I have an activity A which contain 7 fragment. For communication between fragment to activity and fragment to fragment, My activity explictly declare Fagment interface of all the 7 fragment.
The Syntax is like
class A extends Activity implements B.onInteraction, C.onInteraction, D.OnInteration .... {
}
This becomes long and i don't like explicity declaring it in on top of activity.
The other solution i can think of is define a method setOnInteractionListener() in each fragment and pass anonymous class to it like.
class B extends Fragment {
public void setOnFragmentInteractionListener(OnFragmentInteraction listener) {
}
}
By this way i don't need to override onAttach() of fragment and i don't need to explicty declare fragment interface on top.
My Question is: Is this a good way of doing things? What are the cons of using anonymous class here. Is there any better approach to do this or i should stick to explictly declaring interface while creating activity.
I'm not sure if I understand the question cause I'm a beginner. In my oppinion can create an interface for all your fragments:
public interface ActivityListener {
void onCall(Fragment fragment);
}
your activity:
public class MainActivity extends AppCompatActivity implements ActivityListener {
#Override
public void onCall(Fragment fragment) {
switch (fragment.getTag()) {
case YOUR_TAG:
Log.d("listener", "called");
break;
}
}
}
in your fragment use onAttach() method to get the interface.
I prefer to use EventBus (especially https://github.com/greenrobot/EventBus, someone prefer http://square.github.io/otto/) to communicate between Fragments and Activity.
You need to register (and unregister) the listener (activity, for example, or another fragment) and create a method with onEvent(<CustomEventclass> event);
EventBus.getDefault().register(this); //and unregister
And just post the event from the fragment like
EventBus.getDefault().post(<CustomEventClass> instance);
Making BaseFragment and pass the listener is also a normal way. This is just a developer choice.
Related
I have an activity which calls another fragmentA .Now this fragmentA calls another fragmentB .Now I want to transfer data from fragmentB to my activity
check this: Communicating with Other Fragments
Define an Interface (In fragment)
To allow a Fragment to communicate up to its Activity, you can define an interface in the Fragment class and implement it within the Activity. The Fragment captures the interface implementation during its onAttach() lifecycle method and can then call the Interface methods in order to communicate with the Activity.
Here is an example of Fragment to Activity communication:
public class HeadlinesFragment extends ListFragment {
OnHeadlineSelectedListener mCallback;
// Container Activity must implement this interface
public interface OnHeadlineSelectedListener {
public void onArticleSelected(int position);
}
#Override
public void onAttach(Activity activity) {
super.onAttach(activity);
// This makes sure that the container activity has implemented
// the callback interface. If not, it throws an exception
try {
mCallback = (OnHeadlineSelectedListener) activity;
} catch (ClassCastException e) {
throw new ClassCastException(activity.toString()
+ " must implement OnHeadlineSelectedListener");
}
}
...
}
Now the fragment can deliver messages to the activity by calling the onArticleSelected() method (or other methods in the interface) using the mCallback instance of the OnHeadlineSelectedListener interface.
For example, the following method in the fragment is called when the user clicks on a list item. The fragment uses the callback interface to deliver the event to the parent activity.
#Override
public void onListItemClick(ListView l, View v, int position, long id) {
// Send the event to the host activity
mCallback.onArticleSelected(position);
}
Implement the Interface (in activity)
In order to receive event callbacks from the fragment, the activity that hosts it must implement the interface defined in the fragment class.
For example, the following activity implements the interface from the above example.
public static class MainActivity extends Activity
implements HeadlinesFragment.OnHeadlineSelectedListener{
...
public void onArticleSelected(int position) {
// The user selected the headline of an article from the HeadlinesFragment
// Do something here to display that article
}
}
PS1: EventBus works for you, but use it carefully if you need, it may make your code harder to read.
PS2: Don't pass an activity instance in Fragment.newInstance() and communicate using it. The activity instance may be destroyed in background. Get activity instance in Fragment.onAttach() like the example, the framework will handle the destroy & recreate & rebind for you.
You can get the Activity instance by overriding onAttach() method
Method: 1
#Override
public void onAttach(Activity activity) {
// TODO Auto-generated method stub
super.onAttach(activity);
this.activity=(ActivityName) activity;
}
and
activity.setdata(yourdata);
or
Method : 2
((ActivityName)getActivity()).setdata(yourdata);
In these ways you need to create a setter method in your activity
It is easiest way to get callback from any fragment to its parent activity .Very well explained by Dev Doc here
You can get the instance of the activity by calling getActivity() in fragmentB and pass the data using an interface.
You could use EventBus if you think that, you will need a similar functionality in different parts of the app and you don't want to write many interfaces for this porpoise.
You could use https://github.com/greenrobot/EventBus
Example:
Add compile 'de.greenrobot:eventbus:2.4.0',
Register on activities
OnCreate -
EventBus.getDefault().register(this);
and OnDestroy-
EventBus.getDefault().unregister(this);
Than add a method with a receiving object parameter and with onEventMainThread name:
public void onEventMainThread(YourObject name) {...}
Now from any Fragament you can call
EventBus.getDefault().post(yourObjectInstance);
And activity will detect it.
Or you could use RxJava to get similar effect -
http://nerds.weddingpartyapp.com/tech/2014/12/24/implementing-an-event-bus-with-rxjava-rxbus/
I am trying to find a callback for my FragmentActivity that happens 'after' all of the fragments have called 'onCreateView'.
The reason for this is that my Fragment implement my interface:
public interface LifeCycleFragment {
public void onResumeFragment();
}
and when i call the fragment from MyActivity:
class MyActivity extends Activity
onCreate()
fragment.onResumeFragment()
getActivity() ends up being null:
class MyFragment extends Fragment implements LifeCycleFragment
#Override
public void onResumeFragment() {
Log.e(TAG, "- ON RESUME -");
FragmentActivity activity = getActivity();
// *****ACTIVITY IS NULL HERE AND THAT'S A PROBLEM ***//
I am not sure how to tackle this problem and any help would be appreciated.
Place getActivity() in override onActivityCreated method, and save it in the class for onResumeFragment(). I hope the Activity is still kept the same during onPause().
Would you like sample code to communicate between Fragment and Activity? I posted an answer in SO about it # Passing data between fragments contained in an activity. The respective Google webpage is # Communicating with Other Fragments.
Good luck and have fun...
There are 2 Fragments
I'm calling a service from Fragment 1. I have a ResultReceiver in Fragment 1 which listens to the result and onReceiveResult will call method1().
I want a ResultReceiver in Fragment 2 to listen to the same response but onReceiveResult will be calling method2()
How can I achieve this?
You could specify an interface:
interface Receiver {
void onResult();
}
Have your two Fragments implement this interface. Fragment1's implementation simply calls method1(), and Fragment2's implementation simply calls method2():
public class Fragment1 extends Fragment implements Receiver {
// Remember to register and remove the receiver (e.g. in onAttach and onDetach respectively).
private MyReceiver mBroadcast = new MyReceiver(this);
public void onResult() {
this.method1();
}
}
public class Fragment2 extends Fragment implements Receiver {
// Remember to register and remove the receiver (e.g. in onAttach and onDetach respectively).
private MyReceiver mBroadcast = new MyReceiver(this);
public void onResult() {
this.method2();
}
}
Then specify the BroadcastReceiver as a standalone (or inner static) class such that both Fragment1 and Fragment2 will be able to instantiate it:
public class MyReceiver extends BroadcastReceiver {
private Receiver mFragment;
public MyReceiver(Receiver fragment) {
mFragment = fragment;
}
public void onReceive(Context context, Intent intent) {
if(intent.getAction().equals(YOUR_ACTION) {
mFragment.onResult();
}
}
}
I don't think that you can receive results in two different fragments simultaneously.
But there are many ways to achieve this..
1.
I believe the easiest way will be to use object reference..
There are two possibilities.. Either create a static method in Fragment 2 and call it from fragment 1 from onReceiveResult(). Or Create an object of Fragment 2 in fragment 1 and from fragment 2 , assign that it is the same as the instance created by fragment1. Then just call
object_of_frgament2.method2() from the onReceiveResult() of fragment 1.
2.
Using interface.Create a custom interface and make the Fragment 2 implement the interface and create an instance of the interface in Fragment 1.
and within onReceiveResult() of Fragment1 you can call the interface method.
While implementing the interface, you can get the result in fragment 2 in the interface method.
Just call method2() from the function....
3.Using Broadcast Receiver..
Create a custom broadcast receiver and make all the fragments/activities which need the results to listen to it. and within onReceiveResult() of Fragment1 just broadcast the result..
I believe there are still other ways to do it..
just pass into your service two different ResultReceiver's ... If the service is already started calling startService(Intent) again just makes you call onStartCommand(...) and then you can set your resultReciever each time. So you can keep an array of resultreciever's if you want.
saying that, i would never do it this way. Research Java Observer pattern. Java has a default implementation of the Observer pattern. Here is a link
I'm writing an app that has a parent Activity and several child Fragments. I am trying to get the Fragment to communicate back to the parent Activity. I know there are several ways to do this, including making an interface and implementing that in the parent Activity. However, I am interested in this method:
ParentActivity activity = (ParentActivity) getActivity();
activity.someMethod();
This approach takes less code and is less complex. However, is this cast safe to do in production code? Or is an interface safer?
You can use this -
private ParentActivity callback;
#Override
public void onAttach(Activity activity)
{
//callback = (ParentActivity ) activity;
// make sure there is no cast exception
callback = (ParentActivty.class.isAssignableFrom(activity
.getClass())) ? (ParentActivity) activity : null;
super.onAttach(activity);
}
#Override
public void onDetach()
{
callback = null;
super.onDetach();
}
now when you do any method call , call it like this -
if(callback!=null)
{
callback.someMethod();
}
this method is safe .
It is safe (i.e. you won't get a ClassCastException), as long as you make sure that only ParentActivity ever creates/adds your Fragment.
These classes are now effectively coupled, which is, in general, not a good thing.
By casting to a specific Activity class (ParentActivity), you are losing the ability to re-use the fragment with different activities. It's safe to cast, as long as you only use the fragment with that one activity.
Using an interface allows the fragment to be used with multiple activities - you just need to implement the interface in the activities that use the fragment.
Another option is to use an Event Bus - like GreenRobot's EventBus or Square's Otto
Directly from the Android documentation:
To allow a Fragment to communicate up to its Activity, you can define an interface in the Fragment class and implement it within the Activity. The Fragment captures the interface implementation during its onAttach() lifecycle method and can then call the Interface methods in order to communicate with the Activity.
Here is an example of Fragment to Activity communication:
// HeadlinesFragment.java
public class HeadlinesFragment extends ListFragment {
OnHeadlineSelectedListener mCallback;
public void setOnHeadlineSelectedListener(Activity activity) {
mCallback = activity;
}
// Container Activity must implement this interface
public interface OnHeadlineSelectedListener {
public void onArticleSelected(int position);
}
// ...
}
// MainActivity.java
public static class MainActivity extends Activity
implements HeadlinesFragment.OnHeadlineSelectedListener{
// ...
#Override
public void onAttachFragment(Fragment fragment) {
if (fragment instanceof HeadlinesFragment) {
HeadlinesFragment headlinesFragment = (HeadlinesFragment) fragment;
headlinesFragment.setOnHeadlineSelectedListener(this);
}
}
}
It is safe if you know that the fragment won't be used in another activity. You can also do checks with instanceof so you can be sure that it will be the right type.
There are some possibilities where getActivity() might return null (when the fragment is not attached) so it's a good habit to check if the activity is null, or even better: myFragment.isAdded(). Otherwise you would get a NullPointerException when calling activity.someMethod().
So the safe code would be:
if (isAdded() && getActivity() instanceof ParentActivity){
ParentActivity activity = (ParentActivity) getActivity();
activity.someMethod();
}
Of course there are some other approaches, like passing listeners to the fragments or using a shared eventbus like Guava or Otto, which also have their pros and cons. The easiest way is the one described above, and if you use it carefully (check against null, correct class) it will work as expected.
I guess ParentActivity is derived from Activity.
getActivity() will provide you a pointer to the parent activity. So, there's no problem in the cast.
It is not "the Android way" to do things, but anyway, neither Google does lots of thing "the Android way" and this cast will surely continue to work ok in future Android versions.
As you said yourself, this not a good approach, google own documentation recommends using the interface, but if you choose to use this approach try something like:
Activity mActivity;
#Override
public void onAttach(Activity activity) {
super.onAttach(activity);
this.mActivity = activity;
}
to avoid the type NullPointerException error
if(this.mActivity != null){
this.mActivity.someMethod();
}
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 FragmentA called AListener. In the onAttach() method of FragmentA I use the suggested method of checking that the FragmentActivity implements AListener. When the button in FragmentA is clicked I use one of the callback methods from AListener to communicate the click event to the FragmentActivity. In the FragmentActivity I create an instance of FragmentB and add it to the container in FragmentActivity. Then if some event happens in FragmentB I use the same scheme to communicate the event to the FragmentActivity and do something interesting.
So what's the problem?
For my application I have found this scheme of having Fragments call back to the FragmentActivity and then having the FragmentActivity create a new fragment or call forward to and existing fragment very cumbersome. I have many fragments that need to be displayed by the FragmentActivity and therefore I am implementing an interface for every type of fragment that needs to be displayed (Each fragment is different so they each have their own interface). This causes clashes when I have two interfaces that have the same method signatures and I'm forced to rename one of the methods.
For instance, if I want to attach a listener to a fragment using the onAttach() method of the fragment, then my FragmentActivity must implement the interface. I have found several instances where I have callback methods that have the same name (or I'm forced to name them something similar but different because of a namespace collision). One solution to this would be to use an anonymous classes as callbacks instead of having the FragmentActivity implement the interface. This seems to work well enough, but goes against what the Android documentation says about using the onAttach() method to set the listener.
Are there any elegant ways to approach this problem? It seems to me the tradeoff is that you either force the FragmentActivity to implement an interface for each Fragment that you want to display in it and have the fun problem of watching out for method signature collisions, or you go against the Android documentation and use Anonymous classes to handle the callbacks (not sure of the implications of this).
I am fairly new to Java and feel like I could be missing a concept here that would solve my problem. Can anyone set me straight on how to solve this problem elegantly?
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
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.