Develop Reference

RecylcerView adapter with viewModel and Live data

I am starting to use android jetpack arch components and have run into some confusion. Also please note data binding is not a option.
I have an activity that has a RecylcerView. I have a ViewModel that looks like the following
public class Movie extends ViewModel {
public Movie movie;
public URL logoURL;
private MutableLiveData<Drawable> logo;
public MutableLiveData<Drawable> getLogo() {
if (logo == null) {
logo = new MutableLiveData<>();
}
return logo;
}
public PikTvChannelItemVM(Movie movie, URL logo) {
this.movie = movie;
this.logoURL = logoURL;
}
public Bitmap getChannelLogo() {
//Do some network call to get the bitmap logo from the url
}
}
The above is all fine although in my I recyclerview have the following code below. Although in onbindviewholder when I try to observe for the returned image from the viewmodels live data it needs a life cycle owner reference which I don't have in my recycler view. Please help thanks
public class MovieRecyclerViewAdapter extends RecyclerView
.Adapter<MovieRecyclerViewAdapter.MovieItemViewHolder> {
public List<MovieViewModel> vmList;
public MovieRecyclerViewAdapter(List<MovieViewModel> vmList) {
this.vmList = vmList;
setHasStableIds(true);
}
#Override
public MovieItemViewHolder onCreateViewHolder(ViewGroup parent, int viewType) {
MovieView itemView = new MovieView(parent.getContext(), null);
itemView.setLayoutParams(new ViewGroup.LayoutParams(
ViewGroup.LayoutParams.MATCH_PARENT,
ViewGroup.LayoutParams.WRAP_CONTENT
));
return new MovieItemViewHolder(itemView);
}
#Override
public void onBindViewHolder(#NonNull MovieItemViewHolder holder, int position) {
vmList.get(position).observe(?????, users -> {
// As you can see I have no reference to the life cycle owner
holder.imageView.setimage(some drawable returned by the View Model)
});
}
#Override
public long getItemId(int position) {
return position;
}
#Override
public int getItemViewType(int position) {
return position;
}
#Override
public int getItemCount() {
return vmList.size();
}
class MovieItemViewHolder extends RecyclerView.ViewHolder {
private MovieView channelView;
public MovieItemViewHolder(View v) {
super(v);
channelView = (MovieView) v;
}
public MovieView getChannelView() {
return channelView;
}
}
}

I would try to send a list to the adapter to display it. I would observe the data outside of the adapter, as it is not the adapter's responsibility to observe the data but rather to display it.

Your adapter list type should not be viewmodel. If you want to use live data without binding, you want auto ui change when your list update.
You can do it like this:
First of all, your movie class must be a model class, not be a viewmodel.
Do it adapter like normal. Just add a setList(Movie) method. This method should update the adapter list. Do not forget notify adapter after update list.
Then create livedata list like
MutableLiveData<List<Movie>> movieLiveData =
new MutableLiveData<>();
where you want.
Observe this list in the activity and call adapters setList(Movie)method inside observe{}.
After all this if your list updated, setList(Movie) medhod will be triggered then your ui will be update.

You can do something like this:
ViewModel:
class MyViewModel : ViewModel() {
private val items = MutableLiveData<List<String>>()
init {
obtainList()
}
fun obtainList() { // obtain list from repository
items.value = listOf("item1", "item2", "item3", "item4")
}
fun getItems(): LiveData<List<String>> {
return items
}
}
Your Fragment (or Activity):
public class ContentFragment extends Fragment {
private MyViewModel viewModel;
private RecyclerView recyclerView;
private MyAdapter adapter;
#Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
viewModel = new ViewModelProvider(this).get(MyViewModel.class);
}
#Override
public View onCreateView(#NonNull LayoutInflater inflater, ViewGroup container,
Bundle savedInstanceState) {
View root = inflater.inflate(R.layout.fragment_main, container, false);
recyclerView = root.findViewById(R.id.recycler_view);
recyclerView.setLayoutManager(new GridLayoutManager(getActivity(), 4));
// add observer
viewModel.getItems().observe(this, items -> {
adapter = new MyAdapter(items); // add items to adapter
recyclerView.setAdapter(adapter);
});
return root;
}
Adapter:
class MyAdapter(val list: List<String>) : RecyclerView.Adapter<MyAdapter.TextViewHolder {
...
override fun onBindViewHolder(holder: TextViewHolder, position: Int) {
holder.textView.text = list[position] // assign titles from the list.
...
}
}
Any custom objects can be used instead of String objects.

Send data from Activity to Fragment when fragment is onCreateView

Sorry for my english. I have one activity and in this activity in FragmentPagerAdapter exist 5 fragments. All fragments use one object model for inforation(product name, product image ...).
My activity get data from data base. And then it data send to all fragments. My example Activity:
#BindView(R.id.tabs_sep_prod) TabLayout tabs_sep_prod;
#BindView(R.id.viewpager_sep_prod) ViewPager viewpager_sep_prod;
PrepBaseProdFragment prepBaseProdFragment;
#Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_sep_product);
ButterKnife.bind(this);
prepBaseProdFragment = new PrepBaseProdFragment();
// there i have another fragments
// ...
setupViewPager(viewpager_sep_prod);
tabs_sep_prod.setupWithViewPager(viewpager_sep_prod);
}
private void setupViewPager(ViewPager viewPager) {
SepProductActivity.ViewPagerAdapter adapter = new SepProductActivity.ViewPagerAdapter(
adapter.addFrag(prepBaseProdFragment, getString(R.string.sep_prep_base));
// there i have another addFrag
// ...
viewPager.setOffscreenPageLimit(5);
viewPager.setAdapter(adapter);
}
#Override
public void onResume() {
super.onResume();
// this i call method from presenter, it return data in method setData
if(idCat != null && idProd != null)
sepProductPresenter.getSepProd(idCat, idProd);
}
#Override
public void setData(SepProductModel sepProductModel) {
// there i send data to fragment
prepBaseProdFragment.setDataInf(sepProductModel);
// ...
}
class ViewPagerAdapter extends FragmentPagerAdapter {
private final List<Fragment> mFragmentList = new ArrayList<>();
private final List<String> mFragmentTitleList = new ArrayList<>();
public ViewPagerAdapter(FragmentManager manager) {
super(manager);
}
#Override
public Fragment getItem(int position) {
return mFragmentList.get(position);
}
#Override
public int getCount() {
return mFragmentList.size();
}
public void addFrag(Fragment fragment, String title) {
mFragmentList.add(fragment);
mFragmentTitleList.add(title);
}
#Override
public CharSequence getPageTitle(int position) {
return mFragmentTitleList.get(position);
}
}
my fragment
public class PrepBaseProdFragment extends BaseFragment {
#BindView(R.id.text) TextView text;
#Override
public View onCreateView(LayoutInflater inflater, ViewGroup parent, Bundle savedInstanceState) {
View view = inflater.inflate(R.layout.fragment_about_prod_prepare_base, parent, false);
ButterKnife.bind(this, view);
Log.e("PrepBaseProdFragment", "PrepBaseProdFragment");
return view;
}
public void setDataInf(SepProductModel sepProductModel) {
text.setText(sepProductModel.getPROPERTY_PR_SUBSTRPREP_UA_VALUE().getTEXT());
}
}
My question: when i send data from activity to fragment, my view do not have time to initialize. In fragment line text.setText(sepProductModel.getPROPERTY_PR_SUBSTRPREP_UA_VALUE().getTEXT()); error
java.lang.NullPointerException: Attempt to invoke virtual method 'void
android.widget.TextView.setText(java.lang.CharSequence)' on a null
object reference
Please, help me solve my problem. I spend many times for this

You can check if the text view is null save the data in a variable inside the fragment and in onCreateView use the data variable if it is filled and set the textview text.
Something like this:
// Inside the Fragment body
private SepProductModel sepProductModel;
#Override
public View onCreateView(LayoutInflater inflater, ViewGroup parent, Bundle savedInstanceState) {
View view = inflater.inflate(R.layout.fragment_about_prod_prepare_base, parent, false);
ButterKnife.bind(this, view);
Log.e("PrepBaseProdFragment", "PrepBaseProdFragment");
if(this.sepProductModel != null)
text.setText(this.sepProductModel.getPROPERTY_PR_SUBSTRPREP_UA_VALUE().getTEXT());
return view;
}
public void setDataInf(SepProductModel sepProductModel) {
if(text != null){
// use text
}
else this.sepProductModel=sepProductModel;
}

I can advise you to wait for your data and then show fragments to adapter, moreover all of them use the same model. While you dont have data, you can show progress bar.
When you have needed model, you can create instances of your fragments and set bundle arguments for them. You can use method like this:
public static MyFragment newInstance(MyModel model){
MyFragment fragment = new MyFragment();
Bundle args = new Bundle();
args.putSerializable(KEY, model);//or args.putParcelable(KEY, model);
fragment.setArguments(args);
return fragment;
}
Notice: your model need to implement Serializable or Parcelable to be putted in bundle. You may read about difference here.
Then in your set data method, when you already have your model you can setup your adapter and set it to view pager, but with this approach:
adapter.addFrag(MyFragment.newInstance(model), getString(R.string.sep_prep_base));
It have to help you, ask me if you have some questions.

Android onClick custom PageAdapter

So I have created a generic PageAdapter to be used in various parts on the app, which looks like this:
public class ImagePagerAdapter extends PagerAdapter {
private final LayoutInflater layoutInflater;
private final Picasso picasso;
private final int layoutResId;
private final List<AssociatedMedia> images;
public ImagePagerAdapter(Context context, int layoutResId) {
layoutInflater = LayoutInflater.from(context);
picasso = Injector.getInstance().getPicasso();
this.layoutResId = layoutResId;
this.images = new ArrayList<>();
}
public void setMedia(List<AssociatedMedia> media) {
images.clear();
for (AssociatedMedia productMedia : media) {
if (productMedia.type == AssociatedMediaType.IMAGE) {
images.add(productMedia);
}
else {
// non-images all at the end
break;
}
}
}
#Override
public Object instantiateItem(ViewGroup container, int position) {
AssociatedMedia image = images.get(position);
ImageView imageView = (ImageView) layoutInflater.inflate(layoutResId, container, false);
container.addView(imageView);
picasso.load(Uri.parse(image.urls[0])).into(imageView);
return imageView;
}
#Override
public void destroyItem(ViewGroup container, int position, Object object) {
ImageView imageView = (ImageView) object;
container.removeView(imageView);
picasso.cancelRequest(imageView);
}
#Override
public int getCount() {
return images.size();
}
#Override
public boolean isViewFromObject(View view, Object object) {
return view == object;
}
}
I then call this adapter in a fragment, like this:
ImagePagerAdapter productImageAdapter = new ImagePagerAdapter(getActivity(), R.layout.photo_container_small);
productImageAdapter.setMedia(medias);
productImage.setAdapter(productImageAdapter);
My question is, how can I invoke a onClickListener in the fragment. So my scenario is that, we have a carousel of images, and once the user click on an image, it will open a large view on that image, so sort of need an onItemClickListener, but this can only be invoked in the pagerAdapter.
So is there a way to either call a onClickListener in the fragment, or notify the fragment from the adapter when an item has been clicked?

This is a response to your comment. For formating and size reasons I use an answer for it. It is a general example on how to use an interface to de-couple a fragment from an adapter class which makes the adapter re-usable in several fragments (and even other projects).
public class MyAdapter {
MyAdapterListener listener;
private MyAdapter() {}
public MyAdapter(MyAdapterListener listeningActivityOrFragment) {
listener = listeningActivityOrFragment;
}
}
public interface MyAdapterListener {
void somethingTheFragmentNeedsToKnow(Object someData);
}
public class SomeFragment extends Fragment implements MyAdapterListener {
#Override
public View onCreateView(LayoutInflater inflater, ViewGroup container,
Bundle savedInstanceState) {
// Inflate the layout for this fragment
View view = inflater.inflate(R.layout.my_view, container, false);
// Do everyhting here to init your view.
// Create an Adapter and bind it to this fragment
MyAdapter myAdapter = new MyAdapter(this);
return view;
}
// Implement the listener interface
#Override
public void somethingTheFragmentNeedsToKnow(Object someData) {
// Get the data and process it.
}
}
So in your case the method within the interface may well be onClick(int position); If you need more than one method, then just add them.

Android: Communication between fragments in a view pager

Just for reference I am been trying to follow the answer to this question
Basic Communication between two fragments
I have 2 Fragments within a ViewPager Adapter along with an Actionbar.
What I have is one fragment produces some data which can (if chosen) inserted to an SQLite table.
The second Fragment simply displays all data in the table, however I am trying to make some communication that as soon as Fragment 1 inserts data into the SQLite table. Fragment 2 is called to refresh its select query (as in do the query again) to automatically show the latest data. At the moment this is manually done with a button which I feel is not great.
This is my interface in Fragment 1
onNumbersSavedListener mCallback;
public interface onNumbersSavedListener
{
public void RequestQueryRefresh();
}
#Override
public void onAttach(Activity activity) {
// TODO Auto-generated method stub
super.onAttach(activity);
try
{
mCallback = (onNumbersSavedListener) activity;
}
catch(ClassCastException e)
{
e.printStackTrace();
}
}
This is the main Activity which contains the ViewPager and implements the interface
public class MainActivity extends FragmentActivity implements TabListener, GenerateFragment.onNumbersSavedListener
This is the main problem I am having which I do not have IDs for the fragments which answer referred in the link stated above does so.
#Override
public void RequestQueryRefresh() {
// TODO Auto-generated method stub
}
TLDR: I am just looking for an easy and clean way for as soon as Fragment 1 saves into DB, fragment 2 updates its list view by re-running its query.

see more about otto lib here : http://square.github.io/otto/
Edited:
public class FragmentA extends Fragment {
#Override
public View onCreateView(LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState) {
return super.onCreateView(inflater, container, savedInstanceState);
}
public void saveData(){
//save datas before
BusProvider.getInstance().post(new EventUpdateOtto());
}
}
public class EventUpdateOtto{
public EventUpdateOtto(){
}
}
public class FragmentB extends Fragment {
#Override
public View onCreateView(LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState) {
return super.onCreateView(inflater, container, savedInstanceState);
}
#Subscribe
public void subUpdateList(EventUpdateOtto mEventUpdateOtto){
//update yout list here
}
#Override
public void onResume() {
BusProvider.getInstance().register(this);
super.onResume();
}
#Override
public void onPause() {
BusProvider.getInstance().unregister(this);
super.onPause();
}
}
public class BusProvider {
private static final Bus BUS = new Bus();
public static Bus getInstance() {
return BUS;
}
private BusProvider() {
// No instances.
}
}

In your case you can improve your interface:
public interface onNumbersSavedListener
{
public void RequestQueryRefresh(Bunde bundle/*or something other*/);
}

If you are using a cursor loader, the change should automatically be reflected in the fragment displaying it. However, the fragment that wants immediate updates whenever the table is changed can register as an observer to that table:
// observer to the table
class MyObserver extends ContentObserver {
final Handler mHandler;
public MyObserver(Handler handler) {
super(handler);
// I used a handler to get back to my UI thread
mHandler = handler;
}
#Override
public void onChange(boolean selfChange) {
this.onChange(selfChange, null);
}
#Override
public void onChange(boolean selfChange, Uri uri) {
Log.i(TAG, "MyObserver: onChange");
// do what you want to do - this is what I implemented
mHandler.post(myRunnable);
}
}
Then, register it:
mHandler = new Handler();
mObserver = new MyObserver(mHandler);
ContentResolver resolver = getContext().getContentResolver();
resolver.registerContentObserver(uri, false, mEventLogObserver);
The other fragment should then do a notify:
getContext().getContentResolver().notifyChange(uri, null);
The key is the uri - one watches it, the other notifies.

Subscriber not getting fired when using Otto

I'm trying out Otto on Android and i'm trying to send back a message from my Fragment to the Activity. Here's the basics of my code:
My Bus provider:
public final class BusProvider {
private static final Bus mInstance = new Bus();
private BusProvider() {}
public static Bus getBusProviderInstance() {
return mInstance;
}
}
My Activity has the following code:
public class MyActivity
extends BaseActivity {
// ....
#Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
BusProvider.getBusProviderInstance().register(this);
// ....
}
#OnClick(R.id.profile_image)
public void onImageClicked() {
// ...
MyFragment fragment = MyFragment.newInstance(choices);
fragment.show(getFragmentManager(), "myChoices");
}
#Subscribe
public void onButtonChoicePicked(MyFragment.ChoicePickedEvent event) {
Toast.makeText(this, "reaching here", Toast.LENGTH_SHORT).show();
}
#Override
protected void onStop() {
super.onStop();
BusProvider.getBusProviderInstance().unregister(this);
}
// ...
}
and these are the important bits of code from my Fragment:
public class MyFragment
extends BaseDialogFragment {
// ...
#Override
public View onCreateView(LayoutInflater inflater,
ViewGroup container,
Bundle savedInstanceState) {
LinearLayout layout = (LinearLayout) inflater.inflate(R.layout.dialog_choices,
container,
false);
setupDialogButtons(inflater, layout);
return layout;
}
private void setupDialogButtons(LayoutInflater inflater, LinearLayout parentView) {
ChoiceButtonViewHolder holder;
holder = new ChoiceButtonViewHolder(inflater, parentView);
holder.populateContent("First Choice", 1);
parentView.addView(holder.mChoiceTextView);
}
class ChoiceButtonViewHolder {
#InjectView(R.id.item_dialog_choice_desc) TextView mChoiceTextView;
private int mPosition;
ChoiceButtonViewHolder(LayoutInflater inflater, ViewGroup container) {
TextView mChoiceTextView = (TextView) inflater.inflate(R.layout.item_dialog_choice, container, false);
ButterKnife.inject(this, mChoiceTextView);
}
public void populateContent(String choiceDesc, int position) {
mChoiceTextView.setText(choiceDesc);
mPosition = position;
}
#OnClick(R.id.item_dialog_choice_desc)
public void onChoiceClicked() {
MyFragment.this.mDialog.dismiss();
BusProvider.getBusProviderInstance().post(new ChoicePickedEvent(1));
}
}
public static class ChoicePickedEvent {
public int mPositionClicked;
ChoicePickedEvent(int position) {
mPositionClicked = position;
}
}
}
I don't get any errors. But when i click my button from the fragment, the event onButtonChoicePicked doesn't get called.
Am I doing something wrong?
Am i misunderstanding how Otto works?
Is it a weird combination of ButterKnife and Otto that makes it not work?

Make sure you are importing "com.squareup.otto.Subscribe" not "com.google.common.eventbus.Subscribe"

The example code works without any issues independently. The reason i was facing this problem initially (as was rightly pointed out by #powerj1984): There was a misconfiguration in my project, where the bus that was being injected (via Dagger) was different from the bus instance that was being subscribed to for updates :P.
Lesson learnt: make sure the bus you use, is the same instance in both cases.