Stuck in implementing Pagination in Android

I am implementing pagination for ListView in Android . I am extending the BaseAdapater class for customising the ListView.

Already I have the code working fine for the Customised ListView. Below is the new requirement.

1>I am fetching 6 items from server & displaying them . Now when the user scrolls to the 6th item(end of list) , I need to call the server to fetch the next 6 items & update the Listview

I have overriden the methods

i>public void onScroll(AbsListView view, int firstVisibleItem,int visibleItemCount, int totalItemCount)

ii>public void onScrollStateChanged(AbsListView view, int scrollState)

In the first response from the server, I get the total no of pages from the server & for each time I call the server , I get the current page value .

Kindly provide me the steps/sample code on how to check 开发者_StackOverflow中文版the last item of the list & update the list . The code should be iterative since I may need to call multiple times & fetch from server.

Warm Regards,

CB

Why not just download it all in the background rather than doing it every time there is a request? I have an app where I had considered doing the same thing you are doing but decided to use a background thread to do it instead.

Here is a great example of how to use threads

http://mindtherobot.com/blog/159/android-guts-intro-to-loopers-and-handlers/

How I implemented it was that I retrieve the total count of records available first and then start a new thread for each "page" of records I want to retrieve.

// Create and launch the download thread
    downloadThread = new DownloadThread(this);
    downloadThread.start();

    // Create the Handler. It will implicitly bind to the Looper
    // that is internally created for this thread (since it is the UI
    // thread)
    handler = new Handler();

    resultCount = getResultCount(search).trim();
    resultsCount = Integer.parseInt(resultCount);
    page = 1;
    if (resultsCount > 0) {
        downloadThread
                .enqueueDownload(new DownloadTask(page));
    }

I added my method to retrieve the records to DownloadTask.java from the example above and call it from run() and I added another public method to retrieve the results once the

I modified DownloadThread.java so that the synchronized call to task (DownloadTask) calls my method in DownloadTask >> task.run() and in finally{} I retrieve the returned results

public synchronized void enqueueDownload(final DownloadTask task) {
    // Wrap DownloadTask into another Runnable to track the statistics
    handler.post(new Runnable() {
        @Override
        public void run() {
            try {
                task.run();
            } finally {                 
                // register task completion
                synchronized (DownloadThread.this) {
                    results = task.getResults();
                    totalCompleted++;
                }
                // tell the listener something has happened
                signalUpdate();
            }               
        }
    });

Then I added a new method to DownloadThread.java which allows me to retrive the results from the update notification in my activity

public synchronized ArrayList<Result> getResults() {
    return results;
}

For example, if there are 60 records and each page contains 6 records, I start a thread to retrieve the first 6 and then when the handleDownloadThreadUpdate() is called I populate the array with those results and call a method in my Adapter called update() that calls notifyDataSetChanged().

public void handleDownloadThreadUpdate() {
    handler.post(new Runnable() {
        @Override
        public void run() {
            for (Result res : downloadThread.getResults()) {
                if (!results.contains(res)) {
                    results.add(intern(res));
                }
            }
            arrayAdapter.update();
            int pages = (int) Math.ceil(resultsCount / 6);
            if (page < pages) {
                page = page + 1;
                downloadThread.enqueueDownload(new DownloadTask(page));
            }
        }
    });
}

So it recursively downloads the pages and adds the results to my list.

One more thing I forgot to mention. I have a class called Result which holds each result that I store in an ArrayList. Just in case the results try to use too much memory I am caching them in a WeakReference HashMap... as you can see the call to intern() when it's added to the ArrayList above.

private Map<Result, WeakReference<Result>> myInternMap = new HashMap<Result, WeakReference<Result>>();

public Result intern(Result value) {
    synchronized (myInternMap) {
        WeakReference<Result> curRef = myInternMap.get(value);
        Result curValue = ((curRef != null) ? curRef.get() : null);
        if (curValue != null) {
            return curValue;
        }

        myInternMap.put(value, new WeakReference<Result>(value));
        return value;
    }
}