The RecyclerView.Adapter that makes your life easy!

• Based on the SortedList: Uses a Comparator to sort the elements in your RecyclerView. By using a Comparator the SortedList takes care of managing the models in the Adapter in an efficient way and triggers all view animations for you!
• Reduces boilerplate: All you have to do is implement your ViewHolder based on SortedListAdapter.ViewHolder. The SortedListAdapter takes care of binding data and calls to the notify methods when you add or remove models to the SortedListAdapter.
• High Performance: SortedListAdapter also works effortlessly with large lists up to 100.000 items!

SortedListAdapter is based on the ModularAdapter you can find the GitHub project here.

Just add this dependency to your build.gradle file:

compile 'com.github.wrdlbrnft:sorted-list-adapter:0.2.0.19'

You can find a simple example project in this GitHub Repository.

Or if you first want to see what this library can do for yourself then download the example app from the Play Store here:

There are two ways to create a SortedListAdapter in your project. First you can subclass it like any other Adapter:

public class ExampleAdapter extends SortedListAdapter<ExampleModel> {

    public ExampleAdapter(Context context, Comparator<ExampleModel> comparator) {
        super(context, ExampleModel.class, comparator);
    }

    @Override
    protected ViewHolder<? extends ExampleModel> onCreateViewHolder(LayoutInflater inflater, ViewGroup parent, int viewType) {
        final View itemView = inflater.inflate(R.layout.item_example, parent, false);
        return new ExampleViewHolder(itemView);
    }
}

As you can see above in that case all you have to do is implement the onCreateViewHolder() method. The SortedListAdapter takes care of binding the data.

However you can also quickly create a SortedListAdapter using the SortedListAdapter.Builder class:

final SortedListAdapter<ExampleModel> adapter = new SortedListAdapter.Builder<>(context, ExampleModel.class, comparator)
        .add(ExampleModel.class, new SortedListAdapter.ViewHolderFactory<SortedListAdapter.ViewHolder<ExampleModel>>() {
            @Override
            public SortedListAdapter.ViewHolder<ExampleModel> create(LayoutInflater layoutInflater, ViewGroup viewGroup) {
                final View itemView = inflater.inflate(R.layout.item_example, parent, false);
                return new ExampleViewHolder(itemView);
            }
        })
        .build();

Both ways are equivalent, however when you have lists with many simple models the second method is usually favourable. If you are reusing the Adapter in many places and/or want to implement complex behavior you should go with the first method.

The Comparator instance you see in the constructor of both cases is used to determine the order of the items in your RecyclerView. This is the trade off the SortedListAdapter offers you: You gain high performance and seamless item animations even when dealing with hundreds of thousands of items in your RecyclerView and pay the price with the added complexity of having to implement a Comparator which sorts the items in your list in exactly the way you want.

However the SortedListAdapter comes with a handy tool to make this job a little easier. You can use the SortedListAdapter.ComparatorBuilder which greatly simplifies your work when dealing with multiple different models in your list. It is used like this:

final Comparator<SortedListAdapter.ViewModel> comparator = new SortedListAdapter.ComparatorBuilder<>()
        .setGeneralOrder(SomeModel.class, AnotherModel.class)
        .setOrderForModel(SomeModel.class, new Comparator<SomeModel>() {
            @Override
            public int compare(SomeModel a, SomeModel b) {
                return a.getText().compareTo(b.getText());
            }
        })
        .setOrderForModel(AnotherModel.class, new Comparator<AnotherModel>() {
            @Override
            public int compare(AnotherModel a, AnotherModel b) {
                return Integer.signum(a.getRank() - b.getRank());
            }
        })
        .build();

In the above example setGeneralOrder() is used to set the order of models based on type. In this specific example it means all SomeModel models will appear before AnotherModel models. The setOrderForModel() calls below it are used to set how each type of model should be ordered specifically. In this case it means that SomeModel instances are ordered by comparing their text field and AnotherModel instances are ordered based on their rank field.

All models used in a SortedListAdapter have to implement the SortedListAdapter.ViewModel interface. This interface requires you to implement two methods in your model:

1. isSameModelAs(): This method is used to determine if two models refer to the same thing. Imagine it like this: If you have a list of movies and you update the list (for example when the user is filtering the list) isSameModelAs() will be used by the SortedListAdapter to determine if the same model is still present in the list.
2. isContentTheSameAs(): This method is used to determine if the content of a model is equal to some other model. For example after two "same" model have been found using isSameModelAs() then isContentTheSameAs() will be used to check if data in the model has been modified and if a change animation has to be played in the RecylerView.

The canonical way to implement the above methods is like this:

public class ExampleModel implements SortedListAdapter.ViewModel {

    private final long mId;
    private final String mValue;

    public ExampleModel(long id, String value) {
        mId = id;
        mValue = value;
    }

    public long getId() {
        return mId;
    }

    public String getValue() {
        return mValue;
    }

    @Override
    public <T> boolean isSameModelAs(T item) {
        if (item instanceof ExampleModel) {
            final ExampleModel other = (ExampleModel) item;
            return other.mId == mId;
        }
        return false;
    }

    @Override
    public <T> boolean isContentTheSameAs(T item) {
        if (item instanceof ExampleModel) {
            final ExampleModel other = (ExampleModel) item;
            return mValue != null ? mValue.equals(other.mValue) : other.mValue == null;
        }
        return false;
    }
}

ViewHolders used in a SortedListAdapter have to be subclasses of SortedListAdapter.ViewHolder. They are responsible for binding the data to the Views in your RecyclerView. An example implementation looks like this:

public class ExampleViewHolder extends SortedListAdapter.ViewHolder<ExampleModel> {

    private final TextView mValueView;

    public ExampleViewHolder(View itemView) {
        super(itemView);
        
        mValueView = itemView.findViewById(R.id.value);
    }

    @Override
    protected void performBind(ExampleModel item) {
        mValueView.setText(item.getValue());
    }
}

The method performBind() is called by the SortedListAdapter when it is necessary to bind new data to the View managed by your ViewHolder.

Once you have implemented the Adapter you can add and remove models to it with an Editor object which can be accessed through the edit() method. All changes you make with this Editor object are batched and executed together once you call commit() on the Editor instance:

final Comparator<ExampleModel> alphabeticalComparator = new Comparator<ExampleModel>() {
    @Override
    public int compare(ExampleModel a, ExampleModel b) {
        return a.getText().compareTo(b.getText());
    }
};

final ExampleAdapter adapter = new ExampleAdapter(context, alphabeticalComparator);
recyclerView.setAdapter(adapter);

adapter.edit()
        .add(modelsToAdd)
        .commit();

As you can see above you can add models to the Adapter with add(). The same way you can remove models with remove():

adapter.edit()
        .remove(modelsToRemove)
        .commit();

You can also completely replace all models in the Adapter with another List of models with the replaceAll() method:

adapter.edit()
        .replaceAll(newModels)
        .commit();

Or you can remove all models with removeAll():

adapter.edit()
        .removeAll()
        .commit();

All changes you make this way will automatically be animated in the RecyclerView!

Usually all you need is the replaceAll() method. If you have a List of models that you want to show you can add them to the Adapter and if you later get an updated List of models through some network call you can just use replaceAll() to swap them out. The SortedListAdapter will automatically figure out the difference between the two Lists and animate the difference!