从Firebase读取数据，并在ListView中填充 [英] Read data from firebase, and populate in listview

查看：276 发布时间：2017/11/10 20:55:51 android listview firebase firebase-database

本文介绍了从Firebase读取数据，并在ListView中填充的处理方法，对大家解决问题具有一定的参考价值，需要的朋友们下面随着小编来一起学习吧！

问题描述

我正在开发一个应用程序，我想从我的firebase数据库读取数据，并将其放入我的listView中。

有3种不同的读取操作I希望拥有。

当应用程序首次启动时，我想要读取10个最近的行。

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老的一行开始。

当我拉到listView的顶部时，我想要获得所有现在显示为第一个行的行。（这是可以理解的...？）

$ b

注意：我已经实现了侦听器因为当我阅读listview的顶部和末尾时，所以它只是我需要的firebase-calls。

这应该怎么做？

解决方案

我已经解决了这个问题，这里是我所做的。强> 1。当应用程序第一次启动时，我想要读取最近10行。

  //读取（15）.addListenerForSingleValueEvent（new ValueEventListener（）{
 @Override 
 public void onDataChange（DataSnapshot dataSnapshot）{
 //读取每个（DataSnapshot child：dataSnapshot.getChildren（））
 {
 //如果这是我们阅读的第一行，那么这将是最旧的帖子，被读取，
 //因此我们保存这篇文章的名字作进一步阅读
 if（prevOldestPostId.equals（oldestPostId））
 {
 //保存上次阅读的帖子，以后的阅读
 oldestPostId = child.getName（）; 
} 
 //这个if-statment只是一个故障安全，因为我在帖子中有一个计数器，那一个我不想读。
 if（child.getName（）！=nrOfPosts）
 {
 //从数据库中收集数据
 UserPost readPost = new UserPost（）; 
 for（DataSnapshot childLvl2：child.getChildren（））{
 if（childLvl2.getName（）==post）
 readPost.setMessage（childLvl2.getValue（）。toString（） ）; 
 else 
 readPost.setDate（childLvl2.getValue（）。toString（））; 
 
 //将数据添加到临时列表
 toAdd.add（0，readPost）; 
} 
 //保留已读取的最新帖子的名称，我们将其保存以供进一步读取。 
 newestPostId = child.getName（）; 
} 
 // prevOlddestPostId正在帮助我们保留当前最古老的后期名称。 
 prevOldestPostId = oldestPostId; 
 //将新的帖子从数据库添加到连接到适配器的列表中，然后在ListView上添加。 
 for（UserPost aToAdd：toAdd）thePosts.add（aToAdd）; 
 
 //我们需要通知适配器数据已被更改
 mAdapter.notifyDataSetChanged（）; 
 
 //当LoadMore任务完成
 mListView.onRefreshComplete（）时，调用onLoadMoreComplete; 
} 
 
 @Override 
 public void onCancelled（FirebaseError firebaseError）{
 $ b} 
}）;

2。当我到达listView的末尾时，我想再获得10行，从迄今为止读到的最老的行开始。

  postQuery.endAt（1，oldestPostId）.limit（15）.addListenerForSingleValueEvent（new ValueEventListener（）{
 @Override 
 public void onDataChange（DataSnapshot dataSnapshot）{
 //收集数据
 for（DataSnapshot child：dataSnapshot.getChildren（））
 {
 if（prevOldestPostId.equals（oldestPostId）&&！child.getName（）。equals nrOfPosts））
 {
 //保存上次读取的文章的名字，用于以后的阅读
 oldestPostId = child.getName（）; 
} 
 
 if（child.getName（）！=nrOfPosts&&！prevOldestPostId.equals（child.getName（）））
 {
 UserPost readPost = new UserPost（）; $ b （DataSnapshot childLvl2：child.getChildren（））{
 
 $ b if（childLvl2.getName（）==post）
 readPost.setMessage（childLvl2.getValue（）。toString（））; 
 else 
 readPost.setDate（childLvl2.getValue（）。toString（））; 
} 
 toAdd.add（0，readPost）; 
 
} 
} 
 prevOldestPostId = oldestPostId; 
 
 //将它插入listView列表
（UserPost aToAdd：toAdd）
 {
 thePosts.add（aToAdd）; 
 
 
 //我们需要通知适配器数据已被更改
 mAdapter.notifyDataSetChanged（）; 
 
 
 $ b @Override 
 public void onCancelled（FirebaseError firebaseError）{
 
 
}）;

3。当我拉到列表视图的顶部，我想要获得所有行后，现在显示为第一个行。（这是可以理解的...？）

  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（）; 
 
（DataSnapshot childLvl2：child.getChildren（））{
 if （childLvl2.getName（）==post）
 readPost.setMessage（childLvl2.getValue（）。toString（））; 
 else 
 readPost.setDate（childLvl2.getValue（）。 toString（））; 
} 
 //防止再次获取当前最新的帖子... 
 if（！readPost.getMessage（）。equals（thePosts.get（0）.getMessage （）））
 toAdd.add（re adPost）; 
 
 //保存上次阅读的文章的名称，以供以后阅读
 newestPostId = child.getName（）; 
 
 
（UserPost aToAdd：toAdd）
 {
 thePosts.add（0，aToAdd）; 
 
 //当LoadMore任务完成
 mListView.onRefreshComplete（）时，调用onLoadMoreComplete; 
 
 
 $ b @Override 
 public void onCancelled（FirebaseError firebaseError）{
 
 
}）;

我希望我可以帮助至少一个人。

I am developing an app in which I want to read data from my firebase database, and put it in my listView.

there are 3 different read-actions I want to have.

When the app is first started, I want to get the 10 most recent rows read.
When I reach the end of the listView, I want to get 10 more rows, starting at the oldest one that has been read so far.
when I pull to the top of the listView, I want to get all the rows that has been made after the row that is now displayed as the first one. (Is that understandable...?)

Note: I have already implemented listeners for when I read the top and the end of the listview, so it's only the firebase-calls that I need.

How should this be done?

解决方案

I have solved the issue, and here is what I have done.

1. When the app is first started, I want to get the 10 most recent rows read.

//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. When I reach the end of the listView, I want to get 10 more rows, starting at the oldest one that has been read so far.

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. when I pull to the top of the listView, I want to get all the rows that has been made after the row that is now displayed as the first one. (Is that understandable...?)

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) {

    }
});

I hope I can be of help to someone atleast.

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从Firebase读取数据，并在ListView中填充 [英] Read data from firebase, and populate in listview

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