我正在尝试从聊天应用程序的自定义适配器中获取项目计数，但它总是返回零如何解决此问题？

Question

>我正在使用RecyclerView和List类制作聊天应用程序来存储来自Firebase数据库的消息，并希望在打开聊天活动时在recylcerView的底部滚动，但错误是.....适配器在调用 adapter.getItemcount(( 方法时始终返回零。显示所有消息都没有问题。

自定义适配器 java 文件

public class ChatCustomAdapter extends RecyclerView.Adapter<RecyclerView.ViewHolder>{
private FirebaseUser mUser;
private String currentUser;
private List<ChatModel> msgList;
//Constructor
public ChatCustomAdapter(List<ChatModel> msgList) {
this.msgList = msgList;
FirebaseAuth mAuth = FirebaseAuth.getInstance();
mUser = mAuth.getCurrentUser();
currentUser = mUser.getUid();
}
@Override
public int getItemCount() {
return msgList.size(); 
}

@Override
public RecyclerView.ViewHolder onCreateViewHolder(ViewGroup parent, int viewType) {
View v;
if(viewType==0){
v = LayoutInflater.from(parent.getContext()).inflate(R.layout.chat_single__user_item_layout,parent,false);
return new SelfViewHolder(v);
}else if(viewType==1){
v = LayoutInflater.from(parent.getContext()).inflate(R.layout.chat_single_other_user_item_layout,parent,false);
return new OtherViewHolder(v);
}else{
return null;
}
}
@Override
public void onBindViewHolder(RecyclerView.ViewHolder holder, int position) {
int layout = holder.getItemViewType();
ChatModel model = msgList.get(position);
String msg = model.getMsg();
if(layout==0){
SelfViewHolder sHolder = (SelfViewHolder)holder;
sHolder.setSelfMsgItems(msg);
}else if(layout==1){
OtherViewHolder oHolder = (OtherViewHolder)holder;
oHolder.setOtherMsgItems(msg);
}
}
@Override
public int getItemViewType(int position) {
super.getItemViewType(position);
int layout;
ChatModel model = msgList.get(position);
String from = model.getFrom();
if(from.equals(currentUser)){
layout=0;
}else{
layout=1;
}
return layout;
}

class SelfViewHolder extends RecyclerView.ViewHolder{
TextView msgtxt,timetxt;
SelfViewHolder(View itemView) {
super(itemView);
msgtxt = itemView.findViewById(R.id.chat_sinhle_user_item_textview);
timetxt = itemView.findViewById(R.id.chat_sinhle_user_item_timeview);
}
void setSelfMsgItems(String data){
msgtxt.setText(data);
}
}
class OtherViewHolder extends RecyclerView.ViewHolder{
TextView msgtxt,timetxt;
public OtherViewHolder(View itemView) {
super(itemView);
msgtxt = itemView.findViewById(R.id.chat_other_user_item_textview);
timetxt = itemView.findViewById(R.id.chat_other_user_item_timeview);
}
public void setOtherMsgItems(String data){
msgtxt.setText(data);
}
}
}

聊天活动爪哇文件

protected void onStart() {
super.onStart();
//region RETREIVING MESSAGES FROM SERVER
msgQ = mDatabase.child("messages").child(current_user).child(otherusername).orderByChild("time");
msgQ.addChildEventListener(new ChildEventListener() {
@Override
public void onChildAdded(DataSnapshot dataSnapshot, String s) {
ChatModel model = dataSnapshot.getValue(ChatModel.class);
mLsit.add(msgposition++, model);
mAdapter.notifyDataSetChanged();
}
@Override
public void onChildChanged(DataSnapshot dataSnapshot, String s) {
}
@Override
public void onChildRemoved(DataSnapshot dataSnapshot) {
}
@Override
public void onChildMoved(DataSnapshot dataSnapshot, String s) {
}
@Override
public void onCancelled(DatabaseError databaseError) {
}
});
//endregion
recyclerView.scrollToPosition(mAdapter.getItemCount()-1);
}

Answer 1

我认为getItemCount()返回零，因为您在ChildEventListener之外调用此方法。因此，当mLsit中还没有元素时，您可以检索 itemcount。 这里最快且有点肮脏的解决方案是将scrollToPosition放入onChildAdded方法中。另外，我会以这种方式修改代码

protected void onStart() {
super.onStart();
//region RETREIVING MESSAGES FROM SERVER
msgQ = mDatabase.child("messages").child(current_user).child(otherusername).orderByChild("time");
msgQ.addChildEventListener(new ChildEventListener() {
@Override
public void onChildAdded(DataSnapshot dataSnapshot, String s) {
ChatModel model = dataSnapshot.getValue(ChatModel.class);
mLsit.add(msgposition, model);
mAdapter.notifyItemInserted(msgposition)
recyclerView.scrollToPosition(msgposition);
msgposition++;
}
@Override
public void onChildChanged(DataSnapshot dataSnapshot, String s) {
}
@Override
public void onChildRemoved(DataSnapshot dataSnapshot) {
}
@Override
public void onChildMoved(DataSnapshot dataSnapshot, String s) {
}
@Override
public void onCancelled(DatabaseError databaseError) {
}
});
//endregion
}