Epoxy

Epoxy is an Android library for building complex screens in a RecyclerView. Models are automatically generated from custom views, databinding layouts, or Litho components via annotation processing. These models are then used in an EpoxyController to declare what items to show in the RecyclerView.

This abstracts the boilerplate of view holders, diffing items and binding payload changes, item types, item ids, span counts, and more, in order to simplify building screens with multiple view types. Additionally, Epoxy adds support for saving view state and automatic diffing of item changes.

We developed Epoxy at Airbnb to simplify the process of working with RecyclerViews, and to add the missing functionality we needed. We now use Epoxy for most of the main screens in our app and it has improved our developer experience greatly.

• Installation
• Basic Usage
• Documentation
• Min SDK
• Contributing
• Sample App

Installation

Gradle is the only supported build configuration, so just add the dependency to your project build.gradle file:

dependencies {
  implementation 'com.airbnb.android:epoxy:3.x.y'
  // Add the annotation processor if you are using Epoxy's annotations (recommended)
  annotationProcessor 'com.airbnb.android:epoxy-processor:3.x.y'
}

Replace x and y with the latest version number:

See the releases page for up to date release versions and details

Kotlin

If you are using Kotlin you should also add

apply plugin: 'kotlin-kapt'

kapt {
    correctErrorTypes = true
}

so that AutoModel annotations work properly. More information here

Also, make sure to use kapt instead of annotationProcessor in your dependencies in the build.gradle file.

Library Projects

If you are using layout resources in Epoxy annotations then for library projects add Butterknife's gradle plugin to your buildscript.

buildscript {
  repositories {
    mavenCentral()
   }
  dependencies {
    classpath 'com.jakewharton:butterknife-gradle-plugin:10.1.0'
  }
}

and then apply it in your module:

apply plugin: 'com.android.library'
apply plugin: 'com.jakewharton.butterknife'

Now make sure you use R2 instead of R inside all Epoxy annotations.

@ModelView(defaultLayout = R2.layout.view_holder_header)
public class HeaderView extends LinearLayout {
   ....
}

This is not necessary if you don't use resources as annotation parameters, such as with custom view models.

Basic Usage

There are two main components of Epoxy:

1. The EpoxyModels that describe how your views should be displayed in the RecyclerView.
2. The EpoxyController where the models are used to describe what items to show and with what data.

Creating Models

Epoxy generates models for you based on your view or layout. Generated model classes are suffixed with an underscore (_) are are used directly in your EpoxyController classes.

From Custom Views

Add the @ModelView annotation on a view class. Then, add a "prop" annotation on each setter method to mark it as a property for the model.

@ModelView(autoLayout = Size.MATCH_WIDTH_WRAP_HEIGHT)
public class HeaderView extends LinearLayout {

  ... // Initialization omitted

  @TextProp
  public void setTitle(CharSequence text) {
    titleView.setText(text);
  }
}

A HeaderViewModel_ is then generated in the same package.

More Details

From DataBinding

If you use Android DataBinding you can simply set up your xml layouts like normal:

<layout xmlns:android="http://schemas.android.com/apk/res/android">
    <data>
        <variable name="title" type="String" />
    </data>

    <TextView
        android:layout_width="120dp"
        android:layout_height="40dp"
        android:text="@{title}" />
</layout>

Then, create a package-info.java file in any package and add an EpoxyDataBindingLayouts annotation to declare your databinding layouts.

@EpoxyDataBindingLayouts({R.layout.header_view, ... // other layouts })
package com.airbnb.epoxy.sample;

import com.airbnb.epoxy.EpoxyDataBindingLayouts;
import com.airbnb.epoxy.R;

From this layout name Epoxy generates a HeaderViewBindingModel_.

More Details

From ViewHolders

If you use xml layouts without databinding you can create a model class to do the binding.

@EpoxyModelClass(layout = R.layout.header_view)
public abstract class HeaderModel extends EpoxyModelWithHolder<Holder> {
  @EpoxyAttribute String title;

  @Override
  public void bind(Holder holder) {
    holder.header.setText(title);
  }

  static class Holder extends BaseEpoxyHolder {
    @BindView(R.id.text) TextView header;
  }
}

A HeaderModel_ class is generated that subclasses HeaderModel and implements the model details.

More Details

Using your models in a controller

A controller defines what items should be shown in the RecyclerView, by adding the corresponding models in the desired order.

The controller's buildModels method declares which items to show. You are responsible for calling requestModelBuild whenever your data changes, which triggers buildModels to run again. Epoxy tracks changes in the models and automatically binds and updates views.

As an example, our PhotoController shows a header, a list of photos, and a loader (if more photos are being loaded). The controller's setData(photos, loadingMore) method is called whenever photos are loaded, which triggers a call to buildModels so models representing the state of the new data can be built.

public class PhotoController extends Typed2EpoxyController<List<Photo>, Boolean> {
    @AutoModel HeaderModel_ headerModel;
    @AutoModel LoaderModel_ loaderModel;

    @Override
    protected void buildModels(List<Photo> photos, Boolean loadingMore) {
      headerModel
          .title("My Photos")
          .description("My album description!")
          .addTo(this);

      for (Photo photo : photos) {
        new PhotoModel()
           .id(photo.id())
           .url(photo.url())
           .addTo(this);
      }

      loaderModel
          .addIf(loadingMore, this);
    }
  }

Or with Kotlin

An extension function is generated for each model so we can write this:

class PhotoController : Typed2EpoxyController<List<Photo>, Boolean>() {

    override fun buildModels(photos: List<Photo>, loadingMore: Boolean) {
        header {
            id("header")
            title("My Photos")
            description("My album description!")
        }

        photos.forEach {
            photoView {
                id(it.id())
                url(it.url())
            }
        }

        if (loadingMore) loaderView { id("loader") }
    }
}

Integrating with RecyclerView

Get the backing adapter off the EpoxyController to set up your RecyclerView:

MyController controller = new MyController();
recyclerView.setAdapter(controller.getAdapter());

// Request a model build whenever your data changes
controller.requestModelBuild();

// Or if you are using a TypedEpoxyController
controller.setData(myData);

If you are using the EpoxyRecyclerView integration is easier.

epoxyRecyclerView.setControllerAndBuildModels(new MyController());

// Request a model build on the recyclerview when data changes
epoxyRecyclerView.requestModelBuild();

Kotlin

Or use Kotlin Extensions to simplify further and remove the need for a controller class.

epoxyRecyclerView.withModels {
        header {
            id("header")
            title("My Photos")
            description("My album description!")
        }

        photos.forEach {
            photoView {
                id(it.id())
                url(it.url())
            }
        }

        if (loadingMore) loaderView { id("loader") }
    }
}

More Reading

And that's it! The controller's declarative style makes it very easy to visualize what the RecyclerView will look like, even when many different view types or items are used. Epoxy handles everything else. If a view only partially changes, such as the description, only that new value is set on the view, so the system is very efficient

Epoxy handles much more than these basics, and is highly configurable. See the wiki for in depth documentation.

Documentation

See examples and browse complete documentation at the Epoxy Wiki

If you still have questions, feel free to create a new issue.

Min SDK

We support a minimum SDK of 14. However, Epoxy is based on the v7 support libraries so it should work with lower versions if you care to override the min sdk level in the manifest.

If you are using the optional Litho integration then the min SDK is 15 due to Litho's SDK requirement.

Contributing

Pull requests are welcome! We'd love help improving this library. Feel free to browse through open issues to look for things that need work. If you have a feature request or bug, please open a new issue so we can track it.

License

Copyright 2016 Airbnb, Inc.

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.