Okhttp response callbacks on the main thread

Question

I have created a helper class to handle all of my http calls in my app. It is a simple singleton wrapper for okhttp that looks like this (I have omitted some unimportant parts):

public class HttpUtil {      private OkHttpClient client;     private Request.Builder builder;      ...      public void get(String url, HttpCallback cb) {         call("GET", url, cb);     }      public void post(String url, HttpCallback cb) {         call("POST", url, cb);     }      private void call(String method, String url, final HttpCallback cb) {         Request request = builder.url(url).method(method, method.equals("GET") ? null : new RequestBody() {             // don't care much about request body             @Override             public MediaType contentType() {                 return null;             }              @Override             public void writeTo(BufferedSink sink) throws IOException {              }         }).build();          client.newCall(request).enqueue(new Callback() {             @Override             public void onFailure(Request request, Throwable throwable) {                 cb.onFailure(null, throwable);             }              @Override             public void onResponse(Response response) throws IOException {                 if (!response.isSuccessful()) {                     cb.onFailure(response, null);                     return;                 }                 cb.onSuccess(response);             }         });     }       public interface HttpCallback  {          /**          * called when the server response was not 2xx or when an exception was thrown in the process          * @param response - in case of server error (4xx, 5xx) this contains the server response          *                 in case of IO exception this is null          * @param throwable - contains the exception. in case of server error (4xx, 5xx) this is null          */         public void onFailure(Response response, Throwable throwable);          /**          * contains the server response          * @param response          */         public void onSuccess(Response response);     }  } 

Then, in my main activity, I use this helper class :

HttpUtil.get(url, new HttpUtil.HttpCallback() {             @Override             public void onFailure(Response response, Throwable throwable) {                 // handle failure             }              @Override             public void onSuccess(Response response) {                 // <-------- Do some view manipulation here             }         }); 

onSuccess throws an exception when the code runs :

android.view.ViewRootImpl$CalledFromWrongThreadException: Only the original thread that created a view hierarchy can touch its views.

From my understanding, Okhttp callbacks run on the main thread so why do I get this error ?

** Just as a side note, I have created HttpCallback interface to wrap Okhttp's Callback class because I wanted to change the behaviour of onResponse and onFailure so I could unite the logic of handling failed responses due to i/o exception and failed responses due to server problems.

Thanks.

Answer 1

From my understanding, Okhttp callbacks run on the main thread so why do I get this error ?

This is not true. Callbacks run on a background thread. If you want to immediately process something in the UI you will need to post to the main thread.

Since you already have a wrapper around the callback you can do this internally in your helper so that all HttpCallback methods are invoked on the main thread for convenience.