分页库使数据源无效 | 分页库使数据源无效

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问题描述

最近我正在尝试:

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，并且该保存按钮将作业状态从未保存状态更新为已保存状态(反之亦然) )添加到数据库中，一旦更新，它将使数据源无效，现在，无效应立即导致当前页面的重新加载，但这没有发生.

I have a list of jobs backed by data source (I am using paging library) and each item in job list is having a save button, and that save button updates the status of the job from unsaved to saved (or vice versa) in database and once updated it invalidates the DataSource, now that invalidation should cause reload for the current page immediately, but that isn't happening.

我检查了数据库中的值，这些值实际上得到了更新，但UI并非如此.

I checked values in database they actually get updated but that isn't the case with the UI.

代码:

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:

Here is my custom datasource:

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;
}
}

这是JobsRepository中的代码，用于将作业从未保存状态更新为已保存状态:

Here is the code in JobsRepository that updates job from unsaved to saved:

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();
}

这是作业列表的差异逻辑:

Here is the Diffing logic for job list:

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(以下仅提及相关部分):

JobListDataSource in JobRepository (only relevant portion is mentioned below):

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

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

}

JobsRepository中的

getJobs():

getJobs() in JobsRepository:

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);
}

jobsRepository中的updateJobList:

updateJobList in jobsRepository:

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

推荐答案

阅读DataSource的源代码后，我意识到了这一点:

After reading the source code of DataSource I realized this:

一旦失效的数据源将不再有效.
invalidate()说:如果已经调用了invalidate，则此方法不执行任何操作.

A DataSource once invalidated will never become valid again.
invalidate() says: If invalidate has already been called, this method does nothing.

我实际上有一个由JobsPagedListProvider提供的自定义数据源(JobListDataSource)的单例，因此当我在saveJob()(在JobsRepository中定义)中使我的DataSource无效时，它试图获取新的DataSource实例(通过再次调用loadRange()来获取最新数据-这就是刷新DataSource的工作方式)但是由于我的DataSource是单身人士，并且已经无效，所以没有进行loadRange()查询！

I was actually having a singleton of my custom DataSource (JobListDataSource) provided by JobsPagedListProvider, so when I was invalidating my DataSource in saveJob() (defined in JobsRepository), it was trying to get new DataSource instance (to fetch latest data by again calling loadRange() - that's how refreshing a DataSource works)but since my DataSource was singleton and it was already invalid so no loadRange() query was being made!

因此，请确保没有DataSource的单例，并手动(通过调用invalidate())或在DataSource的构造函数中有InvalidationTracker来使DataSource无效.

So make sure you don't have a singleton of DataSource and invalidate your DataSource either manually (by calling invalidate()) or have a InvalidationTracker in your DataSource's constructor.

所以最终的解决方案是这样的:

So the final solution goes like this:

JobsPagedListProvider中没有单例:

Don't have a singleton in JobsPagedListProvider:

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);
}
}

还要确保如果您要从网络中获取数据，则需要具有正确的逻辑以在查询网络之前检查数据是否陈旧，否则它将在DataSource每次失效时重新查询.我通过在JobEntity中具有insertAt字段来解决此问题，该字段跟踪该项目何时插入DB中，并检查它在JobsRepository的getJobs()中是否陈旧.

这是getJobs()的代码:

Also make sure if you're fetching data from network you need to have right logic to check whether data is stale before querying the network else it will requery everytime the DataSource gets invalidated.I solved it by having a insertedAt field in JobEntity which keeps track of when this item was inserted in DB and checking if it is stale in getJobs() of JobsRepository.

Here is the code for getJobs():

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，因为我们正在手动处理无效，所以在JobListDatasource中删除InvalidationTracker:

Finally remove InvalidationTracker in JobListDatasource as we are handling invalidation manually:

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;
}
}

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