关于实现点赞功能的问题（Paging）

[qingmei2]

关于实现点赞功能的问题（Paging）

[qingmei2]

@windows7lake

你好，不好意思我没有太理解你的意思：

但是因为DiffUtil.ItemCallback中的areContentsTheSame(oldItem: Repo, newItem: Repo)方法返回的oldItem和newItem是相同的，导致点赞状态不会被更新。

这时的对象为何会是相同的呢，我的理解是item.forksCount发生了变化，Paging内部会自动执行onItemChanged的更新逻辑呀。

[windows7lake]

@qingmei2 我的想法是和你一样的，我也认为Paging内部应该会自动执行onItemChanged的更新逻辑才对，所以我就一直寻找问题的原因，直到打印areContentsTheSame(oldItem: Repo, newItem: Repo)中的log时才发现：点击同一个item时，返回的oldItem和newItem是相同的。
我也看了一下DiffUtil的相关源码，也没有什么收获。你之前有用paging实现过类似的功能吗？是怎么处理的呢？

[windows7lake]

下面是连续点击同一个item时输出的log：
submitList是提交给PageList的数据，areContentsTheSame 是DiffUtil打印的数据

2019-08-14 16:07:56.312 29145-29145/com.qingmei2.sample E/ReposFragment$override: =============submitList  id: 200820107   count: 1
2019-08-14 16:07:56.314 29145-29759/com.qingmei2.sample E/ReposPagedAdapter$Companion$diffCallback$1$override: =============areContentsTheSame id: 200820107  ==  oldItem: 1   ==   newItem: 1  

2019-08-14 16:07:59.610 29145-29145/com.qingmei2.sample E/ReposFragment$override: =============submitList  id: 200820107   count: 1000
2019-08-14 16:07:59.612 29145-29904/com.qingmei2.sample E/ReposPagedAdapter$Companion$diffCallback$1$override: =============areContentsTheSame id: 200820107  ==  oldItem: 1   ==   newItem: 1000  

2019-08-14 16:08:12.650 29145-29145/com.qingmei2.sample E/ReposFragment$override: =============submitList  id: 200820107   count: 1
2019-08-14 16:08:12.652 29145-29759/com.qingmei2.sample E/ReposPagedAdapter$Companion$diffCallback$1$override: =============areContentsTheSame id: 200820107  ==  oldItem: 1   ==   newItem: 1  

2019-08-14 16:08:21.999 29145-29145/com.qingmei2.sample E/ReposFragment$override: =============submitList  id: 200820107   count: 1000
2019-08-14 16:08:22.003 29145-29904/com.qingmei2.sample E/ReposPagedAdapter$Companion$diffCallback$1$override: =============areContentsTheSame id: 200820107  ==  oldItem: 1   ==   newItem: 1000  
`

[windows7lake]

快速点击item的log，快速点击同一个item的时候，forksCount在界面上的显示有时会变化：

2019-08-14 16:13:07.925 29145-29145/com.qingmei2.sample E/ReposFragment$override: =============submitList  id: 200820107   count: 1
2019-08-14 16:13:07.928 29145-29759/com.qingmei2.sample E/ReposPagedAdapter$Companion$diffCallback$1$override: =============areContentsTheSame id: 200820107  ==  oldItem: 1   ==   newItem: 1  
2019-08-14 16:13:15.385 29145-29145/com.qingmei2.sample E/ReposFragment$override: =============submitList  id: 200820107   count: 1000
2019-08-14 16:13:15.387 29145-29904/com.qingmei2.sample E/ReposPagedAdapter$Companion$diffCallback$1$override: =============areContentsTheSame id: 200820107  ==  oldItem: 1   ==   newItem: 1000  
2019-08-14 16:13:16.361 29145-29145/com.qingmei2.sample E/ReposFragment$override: =============submitList  id: 200820107   count: 1
2019-08-14 16:13:16.364 29145-29759/com.qingmei2.sample E/ReposPagedAdapter$Companion$diffCallback$1$override: =============areContentsTheSame id: 200820107  ==  oldItem: 1   ==   newItem: 1  
2019-08-14 16:13:17.043 29145-29145/com.qingmei2.sample E/ReposFragment$override: =============submitList  id: 200820107   count: 1000
2019-08-14 16:13:17.045 29145-29904/com.qingmei2.sample E/ReposPagedAdapter$Companion$diffCallback$1$override: =============areContentsTheSame id: 200820107  ==  oldItem: 1   ==   newItem: 1000  
2019-08-14 16:13:17.747 29145-29145/com.qingmei2.sample E/ReposFragment$override: =============submitList  id: 200820107   count: 1
2019-08-14 16:13:17.749 29145-29759/com.qingmei2.sample E/ReposPagedAdapter$Companion$diffCallback$1$override: =============areContentsTheSame id: 200820107  ==  oldItem: 1   ==   newItem: 1  
2019-08-14 16:13:18.325 29145-29145/com.qingmei2.sample E/ReposFragment$override: =============submitList  id: 200820107   count: 1000
2019-08-14 16:13:18.327 29145-29904/com.qingmei2.sample E/ReposPagedAdapter$Companion$diffCallback$1$override: =============areContentsTheSame id: 200820107  ==  oldItem: 1   ==   newItem: 1000  
2019-08-14 16:13:19.511 29145-29145/com.qingmei2.sample E/ReposFragment$override: =============submitList  id: 200820107   count: 1000
2019-08-14 16:13:19.512 29145-29759/com.qingmei2.sample E/ReposPagedAdapter$Companion$diffCallback$1$override: =============areContentsTheSame id: 200820107  ==  oldItem: 1000   ==   newItem: 1000  
2019-08-14 16:13:21.042 29145-29145/com.qingmei2.sample E/ReposFragment$override: =============submitList  id: 200820107   count: 1
2019-08-14 16:13:21.044 29145-29904/com.qingmei2.sample E/ReposPagedAdapter$Companion$diffCallback$1$override: =============areContentsTheSame id: 200820107  ==  oldItem: 1000   ==   newItem: 1  
2019-08-14 16:13:21.844 29145-29145/com.qingmei2.sample E/ReposFragment$override: =============submitList  id: 200820107   count: 1000
2019-08-14 16:13:21.846 29145-29759/com.qingmei2.sample E/ReposPagedAdapter$Companion$diffCallback$1$override: =============areContentsTheSame id: 200820107  ==  oldItem: 1000   ==   newItem: 1000  
2019-08-14 16:13:23.058 29145-29145/com.qingmei2.sample E/ReposFragment$override: =============submitList  id: 200820107   count: 1
2019-08-14 16:13:23.060 29145-29904/com.qingmei2.sample E/ReposPagedAdapter$Companion$diffCallback$1$override: =============areContentsTheSame id: 200820107  ==  oldItem: 1000   ==   newItem: 1  
2019-08-14 16:13:23.959 29145-29145/com.qingmei2.sample E/ReposFragment$override: =============submitList  id: 200820107   count: 1000
2019-08-14 16:13:23.961 29145-29759/com.qingmei2.sample E/ReposPagedAdapter$Companion$diffCallback$1$override: =============areContentsTheSame id: 200820107  ==  oldItem: 1000   ==   newItem: 1000  
2019-08-14 16:13:24.545 29145-29145/com.qingmei2.sample E/ReposFragment$override: =============submitList  id: 200820107   count: 1
2019-08-14 16:13:24.547 29145-29904/com.qingmei2.sample E/ReposPagedAdapter$Companion$diffCallback$1$override: =============areContentsTheSame id: 200820107  ==  oldItem: 1000   ==   newItem: 1  
2019-08-14 16:13:25.030 29145-29145/com.qingmei2.sample E/ReposFragment$override: =============submitList  id: 200820107   count: 1000
2019-08-14 16:13:25.031 29145-29759/com.qingmei2.sample E/ReposPagedAdapter$Companion$diffCallback$1$override: =============areContentsTheSame id: 200820107  ==  oldItem: 1000   ==   newItem: 1000  
2019-08-14 16:13:25.663 29145-29145/com.qingmei2.sample E/ReposFragment$override: =============submitList  id: 200820107   count: 1
2019-08-14 16:13:25.666 29145-29904/com.qingmei2.sample E/ReposPagedAdapter$Companion$diffCallback$1$override: =============areContentsTheSame id: 200820107  ==  oldItem: 1000   ==   newItem: 1  

[qingmei2]

1和1000本质没有区别，既然点赞能够响应在ui上，取消点赞也能响应在ui上。

会不会是哪里代码实现有问题呢（比如为Dao的接口上试试为@update配置下冲突策略如OnConflictStrategy.REPLACE）？公司的项目是有实现点赞功能的，但合同约定不能放代码，这个只能靠个人debug了。

[windows7lake]

Room的Insert和Update以及冲突策略OnConflictStrategy.REPLACE，我都试过了，没有什么变化。我之前是在我自己的代码上操作的，我觉得可能是我某些代码的原因，但是我把上面的代码放到clone下来的MVVM-Rhine中也是同样的问题？
另外开始我怀疑可能是AutoDisposeViewHolder问题，所以也尝试把AutoDisposeViewHolder替换成RecyclerView.ViewHolder，可是问题依然存在。

[qingmei2]

@windows7lake

感谢你的反馈，个人的想法是，尝试一下在源码中打一下断点呢，或者使用相关工具查询一下数据库最新的数据？

[windows7lake]

@qingmei2
谢谢你的提议，我查看了每次写入后的数据库，发现数据是有正常写入的。
然后我断点看了submitList的源码，发现mPagedList 会在某个时间被赋值为当前状态的PagedList，进而导致oldSnapshot 和newSnapshot 一致。
AsyncPagedListDiffer的submitList代码：

public void submitList(@Nullable final PagedList<T> pagedList,
@Nullable final Runnable commitCallback) {

    ......

    if (mPagedList != null) {
        // first update scheduled on this list, so capture mPages as a snapshot, removing
        // callbacks so we don't have resolve updates against a moving target
        mPagedList.removeWeakCallback(mPagedListCallback);
        mSnapshot = (PagedList<T>) mPagedList.snapshot();
        mPagedList = null;
    }

    if (mSnapshot == null || mPagedList != null) {
        throw new IllegalStateException("must be in snapshot state to diff");
    }

    final PagedList<T> oldSnapshot = mSnapshot;
    final PagedList<T> newSnapshot = (PagedList<T>) pagedList.snapshot();
    mConfig.getBackgroundThreadExecutor().execute(new Runnable() {
        @Override
        public void run() {
            final DiffUtil.DiffResult result;
            result = PagedStorageDiffHelper.computeDiff(
                    oldSnapshot.mStorage,
                    newSnapshot.mStorage,
                    mConfig.getDiffCallback());

            mMainThreadExecutor.execute(new Runnable() {
                @Override
                public void run() {
                    if (mMaxScheduledGeneration == runGeneration) {
                        latchPagedList(pagedList, newSnapshot, result,
                                oldSnapshot.mLastLoad, commitCallback);
                    }
                }
            });
        }
    });
}

我有点好奇你的DiffUtil.ItemCallback和我的有什么区别吗？还是说做了什么特殊的处理？另外你的paging-runtime版本是多少呢？能不能提供一个小demo学习一下。谢谢！

[windows7lake]

能讲一下你那边用paging实现点赞的方法吗？感觉像是paging的问题