Question

I want to write an Android application that can display some data received(polled) from an internet resource.

I guess that I need to write some logic that will periodically call and get data from some endpoint, parse the response and display it. Is there a good tutorial for all this steps?

I know very little about Android programming at the momment and maybe it is better to start with something simpler. I just want to know what to look for while learning an gather some resources on this.

Answer 1

What you want to do is developing a rest api that provides data for your android app. E.g. you website has some content that you want use in your app, then you could write a php script that just returns that data in a specific format.

E.g. mysite.net/rest/fetchAllLocations.php?maybe_some_parameters

This would return locations in e.g. json format, here is an example how that looks like:

[{“id”:1,”shop_lng”:8.5317153930664,”shop_lat”:52.024803161621,”shop_zipcode”:33602,”shop_city”:”Bielefeld”,”shop_street”:”Arndtstra\u00dfe”,”shop_snumber”:3,”shop_name”:”M\u00fcller”,”shop_desc”:”Kaufhaus”}]

Here is an example for a rest api request:

http://shoqproject.supervisionbielefeld.de/public/gateway/gateway/get-shops-by-city/city/Bielefeld

So when you have your rest api set up you can deal with receiving that data with your android phone. I use a static method to get this data:

public class JsonGrabber{

    public static JSONArray receiveData(){  
        String url = "your url";
        String result = "";

        DefaultHttpClient client = new DefaultHttpClient();
        HttpGet method = new HttpGet(url);
        HttpResponse res = null;

        try {
            res = client.execute(method);
        } catch (ClientProtocolException e1) {
            e1.printStackTrace();
        } catch (IOException e1) {
            e1.printStackTrace();
        }

        try{
            InputStream is = res.getEntity().getContent();
    BufferedReader reader = new BufferedReader(new InputStreamReader(is,"iso-8859-1"));
             StringBuilder sb = new StringBuilder();
             String line = null;
             while ((line = reader.readLine()) != null) {
                     sb.append(line + "\n");
             }
             is.close();
             result = sb.toString();
        }catch(Exception e){
             Log.e("log_tag", "Error converting result "+e.toString());
        }

        JSONArray jArray = null;

        try{
             jArray = new JSONArray(result);
        }catch(JSONException e){
                Log.e("log_tag", "Error parsing data "+e.toString());
        }

        return jArray;
    }
}

Well thats all, once you have your data in json format you just have to parse it:

JSONArray test = (JSONArray) JsonGrabber.receiveData() 

try { 
    for(int i=0;i<test.length();i++){
    JSONObject json_data = test.getJSONObject(i);
    int id = json_data.getInt("id");
    }
}

The web request should run in another thread, because it can be a time consuming process. So you need to deal with AsyncTask. Here are some resources:

Painless Threading
Multithreading for performance
Hello Android Tutorial