Dynamically add optional parameters to API requests

Question

I have an Android app that communicates with a REST API.

For each request, I want my app to be able to add optional parameters in addition to the mandatory parameters.

How can I implement this with Retrofit? Currently all the parameters are hard-coded in the interface:

@GET("/user/{id}/comments?position={pos}")  
void getComments(@Path("id") int id, @Query("pos") int pos, Callback<String> cb);

@GET("/user/{id}/likes?n={number}")  
void getLikes(@Path("id") int id, @Query("number") int number, Callback<String> cb);

/* etc */

Is it possible to "sub-class" the RestAdapter or something to be able to dynamically add optional parameters to my requests?

Answer 1

You have a few ways to achieve that:

• By default Retrofit handles nulls correctly for all null query parameters, so you can do something like:

  @GET("/user/{id}/likes")  
  void getLikes(@Path("id") int id, @Query("n") Integer number, @Query("pos") Integer pos Callback<String> cb);
  

If you use Object instead of int you can call to the method using null for the optional parameters:

    getLikes(1, null, null, cb); // to get /user/1/likes
    getLikes(1, 2, null, cb); // to get /user/1/likes?n=2

• By using RequestInterceptor:

  RestAdapter.Builder builder= new RestAdapter.Builder()
  .setRequestInterceptor(new RequestInterceptor() {
              @Override
              public void intercept(RequestFacade request) {
                  request.addHeader("Accept", "application/json;versions=1");
                  if(/*condition*/){
                     request.addQueryParam(arg0, arg1)
                  }                      
              }
          });
  

Answer 2

Support for Map<String,String> is now available. Just use @QueryMap Map<String, String> params.

From http://square.github.io/retrofit/:

For complex query parameter combinations a Map can be used.

Example:

@GET("/group/{id}/users")
List<User> groupList(@Path("id") int groupId, @QueryMap Map<String, String> options);