A native android app that provides immersive browsing experience of 500px photos.

There are three activities in total in this app: StartActivity, MainActivity and PhotoActivity.

StartActivity: The purpose of the StartActivity is to display something when the app is loading the first batch of photos.

MainActivity: The main grid view of the app. The gird view in this activity is implemented with RecyclerView.

PhotoActivity: Fullscreen paged UI.

StartActivity -> MainActivity <-> PhotoActivity

Square Stack: Okhttp, Retrofit, Picasso. These libraries all have very simple and clean interfaces. They all helped me of writing simpler and cleaner code.

Dagger & ButterKnife: These two library are used for eliminating boilerplate code, so that I don't need to rewrite singleton instantiation and findViewById in every single class I created.

RxJava & RxAndroid: These library are used for async network calls. They're supported by retrofit.

To run the integration tests:

./gradlew connectedAndroidTest

Note: There are some weird glitches using tests with emulators, it is recommended to use a phone to run the tests.

Part 1, 2, 4 are omitted as they are all implemented in the later parts.

The number of spans in the RecyclerView is calculated according to the size of the screen and photo(440px).

Android has a ViewPager widget that supports most of the desired functionalities, but it was originally designed for the transition between fragments with finite pages.

I searched for some libraries that support infinite pages on Github, but most of them overcomplicate the problem. Thus, I wrote a InfinitePagerAdapter that satisfies all our needs.

I think this part is the hardest of the project, and I spent most of my time on this part as well.

Since I chose to use another activity (PhotoActivity) for displaying full screen photos, activity transition (which was add in Lolipop(API 21)) is used. The good thing about activity transition is that it is very simple to use; all I need is couple of lines of code.

But the downside is that it is very hard to modify the internal transition mechanism, since most of related instances are private fields in the Activity class, and these instance's implementations are not public. At the end, I managed to animate the enter transition, but the reenter transition back to the MainActivity was not behaving correctly. The reenter transition by default is disabled, it can be enabled from the debug settings on the right drawer in the MainActivity.

I would love to talk more about this part if I'm invited for an on-site interview.

Since we want to share the "state" of photos in both grid view and full screen view, I created a PhotoProvider that wraps around a list of photos and this object is shared by these two views. In addition, PhotoProvider handles most of the API calls. It hides the paging of the API from the UI code.

In the process of implementing this project, I noticed that memory and performances are very important in a photo app. Due to the nature of the photos (Bitmap), a large fullscreen photo may take all of heap ram for a app. To enhance the user experience, loading time of high resolution photos also needs to be minimized.