Retrofiti A Pragmatic Approach to using Retrofit in Android ~ Roger Taracha ~ @thedancercodes 

About Me ● Software Engineer. ● Python, JS, Android ● Dance Choreographer. ● Traveling. ● Community Development. ● DIY Hobbyist. ● Learning Facilitator/ Lead Android Engineer - Andela 

Choosing a HTTP Client: (1) HttpURLConnection In HttpUrlConnection is an Android SDK HTTP Client. PROS: ● Low level code; can do anything ● Supports all basic HTTP features. ● In active development & maintenance by the Android Dev team. CONS: ● Can require more code than higher level libraries. 

Choosing a HTTP Client: (2) Square’s OkHttp ● Used by Android internally, can also be used explicitly. ● Supports connection pooling and response caching. ● Replaces HttpUrlConnection; mimics its API. 

Choosing a HTTP Client: (3) Google’s Volley ● Volley is built on top of HttpUrlConnection or OkHttp. ● Support Parallel requests -> Multiple requests over the web. ● Uses Gson library to decode JSON-formatted content. ● Handles device configuration changes elegantly. ○ EXAMPLE: If the device orientation changes in the middle of request/response cycle, the cycle won’t be interrupted. 

Choosing a HTTP Client: (4) Square’s Retrofit ● Popular HTTP Client Library for Android as a result of its simplicity and its great performance ● Automatically decodes JSON content to typed objects. ○ Saves the decoded content as strongly typed objects ● Retrofit lets you define your web service calls in Java interfaces. ○ You then use those interfaces to make requests and handle the responses. ● Custom Converters and other features ○ Includes classes and interfaces to convert data from one format to another. 

“Higher level libraries reduce your code and make your app run faster and better.” - Pro Tip - 

Project Setup ● Version of Android Studio and gradle being used. ○ Android Studio 3.0.1 ○ Gradle 3.0.1 ● Clone the repo and check out to the start branch: ○ http://bit.ly/2o9ymmo ○ Check out to the 00-Retrofiti-Exercise branch ● Get API KEY from TheMovieDB: ○ https://www.themoviedb.org/ ● APPROACH: Package by Feature 

TODO 0: Setup API Key ● Set up the API KEY in secrets.properties file. ○ Create the file in the root folder of your project ○ You need to secure your API key without pushing to remote repository ○ NB: This file is added to the .gitignore file. 

TODO 1: Add Required Dependencies ● Add the following dependencies in app/build.gradle: ○ Design ○ RecyclerView ○ Cardview ○ Glide ○ Retrofit ○ Converter-gson ○ ConstraintLayout ● Sync the project 

TODO 2: Set Internet Permission ● Set the Internet Permission in the Manifest file: ○ app/src/main/AndroidManifest.xml 

TODO 3: Movie Encapsulation Class and its Response ● Get JSON Response from this url: ○ http://api.themoviedb.org/3/movie/top_rated?api_key=YOUR_API_KEY ● Use this JSON Viewer to beautify the JSON Response: ○ https://codebeautify.org/jsonviewer ● Use JsonSchema2Pojo tool to convert the JSON Response to POJO classes: ○ http://www.jsonschema2pojo.org/ 

TODO 3: Movie Encapsulation Class and its Response ● Movie class contains Getter and Setter Methods for the app. ● Gets & Sets the key value pairs for the main movie information. ○ (ie) poster_path, overview, release_date, genre_ids etc. ● TODO 3a: Create a Movie Constructor ● TODO 3b: Add an Image URL Field ● TODO 3c: Append the Image URL Field ○ Append to getPosterPath() ● NOTE: See images in the next slide. 

TODO 3: Movie Encapsulation Class and its Response 

TODO 3: Movie Encapsulation Class and its Response 

TODO 4: Define API Client & Service ● The Client contains code that instantiates a new Retrofit instance. ○ The Retrofit object requires the base URL -> the base on which these relative paths will be appended. ○ This is where the configuration lies ● The Service contains the interface ○ Use interface as source of truth and add a little metadata to it to describe what the actual corresponding requests should look like. ○ Annotate method with the API path we want to hit @GET(“/movie/popular/”) ○ Wrap the request in a Call (A request wrapped up in an object that you can either execute synchronously or asynchronously) 

TODO 4: Define API Client & Service 

TODO 4: Define API Client & Service 

TODO 5: Movie Adapter ● An Adapter is a bridge between an AdapterView and the underlying data for that view. ● Handle onClick listeners on every card in the grid layout of the RecyclerView. ○ Passing Extras into the Intent to another Activity (Detail Activity). ● JSON API calls with image caching were made seamlessly easy using Retrofit and Glide. 

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TODO 5: Movie Adapter 

TODO 6: Main Activity ● Create initViews() helper method. ○ This method initialises the Views. ● Create loadJson() helper method. ○ This method handles loading of JSON ○ This process runs in a background thread that doesn't affect the UI Thread. ● Use try/catch for error handling. ○ Check for an empty API KEY 

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TODO 6: Main Activity 

Run the App You should see a list of top rated movies 

Further Reading ● https://futurestud.io/tutorials/retrofit-2-share-okhttp-client-and-convert ers-between-retrofit-instances ● https://guides.codepath.com/android/consuming-apis-with-retrofit ● http://jakewharton.com/making-retrofit-work-for-you/ 

This is the most important takeaway that everyone has to remember. 

Thank you @thedancercodes TheDancerCodes TheDancerCodes