com.google.firebase.database.DatabaseException：无法将 java.lang.String 类型的对象转换为 com.example.prj.User 类型
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【中文标题】com.google.firebase.database.DatabaseException：无法将 java.lang.String 类型的对象转换为 com.example.prj.User 类型【英文标题】：com.google.firebase.database.DatabaseException: Can't convert object of type java.lang.String to type com.example.prj.User 【发布时间】：2020-08-17 17:26:18 【问题描述】：我正在尝试从 Firebase 实时数据库中检索数据，并希望在 TextView 的屏幕上显示它们，但遇到错误。 我的数据库结构是
logcat 中显示的错误是
UserFragment类的代码如下
package com.example.prj;
import android.os.Bundle;
import androidx.annotation.NonNull;
import androidx.fragment.app.Fragment;
import android.view.LayoutInflater;
import android.view.View;
import android.view.ViewGroup;
import android.widget.ImageView;
import android.widget.TextView;
import com.google.firebase.auth.FirebaseAuth;
import com.google.firebase.database.DataSnapshot;
import com.google.firebase.database.DatabaseError;
import com.google.firebase.database.DatabaseReference;
import com.google.firebase.database.FirebaseDatabase;
import com.google.firebase.database.ValueEventListener;
/**
* A simple @link Fragment subclass.
* Use the @link UserFragment#newInstance factory method to
* create an instance of this fragment.
*/
public class UserFragment extends Fragment
// TODO: Rename parameter arguments, choose names that match
// the fragment initialization parameters, e.g. ARG_ITEM_NUMBER
private static final String ARG_PARAM1 = "param1";
private static final String ARG_PARAM2 = "param2";
// TODO: Rename and change types of parameters
private String mParam1;
private String mParam2;
ImageView profile;
TextView shopName, ownerName, address, phoneNumber , gstNumber, email, policyLink;
DatabaseReference myRef;
public UserFragment()
// Required empty public constructor
/**
* Use this factory method to create a new instance of
* this fragment using the provided parameters.
*
* @param param1 Parameter 1.
* @param param2 Parameter 2.
* @return A new instance of fragment UserFragment.
*/
// TODO: Rename and change types and number of parameters
public static UserFragment newInstance(String param1, String param2)
UserFragment fragment = new UserFragment();
Bundle args = new Bundle();
args.putString(ARG_PARAM1, param1);
args.putString(ARG_PARAM2, param2);
fragment.setArguments(args);
return fragment;
@Override
public void onCreate(Bundle savedInstanceState)
super.onCreate(savedInstanceState);
if (getArguments() != null)
mParam1 = getArguments().getString(ARG_PARAM1);
mParam2 = getArguments().getString(ARG_PARAM2);
@Override
public View onCreateView(LayoutInflater inflater, ViewGroup container,
Bundle savedInstanceState)
// Inflate the layout for this fragment
View v = inflater.inflate(R.layout.fragment_user, container, false);
String u = FirebaseAuth.getInstance().getCurrentUser().getUid();
myRef = FirebaseDatabase.getInstance().getReference(u).child("User");
profile = v.findViewById(R.id.profile_image);
shopName = v.findViewById(R.id.owner_name);
ownerName = v.findViewById(R.id.owner_name);
address = v.findViewById(R.id.address);
phoneNumber = v.findViewById(R.id.phone_number);
gstNumber = v.findViewById(R.id.gst_number);
email = v.findViewById(R.id.email);
policyLink = v.findViewById(R.id.policy_link);
myRef.addValueEventListener(new ValueEventListener()
@Override
public void onDataChange(@NonNull DataSnapshot dataSnapshot)
for(DataSnapshot detailSnapshot:dataSnapshot.getChildren())
User user= detailSnapshot.getValue(User.class);
shopName.setText(user.getShopname());
ownerName.setText(user.getOwner());
address.setText(user.getAddress());
String p = user.getPhone1()+" , "+user.getPhone2();
phoneNumber.setText(p);
gstNumber.setText(user.getGst());
email.setText(user.getEmail());
@Override
public void onCancelled(@NonNull DatabaseError databaseError)
);
return v;
UserFragment布局的XML文件如下
<?xml version="1.0" encoding="utf-8"?>
<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:tools="http://schemas.android.com/tools"
android:layout_
android:layout_
tools:context=".UserFragment">
<ImageView
android:layout_
android:layout_
android:layout_marginTop="10dp"
android:background="@drawable/profile_pic"
android:layout_marginRight="20dp"
android:layout_marginLeft="20dp"
android:id="@+id/logo"
/>
<TextView
android:layout_
android:layout_
android:layout_marginRight="20dp"
android:layout_marginLeft="20dp"
android:layout_below="@+id/logo"
android:layout_marginTop="5dp"
android:textSize="20dp"
android:id="@+id/shop_name"
/>
<TextView
android:layout_
android:layout_
android:layout_marginRight="20dp"
android:layout_marginLeft="20dp"
android:layout_below="@+id/shop_name"
android:layout_marginTop="5dp"
android:textSize="20dp"
android:id="@+id/owner_name"
/>
<TextView
android:layout_
android:layout_
android:layout_marginRight="20dp"
android:layout_marginLeft="20dp"
android:layout_below="@+id/owner_name"
android:layout_marginTop="5dp"
android:textSize="20dp"
android:id="@+id/address"
/>
<TextView
android:layout_
android:layout_
android:layout_marginRight="20dp"
android:layout_marginLeft="20dp"
android:layout_below="@+id/address"
android:layout_marginTop="5dp"
android:textSize="20dp"
android:id="@+id/phone_number"
/>
<TextView
android:layout_
android:layout_
android:layout_marginRight="20dp"
android:layout_marginLeft="20dp"
android:layout_below="@+id/phone_number"
android:layout_marginTop="5dp"
android:textSize="20dp"
android:id="@+id/gst_number"
/>
<TextView
android:layout_
android:layout_
android:layout_marginRight="20dp"
android:layout_marginLeft="20dp"
android:layout_below="@+id/gst_number"
android:layout_marginTop="5dp"
android:textSize="20dp"
android:id="@+id/email"
/>
<TextView
android:layout_
android:layout_
android:layout_marginRight="20dp"
android:layout_marginLeft="20dp"
android:layout_below="@+id/email"
android:layout_marginTop="5dp"
android:textSize="20dp"
android:id="@+id/policy_link"
/>
</RelativeLayout>
User类的代码如下
package com.example.prj;
public class User
private static final String TAG = "User";
String address, email, gst, owner, phone1, phone2, shopname;
public User()
public User(String address, String email, String gst, String owner, String phone1, String phone2, String shopname)
this.address = address;
this.email = email;
this.gst = gst;
this.owner = owner;
this.phone1 = phone1;
this.phone2 = phone2;
this.shopname = shopname;
public static String getTAG()
return TAG;
public String getAddress()
return address;
public void setAddress(String address)
this.address = address;
public String getEmail()
return email;
public void setEmail(String email)
this.email = email;
public String getGst()
return gst;
public void setGst(String gst)
this.gst = gst;
public String getOwner()
return owner;
public void setOwner(String owner)
this.owner = owner;
public String getPhone1()
return phone1;
public void setPhone1(String phone1)
this.phone1 = phone1;
public String getPhone2()
return phone2;
public void setPhone2(String phone2)
this.phone2 = phone2;
public String getShopname()
return shopname;
public void setShopname(String shopname)
this.shopname = shopname;
我试图在 Firebase 中显示这些子节点的值，但由于错误而无法这样做。
【问题讨论】：
【参考方案1】：在路径/$uid/User 中，您保留了单个用户的数据，因此当您读取该数据时，您将获得包含单个用户数据的快照。但是您的 onDataChange 会循环结果，就好像有多个用户一样。你应该删除这个循环，所以：
myRef.addValueEventListener(new ValueEventListener()
@Override
public void onDataChange(@NonNull DataSnapshot dataSnapshot)
User user= dataSnapshot.getValue(User.class);
...
【讨论】：
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