Power Adapters

Universally compatible adapter classes that provide commonly required functionality, such as:

• Headers and footers
• Show a loading to indicate a loading state
• Show an item to indicate the underlying data set is empty
• Concatenate multiple adapters together
• Add dividers in between items of an existing adapter
• Present hierarchical data structures

Power adapters are compatible with ListView, GridView (technically anything that accepts a normal Adapter), and RecyclerView.

Usage

Adapter Decoration

All adapters are designed to wrap an existing adapter, allowing you to maintain a separation of concerns. For example, say you want to present a list of tweets, but show an empty message when there are no tweets, you can do the following:

PowerAdapter adapter = new TweetsAdapter();
adapter = new EmptyAdapterBuilder()
    .resource(R.layout.tweets_empty_item)
    .build(adapter);

listView.setAdapter(PowerAdapters.toListAdapter(adapter));

This lets you write a simple TweetAdapter class, the only responsibility of which is to present tweets. By applying the empty adapter as such, the TweetAdapter need not be modified to present the empty state, and can be potentially reused elsewhere more easily.

This also means you can apply as many or as few wrapper adapters as you need to solve your problem. Need to show a loading indicator as well? Just wrap the PowerAdapter instance with LoadingAdapterBuilder. By using the decorator pattern, you can also control the order of each effect applied.

Binding

Included in Power Adapters is the ability to bind elements in your data set to views in a reusable and readable manner. You can get started by using a BindingAdapter.

Binder

The primary type needed to achieve this is a Binder. These have a couple of responsibilities:

• Construct a View to be bound, and re-used by the adapter/recycler view
• Bind an object and/or data set index to the View

Multiple types of commonly required binders are supplied: TypedBinder and ViewHolderBinder.

Mapper

The second class involved is the Mapper. It is consulted to determine which Binder to use for presenting a particular element in your data set. The most common type of Mapper you're likely to use is PolymorphicMapperBuilder. This class allows you to specify a binder based on the Class of the object. If no binder is found, it will walk upwards through the class hierarchy attempting to find a suitable binder.

Example:

Mapper mapper = new PolymorphicMapperBuilder()
    .bind(Tweet.class, new TweetBinder())
    .build();
PowerAdapter adapter = new BindingAdapter(mapper) {
    // your implementation
}

Samples

Check the included sample project for a wide array of usage pattern examples.

Build

Building instructions:

$ git clone <github_repo_url>
$ cd power-adapters
$ ./gradlew clean build

Migration Notes

Some users may be familiar with earlier iterations of this library. Below are tips for migrating to Power Adapters from the previous generation called Databind.

DisposeableListAdapter

The DisposeableListAdapter interface has been eliminated. You no longer need to dispose of adapters. Instead, adapters keep track of external observers, and use a reference counting system to automatically unregister their own internal observers once no external clients are observing.