Introduction

Simple image search app using the Flickr Image Search API.

Features:

• Endless scrolling of search results
• 3 column grid view of images
• Auto search as you type

Demo

Overview

• RxJava - Used RxJava for easier concurrency and thread management. Example:
  • Searching: Ability to search as you type by debouncing keystrokes to avoid unnecessary requests
  • Cancel existing network requests (both query and paging) when search query changes using switchMap operator.
  • Manage a bound thread pool of size 6 to fetch and decode images concurrently.
• OkHttp - Used for easier networking to fetch json and input stream for Bitmaps.

Architecture

MVP with Repository to avoid logical code in Activity and separate data related code. Loose coupling by making code dependent on interfaces rather than implementations eg: ImageCache, ImagesDataSource, ImageLoader. Explicit dependency on Flickr is avoided and is accessed through contracts.

• data - ImagesDataSource is a contract for a source that provides paged searching. FlickrImagesDataSource is an implementation backed by Flickr API. Also includes data classes for parsing json response.

• DepedencyInjector - Utility class to manage dependencies throughout the app. Responsible for managing and providing dependencies when requested. Eg: DependencyInjector.provideHomePresenter.

• Image Loading - ImageLoader and ImageCache are contracts for a system that loads images efficiently by reducing sample size, perform concurrent requests and caching.

  • DefaultImageLoader - Loader backed by Rx to handle multiple requests and decode images.
  • MemoryImageCache - Lru based memory cache to hold few Bitmaps in memory.

• SchedulerProvider - Contract to provide various type of Schedulers for concurrency. Can be replaced during testing via DI.

• Home - Home feature package that contains, presenter for communicating with data layer, adapter for rendering grid and HomeActivity

• Test - Presenter test for search term achieved by injecting MockImagesDataSource and testing paging and searches.

Possible improvements

• ImageLoading - While current implementation automatically uses ImageViews dimensions to downsize source image, there are other cases that could handled for better performance. Currently the load request is not cancelled when the ImageView is detached from window and relies on RecyclerView.Adapter.onViewRecycled to cancel the request, this could be changed to use View.onAttachStateListener to free one of the threads thereby improving load performance during scrolling. - Could use battle tested solutions like Glide or Picasso.
• Paging - By using PagedList and PageKeyedDataSource to simplify scroll listening, load more and concentrate on API implementations
• Dagger 2 - Use Dagger 2 instead of custom DependencyInjector to achieve compilation safety and scaling.
• State Restoration - Currently only the search term is restored upon a config change, this could be changed to use ViewModel pattern to cache the image list as well to avoid additional network calls.
• Better Error handling - When a paged list fails to load, possibly a retry button could be used to restart failed requests.
• Test - Additional integration tests to avoid breakage due to 3rd parties.
• LocalDataSource - Implement a local data source for provide search results stored on disk.