Persistent Model Framework for Android

A few months ago, a fellow student of mine came back from SAP in South Africa and told me about his new Android project: Androrm, which is a persistent relational data mapper especially for Android. Since I really hate writing ContentProviders and SQL queries, I gave it a try – and as luck would have it, I’m now using it in two of my projects!

Let me just give you a quick overview on what Androrm is about and how easy it is to define your data model with it. Basically it works like this:

1. Defining models

Let’s take two simple models: We have books and authors. All you have to do is extending the Model class and defining your fields:

Note: The source code was taken from the Android documentation and modified by me.

public class Book extends Model {
    // fields visibility is set to protected,
    // so the Model class can access it
    protected CharField mTitle;
    // zero-argument constructor, that can be called 
    // by androrm, to gather field information
    public Book() {
        // set up field with maxLength parameter
        mTitle = new CharField(80);

    public String getTitle() {
        return mTitle.get();

public class Author extends Model {
    protected CharField mName;
    public Author() {
        mName = new CharField(80);

    public String getName() {
         return mName.get();

    public void setName(String name) {

As you can see, there is a DataField type for each basic data type in java. Use them to define your model’s fields. They have set() and get() methods so you can easily set and get your values.

2. Creating a database

Once your models are defined, call this code in your onCreate() method of your app’s start activity to initialize the Androrm database and register your models:

List<Class<? extends Model>> models = new ArrayList<Class<? extends Model>>(); 
DatabaseAdapter adapter = new DatabaseAdapter(getApplicationContext());        

In a next step, we want our books to be connected to their authors:

3. Creating relations

For relations, there is a special DataField called ForeignKeyField. It lets you extend your models with new classes, if basic data types are not enough. You just need a few lines of code:

public class Book extends Model {
    // fields visibility is set to protected,
    // so the Model class can access it
    protected CharField mTitle;
    // Link the Author model to the Book model.
    protected ForeignKeyField<Author> mAuthor;
    // zero-argument constructor, that can be called 
    // by androrm, to gather field information
    public Book() {
        // set up field with maxLength parameter
        mTitle = new CharField(80);
        // initialize the foreign key relation
        mAuthor = new ForeignKeyField<Author>(Author.class);

    public String getTitle() {
        return mTitle.get();

   public void setAuthor(Author author) {

4. Insert your data

This is the part which amazed me the most when I first saw it. You just create your objects – business as usual – and then the magic happens:

// In your activity

Author author = new Author();
author.setName("My Author");;

Book book = new Book();
book.setName("Book name");

That’s it! You just create an instance of your class, do whatever you like and call save() to persist it. No SQL, no complicated ContentProviders. Of course, you can do a lot more with Androrm like querying your data and defining more complex relationships between your models. This was just a quick overview – for more details, please have a look at the documentation.

Androrm is still in an early stage, but – as far as I can tell – it works pretty stable! It is open source and hosted on GitHub, so feel free to contribute or file bugs!
If you find any related projects, please comment on this post!

That’s it for now, thanks for reading!


Dropbox SDK for Android

Last night I had a great idea for an app, which should be pretty easy to implement, I thought. I needed to use the Dropbox API for that and so I went to their website and found out that they have an own Android SDK. I could not find any instructions on how to use it and so I tried to find out by myself and downloaded that package. Next thing I tried was importing it to Eclipse, and that’s where the trouble took its course…

What went wrong?

First thing I noticed: The package didn’t contain any Eclipse project file. So I created a new Android Project in Eclipse and imported their source code – Build Error. I found out that I had to add the .jar files included in the package to my project’s Java build path. Bingo! It compiled and started the Demo application.

Cool! I could sign in and out. Now I just had to reference it as an Android Library and use it in my own project, right? The answer is no. Despite the .jar for the Dropbox Java API implementation, the “SDK” includes only two files: (the Activity) and
. The second one handles all the login stuff and would be very handy when writing an app which should be connected to Dropbox, but it is so tightly coupled to the sample Activity, that it’s impossible to reuse it anywhere else. That made me pretty angry and so I decided to refactor the SDK.

Refactoring an SDK

I have used a couple of SDKs before and what I wanted to have was this:

  • An isolated Android Library Project containing only SDK classes
  • A project containing the sample application, which references the SDK project
  • A decoupled
  • A small set of helper classes providing the easiest way to use the SDK

Long story short – The result is a Github project containing two projects: One SDK project, which is an Android Library, and a Sample Application. As I said before, I decoupled the and made the SDK easier to use. I added a class, which encapsulates the login procedure, and a LoginListener class as a simple callback. Here are some code snippets on how to use it in your Activity:

Creating the Dropbox object and checking existing logins:

final static private String CONSUMER_KEY = "PUT_YOUR_CONSUMER_KEY_HERE";

// ... //

mDropbox = new Dropbox(getBaseContext(), CONSUMER_KEY, CONSUMER_SECRET);
if (mDropbox.authenticate()) {
        	// We can query the account info already, since we have stored 
        	// credentials

Handling the login callback:

    // Notifies our Activity when a login process succeeded or failed.     
    DropboxLoginListener mLoginListener = new DropboxLoginListener() {

		public void loginFailed(String message) {			
			showToast("Login failed: "+message);

		public void loginSuccessfull() {
			showToast("Logged in!");

Logging in:

 private void getAccountInfo() {
    	if (mDropbox.isAuthenticated()) {
		// Access credentials are already stored, just login
    	} else {
    		// Code for getting email and password goes here //

	        mDropbox.login(mLoginListener, email, password);	        

For more details, just have a look at the Sample Application! If you have any feedback, feel free to comment.

Thanks so far

Android UI pattern implementations

Most Android users may have recognized more and more common UI elements in Android applications these days. Widgets like ActionBar and QuickActions are a great approach to standardize the way Android applications are used. Google posted some design proposals and took the Twitter for Android app as a great example for Android design patterns. A more precise definition for these and more patterns can be found at
Of course, I immediately needed to have some of these in my own applications. So I started looking for Google’s implementation examples or developer documentation – nothing! Not even a code snippet. Fortunately, I was not the only one with that problem. I found some pretty good implementations for ActionBar and QuickActions, but I was looking for a more “integrated” solution, so I continued my research. Hours of googling later, I found a video from a talk at Google I/O 2010, which pointed me at the Google I/O app, which seems to be a good reference. But I wanted a library, not an example implementation and so I kept on searching. Finally, I found this awesome project, which perfectly fits my needs: Greendroid!


… is the most complete library for android UI patterns I found by now. Just load the Greendroid project into Eclipse, add it as a library to your project and you’re ready to go! To give you an example, creating an ActionBar and filling it with items is as easy as this:

1. Put this into your XML layout:

	android:layout_width="fill_parent" />

2. Fill your ActionBar with items and a title:

	public void fillActionBar(final ActionBar mActionBar) {
		mActionBar.setTitle("My ActionBar");
		mActionBar.setOnActionBarListener(new OnActionBarListener() {

			public void onActionBarItemClicked(int position) {
				switch(position) {
				case 0:
					// Compose action
				case 1:
					// Refresh action
					LoaderActionBarItem item = (LoaderActionBarItem) mActionBar.getItem(position);
					// Turn the item into a progress indicator
				case 2:
					// Map action
 					// Action for home button

I recommend you to take a look at their example application (also included in the repository) to see what else you can do with Greendroid. There isn’t really a documentation, but the example application is pretty much everything you need to understand how Greendroid should be used.

I hope we’ll see more applications use the UI patterns in the future to give the Android application landscape a more consistent look.
Have fun!