Question

This is a bit of a general question, but I will give a specific example for you.

I have a bunch of activities in an App. In all of the activities, there is a Facebook button. When you click the button it takes you to a specific Facebook page. I wish for the button to behave exactly the same way on every page.

Right now, in every single Activity, I create an onClickListener() for the Facebook button and make the intent and start the activity. It’s the same code in every single Activity.

What is the best way to write this code once and include it in multiple activities? Is there anyway to include other .java files?

One solution that I know would work, is to make a base CustomActivity class that extends Activity and then have all activities extend CustomActivity. Then put my onClickListener() code in CustomActivity. I’m new to Java though and I wasn’t sure if that was the best approach or not. Some of my Activities already extend other custom activity classes as is, so extending things that extend more things might get kinda messy, I dunno.

UPDATE

Playing the devil’s advocate here: Lets say I went with the inheritance route and I create some CustomActivity that I want my Activities to extend. CustomActivity would contain a bunch of general code that I need to use for all Activities, including but not limited to the Facebook button functionality. What happens when there is an Activity that I need to use generic code from the CustomActivity but there is no Facebook button in that specific Activity?

Answer 1

A common base class is perhaps the best approach. (It doesn’t work quite so well if some of your activities extend Activity and some extend Activity subclasses (such as ListActivity).

An alternate approach is to create a separate class that implements the logic of your click listener. This doesn’t eliminate all duplicate code — each activity still needs to instantiate and register a listener — but the logic for what to do will only need to be written once in the listener class.

In either alternative, you might consider assigning the android:onClick attribute to the button. That way you don’t need to register a click listener; you just need to implement the target method in each activity. This is particularly useful with the base class approach.

UPDATE

Suppose you go the inheritance route and you want an activity with no Facebook button. If you are using the android:onClick technique, then you don’t have to do anything different in your code — since no button will invoke your onClick method, the method will just sit there doing nothing. If you are installing an OnClickListener in code, then you just need to test that the button exists (i.e., that findViewById() did not return null) before registering the listener.