Firebase 无限滚动列表视图在滚动时加载 10 个项目 [英] Firebase infinite scroll list view Load 10 items on Scrolling
问题描述
我正在寻找一种在 Firebase 应用中实现简单列表视图滚动的方法，但我没有找到任何实现方法.我已经尝试了 Internet 上可用的 2-3 个教程和文档，但没有达到所需的结果.
I'm looking for a way to implement a simple list view scrolling in my Firebase app, but I am not getting any way out how to implement this. I have already tried 2-3 tutorials and documentation available on the Internet, but didn't the required result.
在我的应用程序中，我想在开始加载前 10 个列表项时滚动，然后每次滚动下一个 10 或 20 个项目时将加载，直到最后一个项目出现在列表底部.
In my app I want scrolling like at starting first 10 list items load then each time on scrolling next 10 or 20 items will load until the last item appears at the bottom of the list.
所以我尝试通过以下方式检索前 10 个项目:
So I tried retrieving first 10 items the following way :
ArrayList<Event> event=new ArrayList<>();
Dbref = FirebaseDatabase.getInstance().getReference("/event");
Dbref.startAt(1).limitToLast(10).addValueEventListener(new ValueEventListener() {
@Override
public void onDataChange(DataSnapshot dataSnapshot) {
for (DataSnapshot snapshot : dataSnapshot.getChildren()) {
Log.e("Events.java ", "range query started! : " + dataSnapshot.getChildrenCount());
String event_id = snapshot.child("details").child("event_id").getValue().toString();
e=new Event(event_id); //Event is a model class for list items
event.add(e);
Log.e("ShowEventInfo : ", "" + event_id);
}
}
@Override
public void onCancelled(DatabaseError databaseError) {
}
});
adapter=new Event_CustomAdapter(getActivity(),event);
ls.setAdapter(adapter); //here ls is instance of ListView
我参考了这个 Youtube 视频来实现这个功能:(https://www.youtube.com/watch?annotation_id=annotation_3916642001&feature=iv&src_vid=YMJSBHAZsso&v=XwIKb_f0Y_w)
I referred this Youtube Video to implement this feature: (https://www.youtube.com/watch?annotation_id=annotation_3916642001&feature=iv&src_vid=YMJSBHAZsso&v=XwIKb_f0Y_w)
在上面的代码中，如您所见，我正在生成 Log 以检查是否从 firebase 获取数据，但我没有输出 Android 监视器.
In the above code, as you can see I am generating Log to check if data is fetched from the firebase, but I got no output Android monitor.
我不知道如何在列表视图中实现 Firebase 滚动.我认为这是那些在回收站视图/列表视图中实现无限滚动的人的常见问题.
I have no idea how can I implement Firebase Scrolling in my list view. I think this is a common problem for those who implement infinite-scroll in recycler view/ list view.
你能帮我实现这个功能吗?谢谢.
Could you please help me implementing this feature. Thanks.
推荐答案
这里我们将使用 DatabaseReference;s 方法，它们是 limitToFirst(int) OR limitToLast(int) 从 FireBase 获取第一条或最后一条记录.
Here we will use the DatabaseReference;s methods which are limitToFirst(int) OR limitToLast(int) to get the first or last records from FireBase.
在下面的示例中，我使用 limitToFirst(int) 仅从 Firebase 获取指定的最高记录.在这里，我正在使用 oldestPostId，这是我们记录的最后一个或 第 10 个 键.
In below example i am using the limitToFirst(int) to get only top specified records from Firebase. Here i am playing with oldestPostId which is the last or 10th key of our record.
private String oldestPostId;
DatabaseReference Dbref = FirebaseDatabase.getInstance().getReference("/event");
/////GETTING FIRST 10 RECORDS FROM THE FIREBASE HERE
Dbref.limitToFirst(10).addListenerForSingleValueEvent(new ValueEventListener() {
@Override
public void onDataChange(DataSnapshot dataSnapshot) {
for (DataSnapshot child : dataSnapshot.getChildren()) {
oldestPostId = child.getKey(); ////HERE WE ARE SAVING THE LAST POST_ID FROM URS POST
dataSnapshot.getChildrenCount());
String event_id = snapshot.child("details").child("event_id").getValue().toString();
e=new Event(event_id); //Event is a model class for list items
event.add(e);
Log.e("ShowEventInfo : ", "" + event_id);
}
}
@Override
public void onCancelled(DatabaseError databaseError) {
}
});
从上面的代码中，我已经从 firebase 获得了前 10 条记录，现在我们将实现加载更多功能，所以我使用了 Listview 的 onscrolllistener在 isScrollCompleted() 上，我们将使用 orderByKey() 使用 limitToFirst() 方法进一步获取 10 个记录.我已经实现了整个代码以获取关于 isScrollCompleted() 的更多数据，请查看下面的示例.
From above code , i have get the first 10 records from firebase, Now we will implement load more functionality so i am using the Listview's onscrolllistener
On isScrollCompleted() we will use orderByKey() for getting further 10 more record with limitToFirst() method. I have implemented the whole code to get further data on isScrollCompleted() , please check below example.
YOUR_LISTVIEW.setOnScrollListener(new OnScrollListener() {
private int currentVisibleItemCount;
private int currentScrollState;
private int currentFirstVisibleItem;
private int totalItem;
private LinearLayout lBelow;
@Override
public void onScrollStateChanged (AbsListView view,int scrollState){
// TODO Auto-generated method stub
this.currentScrollState = scrollState;
this.isScrollCompleted();
}
@Override
public void onScroll (AbsListView view,int firstVisibleItem,
int visibleItemCount, int totalItemCount){
// TODO Auto-generated method stub
this.currentFirstVisibleItem = firstVisibleItem;
this.currentVisibleItemCount = visibleItemCount;
this.totalItem = totalItemCount;
}
private void isScrollCompleted () {
if (totalItem - currentFirstVisibleItem == currentVisibleItemCount
&& this.currentScrollState == SCROLL_STATE_IDLE) {
/** To do code here*/
Dbref.orderByKey().startAt(oldestPostId).limitToFirst(10).addListenerForSingleValueEvent(new ValueEventListener() {
@Override
public void onDataChange(DataSnapshot dataSnapshot) {
for (DataSnapshot child : dataSnapshot.getChildren()) {
oldestPostId = child.getKey();
String event_id = snapshot.child("details").child("event_id").getValue().toString();
e = new Event(event_id); //Event is a model class for list items
event.add(e);
Log.e("ShowEventInfo : ", "" + event_id);
}
}
@Override
public void onCancelled(DatabaseError databaseError) {
}
});
}
});
});
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