MediatorLiveData onChanged未被调用

    MediatorLiveData<Content> mediatorLiveData = new MediatorLiveData<>();
    appExecutors.diskIO().execute(() -> {
                    long id = contentDao.insert(content);
                    Log.i("LIVE", id + "");
                    LiveData<Content> content = contentDao.getContentById(id);

                    mediatorLiveData.addSource(content, new Observer<Content>() {
                        @Override
                        public void onChanged(@Nullable Content content) {
                            Log.i("LIVE", "FIRED");
                        }
                    });

                });

首先,我尝试向数据库中插入一个新的内容对象。我在下一行中记录插入对象的id。我有一些身份证,这是好的。在此之后,我使用id查询同一个对象。查询返回一个LiveData。( )

MediatorLiveData . 不幸的是,mediatorLiveData的onChange方法从未触发。因此日志也不会被打印出来。

@Dao
public interface ContentDao {

    @Insert
    long insert(Content content);

    @Query("SELECT * FROM my_table WHERE id = :id")
    LiveData<Content> getContentById(long id);
}

我不明白我做错了什么。有人能帮忙吗。谢谢!!

编辑:为了澄清,这是代码的外观。

return new NetworkBoundResource<Content, CreateContent>(appExecutors) {
    @Override
    protected void saveCallResult(@NonNull CreateContent item) {
       //Something
    }

    @Override
    protected boolean shouldCall(@Nullable Content data) {
        //Something;
    }

    @Override
    protected LiveData<Content> createDbCall() {
        MediatorLiveData<Content> mediatorLiveData = new MediatorLiveData<>();
        appExecutors.diskIO().execute(() -> {
                    long id = contentDao.insert(content);
                    Log.i("LIVE", id + "");
                    LiveData<Content> content = contentDao.getContentById(id);

                    mediatorLiveData.addSource(content, new Observer<Content>() {
                        @Override
                        public void onChanged(@Nullable Content c) {
                            Log.i("LIVE", "FIRED");                                                
                            mediatorLiveData.removeSource(content);
                            mediatorLiveData.postValue(c);
                        }
                    });

            });
        return mediatorLiveData;
    }

    @NonNull
    @Override
    protected LiveData<ApiResponse<CreateContent>> createCall() {
        //Something
    }
}.asLiveData();

值将返回给构造函数。

@MainThread
    public NetworkBoundResource(AppExecutors appExecutors) {
        this.appExecutors = appExecutors;
        result.setValue(Resource.loading(null));
        //TODO:: Add method to check if data should be saved. This should apply for search data.
        LiveData<ResultType> dbSource = createDbCall();
        result.addSource(dbSource, data -> {
            result.removeSource(dbSource);
            if (shouldCall(data)) {
                fetchFromNetwork(dbSource);
            } else {
                result.addSource(dbSource, newData -> setValue(Resource.success(newData)));
            }
        });
    }