java - 无法将字符串转换到 Android map

Question

我正在做一个项目，其中作为经理的 User 可以创建一个 Team 并加入它。使用 ArrayAdapter 将所有团队名称显示在列表中。我可以显示所有的球队名称，所以AFL1、AFL2、AHL1、AHL3 并且当 User 选择一个时，他将被添加到 Team 和 User 对象中。当我尝试显示 User 经理加入的所有团队时，AHL1 和 AHL2 出现以下错误:

02-07 19:23:19.300 9813-9813/com.example.cianm.testauth E/AndroidRuntime: FATAL EXCEPTION: main
 Process: com.example.cianm.testauth, PID: 9813
                                                                  java.lang.ClassCastException: java.lang.String cannot be cast to java.util.Map
                                                                      at com.example.cianm.testauth.SelectTeam.collectTeamNames(SelectTeam.java:89)
                                                                      at com.example.cianm.testauth.SelectTeam.access$000(SelectTeam.java:28)
                                                                      at com.example.cianm.testauth.SelectTeam$1.onDataChange(SelectTeam.java:62)
                                                                      at com.google.firebase.database.zzp.onDataChange(Unknown Source)
                                                                      at com.google.android.gms.internal.zzegf.zza(Unknown Source)
                                                                      at com.google.android.gms.internal.zzeia.zzbyc(Unknown Source)
                                                                      at com.google.android.gms.internal.zzeig.run(Unknown Source)
                                                                      at android.os.Handler.handleCallback(Handler.java:808)
                                                                      at android.os.Handler.dispatchMessage(Handler.java:103)
                                                                      at android.os.Looper.loop(Looper.java:193)
                                                                      at android.app.ActivityThread.main(ActivityThread.java:5299)
                                                                      at java.lang.reflect.Method.invokeNative(Native Method)
                                                                      at java.lang.reflect.Method.invoke(Method.java:515)
                                                                      at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:829)
                                                                      at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:645)
                                                                      at dalvik.system.NativeStart.main(Native Method)

这是我的代码的第 89 行:

Map singleTeam = (Map) entry.getValue();

这是我的完整代码，有错误:

package com.example.cianm.testauth;

import android.content.Intent;
import android.support.v7.app.AppCompatActivity;
import android.os.Bundle;
import android.view.View;
import android.widget.AdapterView;
import android.widget.ArrayAdapter;
import android.widget.Button;
import android.widget.ListView;
import android.widget.ProgressBar;
import android.widget.Toast;

import com.example.cianm.testauth.Entity.CurrentTeam;
import com.example.cianm.testauth.Entity.User;
import com.google.firebase.auth.FirebaseAuth;
import com.google.firebase.auth.FirebaseUser;
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.Query;
import com.google.firebase.database.ValueEventListener;

import java.util.ArrayList;
import java.util.Map;

public class SelectTeam extends AppCompatActivity {

    private DatabaseReference mDatabaseT, mDatabaseU;
    private FirebaseAuth mAuth;
    private FirebaseUser fbUser;
    private Query mDatabaseQuery;

    ListView lv;
    Button mJoinTeam;
    ProgressBar mProgressBar;

    User user;
    String teamID, userType;

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

        lv = (ListView) findViewById(R.id.selectTeamListView);
        mJoinTeam = (Button) findViewById(R.id.joinTeamBtn);
        mProgressBar = (ProgressBar) findViewById(R.id.progressBar);

        mProgressBar.setVisibility(View.GONE);

        mDatabaseT = FirebaseDatabase.getInstance().getReference("Team");
        mDatabaseU = FirebaseDatabase.getInstance().getReference("User");
        mAuth = FirebaseAuth.getInstance();
        fbUser = mAuth.getCurrentUser();

        mDatabaseQuery = FirebaseDatabase.getInstance().getReference("User").child(fbUser.getUid()).child("team");
        mDatabaseQuery.addListenerForSingleValueEvent(new ValueEventListener() {
            @Override
            public void onDataChange(DataSnapshot dataSnapshot) {
                collectTeamNames((Map<String, Object>) dataSnapshot.getValue());
            }

            @Override
            public void onCancelled(DatabaseError databaseError) {

            }
        });

        mJoinTeam.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View view) {
                startActivity(new Intent(SelectTeam.this, JoinTeam.class));
            }
        });
    }



    private void collectTeamNames(Map<String, Object> team){

        String teamKey = mDatabaseU.child("team").push().getKey();

        final ArrayList<String> teamNames = new ArrayList<>();

        for (Map.Entry<String, Object> entry : team.entrySet()){

            Map singleTeam = (Map) entry.getValue();
            teamNames.add((String) singleTeam.get(teamKey));

        }
        ArrayAdapter<String> arrayAdapter = new ArrayAdapter<String>(SelectTeam.this, android.R.layout.select_dialog_singlechoice, teamNames);
        lv.setAdapter(arrayAdapter);
        lv.setOnItemClickListener(new AdapterView.OnItemClickListener() {
            @Override
            public void onItemClick(AdapterView<?> adapterView, View view, int i, long l) {
                mProgressBar.setVisibility(View.VISIBLE);
                mJoinTeam.setVisibility(View.GONE);
                teamID = adapterView.getItemAtPosition(i).toString();
                mDatabaseU.child(fbUser.getUid()).addValueEventListener(new ValueEventListener() {
                    @Override
                    public void onDataChange(DataSnapshot dataSnapshot) {
                        user = dataSnapshot.getValue(User.class);
                        userType = user.getType();
                        ((CurrentTeam) SelectTeam.this.getApplication()).setCurrentTeam(teamID);
                        if (user.getType().equalsIgnoreCase("Manager")) {
                            startActivity(new Intent(SelectTeam.this, ManagerHome.class));
                        } else if (user.getType().equalsIgnoreCase("Player")){
                            startActivity(new Intent(SelectTeam.this, PlayerHome.class));
                        }
                    }

                    @Override
                    public void onCancelled(DatabaseError databaseError) {

                    }
                });
                Toast.makeText(SelectTeam.this,"Loading data for team " + teamID, Toast.LENGTH_SHORT).show();
//                startActivity(new Intent(SelectTeam.this, ManagerHome.class));
            }
        });
    }
}

这是我的数据库:

{
  "Team" : {
    "AFL1" : {
      "division" : "1",
      "name" : "AFL1",
      "type" : "Football"
    },
    "AFL2" : {
      "division" : "2",
      "manager" : {
        "VoDClWm871fsIX6KO5SfRmjlGEf2" : "Cian McGrane "
      },
      "name" : "AFL2",
      "type" : "Football"
    },
    "AHL1" : {
      "division" : "1",
      "manager" : {
        "VoDClWm871fsIX6KO5SfRmjlGEf2" : "Cian McGrane "
      },
      "name" : "AHL1",
      "type" : "Hurling"
    },
    "AHL3" : {
      "division" : "3",
      "manager" : {
        "VoDClWm871fsIX6KO5SfRmjlGEf2" : "Cian McGrane "
      },
      "name" : "AHL3",
      "type" : "Hurling"
    }
  },
  "User" : {
    "VoDClWm871fsIX6KO5SfRmjlGEf2" : {
      "email" : "cianmcgrane@gmail.com",
      "name" : "Cian McGrane ",
      "password" : "password",
      "team" : {
        "-L4gns3cyu96k3XN8rjl" : "AHL1",
        "-L4gnw1VMco0sefy8-g0" : "AFL2"
      },
      "type" : "Manager"
    }
  }
}

我想在列表中显示 User 对象中的所有团队名称，但我一直收到上述错误。

如有任何帮助，我们将不胜感激。

Answer 1

要简单地显示 User 对象中的所有团队名称，请使用以下代码:

String uid = FirebaseAuth.getInstance().getCurrentUser().getUid();

DatabaseReference rootRef = FirebaseDatabase.getInstance().getReference();
DatabaseReference userTeamRef = rootRef.child("User").child(uid).child("team");
ValueEventListener valueEventListener = new ValueEventListener() {
    @Override
    public void onDataChange(DataSnapshot dataSnapshot) {
        for(DataSnapshot ds : dataSnapshot.getChildren()) {
            String teamName = ds.getValue(String.class);
            Log.d("TAG", teamName);
        }
    }

    @Override
    public void onCancelled(DatabaseError databaseError) {}
};
userTeamRef.addListenerForSingleValueEvent(valueEventListener);

输出将是:

AHL1
AHL2