从 firebase 读取数据，并在 listview 中填充

Question

我正在开发一个应用程序，我想在其中从我的 firebase 数据库中读取数据，并将其放入我的 listView 中。

我想要 3 种不同的阅读操作。

1. 第一次启动应用时，我想读取最近的 10 行。

2. 当我到达 listView 的末尾时，我想再获得 10 行，从目前已读取的最旧的行开始。

3. 当我拉到 listView 的顶部时，我想获取现在显示为第一行的行之后的所有行。 （这可以理解吗...？）

注意：当我阅读列表视图的顶部和末尾时，我已经实现了侦听器，所以我只需要 firebase-calls。

这应该怎么做？

Answer 1

我已经解决了这个问题，这就是我所做的。

1.首次启动应用时，我想读取最近的 10 行。

//read the 15 latest posts from the db
postQuery.limit(15).addListenerForSingleValueEvent(new ValueEventListener() {
    @Override
    public void onDataChange(DataSnapshot dataSnapshot) {
        //Read each child of the user
        for(DataSnapshot child : dataSnapshot.getChildren())
        {
            //If this is the first row we read, then this will be the oldest post that is going to be read,
            //Therefore we save the name of this post for further readings.
            if(prevOldestPostId.equals(oldestPostId))
            {
                //Save the name of the last read post, for later readings
                oldestPostId = child.getName();
            }
            //This if-statment is just a fail-safe, since I have an counter in the post, and that one I do not want to read.
            if(child.getName() != "nrOfPosts")
            {
                //Gather the data from the database
                UserPost readPost = new UserPost();
                for(DataSnapshot childLvl2 : child.getChildren()) {
                    if(childLvl2.getName() == "post")
                        readPost.setMessage(childLvl2.getValue().toString());
                    else
                        readPost.setDate(childLvl2.getValue().toString());
                }
                //Add the data to a temporary List
                toAdd.add(0, readPost);
            }
            //Keep the name of the newest post that has been read, we save this for further readings.
            newestPostId = child.getName();
        }
        //prevOlddestPostId is helping us to keep the the currently oldest post-name.
        prevOldestPostId = oldestPostId;
        //Add the new posts from the database to the List that is connected to an adapter and later on a ListView.
        for (UserPost aToAdd : toAdd) thePosts.add(aToAdd);

        // We need notify the adapter that the data have been changed
        mAdapter.notifyDataSetChanged();

        // Call onLoadMoreComplete when the LoadMore task, has finished
        mListView.onRefreshComplete();
    }

    @Override
    public void onCancelled(FirebaseError firebaseError) {

    }
});

2。当我到达 listView 的末尾时，我想再获得 10 行，从迄今为止读取的最旧的行开始。

postQuery.endAt(1, oldestPostId).limit(15).addListenerForSingleValueEvent(new ValueEventListener() {
    @Override
    public void onDataChange(DataSnapshot dataSnapshot) {
        //Gather the data
        for(DataSnapshot child : dataSnapshot.getChildren())
        {
            if(prevOldestPostId.equals(oldestPostId) && !child.getName().equals("nrOfPosts"))
            {
                //Save the name of the last read post, for later readings
                oldestPostId = child.getName();
            }

            if(child.getName() != "nrOfPosts" && !prevOldestPostId.equals(child.getName()))
            {
                UserPost readPost = new UserPost();

                for(DataSnapshot childLvl2 : child.getChildren()) {
                    if(childLvl2.getName() == "post")
                        readPost.setMessage(childLvl2.getValue().toString());
                    else
                        readPost.setDate(childLvl2.getValue().toString());
                }
                toAdd.add(0, readPost);

            }
        }
        prevOldestPostId = oldestPostId;

        //Insert it to the List for the listView
        for (UserPost aToAdd : toAdd)
        {
            thePosts.add(aToAdd);


            // We need notify the adapter that the data have been changed
            mAdapter.notifyDataSetChanged();
        }
    }

    @Override
    public void onCancelled(FirebaseError firebaseError) {

    }
});

3.当我拉到 listView 的顶部时，我想获取在现在显示为第一行的行之后生成的所有行。 （这可以理解吗...？）

postQuery.startAt(1, newestPostId).addListenerForSingleValueEvent(new ValueEventListener() {
    @Override
    public void onDataChange(DataSnapshot dataSnapshot) {
        for(DataSnapshot child : dataSnapshot.getChildren())
        {
            if(child.getName() != "nrOfPosts")
            {
                UserPost readPost = new UserPost();

                for(DataSnapshot childLvl2 : child.getChildren()) {
                    if(childLvl2.getName() == "post")
                        readPost.setMessage(childLvl2.getValue().toString());
                    else
                        readPost.setDate(childLvl2.getValue().toString());
                }
                //Prevent from get the currently newest post again...
                if(!readPost.getMessage().equals(thePosts.get(0).getMessage()))
                    toAdd.add(readPost);

                //Save the name of the last read post, for later readings
                newestPostId = child.getName();
            }
        }
        for (UserPost aToAdd : toAdd)
        {
            thePosts.add(0, aToAdd);

            // Call onLoadMoreComplete when the LoadMore task, has finished
            mListView.onRefreshComplete();
        }
    }

    @Override
    public void onCancelled(FirebaseError firebaseError) {

    }
});

我希望我至少可以对某人有所帮助。