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 dif

Answer 1

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.

Answer 2

I completely understand your problem since i was dealing it for a long time. Here is the solution i came up right now! It may need some modification based on your need but i it works well.

first of all to to make communicating of event easier in your app use an EventBus! here is the most famous one https://goo.gl/nAEW6 event bus allows you to send event from anywhere to anywhere without need to worry about implementing interfaces, broadcast receivers, threading, etc.

Then add FragmentOrganizer to your app. It's a base class for all of your Fragment Organizers. basically you need one for each activity. Here is the code

public abstract class FragmentOrganizer {

protected FragmentManager fragmentManager;

public FragmentOrganizer(FragmentManager fragmentManager) {
    this.fragmentManager = fragmentManager;
    openFragment(getInitialFragment());
    EventBus.getDefault().register(this);
}

protected abstract Fragment getInitialFragment();
protected abstract void onEvent(Object event);
public abstract boolean handleBackNavigation();

public void freeUpResources(){
    EventBus.getDefault().unregister(this);
}


protected Fragment getOpenFragment(){
    String tag = fragmentManager.getBackStackEntryAt(fragmentManager.getBackStackEntryCount() -1).getName();
    return fragmentManager.findFragmentByTag(tag);
}


protected boolean isFragmentOpen(Fragment fragment){
    return isFragmentOpen(fragment, true);
}

protected boolean isFragmentOpen(Fragment fragment, boolean useArgs){
    String fragmentTag = createFragmentTag(fragment, useArgs);

    if (fragmentManager.getBackStackEntryCount() != 0) {
        String name = fragmentManager.getBackStackEntryAt(fragmentManager.getBackStackEntryCount() - 1).getName();

        if(!useArgs)
            name = name.substring(0, name.indexOf("-"));

            return name.equals(fragmentTag);
    }

    return false;
}


private String createFragmentTag(Fragment fragment, boolean addArgs) {
    StringBuilder stringBuilder = new StringBuilder();
    stringBuilder.append(fragment.getClass().getSimpleName());
    if(addArgs) {
        stringBuilder.append("-");
        if (fragment.getArguments() != null)
            stringBuilder.append(fragment.getArguments().toString());
    }
    return stringBuilder.toString();
}

public void openFragment(Fragment fragment) {
    if(isFragmentOpen(fragment))
        return;

    String fragmentTag = createFragmentTag(fragment, true);


    FragmentTransaction transaction = fragmentManager.beginTransaction();
    transaction.replace(R.id.activity_main_fragment_container, fragment, fragmentTag);
    transaction.addToBackStack(fragmentTag).commit();
}


}

Now you need to create your fragment organizer that inherit from FragmentOrganizer and implements 3 required methods. here the sample

public class MainFragmentOrganizer extends FragmentOrganizer {

public MainFragmentOrganizer(FragmentManager fragmentManager) {
    super(fragmentManager);
}

@Override
protected Fragment getInitialFragment() {
    return HomeFragment.newInstance();
}

@Override
public void onEvent(Object event){
    if(event instanceof ClickedOnPhotoEvent){
        String photoCode = ((ClickedOnPhotoEvent) event).photoCode;
        openFragment(PhotoFragment.newInstance(photoCode));
    }
}

@Override
public boolean handleBackNavigation(){
    Fragment fragment = getOpenFragment();


    if (fragment instanceof HomeFragment){
        return false;
    } else {
        fragmentManager.popBackStack();
        return true;
    }

}
}

And in your activity you just need to insatiate your FragmentManager and let it do the magic!

fragmentManager = getSupportFragmentManager();
fragmentOrganizer = new          MainFragmentOrganizer(getSupportFragmentManager());
@Override
public void onBackPressed() {
    //first let fragment organizer handle back. If it does not activity takes cares of it! 
    if(!fragmentOrganizer.handleBackNavigation()){
        finish();
    }
}
@Override
protected void onDestroy() {
    fragmentOrganizer.freeUpResources();
    super.onDestroy();
}

It may seem a lot of code but as you see most of the code encapsulated in FragmentOrganizer base class and it does all the general works so you just have to copy this file from one project to another.

As i said in the beginning i just came up with this solution right now, so it may not be perfect. I Plan to use this in my next project i hope you do to. And if you do i really appritiate if you share your though. have a good time