如何从Android Studio中的Firebase实时数据库中的ListView中首先获取最后添加的数据 [英] How to get the last added data on first in the listview from firebase realtime database in android studio

问题描述

我有一个列表视图，用于从Firebase实时数据库检索数据.但是问题是我想在列表视图的顶部显示最后添加的数据...这是一个告示板类型的项目，因此，我想在列表视图的上显示最新的通知...找不到一些网络上的好解决方案....

I have a list view to retrieve the data from firebase realtime database. But the problem is I want to show the last added data on the top of the listview...Its a notice board type project so, I want to show the latest notice on the to of the listview...could't find some good solutions on the web....

这是"mainactivity.java"的代码....

here are the codes of "mainactivity.java"....

         package com.example.wrappo;
         import androidx.annotation.NonNull;
         import androidx.annotation.Nullable;
         import androidx.appcompat.app.AppCompatActivity;

         import android.content.Intent;
         import android.os.Bundle;
        import android.os.Handler;
         import android.widget.ArrayAdapter;
         import android.widget.ListView;

          import com.google.firebase.database.ChildEventListener;
        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 java.util.ArrayList;
       import java.util.Timer;
       import java.util.TimerTask;
       public class MainActivity extends AppCompatActivity {

ListView myListView;

ArrayList<String> myArrayList = new ArrayList<>();

DatabaseReference mRef;


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

    final ArrayAdapter<String> myArrayAdapter = new ArrayAdapter<String>(MainActivity.this, 
    android.R.layout.simple_list_item_1, myArrayList);
    myListView = (ListView) findViewById(R.id.listview1);
    myListView.setAdapter(myArrayAdapter);

    mRef = FirebaseDatabase.getInstance().getReference();
    mRef.addChildEventListener(new ChildEventListener() {
        @Override
        public void onChildAdded(@NonNull DataSnapshot dataSnapshot, @Nullable String s) {

            String value = dataSnapshot.getValue(String.class);
            myArrayList.add(value);
            myArrayAdapter.notifyDataSetChanged();
        }

        @Override
        public void onChildChanged(@NonNull DataSnapshot dataSnapshot, @Nullable String s) {

            myArrayAdapter.notifyDataSetChanged();
        }

        @Override
        public void onChildRemoved(@NonNull DataSnapshot dataSnapshot) {

        }

        @Override
        public void onChildMoved(@NonNull DataSnapshot dataSnapshot, @Nullable String s) {

        }

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

        }
        });
        }
      }  

这是xml代码....

here is the xml code....

  <?xml version="1.0" encoding="utf-8"?>
<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:app="http://schemas.android.com/apk/res-auto"
xmlns:tools="http://schemas.android.com/tools"
android:layout_width="match_parent"
android:layout_height="match_parent"
tools:context=".MainActivity">

<ListView
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:id="@+id/listview1"/>

</RelativeLayout>

推荐答案

之前已经讨论了很多次.我建议您查看关于最新动态"的问题和有关反向"的问题.

This has been covered quite a few times before already. I recommend checking out questions on 'newest on top' and on questions on 'reverse'.

最快的入门方法可能是将项目简单地添加到ArrayList的开头而不是结尾:

The quickest way to get started might be to simply add the items to the start of your ArrayList instead of to the end of it:

myArrayList.add(0, value);

这篇关于如何从Android Studio中的Firebase实时数据库中的ListView中首先获取最后添加的数据的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！