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对Realm数据库多线程下被调用的处理

 5 years ago
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Realm是一个非常方便的数据库，但是也有其局限性。正如Realm官方文档所述：

Threads

Although Realm files can be accessed by multiple threads concurrently, you cannot hand over Realms, Realm objects, queries, and results between threads.

虽然每个线程都能取到Realm文件，但是这些文件并不能在线程间通信。当你取出一个RealmObject，若想使用其最新数据，需要调用[RLMRealm refresh]方法，或者将RLMRealm的autorefresh参数设为YES。

而官方文档提到：

Realms are automatically refreshed at the start of every runloop iteration

autorefresh让Realm在每个runloop循环开始的时候自动刷新，所以一般不推荐设置为自动刷新。

[RLMRealm commitWriteTransaction]方法被调用的时候Realm数据也将被刷新。

所以在一个类调用Realm数据时，可以这样处理：

- (RLMObject *)RLMObj {  @synchronized (RLMObj) {      if (!_RLMObj || _RLMObjTread != [NSThread currentThread]) {
          [[RLMRealm defaultRealm] refresh];
          _RLMObjTread = [NSThread currentThread];
          _RLMObj = [RLMObj objectsWhere:@"pid = '12345"];
      }      return _RLMObj;
   }
}

使用一个变量存储当前Realm对象的线程，当线程不一致时，刷新数据库重取，即可在多线程的情况下愉快的使用Realm数据库

附上Realm关于线程的官方文档： https://realm.io/docs/objc/latest/#threading


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