每当我更改屏幕方向时，AsyncTasc…doInBacground都会重复

Question

Lately I am developing an application in android for a web site. For the application I have to get the data from the server. For now I am using AsyncTasc .... doInBackground , in order to get the data in background ans display when they are downloaded.

But I two problems with that: 1. every time I change the orientation of the device the doInBackground starts all over again and the application crashes. ( I have put the orientation of the Activity into Portrait Mode but this is not the solution I want.

1. The data need to be downloaded all before I display them.

Can U please help me how can I improve this solution, or even to use another solution instead.

If its needed: I have used the code below:

private class GetNewsData extends
        AsyncTask<String, Void, ArrayList<DashBoardModel>> {

    protected void onPreExecute() {
        super.onPreExecute();
    }

    @Override
    protected ArrayList<DashBoardModel> doInBackground(String... URL) {

        String categories_url = URL[0]; // Creating JSON Parser instance
        JSONNumberParser jParser = new JSONNumberParser(); // getting JSON
                                                            // string from
        // URL
        JSONArray newsItems = jParser.getJSONFromUrl(categories_url);
        Log.e("lsbsfbsfdbsfd", newsItems.toString());
        try {
            for (int i = 0; i < newsItems.length(); i++) {

                JSONObject c = newsItems.getJSONObject(i);

                .....more code over here....

            }
        } catch (JSONException e) {
            e.printStackTrace();
        }
        .... more code over here...
        return items;
    }

    @Override
    protected void onPostExecute(ArrayList<DashBoardModel> items) {
        customModelAdapter.notifyDataSetChanged();
    }
}

And below is the JSonParser.class that I usually use:

public class JSONParser {

    static InputStream is = null;
    static JSONObject jObj = null;
    JSONArray jArr = null;
    static String json = "";

    // constructor
    public JSONParser() {

    }

    public JSONArray getJSONFromUrl(String url) {

        Log.e("JSON Parser", "U futem tek Jason " );

        // Making HTTP request
        try {
            // defaultHttpClient
            DefaultHttpClient httpClient = new DefaultHttpClient();
            HttpPost httpPost = new HttpPost(url);


            HttpResponse httpResponse = httpClient.execute(httpPost);

            HttpEntity httpEntity = httpResponse.getEntity();

            is = httpEntity.getContent();           
            Log.e("JSON Parser", "vajti " );
        } catch (UnsupportedEncodingException e) {
            e.printStackTrace();
        } catch (ClientProtocolException e) {
            e.printStackTrace();
        } catch (IOException e) {
            e.printStackTrace();
        }

        try {
            BufferedReader reader = new BufferedReader(new InputStreamReader(
                    is,  "UTF-8"), 8);
            StringBuilder sb = new StringBuilder();
            String line = null;
            while ((line = reader.readLine()) != null) {
                sb.append(line + "\n");
            }
            is.close();
            json = sb.toString();
            Log.e("JSON Parser", json );
        } catch (Exception e) {
            Log.e("Buffer Error", "Error converting result " + e.toString());
        }

        // try parse the string to a JSON object
        try {
            JSONTokener jt = new JSONTokener(json);
            Object rootElement = jt.nextValue();
            if (rootElement instanceof JSONObject) {
               // You got an object from the jresponse
                jObj = new JSONObject(json);
            } else if (rootElement instanceof JSONArray) {
                 jArr = new JSONArray(json);
                 Log.e("JSON Parser", "erdhi" );
                 return jArr;
               // You got a JSON array
            }
        } catch (JSONException e) {
            Log.e("JSON Parser", "Error parsing data " + e.toString());
        }

        // return JSON String
        return jArr;

    }
}

Answer 1

It's standard behavior on the Activity, your should leave it. What you can do to avoid double download is to cache the downloaded result somewhere, for instance in a Singleton class..so next time your AsyncTask runs it would check if there's already a 'cached' data, if so it would return immediately, else it would perform the download.

Usually we delegate this logic to another class, which is like a Singleton that is not influenced by the Activity lifecycle..so it wouldn't be affected.

The idea is to make the AsyncTask call a method on the singleton like: singleton.loadData() then it would internally do this logic of checking if there's already data cached or if it needs to download.