Question

I’m writing an application in which i have a set of code which i want to be available in all of my Activities and ActivityGroups. However, to achieve this, I have extended my activities as:

//custom Activity
public abstract class BaseActivity extends Activity
//custom ActivityGroup
public abstract class BaseActivityGroup extends ActivityGroup

//implemented activities in my app
public class PickUser extends BaseActivity
//and
public class Home extends BaseActivityGroup

Now the thing is, whatever the custom code i write in BaseActivity, I have to write the same in BaseActivityGroup too (as in current implementation). This is prone to code-sync problems and i believe not a good technique.

So, how can i make my extensions in such a way that I only write custom code in BaseActivity and my BaseActivityGroup extends ActivityGroup – which is conceived from BaseActivity class?

If i observe how android does this, so the ActivityGroup in android extends Activity class. And I also want to write my custom ActivityGroup class (known as BaseActivityGroup) that actually extends BaseActivity (which is an extended Activity).

Any ideas/suggestions?

Answer 1

First of all ActivityGroups are bad and should not be used. They are deprecated and it is preferred to use a single activity with multiple fragments.

If you must use an activitygroup you are probably best of by implementing a delegate pattern.

Create a delegate that handles all the common methods such as onCreate, onResume and use that in the bases. In this example I save a reference to the activity in the delegate. This circular referencing might not be the pretties. An alternative is to pass on the activity to the methods in the delegate.

public class ActivityDelegate() {
    private Activity mActivity;

    public ActivityDelegate(final Activity activity) {
        mActivity = activity;
    }
    public void onCreate(final Bundle savedInstanceState) {
        // Do stuff.
    }
}


public abstract class BaseActivity extends Activity {
    private ActivityDelegate mDelegate = new ActivityDelegate(this);

    public void onCreate(final Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        mDelegate.onCreate(savedInstanceState);
    }
    ...
}

public abstract class BaseActivityGroup extends ActivityGroup {
    private ActivityDelegate mDelegate = new ActivityDelegate(this);

    public void onCreate(final Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        mDelegate.onCreate(savedInstanceState);
    }
    ...
}