如何在單擊ListView（由Firebase Data Elements創建）中檢索項目的Firebase父ID？

Question

我正在嘗試制作一個允許用戶與使用該應用程序的所有其他用戶對話的ChatApp。 在注冊時，我已經創建了一個用戶數據庫，每個用戶都有一個Firebase生成ID。 在我的ChatSelectionActivity上，我用用戶名和電子郵件填充了ListView。 我試圖做到這一點，以便當在ChatSelection中單擊用戶時，其ID會傳遞給ChattingActivity。 然后，聊天活動能夠檢索與id關聯的數據並使用它設置TextView。 我在獲取被點擊項目的ID時遇到了很多麻煩，因為我沒有使用FirebaseListAdapter，然后將其傳遞給Chatting Activity

這是我的數據結構（我想傳遞每個電子郵件的父ID和名稱）：

   users
    -LJzf1AoOffNpl6hcYMK
               email:"vaenugula01@gmail.com"
               name: "Phaniraj Aenugula"
    -LJzhru4UjIT1LyMyvep
               email:"dunkinchicken@gmail.com"
               name: "D'Andre Black"
    -LK4UT0n_LI27AUvBPQH
               email:"nagapvvs01@gmail.com"
               name:"Pavan Kumar"

這是我的ChatSelectionActivity：

package com.tamir.offen.OddJob;

import android.app.Activity;
import android.app.ListActivity;
import android.content.Intent;
import android.support.annotation.NonNull;
import android.support.constraint.solver.widgets.Snapshot;
import android.support.design.widget.BottomNavigationView;
import android.support.v7.app.AppCompatActivity;
import android.os.Bundle;
import android.view.Menu;
import android.view.MenuItem;
import android.view.View;
import android.widget.AdapterView;
import android.widget.ArrayAdapter;
import android.widget.ListView;

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.List;

import static com.tamir.offen.OddJob.ChatSelectionActivity.getChatterId;

public class ChatSelectionActivity extends AppCompatActivity{
    ListView listViewUsers;

    DatabaseReference databaseUsers;
    List<User> userList;
    private BottomNavigationView bottomNavigationView;
    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_chat_selection);

        listViewUsers = (ListView) findViewById(R.id.listViewUsers);
        databaseUsers = FirebaseDatabase.getInstance().getReference("users");
        userList = new ArrayList<>();

        bottomNavigationView = findViewById(R.id.bottomNavView_Bar);
        Menu menu = bottomNavigationView.getMenu();
        MenuItem menuItem = menu.getItem(0);
        menuItem.setChecked(true);
        bottomNavigationView.setOnNavigationItemSelectedListener(new BottomNavigationView.OnNavigationItemSelectedListener() {
            @Override
            public boolean onNavigationItemSelected(@NonNull MenuItem item) {
                Intent intent;
                switch(item.getItemId()) {
                    case R.id.nav_messages:
                        //intent = new Intent(messages.this, messages.class);
                        //startActivity(intent);
                        break;

                    case R.id.nav_map:
                        intent = new Intent(ChatSelectionActivity.this, map.class);
                        startActivity(intent);
                        overridePendingTransition(R.anim.slide_in_right, R.anim.slide_out_left);
                        break;

                    case R.id.nav_add_work:
                        intent = new Intent(ChatSelectionActivity.this, AddActivity.class);
                        startActivity(intent);
                        overridePendingTransition(R.anim.slide_in_right, R.anim.slide_out_left);
                        break;

                }

                return false;
            }
        });


    }

    @Override
    public void onStart() {
        super.onStart();
        databaseUsers.addValueEventListener(new ValueEventListener() {
            @Override
            public void onDataChange(@NonNull DataSnapshot dataSnapshot) {
                userList.clear();
                for(DataSnapshot userSnapshot: dataSnapshot.getChildren()){
                    User user = userSnapshot.getValue(User.class);
                    userList.add(user);
                }
                final UserList adapter = new UserList(ChatSelectionActivity.this, userList);
                listViewUsers.setAdapter(adapter);
                listViewUsers.setOnItemClickListener(new AdapterView.OnItemClickListener() {
                    @Override
                    public void onItemClick(AdapterView<?> adapterView, View view, int position, long l) {


                        // I don't know how to retrieve the 

                        Intent chatIntent = new Intent(ChatSelectionActivity.this, ChattingActivity.class);
                        startActivity(chatIntent);


                    }
                });


            }

            @Override
            public void onCancelled(@NonNull DatabaseError databaseError) {

            }
        });


    }


}

這是我的聊天活動：

package com.tamir.offen.OddJob;

import android.support.annotation.NonNull;
import android.support.v7.app.AppCompatActivity;
import android.os.Bundle;
import android.widget.RadioGroup;
import android.widget.TextView;
import android.widget.Toast;

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;

public class ChattingActivity extends AppCompatActivity {

    private TextView receiver_name;
    DatabaseReference databaseUsers;



    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_chatting);
        String chat_id = getIntent().getStringExtra("chat_id");
        //the "chat id" in the getString Extra is the id that would have been passed from the ChatSelectionActivity


        receiver_name = (TextView) findViewById(R.id.receiver_name);
        Toast.makeText(ChattingActivity.this, chat_id, Toast.LENGTH_SHORT).show();
    }
}

Answer 1

非常簡單 使用Firebase的DataSnapshot#getKey()方法獲取密鑰/父ID。

在這里，您需要進行以下更改。

User模型類

public class User implements Serializable {  // implement serializable interface as we need to pass object this class in an Intent
  ...
  ...
  private String parentId;  // use private access because we don't want to set this id in Firebase database.

  // constructors if there any

  // other getter/setter methods

  // add these getter and setter methods
  public void setParentId(String parentId) {
     this.parentId = parentId;
  }

  public String getParentId() {
     return parentId;
  }

}

現在，在您的ChatSelectionActivity進行以下更改。

@Override
public void onStart() {
    super.onStart();
    databaseUsers.addValueEventListener(new ValueEventListener() {
        @Override
        public void onDataChange(@NonNull DataSnapshot dataSnapshot) {
            userList.clear();
            for(DataSnapshot userSnapshot: dataSnapshot.getChildren()){

                String parentId = userSnapshot.getKey();  // get id from Firebase snapshot

                User user = userSnapshot.getValue(User.class);

                user.setParentId(parentId);  // set parent id

                userList.add(user);
            }
            final UserList adapter = new UserList(ChatSelectionActivity.this, userList);
            listViewUsers.setAdapter(adapter);
            listViewUsers.setOnItemClickListener(new AdapterView.OnItemClickListener() {
                @Override
                public void onItemClick(AdapterView<?> adapterView, View view, int position, long l) {


                    // get User object from ArrayList
                    User user = userList.get(position);

                    Intent chatIntent = new Intent(ChatSelectionActivity.this, ChattingActivity.class);

                    chatIntent.putExtra("user", user);  // pass user object to intent

                    startActivity(chatIntent);


                }
            });
        }

        @Override
        public void onCancelled(@NonNull DatabaseError databaseError) {

        }
    });
}

最后，在您的ChattingActivity進行以下更改。

private User user;  // create an object of User class outside onCreate() method

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

    user = (User) getIntent().getSerializableExtra("user");  // use the same key as you set in intent object in previous activity

    if (user != null) {
      // now you can get receiver's email, user name, parent id etc. 
      String parentId = user.getParentId();
    }

}