英文:
Sort Firebase data in descending order
问题
private Query reference; //数据库引用
private ListView ListView; //创建列表视图
private ArrayList<String> arrayList = new ArrayList<>(); //创建字符串数组列表
private ArrayAdapter<String> adapter; //创建数组适配器
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_high_scores);
reference = FirebaseDatabase.getInstance().getReference("Highscores").orderByValue(); //引用数据库中的高分部分
ListView = (ListView) findViewById(R.id.list_view); //在XML中找到列表视图
adapter = new ArrayAdapter<String>(this, android.R.layout.simple_list_item_1, arrayList); //将适配器设置为列表
Collections.reverse(arrayList); //反转数组列表
ListView.setAdapter(adapter);
reference.addChildEventListener(new ChildEventListener() { //为数据库添加子监听器
@Override
public void onChildAdded(@NonNull DataSnapshot dataSnapshot, @Nullable String s) {
String value = dataSnapshot.getValue().toString(); //将数据库中的值转换为字符串
arrayList.add(value); //将其添加到数组列表中
adapter.notifyDataSetChanged(); //通知数据集已更改
}
});
}
数据库中的数据：
{
"-M4FPEiJ_DVc9kaQrebz" : 0,
"-M4FPIuMbArT6KjtrDtO" : 6,
"-M4FPP5EdC1CaKgOVECX" : 17,
"-M4FPTWg7JkKRvWakRkH" : 12,
"-M4FPYPNVZIjhBM6gVWW" : 11,
"-M4FPbL9I-fsQwRvVIFX" : 5
}
回答：
通过在数组列表的索引0处添加元素，不管如何都能修复此问题，所有其他元素都会被简单地向右移动，从而导致列表视图以降序显示。
String value = dataSnapshot.getValue().toString(); //将数据库中的值转换为字符串
arrayList.add(0, value); //将其添加到数组列表的索引0处
adapter.notifyDataSetChanged(); //通知数据集已更改
英文:
I want to create a highscores ListView with entries being displayed in descending order, with the use of orderByValue I am getting them sorted in ascending order however when using Collections.reverse() with my arraylist, the entries are still not reversed in the ListView.
private Query reference; //database reference
private ListView ListView; //creating listview
private ArrayList<String> arrayList = new ArrayList<>();
private ArrayAdapter<String> adapter; //creating array adapter
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_high_scores);
reference = FirebaseDatabase.getInstance().getReference("Highscores").orderByValue(); //reference the highscore section in database
ListView = (ListView) findViewById(R.id.list_view); //find the list view in the xml
adapter = new ArrayAdapter<String>(this, android.R.layout.simple_list_item_1, arrayList); // set the adapter to the list
Collections.reverse(arrayList);
ListView.setAdapter(adapter);
reference.addChildEventListener(new ChildEventListener() { // add a child listener for the database
@Override
public void onChildAdded(@NonNull DataSnapshot dataSnapshot, @Nullable String s) {
String value = dataSnapshot.getValue().toString(); // convert the values in the databse to string
arrayList.add(value); //add them to the arraylist
adapter.notifyDataSetChanged(); //notify that the dataset has changed
}
the data in the database is
{
"-M4FPEiJ_DVc9kaQrebz" : 0,
"-M4FPIuMbArT6KjtrDtO" : 6,
"-M4FPP5EdC1CaKgOVECX" : 17,
"-M4FPTWg7JkKRvWakRkH" : 12,
"-M4FPYPNVZIjhBM6gVWW" : 11,
"-M4FPbL9I-fsQwRvVIFX" : 5
}
Answer:
Managed to fix this by simply adding to the arraylist at 0 index no matter what, all other elements were simply shifted to the right leading to a listview in descending order.
String value = dataSnapshot.getValue().toString(); // convert the values in the databse to string
arrayList.add(0, value); //add them to the arraylist
adapter.notifyDataSetChanged(); //notify that the dataset has changed
答案1
得分: 0
reference.addChildEventListener(new ChildEventListener() {
@Override
public void onChildAdded(@NonNull DataSnapshot dataSnapshot, @Nullable String s) {
String value = dataSnapshot.getValue().toString();
arrayList.add(value);
Collections.reverse(arrayList);
adapter.notifyDataSetChanged();
}
});
英文:
reference.addChildEventListener(new ChildEventListener() { // add a child listener for the database
@Override
public void onChildAdded(@NonNull DataSnapshot dataSnapshot, @Nullable String s) {
String value = dataSnapshot.getValue().toString(); // convert the values in the databse to string
arrayList.add(value); //add them to the arraylist
Collections.reverse(arrayList); //add this line for short solution
adapter.notifyDataSetChanged(); //notify that the dataset has changed
}
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