难以获得儿童arraylist（firebase）

Question

大家好，我正在尝试从firebase检索数据，并根据我单击的RecyclerView显示它们，并将名称传递给下一个活动。

每当我尝试这样做时，它总是会关闭应用程序并再次打开。

但是，每当集合中没有“Dates_Log_In”时，它就会运行，但不会显示任何类型的数据。

这是我用来显示RecyclerView中所有数据的类

public class Listing extends AppCompatActivity implements AttendanceListAdapter.OnNoteListener{

    Button back;
    DatabaseReference mRef;

    ArrayList<Attendance> userList;
    RecyclerView recyclerView;
    AttendanceListAdapter adapter;

    TextView name;
    TextView designation;
    TextView activity;
    TextView status;

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

        recyclerView = findViewById(R.id.rcl_List);
        back = findViewById(R.id.btn_go_back);
        name = findViewById(R.id.txt_name1);
        designation = findViewById(R.id.txt_designation1);
        activity = findViewById(R.id.txt_activity1);
        status = findViewById(R.id.txt_status1);

        mRef = FirebaseDatabase.getInstance().getReference("Users");

        recyclerView.setHasFixedSize(true);
        recyclerView.setLayoutManager(new LinearLayoutManager(this));

        userList = new ArrayList<>();
        adapter = new AttendanceListAdapter(this, userList);
        recyclerView.setAdapter(adapter);

        mRef.addValueEventListener(new ValueEventListener() {
            @Override
            public void onDataChange(@NonNull DataSnapshot snapshot) {
                for(DataSnapshot dataSnapshot : snapshot.getChildren()){

                    Attendance user = dataSnapshot.getValue(Attendance.class);
                    userList.add(user);
                }
                adapter.notifyDataSetChanged();
            }

            @Override
            public void onCancelled(@NonNull DatabaseError error) {
                Toast.makeText(Listing.this, "Failed to retrieve Data", Toast.LENGTH_LONG).show();
            }
        });

        back.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View view) {
                finish();
            }
        });
    }

    @Override
    public void onNoteClick(int position) {
        userList.get(position);

    }
}

考勤班

public class Attendance {

    public String fullname, designation, activity, status, date;

    private long maxid = 0;

    private DatabaseReference mref;
    public Attendance(){

    }
    public Attendance(String fullname, String designation, String activity, String status){

        this.fullname = fullname;
        this.designation = designation;
        this.activity = activity;
        this.status = status;
    }

    public void setFullname(String fullname) {
        this.fullname = fullname;
    }

    public void setDesignation(String designation) {
        this.designation = designation;
    }

    public void setActivity(String activity) {
        this.activity = activity;
    }

    public void setStatus(String status) {
        this.status = status;
    }

    public void setDate(String date) {
        this.date = date;
    }

    public String getFullname(){
        return fullname;
    }
    public String getDesignation(){
        return designation;
    }
    public String getActivity(){
        return activity;
    }
    public String getStatus(){
        return status;
    }
    public String getDate(){
        return date;
    }
}

AttendanceListAdapter

public class AttendanceListAdapter extends RecyclerView.Adapter<AttendanceListAdapter.MyViewHolder> {

    ArrayList<Attendance> attendanceArrayList;
    Context context;

    public AttendanceListAdapter(Context context, ArrayList<Attendance> list){
        this.context = context;
        this.attendanceArrayList = list;
    }

    public class MyViewHolder extends RecyclerView.ViewHolder {
        private TextView name, designation, activity, status;

        public MyViewHolder(final View view){
            super(view);
            name = view.findViewById(R.id.txt_name1);
            designation = view.findViewById(R.id.txt_designation1);
            activity = view.findViewById(R.id.txt_activity1);
            status = view.findViewById(R.id.txt_status1);
        }
    }

    @NonNull
    @Override
    public AttendanceListAdapter.MyViewHolder onCreateViewHolder(@NonNull ViewGroup parent, int viewType) {
        View itemView = LayoutInflater.from(parent.getContext()).inflate(R.layout.list_layout, parent, false);
        return new MyViewHolder(itemView);
    }

    @Override
    public void onBindViewHolder(@NonNull AttendanceListAdapter.MyViewHolder holder, int position) {

        Attendance user = attendanceArrayList.get(position);

        holder.name.setText(user.getFullname());
        holder.designation.setText(user.getDesignation());
        holder.activity.setText(user.getActivity());
        holder.status.setText(user.getStatus());
        holder.itemView.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View view) {
                String id = user.getFullname();
                passData(id);

            }
        });

    }

    private void passData(String id) {

        Intent intent = new Intent(context,Logbook.class);
        intent.putExtra("id", id);
        context.startActivity(intent);
    }

    @Override
    public int getItemCount() {
        return attendanceArrayList.size();
    }

    public interface OnNoteListener{
        void onNoteClick(int position);
    }

}

这就是我传递数据的地方，它应该向列表视图显示“Dates_Log_In”（日期登录）（不确定这是否是正确的选择）

public class Logbook extends AppCompatActivity {

    Button back;
    DatabaseReference mRef;
    ListView listView;
    ArrayList<String> userList;
    ArrayAdapter<String> adapter;
    TextView txt_name;
    TextView txt_date;

    date Date;

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

        Intent intent = getIntent();
        String id = intent.getStringExtra("id");

        Date = new date();

        listView = findViewById(R.id.list_date);
        back = findViewById(R.id.btn_go_back2);
        txt_name = findViewById(R.id.txt_nameselected);
        txt_date = findViewById(R.id.txt_date);
        txt_name.setText(id);

        mRef = FirebaseDatabase.getInstance().getReference("Users").child(id);
        userList = new ArrayList<>();
        adapter = new ArrayAdapter<String>(this, R.layout.logbook_layout, R.id.txt_date, userList);

        mRef.addValueEventListener(new ValueEventListener() {
            @Override
            public void onDataChange(@NonNull DataSnapshot snapshot) {
                for(DataSnapshot dataSnapshot : snapshot.getChildren()){
                    Log.i("Dates_Log_In", dataSnapshot.getValue(String.class));
                    Date = dataSnapshot.getValue(date.class);
                    userList.add(Date.getDate());
                }
                listView.setAdapter(adapter);
            }

            @Override
            public void onCancelled(@NonNull DatabaseError error) {
                Toast.makeText(Logbook.this, "Failed to retrieve Data", Toast.LENGTH_LONG).show();
            }
        });

        back.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View view) {
                finish();
            }
        });

在测试运行期间，错误如下所示

E/le.enrollmentq: [qarth_debug:]  get PatchStore::createDisableExceptionQarthFile method fail.
E/AndroidRuntime: FATAL EXCEPTION: main
    Process: com.example.enrollmentqr, PID: 3144
    com.google.firebase.database.DatabaseException: Failed to convert value of type java.util.ArrayList to String
        at com.google.firebase.database.core.utilities.encoding.CustomClassMapper.convertString(CustomClassMapper.java:426)
        at com.google.firebase.database.core.utilities.encoding.CustomClassMapper.deserializeToClass(CustomClassMapper.java:217)
        at com.google.firebase.database.core.utilities.encoding.CustomClassMapper.convertToCustomClass(CustomClassMapper.java:80)
        at com.google.firebase.database.DataSnapshot.getValue(DataSnapshot.java:203)
        at com.example.enrollmentqr.Logbook$1.onDataChange(Logbook.java:64)
        at com.google.firebase.database.core.ValueEventRegistration.fireEvent(ValueEventRegistration.java:75)
        at com.google.firebase.database.core.view.DataEvent.fire(DataEvent.java:63)
        at com.google.firebase.database.core.view.EventRaiser$1.run(EventRaiser.java:55)
        at android.os.Handler.handleCallback(Handler.java:907)
        at android.os.Handler.dispatchMessage(Handler.java:105)
        at android.os.Looper.loop(Looper.java:216)
        at android.app.ActivityThread.main(ActivityThread.java:7625)
        at java.lang.reflect.Method.invoke(Native Method)
        at com.android.internal.os.RuntimeInit$MethodAndArgsCaller.run(RuntimeInit.java:524)
        at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:987)

在logcat中显示

2022-05-05 22:33:21.684 3144-3144/com.example.enrollmentqr W/ClassMapper: No setter/field for Dates_Log_In found on class com.example.enrollmentqr.Attendance
2022-05-05 22:33:21.700 3144-3144/com.example.enrollmentqr W/ClassMapper: No setter/field for Dates_Log_In found on class com.example.enrollmentqr.Attendance

这是我为数据库设定的规则。

{
  "rules": {
    ".read": true,
    ".write": true,
    "Users": {
        "Dates_Log_In":{
          "$uid":{
          ".read": true,
          ".write": true,
          }
        },
        "activity":{
        ".read": true,
        ".write": true,
        },
        "designation":{
        ".read": true,
        ".write": true,
        },
        "fullname":{
        ".read": true,
        ".write": true,
        },
        "status":{
        ".read": true,
        ".write": true,
        }
    }
  }
}

我有点知道，因为我没有在Attendance.class上包含日期，所以它给了一个空值（只是我的直觉）。所以我试着包含它，但这对我来说也没用。我有点猜测我如何调用Firebase有问题？我几天前才开始为我的项目做这个。

Answer 1

这毫无意义：

Log.i("Dates_Log_In", dataSnapshot.getValue(String.class));
Date = dataSnapshot.getValue(date.class);

dataSnapshot可以是字符串，也可以是日期，但不能同时是两者。这意味着这些线路中至少有一条总是会失败。

既然你正在阅读这条路径：

mRef = FirebaseDatabase.getInstance().getReference("Users").child(id);

因此，您正在读取/User/$id，据我所知，它包含单个用户的数据。这意味着您不需要在onDataChange中循环遍历snapshot.getUNICEF，因为快照已经仅包含该单个用户的数据。

然后是下面的数据问题，如果没有看到您的实际JSON，很难确定。我可以推荐的最安全的方法是让Firebase弄清楚，然后在没有类型的情况下调用getValue（）。

mRef.addValueEventListener(new ValueEventListener() {
    @Override
    public void onDataChange(@NonNull DataSnapshot snapshot) {
        Map<String, object> values = dataSnapshot.getValue();
        ...
    }

很可能你会得到一张地图