分页库使数据源无效不起作用

最近我正在尝试这个：

我有一个由数据源支持的作业列表（我正在使用分页库），并且作业列表中的每个项目都有一个保存按钮，并且该保存按钮将数据库中作业的状态从未保存更新为已保存（反之亦然）一旦更新，它就会使数据源失效，现在失效应该会导致当前页面立即重新加载，但这种情况并没有发生。

我检查了数据库中的值，它们实际上已更新，但用户界面的情况并非如此。

Code:

public class JobsPagedListProvider {

private JobListDataSource<JobListItemEntity> mJobListDataSource;

public JobsPagedListProvider(JobsRepository jobsRepository) {
    mJobListDataSource = new JobListDataSource<>(jobsRepository);
}

public LivePagedListProvider<Integer, JobListItemEntity> jobList() {
    return new LivePagedListProvider<Integer, JobListItemEntity>() {
        @Override
        protected DataSource<Integer, JobListItemEntity> createDataSource() {
            return mJobListDataSource;
        }
    };
}

public void setQueryFilter(String query) {
    mJobListDataSource.setQuery(query);
}
}

这是我的自定义数据源：

public class JobListDataSource<T> extends TiledDataSource<T> {

private final JobsRepository mJobsRepository;
private final InvalidationTracker.Observer mObserver;


String query = "";

@Inject
public JobListDataSource(JobsRepository jobsRepository) {
    mJobsRepository = jobsRepository;

    mJobsRepository.setJobListDataSource(this);

    mObserver = new InvalidationTracker.Observer(JobListItemEntity.TABLE_NAME) {
        @Override
        public void onInvalidated(@NonNull Set<String> tables) {
            invalidate();
        }
    };

    jobsRepository.addInvalidationTracker(mObserver);
}

@Override
public boolean isInvalid() {
    mJobsRepository.refreshVersionSync();
    return super.isInvalid();
}

@Override
public int countItems() {
    return DataSource.COUNT_UNDEFINED;
}


@Override
public List<T> loadRange(int startPosition, int count) {
    return (List<T>) mJobsRepository.getJobs(query, startPosition, count);
}


public void setQuery(String query) {
    this.query = query;
}
}

以下是 JobsRepository 中将作业从未保存更新为已保存的代码：

public void saveJob(JobListItemEntity entity) {
    Completable.fromCallable(() -> {
        JobListItemEntity newJob = new JobListItemEntity(entity);
        newJob.isSaved = true;
        mJobDao.insert(newJob);
        Timber.d("updating entity from " + entity.isSaved + " to "
                + newJob.isSaved); //this gets printed in log
        //insertion in db is happening as expected but UI is not receiving new list
        mJobListDataSource.invalidate();
        return null;
    }).subscribeOn(Schedulers.newThread()).subscribe();
}

这是作业列表的比较逻辑：

private static final DiffCallback<JobListItemEntity> DIFF_CALLBACK =  new DiffCallback<JobListItemEntity>() {
    @Override
    public boolean areItemsTheSame(@NonNull JobListItemEntity oldItem, @NonNull JobListItemEntity newItem) {
        return oldItem.jobID == newItem.jobID;
    }

    @Override
    public boolean areContentsTheSame(@NonNull JobListItemEntity oldItem, @NonNull JobListItemEntity newItem) {
        Timber.d(oldItem.isSaved + " comp with" + newItem.isSaved);
        return oldItem.jobID == newItem.jobID
                && oldItem.jobTitle.compareTo(newItem.jobTitle) == 0
                && oldItem.isSaved == newItem.isSaved;
    }
};

JobRepository中的JobListDataSource（下面仅提及相关部分）：

public class JobsRepository {
//holds an instance of datasource
private JobListDataSource mJobListDataSource;

//setter
public void setJobListDataSource(JobListDataSource jobListDataSource) {
    mJobListDataSource = jobListDataSource;
}

}

JobsRepository 中的 getJobs() ：

public List<JobListItemEntity> getJobs(String query, int startPosition, int count) {
    if (!isJobListInit) {

        Observable<JobList> jobListObservable = mApiService.getOpenJobList(
                mRequestJobList.setPageNo(startPosition/count + 1)
                        .setMaxResults(count)
                        .setSearchKeyword(query));

        List<JobListItemEntity> jobs = mJobDao.getJobsLimitOffset(count, startPosition);

        //make a synchronous network call since we have no data in db to return
        if(jobs.size() == 0) {
            JobList jobList = jobListObservable.blockingSingle();
            updateJobList(jobList, startPosition);
        } else {
            //make an async call and return cached version meanwhile
            jobListObservable.subscribe(new Observer<JobList>() {
                @Override
                public void onSubscribe(Disposable d) {

                }

                @Override
                public void onNext(JobList jobList) {
                    updateJobList(jobList, startPosition);
                }

                @Override
                public void onError(Throwable e) {
                    Timber.e(e);
                }

                @Override
                public void onComplete() {

                }
            });
        }
    }

    return mJobDao.getJobsLimitOffset(count, startPosition);
}

更新 jobsRepository 中的 JobList：

private void updateJobList(JobList jobList, int startPosition) {
    JobListItemEntity[] jobs = jobList.getJobsData();
    mJobDao.insert(jobs);
    mJobListDataSource.invalidate();
}

阅读 DataSource 的源代码后我意识到：

1. 数据源一旦失效将永远不会再次有效。
2. invalidate()说：如果已经调用了 invalidate，则此方法不执行任何操作。

我实际上有一个自定义数据源的单例（JobListDataSource） 由...提供JobsPagedListProvider，所以当我使我的DataSource in saveJob()（定义于JobsRepository），它试图获得新的DataSource实例（通过再次调用 loadRange() 来获取最新数据 - 这就是刷新数据源的工作原理） 但自从我的DataSource是单例并且它已经无效所以没有loadRange()正在查询！

所以请确保你没有一个单例DataSource并使你的DataSource手动（通过调用invalidate()）或有一个InvalidationTracker在您的数据源的构造函数中。

所以最终的解决方案是这样的：

JobsPagedListProvider 中没有单例：

public class JobsPagedListProvider {

private JobListDataSource<JobListItemEntity> mJobListDataSource;

private final JobsRepository mJobsRepository;

public JobsPagedListProvider(JobsRepository jobsRepository) {
    mJobsRepository = jobsRepository;
}

public LivePagedListProvider<Integer, JobListItemEntity> jobList() {
    return new LivePagedListProvider<Integer, JobListItemEntity>() {
        @Override
        protected DataSource<Integer, JobListItemEntity> createDataSource() {
            //always return a new instance, because if DataSource gets invalidated a new instance will be required(that's how refreshing a DataSource works)          
            mJobListDataSource = new JobListDataSource<>(mJobsRepository);
            return mJobListDataSource;
        }
    };
}

public void setQueryFilter(String query) {
    mJobListDataSource.setQuery(query);
}
}

还要确保如果您从网络获取数据，则需要有正确的逻辑来在查询网络之前检查数据是否过时，否则每次数据源失效时都会重新查询。 我通过在中添加一个 insertAt 字段解决了这个问题JobEntity它跟踪该项目何时插入数据库并检查它是否过时getJobs() of JobsRepository.

以下是 getJobs() 的代码：

public List<JobListItemEntity> getJobs(String query, int startPosition, int count) {
    Observable<JobList> jobListObservable = mApiService.getOpenJobList(
            mRequestJobList.setPageNo(startPosition / count + 1)
                    .setMaxResults(count)
                    .setSearchKeyword(query));

    List<JobListItemEntity> jobs = mJobDao.getJobsLimitOffset(count, startPosition);

    //no data in db, make a synchronous call to network to get the data
    if (jobs.size() == 0) {
        JobList jobList = jobListObservable.blockingSingle();
        updateJobList(jobList, startPosition, false);
    } else if (shouldRefetchJobList(jobs)) {
        //data available in db, so show a cached version and make async network call to update data
        jobListObservable.subscribe(new Observer<JobList>() {
            @Override
            public void onSubscribe(Disposable d) {

            }

            @Override
            public void onNext(JobList jobList) {
                updateJobList(jobList, startPosition, true);
            }

            @Override
            public void onError(Throwable e) {
                Timber.e(e);
            }

            @Override
            public void onComplete() {

            }
        });
    }

    return mJobDao.getJobsLimitOffset(count, startPosition);
}

最后删除 JobListDatasource 中的 InvalidationTracker，因为我们手动处理失效：

public class JobListDataSource<T> extends TiledDataSource<T> {

private final JobsRepository mJobsRepository;

String query = "";

public JobListDataSource(JobsRepository jobsRepository) {
    mJobsRepository = jobsRepository;
    mJobsRepository.setJobListDataSource(this);
}

@Override
public int countItems() {
    return DataSource.COUNT_UNDEFINED;
}

@Override
public List<T> loadRange(int startPosition, int count) {
    return (List<T>) mJobsRepository.getJobs(query, startPosition, count);
}


public void setQuery(String query) {
    this.query = query;
}
}