Android, Web Services, AsyncTask please help a noo

Ive made edits since the orignal post Im making an android app that connects to an JSON API. Everything so far works ok except if there is a delay from the server. The UI of course can stop responding if it takes too long. Ive read that asynctask can solve my problem. Ive had a really ard time with the examples though.

Here is the restclient class making the http calls... parsing the json and storing custom objects to a public list that my other class can access.

package com.bde.dgcr;

import android.app.Activity;
import android.content.Context;
import android.os.AsyncTask;
import android.util.Log;
import android.view.View;
import android.widget.ListView;
import org.apache.http.HttpEntity;
import org.apache.http.HttpResponse;
import org.apache.http.client.ClientProtocolException;
import org.apache.http.client.HttpClient;
import org.apache.http.client.methods.HttpGet;
import org.apache.http.impl.client.DefaultHttpClient;
import org.json.JSONArray;
import org.json.JSONException;
import org.json.JSONObject;

import java.io.BufferedReader;
import java.io.IOException;
import java.io.InputStream;
import java.io.InputStreamReader;
import java.util.ArrayList;
import java.util.List;

public class RestClient {
static List<ResponseHolder> list = new ArrayList<ResponseHolder>();
protected Context context = this.context;

private static String convertStreamToString(InputStream is) {
    /*
       * To convert the InputStream to String we use the BufferedReader.readLine()
       * method. We iterate until the BufferedReader return null which means
       * there's no more data to read. Each line will appended to a StringBuilder
       * and returned as String.
       */
    BufferedReader reader = new BufferedReader(new InputStreamReader(is));
    StringBuilder sb = new StringBuilder();

    String line = null;
    try {
        while ((line = reader.readLine()) != null) {
            sb.append(line + "\n");
        }
    } catch (IOException e) {
        e.printStackTrace();
    } finally {
        try {
            is.close();
        } catch (IOException e) {
            e.printStackTrace();
        }
    }

    return sb.toString();
}


/* This is a test function which will connects to a given
  * rest service and prints it's response to Android Log with
  * labels "Praeda".
  */
public void  connect(String url) {


    AsyncTask<String, Void, Void> connection = new AsyncTask<String, Void, Void>() {
        protected Context context;
        @Override
        protected Void doInBackground(String... params) {
// Prepare a request object
            HttpGet httpget = new HttpGet(params[0]);

// Execute the request
            HttpResponse response;
            HttpClient httpclient = new DefaultHttpClient();
            try {
                list.clear();
                response = httpclient.execute(httpget);
                // Examine the response status
                Log.i("Praeda", response.getStatusLine().toString());

                // Get hold of the response entity
                HttpEntity entity = response.getEntity();
                // If the response does not enclose an entity, there is no need
                // to worry about connection release

                if (entity != null) {

                    // A Simple JSON Response Read
                    InputStream instream = entity.getContent();
                    String result = convertStreamToString(instream);

                    // A Simple JSONObject Creation
                    //JSONObject json= new JSONObject(result);
                    JSONArray jsonArray = new JSONArray(result);


                    // A Simple JSONObject Parsing
                    for (int i = 0; i < (jsonArray.length()); i++) {
                        JSONObject json_obj = jsonArray.getJSONObject(i);
                        ResponseHolder rh = new ResponseHolder(json_obj);
                        list.add(rh);
                    }


                    instream.close();

                }

            } catch (ClientProtocolException e) {
                // TODO Auto-generated catch block
                e.printStackTrace();
            } catch (IOException e) {
                // TODO Auto-generated catch block
                e.printStackTrace();
            } catch (JSONException e) {
                // TODO Auto-generated catch block
                e.printStackTrace();
            }

            return null;
        }

        @Override
        protected void onPostExecute(Void aVoid) {
             ListView listView1;


            super.onPostExecute(aVoid);    //To change body of overridden methods use       File | Settings | File Templates.
            ResponseHolderAdapter adapter = new ResponseHolderAdapter(context, R.layout.listview_item_row, RestClient.list);
            listView1 = (ListView) findViewById(R.id.listView1);

            View header = (View)         getLayoutInflater().inflate(R.layout.listview_header_row, null);
            listView1.addHeaderView(header);

            listView1.setAdapter(adapter);
        }
    };
    connection.execute(url);

}
}

Here is the class calling the static connect method and using the list for an adapter to go in a list view.

public class JsonGrabber extends Activity {


private final String API_KEY = "key";
private final String SECRET = "secret";
private String state;
private String city;
private String country;
private static String mode;
private String md5;
private String url;
CourseSearch cs;
private ListView listView1;

/**
 * Called when the activity is first created.
 */


public void onCreate(Bundle savedInstanceState) {

    super.onCreate(savedInstanceState);
    setContentView(R.layout.results);
    Bundle extras = getIntent().getExtras();
    state = extras.getString("state");
    city = URLEncoder.encode(extras.getString("city"));
    country = extras.getString("country");
    mode = extras.getString("mode");
    md5 = MD5.getMD5(API_KEY + SECRET + mode);
    System.out.println(md5);
    url = "http://www.api.com/?key=" + API_KEY + "&mode=" + mode + "&id=1&sig=" + md5;
    String findByLocUrl = "http://www.api.com/?key=" + API_KEY + "&mode=" + mode + "&city=" + city + "&state=" + state + "&country=" + country + "&sig=" + md5;
    System.out.println(findByLocUrl);
    RestClient rc = new RestClient();
    rc.connect(findByLocUrl);
    //RestClient.connect(findByLocUrl);
/*        if (RestClient.list.isEmpty())
    {
        setContentView(R.layout.noresults);
    }     else
    {

    ResponseHolderAdapter adapter = new ResponseHolderAdapter(this, R.layout.listview_item_row, RestClient.list);
    listView1 = (ListView) findViewById(R.id.listView1);

    View header = (View) getLayoutInflater().inflate(R.layout.listview_header_row, null);
    listView1.addHeaderView(header);

    listView1.setAdapter(adapter);
    }

 */
}


}

Somehow Im supposed to mesh all this up into using an innerclass extending asyctask to do the API calls in the background parse the json add to my list and set up the adapter. I know i may have some object orientation problems and was hoping before i continue on with my app that you guys can make sure im going in the right direction. I have a few other classes I didnt include. Let me know if it will make more sense if I added the other classes. Thanks In Advance for any help you guys/girls may be able to offer.

回答1:

You can rewrite your connect method using an AsyncTask like this:

public static void connect(String url) {

HttpClient httpclient = new DefaultHttpClient();

AsyncTask<String, Void, Void> connection = new AsyncTask<String, Void, Void>() {

@Override
protected Void doInBackground(String... params) {
// Prepare a request object
HttpGet httpget = new HttpGet(params[0]);

// Execute the request
HttpResponse response;
try {
    list.clear();

    response = httpclient.execute(httpget);
    // Examine the response status
    Log.i("Praeda", response.getStatusLine().toString());

    // Get hold of the response entity
    HttpEntity entity = response.getEntity();
    // If the response does not enclose an entity, there is no need
    // to worry about connection release

    if (entity != null) {

        // A Simple JSON Response Read
        InputStream instream = entity.getContent();
        String result= convertStreamToString(instream);

    // A Simple JSONObject Creation
    //JSONObject json= new JSONObject(result);
    JSONArray jsonArray = new JSONArray(result);


    // A Simple JSONObject Parsing
    for (int i = 0; i < (jsonArray.length()); i++) {
        JSONObject json_obj = jsonArray.getJSONObject(i);
        ResponseHolder rh = new ResponseHolder(json_obj);
        list.add(rh);
    }


     instream.close();
    }
    }
    } catch (ClientProtocolException e) {
    // TODO Auto-generated catch block
    e.printStackTrace();
    } catch (IOException e) {
    // TODO Auto-generated catch block
    e.printStackTrace();
} catch (JSONException e) {
    // TODO Auto-generated catch block
    e.printStackTrace();
}

connection.execute(url);
}

回答2:

If you want to do it right, you should use a contentprovider, service, and a database, here's a good tutorial:

http://mobile.tutsplus.com/tutorials/android/android-fundamentals-downloading-data-with-services/