One of the greater things in newer Android versions is the Fragments. It allows you to split the UI into smaller pieces that can be put together in different ways, depending on different circumstances like screen size and such. However some times you might need to adapt things in one Fragment based on some conditions in another. Talking to an Activity from within a Fragment is easy enough, but Fragments to Fragments is another thing. Especially since it is unadvised to have one specific Fragment talk to another specific one.
A better solution is to have a small message delivery system that works similar to Android's broadcast system. That way you can parse information between Fragments, but without targeting specific ones. For this we need an extended Activity that has these capabilities.
One issue with Java (or not, depending on who you ask) is that Java does not support multi-inheritance. I for one is quite fine with this, but I would like to see something like traits be introduced into the language. In this the problem lies with the many different Activity and Fragment classes that Android has available. We don't want to copy paste everything into each Activity and Fragment sub-class that we want to use.
With the lack of traits or similar, we will be using the famous logic trick instead where we place all the logic into one class, and then only create redirection in each of the Activity and Fragment classes. Not only will this limit the size of each Activity and Fragment class, but it will also make sure that we only have to edit one class if we want to change something.
ActivityLogic.java:
final public class ActivityLogic {
public static interface IActivityLogic {
public void onReceiveMessage(String message, Object data, Boolean sticky);
public void onFragmentAttachment(IActivityLogicFragment fragment);
public void onFragmentDetachment(IActivityLogicFragment fragment);
public void sendMessage(String message, Object data);
public void sendMessage(String message, Object data, Boolean sticky);
}
public static interface IActivityLogicFragment {
public void onReceiveMessage(String message, Object data, Boolean sticky);
}
private final static class ActivityLogic_MessageHandler extends AbstractHandler<ActivityLogic> {
public ActivityLogic_MessageHandler(ActivityLogic reference) {
super(reference);
}
@Override
public void handleMessage(Message msg) {
ActivityLogic logic = getReference();
if (logic != null) {
IActivityLogic activity = logic.ActivityLogic_mActivity.get();
if (activity != null) {
Set<IActivityLogicFragment> fragments = new HashSet<IActivityLogicFragment>(logic.ActivityLogic_mFragments);
Object[] input = (Object[]) msg.obj;
String message = (String) input[0];
Object data = input[1];
activity.onReceiveMessage(message, data, false);
for (IActivityLogicFragment fragment : fragments) {
fragment.onReceiveMessage(message, data, false);
}
}
}
}
}
private Set<IActivityLogicFragment> ActivityLogic_mFragments = Collections.newSetFromMap(new WeakHashMap<IActivityLogicFragment, Boolean>());
private Map<String, Object> ActivityLogic_mStickyMessages = new HashMap<String, Object>();
private ActivityLogic_MessageHandler ActivityLogic_mMessageHandler;
private WeakReference<IActivityLogic> ActivityLogic_mActivity;
public ActivityLogic(IActivityLogic activity) {
ActivityLogic_mActivity = new WeakReference<IActivityLogic>(activity);
ActivityLogic_mMessageHandler = new ActivityLogic_MessageHandler(this);
}
public void onFragmentAttachment(IActivityLogicFragment fragment) {
synchronized (ActivityLogic_mFragments) {
ActivityLogic_mFragments.add(fragment);
for (String message : ActivityLogic_mStickyMessages.keySet()) {
fragment.onReceiveMessage(message, ActivityLogic_mStickyMessages.get(message), true);
}
}
}
public void onFragmentDetachment(IActivityLogicFragment fragment) {
synchronized (ActivityLogic_mFragments) {
ActivityLogic_mFragments.remove(fragment);
}
}
public void sendMessage(String message, Object data) {
sendMessage(message, data, false);
}
public void sendMessage(String message, Object data, Boolean sticky) {
synchronized(ActivityLogic_mFragments) {
if (sticky) {
ActivityLogic_mStickyMessages.put(message, data);
}
ActivityLogic_mMessageHandler.obtainMessage(0, new Object[]{message, data}).sendToTarget();
}
}
}
The above Activity Logic class is only the first step towards getting our message delivery system working. Since this is meant to be used to communicate between Fragments, we still need a Fragment Logic class as well.
FragmentLogic.java:
final public class FragmentLogic {
public static interface IFragmentLogic extends IActivityLogicFragment {
public IActivityLogic getParent();
public void sendMessage(String message, Object data);
public void sendMessage(String message, Object data, Boolean sticky);
}
private WeakReference<IActivityLogic> FragmentLogic_mActivity;
private WeakReference<IFragmentLogic> FragmentLogic_mFragment;
public FragmentLogic(IFragmentLogic fragment) {
FragmentLogic_mFragment = new WeakReference<IFragmentLogic>(fragment);
}
public void onAttach(IActivityLogic activity) {
FragmentLogic_mActivity = new WeakReference<IActivityLogic>(activity);
IFragmentLogic fragment = FragmentLogic_mFragment.get();
if (fragment != null) {
activity.onFragmentAttachment(fragment);
}
}
public void onDetach() {
IFragmentLogic fragment = FragmentLogic_mFragment.get();
IActivityLogic activity = FragmentLogic_mActivity.get();
if (fragment != null && activity != null) {
activity.onFragmentDetachment(fragment);
}
FragmentLogic_mActivity.clear();
}
public IActivityLogic getParent() {
return FragmentLogic_mActivity.get();
}
public void sendMessage(String message, Object data) {
sendMessage(message, data, false);
}
public void sendMessage(String message, Object data, Boolean sticky) {
IActivityLogic activity = getParent();
if (activity != null) {
activity.sendMessage(message, data, sticky);
}
}
}
Now that we have all of the logic behind this delivery system, we need to extend some classes that will be using these classes. Let's start with the Activity class.
AbstractActivity.java:
public abstract class AbstractActivity extends Activity implements IActivityLogic {
private ActivityLogic mLogic;
public AbstractActivity() {
mLogic = new ActivityLogic(this);
}
@Override
public void onFragmentAttachment(IActivityLogicFragment fragment) {
mLogic.onFragmentAttachment(fragment);
}
@Override
public void onFragmentDetachment(IActivityLogicFragment fragment) {
mLogic.onFragmentDetachment(fragment);
}
@Override
public void onReceiveMessage(String message, Object data, Boolean sticky) {}
@Override
public final void sendMessage(String message, Object data) {
mLogic.sendMessage(message, data);
}
@Override
public final void sendMessage(String message, Object data, Boolean sticky) {
mLogic.sendMessage(message, data, sticky);
}
}
And we will of course also need a Fragment class.
AbstractFragment.java:
public abstract class AbstractFragment extends Fragment implements IFragmentLogic {
private FragmentLogic mLogic;
public AbstractFragment() {
mLogic = new FragmentLogic(this);
}
@Override
public final IActivityLogic getParent() {
return mLogic.getParent();
}
@Override
public void onAttach(Activity activity) {
super.onAttach(activity);
mLogic.onAttach((IActivityLogic) activity);
}
@Override
public void onDetach() {
super.onDetach();
mLogic.onDetach();
}
public void onReceiveMessage(String message, Object data, Boolean sticky) {}
public final void sendMessage(String message, Object data) {
mLogic.sendMessage(message, data);
}
public final void sendMessage(String message, Object data, Boolean sticky) {
mLogic.sendMessage(message, data, sticky);
}
}
And that's it. We now have one normal Activity and Fragment class that we can use. Note that these are abstract, this is because we use these to extend our actual ones.
Let's take a small example of how to use these.
SomeFragment.java:
public class SomeFragment extends AbstractFragment {
@Override
public void onResume() {
// Send a message to other Fragments or the Activity
if (someVariable == "someCondition") {
sendMessage("tellSomeone", "someCondition");
}
}
@Override
public void onReceiveMessage(String message, Object data, Boolean sticky) {
// Receive message from other Fragments or the Activity
if (message.equals("someOtherCondition")) {
// Do something
}
}
}
If we need other types as well, like DialogFragment or ActionBarActivity, we can re-use our logic classes to easily create them.
