使用 Google 的分页库更新 PagedList 中的单个项目
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【中文标题】使用 Google 的分页库更新 PagedList 中的单个项目【英文标题】：Update a Single Item in a PagedList using Google's Paging Library 【发布时间】：2020-06-01 22:24:27 【问题描述】：我在 RecyclerView 中有一个简单的 Pokemon 列表，其中只有 Pokemon 的名称和“Favorite”切换按钮。我正在使用带有 PageKeyedDataSource 的 android JetPack 的分页库来检索小块 Pokemon 并将它们显示给用户。只要 Activity 没有被破坏，我只希望数据保持不变（即，我不想将数据保持到 Room 或数据库，而是只要 ViewModel 还活着就让它保持不变）。
Screenshot of app
我希望能够单击任何 Pokemon 项目上的心形按钮并将 SimplePokemon 模型中的“isFavorite”字段更新为 true 或 false。据我了解，如果我想更改该 PagedList 中的单个项目，我需要使 DataSource 无效，并且理论上应该生成一个 PagedList 的新 LiveData，可以将其提供给 Adapter 并显示在屏幕上。
问题：如何在不需要 Room 或其他数据库的情况下使用分页库更新 PagedList 中的单个项目？
将来，我想将此解决方案扩展到社交媒体供稿，用户可以在其中点赞帖子，但我不知道将社交供稿项存储在诸如 Room 之类的数据库中是否必要（或有效），因为这些供稿物品是不断变化的。所以我选择将它们存储在 ViewModel 中，然后在每次用户退出应用时清除它们。
到目前为止，这是我的代码：
SimplePokemon.kt：
data class SimplePokemon(
@SerializedName("name") val name: String,
@SerializedName("url") val url: String,
var isFavorite: Boolean = false
)
PokemonViewModel.kt：
class PokemonViewModel(application: Application) : AndroidViewModel(application)
private val config = PagedList.Config.Builder()
.setPageSize(20)
.setEnablePlaceholders(false)
.build()
private fun initializedPagedListBuilder(config: PagedList.Config): LivePagedListBuilder<String, SimplePokemon>
val dataSourceFactory = object : DataSource.Factory<String, SimplePokemon>()
override fun create(): DataSource<String, SimplePokemon>
return PokemonDataSource()
return LivePagedListBuilder<String, SimplePokemon>(dataSourceFactory, config)
fun pokemonPagedListLiveData(): LiveData<PagedList<SimplePokemon>>
return initializedPagedListBuilder(config).build()
PokemonAdapter.kt：
class PokemonAdapter :
PagedListAdapter<SimplePokemon, PokemonAdapter.PokemonViewHolder>(PokemonDiffUtil())
inner class PokemonViewHolder(v: View) : RecyclerView.ViewHolder(v)
private val pokemonNameTextView: TextView = v.findViewById(R.id.pokemon_name_text_view)
private val pokemonFavoriteToggle: ToggleButton =
v.findViewById(R.id.pokemon_favorite_toggle_button)
fun bind(data: SimplePokemon)
pokemonNameTextView.text = data.name
pokemonFavoriteToggle.isChecked = data.isFavorite
override fun onCreateViewHolder(parent: ViewGroup, viewType: Int): PokemonViewHolder
val view =
LayoutInflater.from(parent.context).inflate(R.layout.item_simple_pokemon, parent, false)
return PokemonViewHolder(view)
override fun onBindViewHolder(holder: PokemonViewHolder, position: Int)
val item = getItem(position)
item?.let holder.bind(it)
PokemonDataSource.kt：
class PokemonDataSource : PageKeyedDataSource<String, SimplePokemon>()
private val api = NetworkService.pokemonNetworkInterface
override fun loadInitial(
params: LoadInitialParams<String>,
callback: LoadInitialCallback<String, SimplePokemon>
)
api.getPokemon().enqueue(object : Callback<PokeResponse<List<SimplePokemon>>>
override fun onFailure(call: Call<PokeResponse<List<SimplePokemon>>>?, t: Throwable?)
Log.e("PokemonDataSource", "Failed to fetch data!")
override fun onResponse(
call: Call<PokeResponse<List<SimplePokemon>>>?,
response: Response<PokeResponse<List<SimplePokemon>>>
)
val listing = response.body()
val pokemon = listing?.results
callback.onResult(pokemon ?: listOf(), listing?.previous, listing?.next)
)
override fun loadAfter(
params: LoadParams<String>,
callback: LoadCallback<String, SimplePokemon>
)
api.getPokemon(url = params.key)
.enqueue(object : Callback<PokeResponse<List<SimplePokemon>>>
override fun onFailure(
call: Call<PokeResponse<List<SimplePokemon>>>?,
t: Throwable?
)
Log.e("PokemonDataSource", "Failed to fetch data! Oh Noooo!")
override fun onResponse(
call: Call<PokeResponse<List<SimplePokemon>>>?,
response: Response<PokeResponse<List<SimplePokemon>>>
)
val listing = response.body()
val pokemon = listing?.results
callback.onResult(pokemon ?: listOf(), listing?.next)
)
override fun loadBefore(
params: LoadParams<String>,
callback: LoadCallback<String, SimplePokemon>
)
api.getPokemon(url = params.key)
.enqueue(object : Callback<PokeResponse<List<SimplePokemon>>>
override fun onFailure(
call: Call<PokeResponse<List<SimplePokemon>>>?,
t: Throwable?
)
Log.e("PokemonDataSource", "Failed to fetch data! Oh Noooo!")
override fun onResponse(
call: Call<PokeResponse<List<SimplePokemon>>>?,
response: Response<PokeResponse<List<SimplePokemon>>>
)
val listing = response.body()
val pokemon = listing?.results
callback.onResult(pokemon ?: listOf(), listing?.previous)
)
我还想确保每次更新 DataSource 时 RecyclerView 都不会跳到顶部。
理想的情况是，只要 Activity 处于活动状态，就保留一个 Pokemon 列表，并且能够在本地更新单个 Pokemon 项目。理论上，我还会向后端发送一个 POST 请求以更新后端的口袋妖怪，但我只是想让问题保持简单。
任何帮助将不胜感激。
【问题讨论】：
你找到解决办法了吗？ 【参考方案1】：为了更新 PagedListAdapter 中的单个项目，我在 PagedListAdapter 中添加了这个方法。 就我而言。
// Adapter Class
public class ChatHistoryAdapter extends PagedListAdapter<ChatHistoryEntity, ChatHistoryAdapter.ViewHolder>
OnClickListener<ChatHistoryEntity> listener;
Context mContext;
public ChatHistoryAdapter(Context context)
super(DIFF_CALLBACK);
mContext = context;
public void setOnClickListener(OnClickListener<ChatHistoryEntity> listener)
this.listener = listener;
@NonNull
@Override
public ViewHolder onCreateViewHolder(@NonNull ViewGroup parent, int viewType)
LayoutInflater layoutInflater = LayoutInflater.from(parent.getContext());
ItemChatHistoryBinding binding =
ItemChatHistoryBinding.inflate(layoutInflater,parent,false);
return new ViewHolder(binding);
@Override
public void onBindViewHolder(@NonNull ViewHolder holder, int position)
ChatHistoryEntity current = getChat(position);
holder.binding.tvSender.setText(current.getName_or_mobile_or_groupName());
holder.binding.tvMessage.setText(current.getSubject());
// holder.binding.tvTimestamp.setText(current.getMessage_date_time().toString());
// holder.tv_sender.setText(current.getContact_name_or_mobile_or_groupName());
// holder.tv_message.setText(current.getMessage());
if (current.isSelected())
holder.binding.mainLayout.setBackgroundColor(ContextCompat.getColor(mContext, R.color.item_selection));
// holder.binding.mainLayout.setBackgroundColor();
else
holder.binding.mainLayout.setBackgroundColor(0);
holder.Bind(current,listener,position);
public ChatHistoryEntity getChat(int position)
return getItem(position);
public void updateItemSelection(int position,boolean isSelect)
ChatHistoryEntity current = getChat(position);
current.setSelected(isSelect);
notifyDataSetChanged();
public void clearSelection()
List<ChatHistoryEntity> collect = StreamSupport.stream(getCurrentList().snapshot())
.peek(o -> o.setSelected(false))
.collect(Collectors.toList());
// submitList(PagedList<ChatHistoryEntity> list = new PagedList<>());
notifyDataSetChanged();
private static final DiffUtil.ItemCallback<ChatHistoryEntity> DIFF_CALLBACK =
new DiffUtil.ItemCallback<ChatHistoryEntity>()
@Override
public boolean areItemsTheSame(@NonNull ChatHistoryEntity oldItem,
@NonNull ChatHistoryEntity newItem)
return oldItem.getId() == newItem.getId();
@Override
public boolean areContentsTheSame(@NonNull ChatHistoryEntity oldItem,
@NonNull ChatHistoryEntity newItem)
return oldItem.getId() == newItem.getId()
&& oldItem.getName_or_mobile_or_groupName()
.equalsIgnoreCase(newItem.getName_or_mobile_or_groupName());
;
public static class ViewHolder extends RecyclerView.ViewHolder
ItemChatHistoryBinding binding;
public ViewHolder(ItemChatHistoryBinding binding)
super(binding.getRoot());
this.binding =binding;
void Bind(ChatHistoryEntity chatEntity, OnClickListener<ChatHistoryEntity> mOnCharacterClick,
int position)
binding.mainLayout.setOnClickListener(v ->
mOnCharacterClick.OnClick(chatEntity,"",position));
// Activity or fragument Class.
public class MainActivity extends AppCompatActivity
mAdapter.setOnClickListener((currentObj, mode, position) ->
// This is how you update single item in PagedListAdapter list.
mAdapter.updateItemSelection(position,!currentObj.isSelected())
);
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