Question

What is the correct way to implement a constructor in android?

It seems that in an Activity or Service ‘onCreate()’ is where the magic happens.

The reason I ask is because I would like to be sure I’m doing the right thing declaring
attributes in the top of my classes (Context in particular) and then setting the attribute values inside onCreate.

// Activity launched via an Intent, with some 'extras'
public class SomeActivity extends Activity {

    private Context context;
    private String foo;

    public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        // Set the object attribute for later use, good or Bad to do this?
        context = getApplicationContext();
        Intent fooIntent = getIntent();
        foo = fooIntent.getStringExtra("foo");
    }

    private void someMethodThatNeedsContext() {
        // For example:
        Cursor c = this.context.getContentResolver().query(foo, xxx, xxx);
        // Or is it better practice to:
        // A) Pass the context as a local variable to this method
        // B) Use getApplicationContext() locally when needed
    }
}

Maybe either of these options is ok, and I’m over thinking it?
Any specific reading and/or suggestions you may have would greatly be helpful to me.

Answer 1

Option B – Since you can call getApplicationContext() from any non-static methods in your Activity class.
In fact, Activity is derived from Context too (Somewhere in the inheritance tree..) so you can just do:

Cursor c = getContentResolver()....

You don’t have to keep a reference to a context. Especially not static, that can cause problems.

And you are correct – since you usually don’t create your own constructor for Activities, you put the code for construction in onCreate.