android - Retrofit API to retrieve a png image

Question

Hi I am new to Retrofit framework for Android. I could get JSON responses from REST services using it but I don't know how to download a png using retrofit. I am trying to download the png from this url: http://wwwns.akamai.com/media_resources/globe_emea.png. What should be response Object to be specified in the Callback<> to achieve this.

Answer 1

Of course we usually use Picasso to load image, but sometimes we really need use Retrofit to load a special image (like fetch a captcha image), you need add some header for request, get some value from header of response (of course you can also use Picasso + OkHttp, but in a project you have already use Retrofit to handle most of net requests), so here introduce how to implement by Retrofit 2.0.0 (I have already implemented in my project).

The key point is that you need use okhttp3.ResponseBody to receive response, else Retrofit will parse the response data as JSON, not binary data.

codes:

public interface Api {
    // don't need add 'Content-Type' header, it's useless
    // @Headers({"Content-Type: image/png"})
    @GET
    Call<ResponseBody> fetchCaptcha(@Url String url);
}

Call<ResponseBody> call = api.fetchCaptcha(url);
call.enqueue(new Callback<ResponseBody>() {
        @Override
        public void onResponse(Call<ResponseBody> call, Response<ResponseBody> response) {
            if (response.isSuccessful()) {
                if (response.body() != null) {
                    // display the image data in a ImageView or save it
                    Bitmap bmp = BitmapFactory.decodeStream(response.body().byteStream());
                    imageView.setImageBitmap(bmp);
                } else {
                    // TODO
                }
            } else {
                // TODO
            }
        }

        @Override
        public void onFailure(Call<ResponseBody> call, Throwable t) {
            // TODO
        }
    });