我在 RecyclerView 中有一个简单的 Pokemon 列表，其中只有 Pokemon 的名称和一个“收藏夹”切换按钮。我使用 Android JetPack 中的分页库和 PageKeyedDataSource 来检索小块 Pokemon 并将其显示给用户。我只希望数据在 Activity 不被破坏的情况下持续存在（即，我不想将数据保留到 Room 或数据库，而是只要 ViewModel 处于活动状态就让它持续存在）。
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
truefalse问题：如何使用分页库更新 PagedList 中的单个项目，而不需要 Room 或其他数据库？
将来，我想将此解决方案扩展到社交媒体提要，用户可以在其中对帖子进行点赞，但我不知道将社交提要项目存储在数据库（例如 Room）中是否必要（或有效），因为这些提要项目是不断变化。因此我选择将它们存储在 ViewModel 中，然后在每次用户退出应用程序时清除它们。
这是迄今为止我的代码：
简单的Pokemon.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不会跳到顶部。
理想的情况是，只要 Activity 处于活动状态，就保留 Pokemon 列表，并且能够在本地更新单个 Pokemon 项目。理论上，我也会向后端发送 POST 请求来更新后端的 Pokemon，但我只是想让问题变得简单。
任何帮助将不胜感激。
要更新 PagedListAdapter 中的单个项目，我已在 PagedListAdapter 中添加了此方法。 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())
});
}