Question

This is a design question, rather than a technical one.

General case: I want an UI event in a Fragment to make Activity-wide changes.

Specific case: I have two fragments, hosted in the same activity. When the user clicks a button in one of those fragments, I want it to be replaced by the other.

I don’t want, however, my Fragments touching my activity. I may want to change the behavior later (maybe, in a bigger screen, show both fragments instead of replacing the first), and I don’t want my Fragment code to have that logic.

What I did was implement a Listener class in my fragments, that reports events back to the Activity. This way, if I want to use another Activity class with different display behavior, I can just change the listener and leave the Fragment code untouched.

Is this a good way to go about it? Is there a standard good practice, or a better design pattern?

Answer 1

Using listeners is the recommended way of communicating between Fragment and your activity.

See this Android documentatin section for infromation. Long story short they just implement a listener interface by the Activity class and cast getActivity() result in a fragment to a listener.

From my personal experience this is very convenient because lets you to:

1. Easilly switch underlying activity (e.g. you host entire fragment in a wrapper activity for compatibility in pre-3.0 and host this fragment along with others in 11+)
2. Easilly control if the wrapper activity supports callbacks or not. Just check is it does implement the listener and do your app specific actions if it doesn’t.