Easy way to bind collections to listviews and recyclerviews with the new Android Data Binding framework.

If you are using androidx use version 4.0.0, this also uses databinding v2

implementation 'me.tatarka.bindingcollectionadapter2:bindingcollectionadapter:4.0.0'
implementation 'me.tatarka.bindingcollectionadapter2:bindingcollectionadapter-recyclerview:4.0.0'
implementation 'me.tatarka.bindingcollectionadapter2:bindingcollectionadapter-viewpager2:4.0.0'

or use the previous stable version

implementation 'me.tatarka.bindingcollectionadapter2:bindingcollectionadapter:2.2.0'
implementation 'me.tatarka.bindingcollectionadapter2:bindingcollectionadapter-recyclerview:2.2.0'

You need to provide your items and an ItemBinding to bind to the layout. You should use an ObservableList to automatically update your view based on list changes. However, you can use any List if you don't need that functionality.

public class ViewModel {
  public final ObservableList<String> items = new ObservableArrayList<>();
  public final ItemBinding<String> itemBinding = ItemBinding.of(BR.item, R.layout.item);
}

Then bind it to the collection view with app:items and app:itemBinding.

<!-- layout.xml -->
<layout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:app="http://schemas.android.com/apk/res-auto">
    <data>
      <import type="com.example.R" />
      <variable name="viewModel" type="com.example.ViewModel"/>
    </data>

    <ListView
      android:layout_width="match_parent"
      android:layout_height="match_parent"
      app:items="@{viewModel.items}"
      app:itemBinding="@{viewModel.itemBinding}"/>

    <androidx.recyclerview.widget.RecyclerView
      android:layout_width="match_parent"
      android:layout_height="match_parent"
      app:layoutManager="androidx.recyclerview.widget.LinearLayoutManager"
      app:items="@{viewModel.items}"
      app:itemBinding="@{viewModel.itemBinding}"/>

    <androidx.viewpager.widget.ViewPager
      android:layout_width="match_parent"
      android:layout_height="match_parent"
      app:items="@{viewModel.items}"
      app:itemBinding="@{viewModel.itemBinding}"/>

    <Spinner
      android:layout_width="match_parent"
      android:layout_height="match_parent"
      app:items="@{viewModel.items}"
      app:itemBinding="@{viewModel.itemBinding}"
      app:itemDropDownLayout="@{R.layout.item_dropdown}"/>
</layout>

In your item layout, the collection item will be bound to the variable with the name you passed into the ItemBinding.

<!-- item.xml -->
<layout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:app="http://schemas.android.com/apk/res-auto">
    <data>
      <variable name="item" type="String"/>
    </data>

    <TextView
      android:id="@+id/text"
      android:layout_width="match_parent"
      android:layout_height="wrap_content"
      android:text="@{item}"/>
</layout>

Note: if app:itemBinding is null, then the adapter will be set to null. This is useful if you don't have an itemBinding right away (ex: need to wait till you load data). If you aren't seeing any views, make sure you have itemBinding defined!

You can use multiple view types by using OnItemBind instead. You can still bind it to the view with app:itemBinding.

public final OnItemBind<String> onItemBind = new OnItemBind<String>() {
  @Override
  public void onItemBind(ItemBinding itemBinding, int position, String item) {
    itemBinding.set(BR.item, position == 0 ? R.layout.item_header : R.layout.item);
  }
};

If you are binding to a ListView, you must also provide the number of item types you have with app:itemTypeCount="@{2}.

Note that onItemBind is called many times so you should not do any complex processing in there. If you don't need to bind an item at a specific position (a static footer for example) you can use ItemBinding.VAR_NONE as the variable id.

You can bind additional variables to items in the list with itemBinding.bindExtra(BR.extra, value). This is useful for components that you don't want the items themselves to care about. For example, you can implement an item click listener as such

public interface OnItemClickListener {
    void onItemClick(String item);
}

OnItemClickListener listener = ...;
ItemBinding<Item> itemBinding = ItemBinding.<Item>of(BR.item, R.layout.item)
    .bindExtra(BR.listener, listener);

<layout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:app="http://schemas.android.com/apk/res-auto">
    <data>
      <variable name="item" type="String"/>
      <variable name="listener" type="OnItemClickListener"/>
    </data>

    <TextView
      android:id="@+id/text"
      android:layout_width="match_parent"
      android:layout_height="wrap_content"
      android:onClick="@{() -> listener.onItemClick(item)}"
      android:text="@{item}"/>
</layout>

You can set a callback to give an id for each item in the list with

adapter.setItemIds(new BindingListViewAdapter.ItemIds<T>() {
  @Override
  public long getItemId(int position, T item) {
    return // Calculate item id.
  }
});

or by defining app:itemIds="@{itemIds}" in the ListView in your layout file. Setting this will make hasStableIds return true which can increase performance of data changes.

You can set a callback for isEnabled() as well with

adapter.setItemEnabled(new BindingListViewAdapter.ItemEnabled<T>() {
  @Override
  public boolean isEnabled(int position, T item) {
    return // Calculate if item is enabled.
  }
});

or by defining app:itemEnabled="@{itemEnabled}"in the ListView in you layout file.

You can set a callback to give a page title for each item in the list with

adapter.setPageTitles(new PageTitles<T>() {
  @Override
  public CharSequence getPageTitle(int position, T item) {
    return "Page Title";
  }
});

or by defining app:pageTitles="@{pageTitles}" in the ViewPager in your layout file.

You can construct custom view holders with

adapter.setViewHolderFactory(new ViewHolderFactory() {
  @Override
  public RecyclerView.ViewHolder createViewHolder(ViewDataBinding binding) {
    return new MyCustomViewHolder(binding.getRoot());
  }
});

or by defining app:viewHolder="@{viewHolderFactory}" in the RecyclerView in your layout file.

Data binding is awesome and all, but you may run into a case where you simply need to manipulate the views directly. You can do this without throwing away the whole of databinding by subclassing an existing BindingCollectionAdapter. You can then bind adapter in your layout to your subclass's class name to have it use that instead. Instead of overriding the normal adapter methods, you should override onCreateBinding() or onBindBinding() and call super allowing you to run code before and after those events and get access to the item view's binding.

public class MyRecyclerViewAdapter<T> extends BindingRecyclerViewAdapter<T> {

  @Override
  public ViewDataBinding onCreateBinding(LayoutInflater inflater, @LayoutRes int layoutId, ViewGroup viewGroup) {
    ViewDataBinding binding = super.onCreateBinding(inflater, layoutId, viewGroup);
    Log.d(TAG, "created binding: " + binding);
    return binding;
  }

  @Override
  public void onBindBinding(ViewDataBinding binding, int bindingVariable, @LayoutRes int layoutId, int position, T item) {
    super.onBindBinding(binding, bindingVariable, layoutId, position, item);
    Log.d(TAG, "bound binding: " + binding + " at position: " + position);
  }
}

<androidx.recyclerview.widget.RecyclerView
  android:layout_width="match_parent"
  android:layout_height="match_parent"
  app:layoutManager="androidx.recyclerview.widget.LinearLayoutManager"
  app:items="@{viewModel.items}"
  app:itemBinding="@{viewModel.itemBinding}"
  app:adapter="@{viewModel.adapter}"/>

Note: databinding will re-evaluate expressions in your layout each time there is a data source change. If you are using a custom adapter you should ensure you are returning the same instance each time or your scroll position etc will not be preserved.

There are a few classes to help with common implementations of OnItemBind.

OnItemBindClass binds an item based on the class of the item in the list.

itemBind = new OnItemBindClass<>()
  .map(String.class, BR.name, R.layout.item_name)
  .map(Footer.class, ItemBinding.VAR_NONE, R.layout.item_footer)
  .map(Item.class, new OnItemBind<Item>() {
                       @Override
                       public void onItemBind(ItemBinding itemBinding, int position, Item item) {
                         itemBinding.clearExtras()
                                    .set(BR.item, position == 0 ? R.layout.item_header : R.layout.item)
                                    .bindExtra(BR.extra, (list.size() - 1) == position);
                       }
                     })
  .map(Object.class, ItemBinding.VAR_NONE, R.layout.item_other);

OnItemBindModel delegates to the items in the list themselves to determine the binding.

itemBind = new OnItemBindModel<Model>();

public class Model implements ItemBindingModel {
  @Override
  public void onItemBind(ItemBinding itemBinding) {
    itemBinding.set(BR.name, R.layout.item_name);
  }
}

There are many times you want to merge multiple data sources together. This can be as simple as adding headers and footers or as complex as concatenating multiple data sources. It is hard to manage these lists yourself since you have to take into account all items when updating a subset.

MergeObservableList solves this by giving you a "merged" view of your data sources.

ObservableList<String> data = new ObservableArrayList<>();
MergeObservableList<String> list = new MergeObservableList<>()
  .insertItem("Header")
  .insertList(data)
  .insertItem("Footer");

data.addAll(Arrays.asList("One", "Two"));
// list => ["Header", "One", "Two", "Footer"]
data.remove("One");
// list => ["Header", "Two", "Footer"]

Say you want to update list 'a' to list 'b' and you don't want to calculate what has changed between the two manually.

DiffObservableList builds off of DiffUtil to automatically calculate the changes between two lists.

DiffObservableList<Item> list = new DiffObservableList(new DiffObservableList.Callback<Item>() {
    @Override
    public boolean areItemsTheSame(Item oldItem, Item newItem) {
        return oldItem.id.equals(newItem.id);
    }

    @Override
    public boolean areContentsTheSame(Item oldItem, Item newItem) {
        return oldItem.value.equals(newItem.value);
    }
});

list.update(Arrays.asList(new Item("1", "a"), new Item("2", "b1")));
list.update(Arrays.asList(new Item("2", "b2"), new Item("3", "c"), new Item("4", "d"));

With large lists diffing might be too costly to run on the main thread. In that case you can calculate the diff on a background thread.

DiffObservableList<Item> list = new DiffObservableList(...);

// On background thread:
DiffUtil.DiffResult diffResult = list.calculateDiff(newItems);

// On main thread:
list.update(newItems, diffResult);

Paging is supported through the bindingcollectionadapter-paging artifact. First add it to your project

implementation 'me.tatarka.bindingcollectionadapter2:bindingcollectionadapter-paging:3.1.1'

Then bind a PagedList and DiffUtil.ItemCallback.

LiveData<PagedList<Item>> pagedList = new LivePagedListBuilder<>(..., 20);
DiffUtil.ItemCallback<Item> diff = ...;

<androidx.recyclerview.widget.RecyclerView
  android:layout_width="match_parent"
  android:layout_height="match_parent"
  app:layoutManager="androidx.recyclerview.widget.LinearLayoutManager"
  app:items="@{pagedList}"
  app:itemBinding="@{itemBinding}"
  app:diffConfig="@{diff}" />

This is likely because you are using the android-apt plugin which broke this in previous versions. Update to 1.6+ to fix it.

If you attempt to retrieve an adapter from a view right after binding it you may find it is null. This is because databinding waits for the next draw pass to run to batch up changes. You can force it to run immediately by calling binding.executePendingBindings().

Live data support has been added in 2.3.0-beta3 and 3.0.0-beta3 (androidx). For most cases it should 'just work'. However, it uses a bit of reflection under the hood and you'll have to call adapter.setLifecycleOwner(owner) if your containing view does not use databinding. This will be fixed whenever this issue gets resolved.

Copyright 2015 Evan Tatarka

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.