如何修复 Java 类中的“在类上找不到要序列化的属性”错误？

Question

这个问题不是重复的。 我尝试了答案中显示的其他方法，但它们似乎不起作用。 我试图遍历“用户”集合中的所有文档以获取每个人的用户名，将其存储到一个 ArrayList 中，并在我的列表视图中显示它。

我的错误显示是

E/AndroidRuntime: FATAL EXCEPTION: main
Process: com.example.example, PID: 17169
java.lang.RuntimeException: No properties to serialize found on class com.example.example.Model
    at com.google.firebase.firestore.util.CustomClassMapper$BeanMapper.<init>(com.google.firebase:firebase-firestore@@21.3.1:714)
    at com.google.firebase.firestore.util.CustomClassMapper.loadOrCreateBeanMapperForClass(com.google.firebase:firebase-firestore@@21.3.1:377)
    at com.google.firebase.firestore.util.CustomClassMapper.convertBean(com.google.firebase:firebase-firestore@@21.3.1:540)
    at com.google.firebase.firestore.util.CustomClassMapper.deserializeToClass(com.google.firebase:firebase-firestore@@21.3.1:253)
    at com.google.firebase.firestore.util.CustomClassMapper.convertToCustomClass(com.google.firebase:firebase-firestore@@21.3.1:100)
    at com.google.firebase.firestore.DocumentSnapshot.toObject(com.google.firebase:firebase-firestore@@21.3.1:210)
    at com.google.firebase.firestore.QueryDocumentSnapshot.toObject(com.google.firebase:firebase-firestore@@21.3.1:116)
    at com.google.firebase.firestore.DocumentSnapshot.toObject(com.google.firebase:firebase-firestore@@21.3.1:188)
    at com.google.firebase.firestore.QueryDocumentSnapshot.toObject(com.google.firebase:firebase-firestore@@21.3.1:97)
    at com.example.example.LeaderboardActivity$1.onSuccess(LeaderboardActivity.java:46)
    at com.example.example.LeaderboardActivity$1.onSuccess(LeaderboardActivity.java:42)
    at com.google.android.gms.tasks.zzn.run(Unknown Source:4)
    at android.os.Handler.handleCallback(Handler.java:873)
    at android.os.Handler.dispatchMessage(Handler.java:99)
    at android.os.Looper.loop(Looper.java:193)
    at android.app.ActivityThread.main(ActivityThread.java:6669)
    at java.lang.reflect.Method.invoke(Native Method)
    at com.android.internal.os.RuntimeInit$MethodAndArgsCaller.run(RuntimeInit.java:493)
    at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:858)

我的排行榜类

import androidx.appcompat.app.AppCompatActivity;
import android.content.Context;
import android.content.Intent;
import android.os.Bundle;
import android.view.MenuItem;
import android.widget.ArrayAdapter;
import android.widget.ListView;

import com.google.android.gms.tasks.OnSuccessListener;
import com.google.android.material.bottomnavigation.BottomNavigationView;
import com.google.firebase.auth.FirebaseAuth;
import com.google.firebase.firestore.CollectionReference;
import com.google.firebase.firestore.FirebaseFirestore;
import com.google.firebase.firestore.QueryDocumentSnapshot;
import com.google.firebase.firestore.QuerySnapshot;

import java.util.ArrayList;


public class LeaderboardActivity extends AppCompatActivity {

ArrayList<String> usersInfo = new ArrayList<>();
FirebaseFirestore fStore = FirebaseFirestore.getInstance();
FirebaseAuth fAuth= FirebaseAuth.getInstance();
String userID= fAuth.getCurrentUser().getUid();

ListView lv;


@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_leaderboard);

    lv = findViewById(R.id.leaderboardlist);
    CollectionReference cr = fStore.collection("users");
    cr.get().addOnSuccessListener(new OnSuccessListener<QuerySnapshot>() {
        @Override
        public void onSuccess(QuerySnapshot queryDocumentSnapshots) {
            for (QueryDocumentSnapshot documentSnapshot : queryDocumentSnapshots){ //Line 42
                Model mod = documentSnapshot.toObject(Model.class);
                String Name = mod.getName();
                usersInfo.add(Name);
                System.out.println(usersInfo); //Line 46
            }
        }
    });
    usersInfo.add("aggg");
    ArrayAdapter adapter = new ArrayAdapter(this,android.R.layout.simple_list_item_1,usersInfo);
    lv.setAdapter(adapter);
    System.out.println(usersInfo);

    final Context context = this;

    BottomNavigationView bottomNavigationView = findViewById(R.id.bottom_navigation);
    bottomNavigationView.setOnNavigationItemSelectedListener(new BottomNavigationView.OnNavigationItemSelectedListener() {
        @Override
        public boolean onNavigationItemSelected(MenuItem item) {

            switch (item.getItemId()) {
                case R.id.action_arcade:
                    Intent intentSettings = new Intent(context, MenuActivity.class);
                    startActivity(intentSettings);
                    finish();
                    break;

                case R.id.action_home:
                    Intent intentHome = new Intent(context, Menu2.class);
                    startActivity(intentHome);
                    finish();
                    break;

                case R.id.action_account:
                    Intent intentAccount = new Intent(context, AccountActivity.class);
                    startActivity(intentAccount);
                    finish();
                    break;
            }
            return false;
        }
    });


}

}

我的模型类

import androidx.annotation.Keep;


import java.io.Serializable;@Keep

public class Model implements Serializable {

public static String Name;
public static String Email;
public static int Coin_Toss_High_Score;
public static int Rps_High_Score;
public static int TicTacToe_High_Score;


public Model() {}

public Model(String name, String email, int ticTacToe_High_Score, int coin_Toss_High_Score, int rps_High_Score){
    this.Name = name;
    this.Email = email;
    this.TicTacToe_High_Score = ticTacToe_High_Score;
    this.Coin_Toss_High_Score = coin_Toss_High_Score;
    this.Rps_High_Score = rps_High_Score;
}

public static String getName() {
    return Name;
}

public static String getEmail() {
    return Email;
}

public static int getCoin_Toss_High_Score() {
    return Coin_Toss_High_Score;
}

public static int getRps_High_Score() {
    return Rps_High_Score;
}

public static int getTicTacToe_High_Score() {
    return TicTacToe_High_Score;
}

public static void setName(String name) {
    Name = name;
}

public static void setEmail(String email) {
    Email = email;
}

public static void setCoin_Toss_High_Score(int coin_Toss_High_Score) {
    Coin_Toss_High_Score = coin_Toss_High_Score;
}

public static void setRps_High_Score(int rps_High_Score) {
    Rps_High_Score = rps_High_Score;
}

public static void setTicTacToe_High_Score(int ticTacToe_High_Score) {
    TicTacToe_High_Score = ticTacToe_High_Score;
}
}

Answer 1

你需要添加这个Gson库

    implementation 'com.squareup.retrofit2:converter-gson:2.6.0'

然后import java.io.Serializable;@Keep删除它并在您的类中导入它

  import com.google.gson.annotations.SerializedName

Answer 2

改变这个：

public static String Name;
public static String Email;
public static int Coin_Toss_High_Score;
public static int Rps_High_Score;
public static int TicTacToe_High_Score;

对此：

public String Name;
public String Email;
public int Coin_Toss_High_Score;
public int Rps_High_Score;
public int TicTacToe_High_Score;

即使你已经有了 getter() setter() 方法，即使你把它公开，你也可以通过 getter() 和 setter() 方法访问所有这些属性。

Answer 3

这应该是这样的：

public class Model implements Serializable {

    private String Name;
    private String Email;
    private int Coin_Toss_High_Score;
    private int Rps_High_Score;
    private int TicTacToe_High_Score;

    public Model(String name, String email, int coin_Toss_High_Score, int rps_High_Score, int ticTacToe_High_Score) {
        Name = name;
        Email = email;
        Coin_Toss_High_Score = coin_Toss_High_Score;
        Rps_High_Score = rps_High_Score;
        TicTacToe_High_Score = ticTacToe_High_Score;
    }

    public String getName() {
        return Name;
    }

    public void setName(String name) {
        Name = name;
    }

    public String getEmail() {
        return Email;
    }

    public void setEmail(String email) {
        Email = email;
    }

    public int getCoin_Toss_High_Score() {
        return Coin_Toss_High_Score;
    }

    public void setCoin_Toss_High_Score(int coin_Toss_High_Score) {
        Coin_Toss_High_Score = coin_Toss_High_Score;
    }

    public int getRps_High_Score() {
        return Rps_High_Score;
    }

    public void setRps_High_Score(int rps_High_Score) {
        Rps_High_Score = rps_High_Score;
    }

    public int getTicTacToe_High_Score() {
        return TicTacToe_High_Score;
    }

    public void setTicTacToe_High_Score(int ticTacToe_High_Score) {
        TicTacToe_High_Score = ticTacToe_High_Score;
    }
 }