Helper library for recyclerviews to create composable view holders without boilerplate code.

The Gradle dependency is available via JCenter. JCenter is the default maven repository used by Android Studio.

The minimum API level supported by this library is API 9.

dependencies {
	// ... other dependencies here
    compile 'com.github.devahamed:multi-view-adapter:1.0.1'
}

Most of the android apps out there uses recyclerview to display content. As with any other system-level api, recyclerview api is also designed in a generic way. So it needs lot of code to be written for displaying a simple list. And it doubles, if you need to display multiple view types. MultiViewAdapter library helps you in removing this boilerplate code while allowing you to truly re-use the viewholder code across various adapters.

There are many other libraries, which provides the same feature. But they do enforce the either or all of the following constraints :

1. Your POJO classes should extend/implement some Base classes. This forces us to make changes in model level.
2. Forces you to implement some boilerplate code - like managing view types by yourself.
3. Doesn't utilise diffutil or payloads from recyclerview api

Now the advantages of the MultiViewAdapter

1. No restrictions on POJO class' parent/hierarchy. Now, your model classes can truly reside inside data layer.
2. No need to cast your models, no need for switch/if-else cases when you are having multiple view types.
3. Takes advantage of diffutil and allows payload while notifying adapter.

1. RecyclerAdapter - This is the adapter class. It can have multiple ItemBinder and DataManagers. It extends from official RecyclerView.Adapter
2. ItemBinder - ItemBinder's responsibility is to create and bind viewholders. ItemBinder has type parameter which accepts the model class need to be displayed. ItemBinder needs to be registered inside RecyclerAdapter. ItemBinder can be registered with multiple adapters.
3. DataManger - Consider it as a List. But internally it calls necessary animations when the list is modified. There are two DataManagers. DataListManager for list of items. DataItemManager for a single item (Header, Footer etc.,).

You can read more about this library here in this Medium article.

1. Supports different span count for different ItemBinders.
2. Adds different ItemDecoration for different ItemBinders.
3. Items can be selected - Single and Multiple selection options are available.
4. Out of the box support for DiffUtil.

To get some idea about the MultiViewAdapter features kindly look at sample app code.

Let us display list of cars. No fuss. Here is the entire code.

CarBinder

class CarBinder extends ItemBinder<CarModel, CarBinder.CarViewHolder> {

  @Override public CarViewHolder create(LayoutInflater inflater, ViewGroup parent) {
    return new CarViewHolder(inflater.inflate(R.layout.item_car, parent, false));
  }

  @Override public boolean canBindData(Object item) {
    return item instanceof CarModel;
  }

  @Override public void bind(CarViewHolder holder, CarModel item) {
    // Bind the data here
  }

  static class CarViewHolder extends BaseViewHolder<CarModel> {
    // Normal ViewHolder code
  }
}

CarAdapter

class CarAdapter extends RecyclerAdapter {

  private DataListManager<CarModel> dataManager;

  public SimpleAdapter() {
    this.dataManager = new DataListManager<>(this);
    addDataManager(dataManager);

    registerBinder(new CarBinder());
  }

  public void addData(List<CarModel> dataList) {
    dataManager.addAll(dataList);
  }
}

Now you are good to go. Just create the CarAdapter object and set it to your recyclerview. When addData() method is called it will show the items in recyclerview.
If you want to show multiple viewtypes just create multiple ItemBinders and register inside the adapter.

If the GridLayoutManager has different span count for different view types, then override the getSpanSize() method inside ItemBinder.

  @Override public int getSpanSize(int maxSpanCount) {
    return 1; // Return any number which is less than maxSpanCount 
  }

Also don't forget to set span size lookup in GridLayoutManager. Adapter has default span size lookup object. Use that object.

layoutManager.setSpanSizeLookup(adapter.getSpanSizeLookup());

Create your own item decoration class implementing ItemDecorator. It goes like this,

public class MyItemDecorator implements ItemDecorator {

  public MyItemDecorator() {
    // Any initialization code
  }

  @Override public void getItemOffsets(Rect outRect, int position, int positionType) {
    // Set item offset for each item
    // outRect.set(0, 0, 0, 0);
  }

  @Override public void onDraw(Canvas canvas, RecyclerView parent, View child, int position,
      int positionType) {
    // Canvas drawing code implementation
    // Unlike default ItemDecoration, this method will be called for individual items. Do not create objects here.
  }
}

The methods, getItemOffsets and onDraw will be called for each item. So avoid creating objects there.
MyItemDecorator will be used with the ItemBinder as follows.

public class CustomItemBinder implements ItemBinder {

  public CustomItemBinder(MyItemDecorator myItemDecorator) {
    super(myItemDecorator);
  }
}

Just extend your adapter from SelectableAdapter instead of RecyclerAdapter. Now the adapter is selectable. To make an ItemBinder as selectable, extend it from SelectableBinder and also extend ViewHolder from SelectableViewHolder. By default, on long press ViewHolder will be selectable if it extends from SelectableViewHolder. You can also call itemSelectionToggled() to make it selected by yourself. Kindly go through the sample repo implementation.
Finally, you can call DataListManager's getSelectedItems() and setSelectedItems(List<E> selectedItems) to get and set selected items respectively.

DataListManager and DataItemManager will take care of diffutil. There is no special code needed. But to enable the payloads, you have to pass PayloadProvider to DataListManager's constructor.

class CarAdapter extends RecyclerAdapter {

  private DataListManager<CarModel> dataManager;
  private PayloadProvider<M> payloadProvider = new PayloadProvider<CarModel>() {
      @Override public boolean areContentsTheSame(CarModel oldItem, CarModel newItem) {
        // Your logic here
        return oldItem.equals(newItem);
      }

      @Override public Object getChangePayload(CarModel oldItem, CarModel newItem) {
        // Your logic here
        return null;
      }
  };

  public CarAdapter() {
    this.dataManager = new DataListManager<>(this, payloadProvider);
    addDataManager(dataManager);

    registerBinder(new CarBinder());
  }

  public void addData(List<CarModel> dataList) {
    dataManager.addAll(dataList);
  }
}

I am actively working on expanding the feature set of this library. While i don't have a exact timeline, but here are the future plans. All these will be taken up once 1.0 is released.

1. Add support for StaggeredGrid layout manager
2. Move diffutil calculation to background thread
3. Adding support for swipe listeners with composability as priority
4. Improve the sample app code and api documentation
5. Expandable item / group

See the project's Releases page for a list of versions with their changelog. View Releases
If you watch this repository, GitHub will send you an email every time there is an update.

Contributing to this library is simple,

1. Clone the repo
2. Make the changes
3. Make a pull request to develop branch
   
   The only requirement is whatever changes you make should be backward compatible. Also make sure its not a too specific feature which maynot be useful for everyone. Kindly make sure your code is formatted with this codestyle - Square Java code style

This library may not suit your needs or imposes too many restrictions. In that case create an issue/feature request. In the mean time check these awesome alternatives as well.

1. MultipleViewTypesAdapter - Original inspiration for this library.
   
2. AdapterDelegates
3. Groupie
4. Epoxy

Copyright 2017 Riyaz Ahamed

Licensed under the Apache License, Version 2.0 (the "License");
you may not use this file except in compliance with the License.
You may obtain a copy of the License at

   http://www.apache.org/licenses/LICENSE-2.0

Unless required by applicable law or agreed to in writing, software
distributed under the License is distributed on an "AS IS" BASIS,
WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
See the License for the specific language governing permissions and
limitations under the License.