Load ListView data when user scrolls

Question

Here is my code displaying a list that is being parsed from an html file.

private class getItemDesc extends AsyncTask<Void, Void, Void> {

    private ArrayList<String> descArray;

    @Override
    protected Void doInBackground(Void... arg0) {
        try {
            File file = new File(dir, getString(R.string.html_file));
            descArray = new ArrayList<String>();
            FileInputStream in = new FileInputStream(file);
            BufferedReader br = new BufferedReader(new InputStreamReader(
                    in, "UTF-8"));
            String line;
            while ((line = br.readLine()) != null) {
                Document doc = Jsoup.parse(line);
                Elements descs = doc.select("p");
                for (Element desc : descs) {
                    descArray.add(desc.text());
                }
            }
            in.close();
            br.close();
        } catch(Exception e) {
            e.printStackTrace();
        }
        return null;
    }
    @Override
    protected void onPostExecute(Void v) {
        MyAdapter mAdapter = new MyAdapter(getApplicationContext(),
            R.layout.list_layout, descArray);
        listView.setAdapter(mAdapter);
    }

There is a lot of data coming from this (over 100 items in the array) and it's taking a while to load. I was wondering if there is a way to load 10 items at a time and use an OnScrollListener to continue loading the data from the file? Any suggestions will be appreciated.

Answer 1

There appear to be many ways to accomplish running background code when you reach the end of a listview, the following snippet is what I chose to implement:

lv.setOnScrollListener(new OnScrollListener() {

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

    @Override
    public void onScrollStateChanged(AbsListView view, int scrollState) {
        int threshold = 1;
        int count = lv.getCount();
        if (scrollState == SCROLL_STATE_IDLE) {
            if (lv.getLastVisiblePosition() >= count - threshold) {
                items = (AddItems) new AddItems().execute(count);
            }
        }
    }
});

As for the class AddItem, what I wanted required creating a custom array object, Gift()

public class Gift {
    private String descs;
    private String itemName;
    private String price;
    private String imageUrl;

    public Gift() {
    }

    public Gift(String p, String i, String d, String u) {
        this.descs = d;
        this.itemName = i;
        this.price = p;
        this.imageUrl = u;
    }

    public String getDetails() {
        return descs;
    }

    public void setDetails(String details) {
        this.descs = details;
    }
} // You get the idea

Then I would have to iterate through the file, adding desired strings to their respect ArrayList, and combine all three lists into an ArrayList<Gift> which is shown below.

private class AddItems extends AsyncTask<Integer, Void, ArrayList<Gift>> {

    @Override
    protected ArrayList<Gift> doInBackground(Integer... integer) {
        try {
            amountArray = new ArrayList<String>();
            itemArray = new ArrayList<String>();
            descArray = new ArrayList<String>();
            imageUrls = new ArrayList<String>();
            finalArray = new ArrayList<Gift>();
            File file = new File(Ids.dir, getString(R.string.html_file));
            FileInputStream in = new FileInputStream(file);
            BufferedReader br = new BufferedReader(new InputStreamReader(
                    in, "UTF-8"));
            String line;
            int itemNumber = 0;
            while ((line = br.readLine()) != null) {
                Document doc = Jsoup.parse(line);
                Elements titles = doc.select("h4[class=title]");
                Elements amounts = doc.select("div[class=price]");
                Elements descs = doc.select("p");
                Elements urls = doc.select("img[class=gallery-image]");
                for (Element price : amounts) {
                    itemNumber++;
                    amountArray.add(price.text());
                }
                for (Element title : titles) {
                    itemArray.add(title.text());
                }
                for (Element desc : descs) {
                    descArray.add(desc.text());
                }
                for (Element url : urls) {
                    imageUrls.add(url.attr("src"));
                }

                // totalShowing is a final integer with a value of 10
                // which only iterates through 10 objects plus 
                // integer[0], which is the total number of items 
                // shown in the listview.
                if (itemNumber == totalShowing + integer[0] + 1) {
                    break;
                }
            }
            in.close();
            br.close();
            finalArray = new ArrayList<Gift>();

            //  Only add to finalArray the items after position integer[0]
            //  so we don't add items we've already added
            for (int i = integer[0]; i < amountArray.size(); i++) {
                finalArray.add(new Gift(amountArray.get(i), itemArray
                        .get(i), descArray.get(i), imageUrls.get(i)));
            }
        } catch (Exception e) {
            e.printStackTrace();
        }
        return finalArray;
    }

    @Override
    protected void onPostExecute(ArrayList<Gift> result) {
        super.onPostExecute(result);
        da.addItems(result);
    }
}

After that, all I had to do was change my adapter to extend ArrayList<Gift> and add the following code:

public void addItems(ArrayList<Gift> newItems) {
    if (null == newItems || newItems.size() <= 0) {
        return;
    }
    if (null == finalArray) {
        finalArray = new ArrayList<Gift>();
    }
    finalArray.addAll(newItems);
    notifyDataSetChanged();
}