我在哪里可以找到片段的ID。 如何从MainActivity类访问片段视图？

Question

I created a tabbed Activity and I have to modify some views from the MainActivity class. How can I get access to any of these three fragments created from that Activity?

I know the method involving the use of getFragmentManager().findFragmentById(R.id.example_fragment); , but I don't know where I can find fragment ID.

Answer 1

While doing the fragment transaction you might consider setting an id by yourself and later you can retrieve the Fragment using that id as well.

Here's how you set up and id/tag for your Fragment which is being launched.

getFragmentManager().beginTransaction().add(R.id.fragment_container, new YourFragment(), "FRAGMENT_1").commit();

Now you can retrieve the Fragment using the id (ie tag) like the following.

getFragmentManager().findFragmentByTag("FRAGMENT_1");

Now to answer your other question, which is how you can access a view component of your Fragment from your Activity class, you can do this in multiple ways.

One possible option of doing this is having a BroadcastReceiver in your Fragment which can be invoked to update views inside the Fragment while the broadcast is received from your Activity . Here's a sample Fragment with a BroadcastReceiver to explain the idea behind.

public class YourFragment extends Fragment {
    @Override
    public View onCreateView(LayoutInflater inflater, @Nullable ViewGroup container, @Nullable Bundle savedInstanceState) {
        super.onCreateView(inflater, container, savedInstanceState);

        // Start listening for the broadcast sent from the Activity
        LocalBroadcastManager.getInstance(getActivity()).registerReceiver(mYourBroadcastReceiver, new IntentFilter("MESSAGE_FROM_ACTIVITY"));

        return inflater.inflate(R.layout.your_fragment_layout, null, true);
    }

    @Override
    public void onDestroyView() {
        // The BroadcastReceiver must be destroyed when your Fragment is being destroyed
        LocalBroadcastManager.getInstance(getActivity()).unregisterReceiver(mYourBroadcastReceiver);
    }

    private final BroadcastReceiver mYourBroadcastReceiver = new BroadcastReceiver() {
        @Override
        public void onReceive(Context context, Intent intent) {
            // This will be invoked when a broadcast is received from your Activity
            // Update your views here
        }
    };
}

Now send the broadcast from your Activity like this when needed.

Intent intent =new Intent("MESSAGE_FROM_ACTIVITY");
sendBroadcast(i);

Hope that helps!