如何使用列表适配器在回收器视图中修改列表？

因此，当我从互联网上获取数据时（例如，当我们不断滚动并进行分页时，就像Youtube），我试图在回收器视图的最后一个索引中添加加载项。像这样

现在我的回收站视图扩展了ListAdapter，不再使用RecyclerView.Adapter

如果使用RecyclerView.Adapter（旧方式），我将为适配器编写如下代码：

public class PaginationAdapter extends RecyclerView.Adapter {
private static final int ITEM = 0;
private static final int LOADING = 1;
private static final String BASE_URL_IMG = "https://image.tmdb.org/t/p/w150";
private List movieResults;
private Context context;
private boolean isLoadingAdded = false;
public PaginationAdapter(Context context) {
this.cOntext= context;
movieResults = new ArrayList<>();
}
public List getMovies() {
return movieResults;
}
public void setMovies(List movieResults) {
this.movieResults = movieResults;
}
@Override
public RecyclerView.ViewHolder onCreateViewHolder(ViewGroup parent,int viewType) {
RecyclerView.ViewHolder viewHolder = null;
LayoutInflater inflater = LayoutInflater.from(parent.getcontext());
switch (viewType) {
case ITEM:
viewHolder = getViewHolder(parent,inflater);
break;
case LOADING:
View v2 = inflater.inflate(R.layout.item_progress,parent,false);
viewHolder = new LoadingVH(v2);
break;
}
return viewHolder;
}
@NonNull
private RecyclerView.ViewHolder getViewHolder(ViewGroup parent,LayoutInflater inflater) {
RecyclerView.ViewHolder viewHolder;
View v1 = inflater.inflate(R.layout.item_list,false);
viewHolder = new MovieVH(v1);
return viewHolder;
}
@Override
public void onBindViewHolder(RecyclerView.ViewHolder holder,int position) {
Movie result = movieResults.get(position); // Movie
switch (getItemViewType(position)) {
case ITEM:
// some code here
break;
case LOADING:
// Do nothing
break;
}
}
@Override
public int getItemCount() {
return movieResults == null ? 0 : movieResults.size();
}
@Override
public int getItemViewType(int position) {
return (position == movieResults.size() - 1 && isLoadingAdded) ? LOADING : ITEM;
}
public void addLoadingFooter() {
isLoadingAdded = true;
movieResults.add(new Moview());
notifyItemInserted(movieResults.size() - 1);
}
public void removeLoadingFooter() {
isLoadingAdded = false;
int position = movieResults.size() - 1;
Movie result = getItem(position);
if (result != null) {
movieResults.remove(position);
notifyItemRemoved(position);
}
}
}


但是现在我正在尝试将ListAdapter用于我的Recycler View。这是我的代码，如果我的回收站视图使用ListAdapter

class GeneralEventRecyclerViewAdapter(val mContext: Context): ListAdapter(DIFF_CALLBACK) {
lateinit var mOnEventKMListener : OnEventKMListener
private val ITEM = 0
private val LOADING = 1
private var isLoadingAdded = false
fun setOnItemClicklistener(listener: OnEventKMListener) {
mOnEventKMListener= listener
}
override fun onCreateViewHolder(parent: ViewGroup,viewType: Int): RecyclerView.ViewHolder {
if (viewType == ITEM) {
val itemView = LayoutInflater.from(parent.context).inflate(R.layout.item_general_event,false)
return GeneralEventViewHolder(itemView,mOnEventKMListener)
} else {
val loadingView = LayoutInflater.from(parent.context).inflate(R.layout.item_progress,false)
return LoadingViewHolder(loadingView)
}
}
override fun onBindViewHolder(holder: RecyclerView.ViewHolder,position: Int) {
if (getItemViewType(position) == ITEM) {
// some code here
}
}
override fun getItemViewType(position: Int): Int {
if (position == currentList.size - 1 && isLoadingAdded) {
return LOADING
} else {
return ITEM
}
}
fun addLoadingFooter() {
isLoadingAdded = true
currentList.add(Event())
notifyItemInserted(currentList.size - 1)
}
fun removeLoadingFooter() {
isLoadingAdded = false
val position: Int = currentList.size - 1
val result: Event? = getItem(position)
if (result != null) {
currentList.removeAt(position)
notifyItemRemoved(position)
}
}
companion object {
private val DIFF_CALLBACK = object : DiffUtil.ItemCallback() {
override fun areItemsTheSame(oldItem: Event,newItem: Event): Boolean {
return oldItem.eventID == newItem.eventID
}
override fun areContentsTheSame(oldItem: Event,newItem: Event): Boolean {
return oldItem == newItem
}
}
}
}


这是我的问题.....

在添加和删除回收站中的加载项时，我试图模仿这两种方法（使用RecyclerView.Adapter）：

public void addLoadingFooter() {
isLoadingAdded = true;
movieResults.add(new Moview());
notifyItemInserted(movieResults.size() - 1);
}
public void removeLoadingFooter() {
isLoadingAdded = false;
int position = movieResults.size() - 1;
Movie result = getItem(position);
if (result != null) {
movieResults.remove(position);
notifyItemRemoved(position);
}
}


我假设如果使用ListAdapter

fun addLoadingFooter() {
isLoadingAdded = true
currentList.add(Event())
notifyItemInserted(currentList.size - 1)
}
fun removeLoadingFooter() {
isLoadingAdded = false
val position: Int = currentList.size - 1
val result: Event? = getItem(position)
if (result != null) {
currentList.removeAt(position)
notifyItemRemoved(position)
}
}


但是当我运行该应用程序时，我会崩溃

java.lang.UnsupportedOperationException
at java.util.AbstractList.add(AbstractList.java:148)
at java.util.AbstractList.add(AbstractList.java:108)


第currentList.add(Event())行

如果使用ListAdapter，似乎无法在列表中添加新项目。那么如何使用列表适配器在回收站视图中修改列表？

如果使用ListAdapter，我不知道如何访问现有列表，看来currentList不能被修改

java或kotlin没问题

最终使用

override fun getItemViewType(position: Int): Int {
if ( position == currentList.lastIndex && isLoadingAdded) {
return LOADING
} else {
return ITEM
}
}
fun addLoadingFooter(currentList: ArrayList) {
isLoadingAdded = true
currentList.add(Event())
submitList(currentList)
notifyItemInserted(currentList.lastIndex)
}
fun removeLoadingFooter(currentList: ArrayList) {
isLoadingAdded = false
val result = currentList[currentList.lastIndex]
currentList.remove(result)
submitList(currentList)
notifyItemRemoved(currentList.size)
}

,

聚会迟到，但您当前的回答并未充分利用ListAdapter。您应该改用 ListAdapter.submitList，它可以完成大部分 notifyItemXXXXXX 工作。

val newList = ArrayList(listAdapter.currentList)
newList.add(Event()) // or to remove / update / ... etc.
listAdapter.submitList(newList)


还有一件重要的事情要知道：submitList 必须使用来自原始对象的新对象（列表）。

val objList = mutableListOf(myObjects)
listAdapter.submitList(objList)
objList.add(newObject)
listAdapter.submitList(objList) // will NOT do updates.
listAdapter.submitList(ArrayList(objList)) // will do updates.


它在另一个 Stack Overflow question 中被提及。