如何在单击 ListView（由 Firebase 数据元素创建）中检索项目的 Firebase 父 ID？

Question

我正在尝试制作一个允许用户与使用该应用程序的所有其他用户交谈的 ChatApp。注册时，我创建了一个用户数据库，每个用户都在 Firebase 生成 ID 下。在我的 ChatSelectionActivity 中，我用用户名和他们的电子邮件填充了一个 ListView。我试图做到这一点，以便当在 ChatSelection 中单击用户时，他们的 id 会传递给 ChattingActivity。然后聊天活动能够检索与 id 关联的数据并使用它设置 TextView。我在获取点击项的 id 时遇到了很多麻烦，因为我没有使用 FirebaseListAdapter，然后将其传递给聊天活动

这是我的数据结构（我想传递每封电子邮件的父 ID 和姓名）：

   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"

这是我的 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) {

            }
        });


    }


}

这是我的聊天活动：

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

这很简单。使用 Firebase 的 DataSnapshot#getKey() 方法获取密钥/父 ID。

这里您需要进行以下更改。

User模型类

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;
  }

}

现在在您的ChatSelectionActivity 中进行以下更改。

@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 中进行以下更改。

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();
    }

}