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Should we use Retrofit ?

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Retrofit is a type-safe REST client for Android developed by Square. The library provides a powerful framework for authenticating and interacting with APIs and sending network requests with OkHttp.The main premise behind type-safe HTTP clients is that you only need to worry about the semantics of the queries that you send over the network, rather than the details of how to construct URLs, specify parameters correctly and so forth. Retrofit makes this easy by requiring you to write just a couple of interfaces, and that’s it!
This library makes downloading JSON or XML data from a web API fairly straightforward. Once the data is downloaded then it is parsed into a Plain Old Java Object (POJO) which must be defined for each "resource" in the response.

The Old Way: AsyncTasks 
As of the latest version, we use the built-in AsyncTasks to retrieve data from Canvas’ servers. A quick Google search will explain the numerous issues with our approach: no orientation-change support, no ability to cancel network calls, as well as no easy way to make API calls in parallel. With the exception of Froyo and Gingerbread, AsyncTasks (by default) run in a serialized fashion. In a practical sense, this means that only one AsyncTask is running at any given time. Views that require multiple API calls (the DashBoard currently has 7) run extremely slow; sometimes taking multiple seconds to load.

We have used Volley as networking library. Today we are going to look at another awesome library Retrofit to make the http calls. Retrofit is denitely the better alternative to volley in terms of ease of use, performance, extensibility and other things. It is a type-­safe REST client for Android built by Square. Using this tool android developer can make all network stuff much more easier.

To work with Retrofit you need basically three classes.

  • Model class which is used to map the JSON data to.

  • Interfaces which defines the possible HTTP operations.

  • Retrofit.Builder class - Instance which uses the interface. Builder API which allows defining the URL end point for the HTTP operation.

Retrofit has you set the base endpoint url for all API calls, then it has you build static interfaces that specify endpoints using Java annotations. You can cleanly and dynamically substitute path-segments, POST/GET variables, etc. into the endpoint at the time of making the API call. In order to make an API call with RetroFit, you call a method on the interface, pass in any substitutions, and it will return to you a java model object. By default, Retrofit does the JSON parsing automatically using GSON (which is really, really fast) although you can plug in your own JSON parser if you want. Even though the setup is slightly different, the actual API calls are done in a similar way. 
it ridiculously fast, but it meshes quite well with our existing architecture. We were able to make a parent Callback Interface that automatically handles the error function, caching, and pagination with little to no effort for our APIs. In order to merge in Retrofit, we have to rename our variables to make our models GSON compliant, write a few simple interfaces, delete functions from the old API, and modify our fragments to not use AsyncTasks. Now that we have a few fragments completely converted, it’s pretty painless. There were some growing pains and issues that we had to overcome, but overall it went smoothly. 
http://www.vogella.com/tutorials/Retrofit/article.html

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