null) {
            throw new IllegalStateException("No default configuration is set.");
        }
    }
}

但即便如此，you'd need to manage the local instances for the given threads where you need them.

public class MainActivity
        extends AppCompatActivity {
    RealmManager realmManager;

    ...

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        realmManager = Injector.get().realmManager();
        realmManager.openLocalInstance();
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        ButterKnife.bind(this);
        ...
    }

    @Override
    protected void onDestroy() {
        super.onDestroy();
        realmManager.closeLocalInstance();
    }

Answer 2

单例实例最有可能让您陷入困境。您应该为每个活动/片段创建一个。

Dagger 2 - 我应该使用单身Realm实例吗？

2 个答案: