2. Tutorials
  3. Retrofit 2 — How to Delete Objects on the Server

Retrofit 2 — How to Delete Objects on the Server

In the Retrofit getting started tutorial you've learned how to create an Android app that connects to the public GitHub API and accesses objects on the server. In following tutorials you've learned how to create new objects and update existing ones.

In this tutorial you'll learn how delete objects on the server. This is usually done with DELETE HTTP requests. If you're not familiar with HTTP requests yet, we recommend our tutorial on network basics.

If you're ready to go, let's start!

Retrofit Series Overview

  1. Getting Started and Creating an Android Client
  2. Basics of API Description
  3. Creating a Sustainable Android Client
  4. URL Handling, Resolution and Parsing
  5. How to Change API Base Url at Runtime
  6. Multiple Server Environments (Develop, Staging, Production)
  7. Share OkHttp Client and Converters between Retrofit Instances
  8. Upgrade Guide from 1.9
  9. Beyond Android: Retrofit for Java Projects
  10. How to use OkHttp 3 with Retrofit 1
  1. Synchronous and Asynchronous Requests
  2. Send Objects in Request Body
  3. Add Custom Request Header
  4. Manage Request Headers in OkHttp Interceptor
  5. Dynamic Request Headers with @HeaderMap
  6. Multiple Query Parameters of Same Name
  7. Optional Query Parameters
  8. Send Data Form-Urlencoded
  9. Send Data Form-Urlencoded Using FieldMap
  10. How to Add Query Parameters to Every Request
  11. Add Multiple Query Parameter With QueryMap
  12. How to Use Dynamic Urls for Requests
  13. Constant, Default and Logic Values for POST and PUT Requests
  14. Cancel Requests
  15. Reuse and Analyze Requests
  16. Optional Path Parameters
  17. How to Send Plain Text Request Body
  18. Customize Network Timeouts
  19. How to Trust Unsafe SSL certificates (Self-signed, Expired)
  20. Dynamic Endpoint-Dependent Interceptor Actions
  21. How to Update Objects on the Server (PUT vs. PATCH)
  22. How to Delete Objects on the Server
  1. Ignore Response Payload with Call<Void>
  2. Receive Plain-String Responses
  3. Crawl HTML Responses with jspoon (Wikipedia Example)
  4. Loading Data into RecyclerView and CardView
  1. Introduction to (Multiple) Converters
  2. Adding & Customizing the Gson Converter
  3. Implementing Custom Converters
  4. How to Integrate XML Converter
  5. Access Mapped Objects and Raw Response Payload
  6. Supporting JSON and XML Responses Concurrently
  7. Handling of Empty Server Responses with Custom Converter
  8. Send JSON Requests and Receive XML Responses (or vice versa)
  9. Unwrapping Envelope Responses with Custom Converter
  10. Wrapping Requests in Envelope with Custom Converter
  11. Define a Custom Response Converter
  1. Simple Error Handling
  2. Error Handling for Synchronous Requests
  3. Catch Server Errors Globally with Response Interceptor
  4. How to Detect Network and Conversion Errors in onFailure
  1. Log Requests and Responses
  2. Enable Logging for Development Builds Only
  3. Log Network Traffic with Stetho and Chrome Developer Tools
  4. Using the Log Level to Debug Requests
  5. Analyze Network Traffic with Android Studio Profiler
  6. Debug and Compare Requests with RequestBin
  1. Introduction to Call Adapters
  2. Custom Call Adapter to Separate OnResponse Callback
  3. How to Integrate RxJava 1.x Call Adapter
  4. How to Integrate RxJava 2.x Call Adapter
  5. How to Integrate Guava Call Adapter
  6. Custom Call Adapter to Separate Network and Gson Errors
  1. Pagination Using Query Parameter
  2. Pagination Using Link Header and Dynamic Urls (Like GitHub)
  3. Pagination Using Range Header Fields (Like Heroku)
  1. How to Upload Files to Server
  2. How to Upload Multiple Files to Server
  3. How to Upload a Dynamic Amount of Files to Server
  4. Upload Files with Progress
  5. Passing Multiple Parts Along a File with @PartMap
  6. How to Download Files from Server
  7. Download Files with Progress Updates
  8. How to Upload Files to Server
  1. Basic Authentication on Android
  2. Token Authentication on Android
  3. OAuth on Android
  4. Hawk Authentication on Android
  5. How to Refresh an Access Token
  1. Activate Response Caching (Etag, Last-Modified)
  2. Check Response Origin (Network, Cache, or Both)
  3. Force Server Cache Support with Response Interceptor
  4. Support App Offline Mode by Accessing Response Caches
  5. Analyze Cache Files
  1. Basics of Mocking Server Responses
  2. Customizing Network Behavior of Mocked Server Responses
  3. Mock APIs with JsonServer
  1. Callbacks
  2. Annotations
  3. Fluent Interface with Builders

Delete Objects via an API

If you've read the previous tutorials, you know how to access, create and change objects. For us app developers deleting objects is actually the simplest request!

Of course, this only works if the server supports the DELETE operation. Before you start implement the content of this tutorial, make sure your API supports this operation!

Let's review how our Retrofit interface declaration looks in the update Gist objects tutorial:

public class Gist {  
    // all Gist properties  
      // ...
}

public interface GistService {  
    // access Gists 
      @GET("gists")
    Call<List<Gist>> getGists();

      // create new Gist
    @POST("gists")
    Call<ResponseBody> createGist(@Body Gist gist);

      // update existing Gist
    @PATCH("gists/{id}")
    Call<ResponseBody> patchGist(@Path("id") String id, @Body Gist gist);

    @PUT("gists/{id}")
    Call<ResponseBody> replaceGist(@Path("id") String id, @Body Gist gist);

      // delete Gist
      // ... coming up!
}

DELETE HTTP Request

Before you can implement the interface declaration, you've to learn how the request itself looks. Because you don't need to send a payload, and are simply sending a command the request is simple:

DELETE /gists/12343

{}

In summary, all you need is the object ID to specify which object you want. The request doesn't have a payload, and you need to use the DELETE HTTP method.

DELETE Implementation in Retrofit

Let's implement this in Retrofit:

public interface GistService {  
    // ...  

      // delete Gist  
      @DELETE("gists/{id}")
    Call<ResponseBody> deleteGist(@Path("id") String id);
}

And that's it! All you really need is the object ID and you're ready to delete whatever you don't like anymore (within your app)!

A last word of warning: make sure deleting an object on the server doesn't have negative side effects in your Android app. For example, if your view of the object is still open, you need to return to a safe state. If you cache objects, you need to remove the deleted object from the cache.

Summary

In this tutorial you've learned how to delete objects on the server. Deleting objects is quite easy with the DELETE HTTP method. Retrofit conveniently offers this as a single line to us developers. Awesome!

Do you have further questions on this topic or about Retrofit in general? Just let us know on Twitter @futurestud_io or leave a comment below.

Enjoy coding & make it rock!

Norman Peitek

android & node.js dev

https://twitter.com/peitek

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