Android Rec Library

Using custom UI libraries has one downside – in xml you have to write the full package name of each View. Android widgets can be used without full name. It’s also possible with custom Views – all we have to do is to replace the default LayoutInflater.

Some time ago my friend showed me a nice library called Calligraphy. The most interesting thing about it is that it adds its attributes to existing Android Views without any custom widgets. After a while with the code I found out how they achieved that and how I can use that techinique to quickly replace Android widgets with Carbon ones.

Let’s start with such layout:

The trick Android does is very simple. If a class doesn’t have any prefix, add ‘android.widget.’ and then try to load it. We can easily create such loader for our package name:

public class CarbonLayoutInflater extends LayoutInflater {
    protected CarbonLayoutInflater(LayoutInflater original, Context newContext) {
        super(original, newContext);
    }

    @Override
    public LayoutInflater cloneInContext(Context newContext) {
        return new CarbonLayoutInflater(this, newContext);
    }

    @Override
    protected View onCreateView(String name, AttributeSet attrs) throws ClassNotFoundException {
        if (Character.isUpperCase(name.charAt(0)))
            return createView(name, "carbon.widget.", attrs);
        return super.onCreateView(name, attrs);
    }
}

This class is very simple and does exactly what I wrote in the previous paraghaph. How to use it? We need a ContextWrapper class which would return our Inflater as an inflater service:

public class CarbonContextWrapper extends ContextWrapper {
    private CarbonLayoutInflater mInflater;

    public CarbonContextWrapper(Context base) {
        super(base);
    }

    @Override
    public Object getSystemService(String name) {
        if (LAYOUT_INFLATER_SERVICE.equals(name)) {
            if (mInflater == null) {
                mInflater = new CarbonLayoutInflater(LayoutInflater.from(getBaseContext()), this);
            }
            return mInflater;
        }
        return super.getSystemService(name);
    }
}

Now all we have to do is to attach our wrapper. Like this:

public class ContextWrapperActivity extends Activity {
    @Override
    public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_contextwrapper);
    }

    @Override
    protected void attachBaseContext(Context newBase) {
        super.attachBaseContext(new CarbonContextWrapper(newBase));
    }
}

Since now, each packageless component will be resolved as a carbon.widget.*. Check out our layout with CarbonContextWrapper attached:
What Calligraphy does is much more complex, but I don’t really need that. Their technique gave me an idea to try to mess with ContextWrapper and LayoutInflater. Carbon has a good number of widgets which can replace Android ones. With custom LayoutInflater you can quickly move to Carbon without replacing all Views in your layouts.