android - 无法从 firebase 实时数据库中检索数据到 recyclerview
问题描述
我正在尝试从 firebase 实时数据库中检索数据到我的 recyclerview 。早些时候,我能够在我的 recyclerview 上检索数据,但不知道发生了什么,它突然开始向我显示错误。我在这一行得到错误
User user=snapshot.getValue(User.class);
而logcat窗口中的这个错误
com.google.firebase.database.DatabaseException:com.shivam.chatapp2.Model.User 类未定义无参数构造函数。如果您使用 ProGuard,请确保未剥离这些构造函数。在 com.google.firebase.database.core.utilities.encoding.CustomClassMapper$BeanMapper.deserialize
我的完整代码
用户适配器.java:
public class UserAdapter extends RecyclerView.Adapter<UserAdapter.ViewHolder> {
private Context mContext;
private List<User> mUsers;
public UserAdapter(Context mContext, List<User> mUsers) {
this.mContext = mContext;
this.mUsers = mUsers;
}
@NonNull
@Override
public UserAdapter.ViewHolder onCreateViewHolder(@NonNull ViewGroup parent, int viewType) {
View view= LayoutInflater.from(mContext).inflate(R.layout.user_item,parent,false);
return new UserAdapter.ViewHolder(view);
}
@Override
public void onBindViewHolder(@NonNull UserAdapter.ViewHolder holder, int position) {
final User user=mUsers.get(position);
holder.username.setText(user.getFirst());
holder.itemView.setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View v) {
Intent intent=new Intent(mContext, MessageActivity.class);
intent.putExtra("UserName",user.getFirst());
intent.putExtra("userid", user.getId());
mContext.startActivity(intent);
}
});
}
@Override
public int getItemCount() {
return mUsers.size();
}
public class ViewHolder extends RecyclerView.ViewHolder{
public TextView username;
public ImageView profile_image;
public ViewHolder(@NonNull View itemView) {
super(itemView);
username=itemView.findViewById(R.id.username);
profile_image=itemView.findViewById(R.id.profile_image);
}
}
}
用户.java:
public class User {
private String id;
private String First;
private String Last;
private String EmailID;
public User(String id, String first, String last, String emailID) {
this.id = id;
First = first;
Last = last;
EmailID = emailID;
}
public User(String userid, String first_name, String eMail) {
}
public String getId() {
return id;
}
public void setId(String id) {
this.id = id;
}
public String getFirst() {
return First;
}
public void setFirst(String first) {
First = first;
}
public String getLast() {
return Last;
}
public void setLast(String last) {
Last = last;
}
public String getEmailID() {
return EmailID;
}
public void setEmailID(String emailID) {
EmailID = emailID;
}
}
用户片段.java:
public class UsersFragment extends Fragment {
private RecyclerView recyclerView;
private UserAdapter mUserAdapter;
private List<User> mUsers;
String TAG = "MyTag";
public UsersFragment() {
// Required empty public constructor
}
@Override
public View onCreateView(LayoutInflater inflater, ViewGroup container,
Bundle savedInstanceState) {
// Inflate the layout for this fragment
View view = inflater.inflate(R.layout.fragment_users, container, false);
recyclerView = view.findViewById(R.id.recycler_view);
recyclerView.setHasFixedSize(true);
recyclerView.setLayoutManager(new LinearLayoutManager(getContext()));
mUsers = new ArrayList<>();
readUser();
return view;
}
private void readUser() {
final FirebaseUser firebaseUser=FirebaseAuth.getInstance().getCurrentUser();
DatabaseReference reference= FirebaseDatabase.getInstance().getReference("Users");
reference.addValueEventListener(new ValueEventListener() {
@Override
public void onDataChange(@NonNull DataSnapshot dataSnapshot) {
mUsers.clear();
for (DataSnapshot snapshot: dataSnapshot.getChildren()) {
User user=snapshot.getValue(User.class);
mUsers.add(user);
}
mUserAdapter=new UserAdapter(getContext(),mUsers);
recyclerView.setAdapter(mUserAdapter);
mUserAdapter.notifyDataSetChanged();
}
@Override
public void onCancelled(@NonNull DatabaseError databaseError) {
}
});
}
}
解决方案
根据您的错误日志,它指出:
User 类没有在 User.class 文件中声明的默认构造函数。
在 User.class 文件中为 User 类添加一个默认构造函数,例如:
public User()
{
}
推荐阅读
- core-data - UTF16 存储的字符串从 CoreData 检索回来后不匹配
- javascript - 在 JavaScript 中从整数构造新日期时检测无效日期值
- python - 转换字典列表,根据键组合列表项
- amazon-web-services - CORS 策略:预检响应中的 Access-Control-Allow-Headers 不允许请求标头字段 access-control-allow-origin
- flutter - 在登录页面中调用 null 的 Flutter 验证
- selenium - 使用 Selenium Webdriver 在 Salesforce Lightning 中创建自定义对象
- mysql - 有没有办法改变当前用户的密码,为密码引入一个变量?
- webpack - Gitlab Pages - Webpack 项目 - 错误 404
- sql - SQL - 如果其中一列具有空值,则删除行
- java - 如何从 Stream 更改
流式传输 爪哇 8