yoki.org

If you have an app in the Android Market of which you want to have both a free version and a paid version, there are basically two ways of doing so. I will describe these two ways in this post. (Disclaimer: This is something that I haven’t tested yet myself, and I’m actually writing this to make sure I won’t forget it myself. On top of that, I don’t know whether there are any other/better ways of doing what I will describe below.)

Two completely separate apps

You can put two completely separate applications in the Market, with the free version covering a subset of the functionality of the paid version. While this is done quite often, this introduces a couple of minor problems:

• If people are satisfied with the free version and want to purchase the paid version, they have to uninstall the free version first and then purchase and install the paid version. If they don’t, they might run into errors (depending on your application and to what extent you messed up your code). You have two separate applications with split download counts in your Developer Console, even though they’re in fact the same application.
• You have to take measures for your development environment to be able to build two different versions of your application with little effort. For quite a lot of people, that can be a bit cumbersome.

A single application with all functionality and a ‘key’ app

To tackle these two problems mentioned above, you can also put all your functionality in a single app, and create a paid app that will serve as a ‘key’ to your app and sign them with the same certificate. Then, you can easily check if the user has installed that paid ‘key’ app if he wants to use a feature that needs to be enabled for paying users only.

Let’s take a look at the following code snippet.

protected boolean isProInstalled(Context context) {
  // the packagename of the 'key' app
  String proPackage = "org.yoki.android.pkgname";

  // get the package manager
  final PackageManager pm = context.getPackageManager();

  // get a list of installed packages
  List<PackageInfo> list = pm.getInstalledPackages(PackageManager.GET_DISABLED_COMPONENTS);

  // let's iterate through the list
  Iterator<PackageInfo> i = list.iterator();
  while(i.hasNext()) {
    PackageInfo p = i.next();
    // check if proPackage is in the list AND whether that package is signed
    //  with the same signature as THIS package
    if((p.packageName.equals(proPackage)) &&
       (pm.checkSignatures(context.getPackageName(), p.packageName) == PackageManager.SIGNATURE_MATCH))
      return true;
  }
  return false;
}

Basically, what this function does is checking whether the paid ‘key’ app is installed. If so, it returns true. If not, it returns false. It’s crucial that you do the check in line 18. If you don’t, then anyone can just create a randomly signed package with the same name as your ‘key’ app after which your app would incorrectly think that the user paid for the ‘key’ app.

If you don’t do anything extra, your users will end up with two icons in their app drawer. Obviously, this is undesirable. However, it’s solved easily by removing a section from your AndroidManifest.xml. Whenever the Android system wants to show the app launcher, it broadcasts a specific intent to which activities can respond. Activities that respond will end up in the launcher with an icon. (This is also why some apps can have multiple entry points in a launcher.) Just remove the intent-filter from your manifest with name ‘android.intent.action.MAIN’ and category ‘android.intent.category.LAUNCHER’ to make sure that your activity won’t respond to that intent.

Be sure to read the post at the Android Developers Blog about the new licensing service. For now, this new licensing service will only apply to your paid app(s) and not your free app(s).

That’s all! If I’m wrong about anything (remember my disclaimer at the top? :)), please leave a comment.