Question

I want to provide common functionality between different activity types such as opening and closing a database connection. Consider the following class:

public class DataActivity extends Activity {

    private DbAdapter mDbAdapter;

    @Override
    protected void onCreate(Bundle savedInstanceState) {

        super.onCreate(savedInstanceState);
        //open database
        mDbAdapter = new DbAdapter(this);
        mDbAdapter.open();

}

    @Override
    protected void onDestroy() {

        super.onDestroy();
        //close database
        mDbAdapter.close();

    }

    public DbAdapter getDbAdapter() {
        return mDbAdapter;
    }

}

I could then simply extend DataActivity and have access to my data throughout the class. However, what if I wanted to do this for a ListActivity or an ExpandableListActivity? I would need to make a copy of DataActivity and have it extend the desired class.

This seems really messy having multiple classes with duplicate implementation code for each activity type I would like to add this to.

Edit
It looks like what I am trying to do above isn’t really possible due do the way Java is designed (no multiple inheritance). There are several ways to minimize duplication of code but inheritance just doesn’t work in this case.

Answer 1

Either by inheriting (I dun recommend) from all these classes and extending them (creating BaseActivity, BaseMapActivity, BaseXXXActivity..) or by using aggregation, which makes more sense: Inheritance vs. Aggregation . Android is based on Java, so all Rules & OOP practive of Java apply.

For example: You could create a the instance variable in your class like this: `private DbAdapter dbAdapter = new DbAdapter(this);

In onCreate, add the open() call, in onDestroy the close() call. I see no need in upper example to have a getAdapter() function. So save some lines of code at least.

To have less code, try adding a DataService class which contains a instance(Context ctx) method – in there you can create the DbHelper if needed.