How to allow users to check for the latest app version from inside the app?

You can use this Android Library: https://github.com/danielemaddaluno/Android-Update-Checker. It aims to provide a reusable instrument to check asynchronously if exists any newer released update of your app on the Store. It is based on the use of Jsoup (http://jsoup.org/) to test if a new update really exists parsing the app page on the Google Play Store:

private boolean web_update(){
    try {       
        String curVersion = applicationContext.getPackageManager().getPackageInfo(BuildConfig.APPLICATION_ID, 0).versionName;   
        String newVersion = curVersion;
        newVersion = Jsoup.connect("https://play.google.com/store/apps/details?id=" + BuildConfig.APPLICATION_ID + "&hl=en")
                .timeout(30000)
                .userAgent("Mozilla/5.0 (Windows; U; WindowsNT 5.1; en-US; rv1.8.1.6) Gecko/20070725 Firefox/2.0.0.6")
                .referrer("http://www.google.com")
                .get()
                .select("div[itemprop=softwareVersion]")
                .first()
                .ownText();
        return (value(curVersion) < value(newVersion)) ? true : false;
    } catch (Exception e) {
        e.printStackTrace();
        return false;
    }
}

And as "value" function the following (works if values are beetween 0-99):

private long value(String string) {
    string = string.trim();
    if( string.contains( "." )){ 
        final int index = string.lastIndexOf( "." );
        return value( string.substring( 0, index ))* 100 + value( string.substring( index + 1 )); 
    }
    else {
        return Long.valueOf( string ); 
    }
}

If you want only to verify a mismatch beetween versions, you can change:

value(curVersion) < value(newVersion) with value(curVersion) != value(newVersion)

If it is an application on the Market, then on app start-up, fire an Intent to open up the Market app hopefully which will cause it to check for updates.

Otherwise implementing and update checker is fairly easy. Here is my code (roughly) for it:

String response = SendNetworkUpdateAppRequest(); // Your code to do the network request
                                                 // should send the current version
                                                 // to server
if(response.equals("YES")) // Start Intent to download the app user has to manually install it by clicking on the notification
    startActivity(new Intent(Intent.ACTION_VIEW, Uri.parse("URL TO LATEST APK")));

Of course you should rewrite this to do the request on a background thread but you get the idea.

If you like something a little but more complex but allows your app to automatically apply the update see here.

Google updated play store two months before. This is the solution working right now for me..

class GetVersionCode extends AsyncTask<Void, String, String> {

    @Override

    protected String doInBackground(Void... voids) {

        String newVersion = null;

        try {
            Document document = Jsoup.connect("https://play.google.com/store/apps/details?id=" + MainActivity.this.getPackageName()  + "&hl=en")
                    .timeout(30000)
                    .userAgent("Mozilla/5.0 (Windows; U; WindowsNT 5.1; en-US; rv1.8.1.6) Gecko/20070725 Firefox/2.0.0.6")
                    .referrer("http://www.google.com")
                    .get();
            if (document != null) {
                Elements element = document.getElementsContainingOwnText("Current Version");
                for (Element ele : element) {
                    if (ele.siblingElements() != null) {
                        Elements sibElemets = ele.siblingElements();
                        for (Element sibElemet : sibElemets) {
                            newVersion = sibElemet.text();
                        }
                    }
                }
            }
        } catch (IOException e) {
            e.printStackTrace();
        }
        return newVersion;

    }


    @Override

    protected void onPostExecute(String onlineVersion) {

        super.onPostExecute(onlineVersion);

        if (onlineVersion != null && !onlineVersion.isEmpty()) {

            if (Float.valueOf(currentVersion) < Float.valueOf(onlineVersion)) {
                //show anything
            }

        }

        Log.d("update", "Current version " + currentVersion + "playstore version " + onlineVersion);

    }
}

and don't forget to add JSoup library

dependencies {
compile 'org.jsoup:jsoup:1.8.3'}

and on Oncreate()

@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_main);


    String currentVersion;
    try {
        currentVersion = getPackageManager().getPackageInfo(getPackageName(), 0).versionName;
    } catch (PackageManager.NameNotFoundException e) {
        e.printStackTrace();
    }

    new GetVersionCode().execute();

}

that's it.. Thanks to this link