使用Android LiveData更新RecyclerView [英] update RecyclerView with Android LiveData

问题描述

有很多示例，如何在LiveData更改时将新列表推送到适配器.

There are many examples how to push new list to adapter on LiveData change.

我正在尝试更新庞大列表中的一行(例如，发表评论的数量).重置整个列表以仅更改一个字段会很愚蠢.

I'm trying to update one row (e.g number of comments for post) in the huge list. It would be stupid to reset whole list to change only one field.

我可以在onBindViewHolder上添加观察者，但我不知道何时删除观察者

I am able to add observer onBindViewHolder, but I can't understand when should I remove observer

@Override
public void onBindViewHolder(ViewHolder vh, int position) {
    Post post = getPost(position);
    vh.itemView.setTag(post);
    post.getLiveName().observeForever(vh.nameObserver);
    ... 
}

推荐答案

就像@Lyla所说，您应该在Fragment或Activity中将整个列表作为LiveData进行观察，当接收到更改时，应该通过DiffUtil将整个列表设置为适配器

Like @Lyla said, you should observe the whole list as LiveData in Fragment or Activity, when receive changes, you should set the whole list to the adapter by DiffUtil.

伪造代码:

PostViewModel {
    LiveData<List<Post>> posts;  // posts comes from DAO or Webservice
}

MyFragment extends LifecycleFragment {
    PostAdapter postAdapter;

    ...

    void onActivityCreated() {
        ...
        postViewModel.posts.observer(this, (postList) -> {
            postAdapter.setPosts(postList);
        }
    }       
}

PostAdapter {
    void setPosts(List<Post> postList) {
        DiffUtil.DiffResult result = DiffUtil.calculateDiff(new DiffUtil.Callback() {...}
        ...
    }
}

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