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groupie

Groupie is a simple, flexible library for complex RecyclerView layouts.

Groupie lets you treat your content as logical groups and handles change notifications for you -- think sections with headers and footers, expandable groups, blocks of vertical columns, and much more. It makes it easy to handle asynchronous content updates and insertions and user-driven content changes. At the item level, it abstracts the boilerplate of item view types, item layouts, viewholders, and span sizes.

Try it out:

Download

implementation "com.xwray:groupie:$groupie_version"

Groupie includes a module for Kotlin and Kotlin Android extensions. Never write a ViewHolder again—Kotlin generates view references and Groupie uses a generic holder. Setup here.

implementation "com.xwray:groupie:$groupie_version"
implementation "com.xwray:groupie-kotlin-android-extensions:$groupie_version"

Groupie also has a support module for Android's view binding. This module also supports Android data binding, so if your project uses both data binding and view binding, you don't have to add the dependency on the data binding support module. Setup here.

implementation "com.xwray:groupie:$groupie_version"
implementation "com.xwray:groupie-viewbinding:$groupie_version" 

Note:

If using groupie-viewbinding in a databinding project is only available when using Android Gradle Plugin 3.6.0 or higher.

If using an older Gradle Plugin version with databinding the you can use the standalone groupie-databinding library to generate view holders. Setup here. This is deprecated and will be removed in a future version in favour of only using groupie-viewbinding.

implementation "com.xwray:groupie:$groupie_version"
implementation "com.xwray:groupie-databinding:$groupie_version" 

You can also use Groupie with Java and your existing ViewHolders.

Which one to choose? It's up to you and what your project already uses. You can even use Kotlin and data binding together.* Or all your existing hand-written Java ViewHolders, and one new Kotlin item to try it out. Go crazy!

Get started

Use a GroupAdapter anywhere you would normally use a RecyclerView.Adapter, and attach it to your RecyclerView as usual.

Kotlin

val adapter = GroupAdapter()
recyclerView.setAdapter(adapter)

Java

GroupAdapter adapter = new GroupAdapter();
recyclerView.setAdapter(adapter);

Groups

Groups are the building block of Groupie. An individual Item (the unit which an adapter inflates and recycles) is a Group of 1. You can add Groups and Items interchangeably to the adapter.

Kotlin

groupAdapter += HeaderItem()
groupAdapter += CommentItem()

val section = Section()
section.setHeader(HeaderItem())
section.addAll(bodyItems)
groupAdapter += section

Java

groupAdapter.add(new HeaderItem());
groupAdapter.add(new CommentItem());

Section section = new Section();
section.setHeader(new HeaderItem());
section.addAll(bodyItems);
groupAdapter.add(section);

Modifying the contents of the GroupAdapter in any way automatically sends change notifications. Adding an item calls notifyItemAdded(); adding a group calls notifyItemRangeAdded(), etc.

Modifying the contents of a Group automatically notifies its parent. When notifications reach the GroupAdapter, it dispatches final change notifications. There's never a need to manually notify or keep track of indices, no matter how you structure your data.

section.removeHeader(); // results in a remove event for 1 item in the adapter, at position 2

There are a few simple implementations of Groups within the library:

  • Section, a list of body content with an optional header group and footer group. It supports diffing and animating moves, updates and other changes
  • ExpandableGroup, a single parent group with a list of body content that can be toggled hidden or shown.

Groupie tries not to assume what features your groups require. Instead, groups are flexible and composable. They can be combined and nested to arbitrary depth.

Life (and mobile design) is complicated, so groups are designed so that making new ones and defining their behavior is easy. You should make many small, simple, custom groups as the need strikes you.

You can implement the Group interface directly if you want. However, in most cases, you should extend Section or the base implementation, NestedGroup. Section supports common RV paradigms like diffing, headers, footers, and placeholders. NestedGroup provides support for arbitrary nesting of groups, registering/unregistering listeners, and fine-grained change notifications to support animations and updating the adapter.

Items

Groupie abstracts away the complexity of multiple item view types. Each Item declares a view layout id, and gets a callback to bind the inflated layout. That's all you need; you can add your new item directly to a GroupAdapter and call it a day.

Item with Kotlin:

The Item class gives you simple callbacks to bind your model object to the generated fields. Because of Kotlin Android extensions, there's no need to write a view holder.

import com.xwray.groupie.kotlinandroidextensions.Item
import com.xwray.groupie.kotlinandroidextensions.GroupieViewHolder
import kotlinx.android.synthetic.main.song.*

class SongItem(private val song: Song) : Item() {

    override fun getLayout() = R.layout.song

    override fun bind(viewHolder: GroupieViewHolder, position: Int) {
        viewHolder.title.text = song.title
        viewHolder.artist.text = song.artist
    }
}

Item with data binding:

The Item class gives you simple callbacks to bind your model object to the generated binding. Because of data binding, there's no need to write a view holder.

public class SongItem extends BindableItem<SongBinding> {

    public SongItem(Song song) {
        this(song);
    }    

    @Override public void bind(SongBinding binding, int position) {
        binding.setSong(song);
    }

    @Override public int getLayout() {
        return R.layout.song;
    }
}

If you're converting existing ViewHolders, you can reference any named views (e.g. R.id.title) directly from the binding instead.

    @Override public void bind(SongBinding binding, int position) {
        binding.title.setText(song.getTitle());
    }

You can also mix and match BindableItem and other Items in the adapter, so you can leave legacy viewholders as they are by making an Item<MyExistingViewHolder>.

Legacy item (your own ViewHolder)

You can leave legacy viewholders as they are by converting MyExistingViewHolder to extend GroupieViewHolder rather than RecyclerView.ViewHolder. Make sure to change the imports to com.xwray.groupie.Item and com.xwray.groupie.GroupieViewHolder.

Finally, in your Item<MyExistingViewHolder>, override

    @Override
    public MyExistingViewHolder createViewHolder(@NonNull View itemView) {
        return new MyExistingViewHolder(itemView);
    }

Note:

Items can also declare their own column span and whether they are draggable or swipeable.

Gradle setup

Kotlin

In your project level build.gradle file, include:

buildscript {
    ext.kotlin_version = '1.3.71'
    repositories {
        jcenter()
    }
    dependencies {
        classpath "org.jetbrains.kotlin:kotlin-gradle-plugin:$kotlin_version"
    }
}

In your app build.gradle file, include:

apply plugin: 'kotlin-android'
apply plugin: 'kotlin-android-extensions'

android {
  ....
  
   // IMPORTANT!  Enables kotlin synthetic view properties.
   // See: https://github.com/Kotlin/KEEP/blob/master/proposals/android-extensions-entity-caching.md
    androidExtensions {
        experimental = true
    }
	
}

dependencies {
    implementation "org.jetbrains.kotlin:kotlin-stdlib:$kotlin_version"
    implementation 'com.xwray:groupie:$groupie_version'
    implementation 'com.xwray:groupie-kotlin-android-extensions:$groupie_version'
}

Remember to include

import kotlinx.android.synthetic.main.my_item_layout.*

in the corresponding Item class for generated view references.

View binding

Add to your app module's build.gradle:

android {
    viewBinding {
        enabled = true
    }
}

dependencies {
    implementation "com.xwray:groupie:$groupie_version"
    implementation "com.xwray:groupie-viewbinding:$groupie_version"
}

WARNING: If using this with Databinding:

Because ViewBinding does not have the util class that can generate an arbitrary binding like DataBindingUtil for DataBinding, you need to override initializeViewBinding to generate the instance of the specified binding:

class MyLayoutItem: BindableItem<MyLayoutBinding>() {

    // You can also use `DataBindingUtil#bind` when using ViewBinding support with DataBinding classes
    override fun initializeViewBinding(view: View): MyLayoutBinding {
        return MyLayoutBinding.bind(view)
    }

    // Other implementations...
}

Note:

If you use groupie-viewbinding with data binding classes and your layouts have some variables or observable objects, don't forget to run executePendingBindings at the last point in bind.

Data binding

Data binding functionality is deprecated. Consider moving to View binding. instead, which supports data binding out of the box.

Add to your app module's build.gradle:

android {
    dataBinding {
        enabled = true
    }
}

dependencies {
    implementation "com.xwray:groupie:$groupie_version"
    implementation "com.xwray:groupie-databinding:$groupie_version"
}

Then, just wrap each item layout in <layout> tags. (The <data> section is optional.)

layout/item_song.xml

<layout xmlns:android="http://schemas.android.com/apk/res/android" 
    xmlns:tools="http://schemas.android.com/tools">
    <data>
        <variable name="song" type="com.example.Song" />
    </data>

    <FrameLayout 
        android:layout_width="match_parent"
        android:layout_height="wrap_content" >

        <TextView
            android:id="@+id/title"
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:layout_gravity="center"
            android:text="@{song.title}"
            tools:text="A Song Title" />

    </FrameLayout>
</layout>

Bindings are only generated for layouts wrapped with tags, so there's no need to convert the rest of your project (unless you want to).

You can add a <data> section to directly bind a model or ViewModel, but you don't have to. The generated view bindings alone are a huge time saver.

Kotlin AND data binding / view binding?

Sure, why not? Follow all the instructions from both sections above. You only need to include the groupie-databinding or groupie-viewbinding dependency, and omit the references to android-extensions. You'll make BindableItems instead of importing and using Kotlin extensions.

Contributing

Contributions you say? Yes please!

Bug report?

  • If at all possible, please attach a minimal sample project or code which reproduces the bug.
  • Screenshots are also a huge help if the problem is visual.

Send a pull request!

  • If you're fixing a bug, please add a failing test or code that can reproduce the issue.

If you try it out, I'd love to know what you think. Please hit up Lisa at [first][last]@gmail.com or on Twitter at @lisawrayz.

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