Android managing fragments from activity elegantly

Question

Description of what I'm trying to accomplish: I have an app that uses a FragmentActivity with a LinearLayout as a container for the fragments. I click different buttons on the FragmentActivity UI and add and remove Fragments to the container in the FragmentActivity. In addition to clicking buttons on the FragmentActivity UI, each Fragment also has buttons that can be clicked which will remove the current fragment and add a different fragment in its place. The Android way of doing things as I understand it: I have been reading up on how to do this and as I understand it, the 'proper' way of doing things is to use the FragmentActivity as sort of a relay station and have each fragment do callbacks to the FragmentActivity to communicate events and deal with them. Scenario: So let's say that the FragmentActivity is displaying Fragment A and when the user clicks a button in FragmentA I want to stop showing FragmentA and start showing FragmentB. To do this I have created an interface in Frag…

Accepted Answer

A co-worker of mine came up with what I consider an elegant solution to this problem.

Remember, what we're trying to achieve is a way for fragments to callback to the parent activity without having the activity implement the interface. Also, we need to be able to automatically set the listener again if the activity is destroyed and then recreated.

Activities have a lifecycle callback called onAttachFragment(Fragment fragment) which is called whenever a fragment is being attached to the activity. So, for instance, when a new fragment is created within the activity, this gets called. It also gets called if an activity that was previously destroyed gets recreated. What you can do is use an interface or an anonymous class to set a listener on the new fragment in onAttachFragment like this:

```
@Override
public void onAttachFragment(Fragment fragment) {
    super.onAttachFragment(fragment);

//Determine which fragment this is by checking its tag 
    if(fragment.getTag().contains(TextFrag.FRAG_TAG)){
        //set a listener on this fragment using an anonymous class or interface
        ((TextFrag)fragment).setListener(new TextFragButtonListener() {
            @Override
            public void onButtonClicked() {
                count++;
                counterTV.setText(String.valueOf(count));
            }
        });
    }
}
```

Using this technique we are able to avoid the activity having to implement an interface for the callback and thus we avoid any naming conflicts with our callback methods. Also, if the activity is destroyed, once it is recreated the listener will be automatically reset so our callbacks will still work.

There are probably many other ways to do this and I'd love to here anyone's criticisms of this technique and suggestions for any other techniques.

Android managing fragments from activity elegantly

Solution

Problem