Firebase加载更多滚动项目（Android） [英] Firebase to load more items on scroll (Android)

问题描述

我试图做一个聊天应用程序，我使用Firebase作为我的后端，
我用最后发送的10条消息填充我的listview onCreate（），
，我只是想当用户滚动^它会每次加载10多个。

我得到了所有的工作，问题是Firebase加载所有数据例如：它在启动时加载10条消息，当我向上滚动时加载20条消息，然后它加载30条消息，而不是一次只加载10条消息。

这是代码：

<$ p $当用户滚动，并达到顶部，即firstVisibleItem == 0

messagesList.setOnScrollListener（new AbsListView.OnScrollListener（）{
@覆盖
public void onScrollStateChanged（AbsListView absListView，int i）{


$ b @Override
public void onScroll（AbsListView view，int f irstVisibleItem，
int visibleItemCount，int totalItemCount）{

if（firstVisibleItem == 0&& ！loading）{
msgNum + = 10;
setMessagesList（msgNum）; //你的加载函数


}）;

// Firebase加载更多滚动代码：
public void setMessagesList（int msgNum）{

MessegesRef2 = database.getReference（chatsMessages）。child （chatID）;
messageValueListener = MessegesRef2.orderByChild（creationDate）。limitToLast（msgNum）.addValueEventListener（new ValueEventListener（）{
@Override
public void onDataChange（DataSnapshot dataSnapshot）{
loading = true;
for（DataSnapshot data：dataSnapshot.getChildren（））{

ChatMessage chatMessage = data.getValue（ChatMessage.class）;

chatMessageAdapter.add （chatMessage）;
chatMessageAdapter.notifyDataSetChanged（）;
}
loading = false;
}

@Override
public void onCancelled DatabaseError databaseError）{

}
}）;

解决方案

a href =https://firebase.google.com/docs/reference/js/firebase.database.Query#endAt =nofollow noreferrer> endAt（）

  ref.orderByChild（creationDate）。limitToLast（pageSize）.endAt（oldestLocalMessageTime）.addValueEventListener 
 // pageSize是您想要的消息数量（10）
 // oldestLocalMessageTime是您从Firebase加载的最旧消息的时间
 //每当您加载/加载更多消息时，您需要更新oldestLocalMessageTime值
  

I'm trying to make a chat application, I use Firebase as my backend, I'm populating my listview onCreate() with the last 10 messages sent, and I just want that when the user scrolls up ^ it will load 10 more every time.

I got all working, the problem is that the Firebase loads all the data every time, and not increasing by 10 the existing data.

For example: it loads 10 messages at startup, and when I scroll up it loads 20 messages, and then it loads 30 messages, instead of just loading 10 more at a time.

This is the code:

//Listview to find when user is scrolling and reach the top i.e firstVisibleItem == 0

messagesList.setOnScrollListener(new AbsListView.OnScrollListener() {
    @Override
    public void onScrollStateChanged(AbsListView absListView, int i) {

    }

    @Override
    public void onScroll(AbsListView view, int firstVisibleItem,
        int visibleItemCount, int totalItemCount) {

        if (firstVisibleItem == 0 && !loading) {
            msgNum += 10;
            setMessagesList(msgNum); //your load more function
        }
    }
});

//Firebase to load more on scroll code:
public void setMessagesList(int msgNum) {

    MessegesRef2 = database.getReference("chatsMessages").child(chatID);
    messageValueListener = MessegesRef2.orderByChild("creationDate").limitToLast(msgNum).addValueEventListener(new ValueEventListener() {
        @Override
        public void onDataChange(DataSnapshot dataSnapshot) {
            loading = true;
            for (DataSnapshot data: dataSnapshot.getChildren()) {

                ChatMessage chatMessage = data.getValue(ChatMessage.class);

                chatMessageAdapter.add(chatMessage);
                chatMessageAdapter.notifyDataSetChanged();
            }
            loading = false;
        }

        @Override
        public void onCancelled(DatabaseError databaseError) {

        }
    });
}

解决方案

I think you can use endAt()

ref.orderByChild("creationDate").limitToLast(pageSize).endAt(oldestLocalMessageTime).addValueEventListener
// pageSize is the number of messages you want to load each time (10)
// oldestLocalMessageTime is the time of oldest message that you have loaded from Firebase
// everytime you load/load more messages you need to update oldestLocalMessageTime value

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