How to reuse data from a JSONArray which got data in onPostExecute

Question

this is my code for getting data from a PHP site into a ListView.

package be.pressd.arrangementen;

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

import org.apache.http.HttpEntity;
import org.apache.http.HttpResponse;
import org.apache.http.NameValuePair;
import org.apache.http.client.HttpClient;
import org.apache.http.client.entity.UrlEncodedFormEntity;
import org.apache.http.client.methods.HttpPost;
import org.apache.http.impl.client.DefaultHttpClient;
import org.json.JSONArray;
import org.json.JSONObject;

import android.app.Activity;
import android.app.ProgressDialog;
import android.content.DialogInterface;
import android.content.DialogInterface.OnCancelListener;
import android.content.Intent;
import android.os.AsyncTask;
import android.os.Bundle;
import android.util.Log;
import android.view.View;
import android.view.View.OnClickListener;
import android.widget.AdapterView;
import android.widget.ArrayAdapter;
import android.widget.Button;
import android.widget.EditText;
import android.widget.ListView;
import android.widget.Toast;

public class MainActivity extends Activity implements OnClickListener{
    Button fetch;
    EditText et;
    String aantalPersonen; 

    private ListView lv;  
    private ArrayAdapter<String> listAdapter ; 

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);

        fetch = (Button) findViewById(R.id.fetchButton);
        et = (EditText) findViewById(R.id.aantalPersonen);

        // Find the ListView resource.     
        lv = (ListView) findViewById(R.id.arrangementenLijst);   
        listAdapter = new ArrayAdapter<String>(this, R.layout.line_row);  

        lv.setOnItemClickListener(new OnItemClickListener() {
            @Override
            public void onItemClick(AdapterView<?> parent, View view, int position, long id) {
                //Toast.makeText(getApplicationContext(), "Click nummer " + position, Toast.LENGTH_LONG).show();
                String arrangement = (String) lv.getItemAtPosition(position);

                // Launching new Activity on selecting single List Item
                Intent i = new Intent(getApplicationContext(), ArrangementItem.class);

                // sending data to new activity
                i.putExtra("arrangement", arrangement);
                startActivity(i);
            }

        });

        fetch.setOnClickListener(this);
    }

    class task extends AsyncTask<String, String, Void>
    {
        private ProgressDialog progressDialog = new ProgressDialog(MainActivity.this);
        InputStream is = null ;
        String result = "";


        protected void onPreExecute() {
            progressDialog.setMessage("Fetching data...");
            progressDialog.show();
            progressDialog.setOnCancelListener(new OnCancelListener() {

                @Override
                public void onCancel(DialogInterface arg0) {
                    task.this.cancel(true);
                }
            });
        }

        @Override
        protected Void doInBackground(String... params) {

            String url_select = "http://mywebsite/thephpform.php?aantpers=" + aantalPersonen;

            HttpClient httpClient = new DefaultHttpClient();
            HttpPost httpPost = new HttpPost(url_select);

            ArrayList<NameValuePair> param = new ArrayList<NameValuePair>();

            try 
            {
                httpPost.setEntity(new UrlEncodedFormEntity(param));

                HttpResponse httpResponse = httpClient.execute(httpPost);
                HttpEntity httpEntity = httpResponse.getEntity();

                //read content
                is =  httpEntity.getContent();                  

            } catch (Exception e) {

                Log.e("log_tag", "Error in http connection "+e.toString());
            }

            try {
                BufferedReader br = new BufferedReader(new InputStreamReader(is));
                StringBuilder sb = new StringBuilder();

                String line = "";

                while((line=br.readLine())!=null)
                {
                    sb.append(line+"\n");
                }

                is.close();
                result=sb.toString();               

            } catch (Exception e) {

                Log.e("log_tag", "Error converting result "+e.toString());
            }
            return null;
        }

        protected void onPostExecute(Void v) {

            try 
            {   listAdapter.clear();
                JSONArray Jarray = new JSONArray(result);

                for(int i=0; i < Jarray.length(); i++)
                {
                    JSONObject Jasonobject = null;
                    Jasonobject = Jarray.getJSONObject(i);

                    String name = Jasonobject.getString("naam");

                    listAdapter.add(name);
                }
                this.progressDialog.dismiss();

                lv.setAdapter( listAdapter);

            } catch (Exception e) {

                Log.e("log_tag", "Error parsing data "+e.toString());
            }
        }
    }

    @Override
    public void onClick(View v) {
        switch(v.getId()) {
            case R.id.fetchButton :

                aantalPersonen = et.getText().toString();
                if (aantalPersonen.trim().equals("")) {
                    Toast.makeText(this, "Gelieve het aantal personen in te geven", Toast.LENGTH_SHORT).show();
                    return;
                }
                else 
                {
                        new task().execute();
                        break;
                }       
        }
    }
}

It is my first Android code ever, so besides my question it is possible that this code can be made better.

What I would like to do is to show ALL data, nicely, which was gotten from the website. But, as a ListView can not contain the ID and other data, I'm wondering if I can reuse the data in the JSONObject to be shown in next screen (on click of ListView item) ?

Greetings and thanks in advance,

Davy

Answer 1

You could

• save the JSON and parse it again later (you would have to do a lot of parsing)
• save the data you parse from the json
  • in sharedpreferences (only if small amount of data)
  • in a local sqlite db (probably cleanest approach with best user experience, but a lot of work since you have to create a class that does all the db CRUD operations)

It depends on your data. For user preferences I would use SharedPreferences, for larger amounts a local DB. Also you could create some objects to store the data you need, maybe as signletons or something, and parse the stored JSONs everytime you start the app.

See the google docs on data storage for reference.

Answer 2

Create variables for which you want to store information and loop through JsonArray and get each JsonObject and parse/extract information that you need and store it in variables.

here is sample code to iterate JsonArray //Here response is JsonArray

Create Simple class like

 public class PersonInfo{

   String name,address; //Create variables of your requirement.


   //Add Getter Setter Methods for these variables

  }

//End of class PersonInfo

  ArrayList<PersonInfo> persons = new ArrayList<PersonInfo>();
  PersonInfo person;
  JSONObject product;


  try
   {
      for (int j = 0; j < response.length(); j++)
       {
          person = new Person();


          product = response.getJSONObject(j);

          person.name =  product.getString("JSON_KEY_NAME"); //like these assign values to each variable of PersonInfo class
          //Other values initialization
       }

     persons.add(person); // Add PersonInfo object to ArrayList        

  }
    catch (Exception e)
    {
           e.printStackTrace();
    }

something like that .

you can get json values upon your requirments. This is just sample code .

Answer 3

To save data you are getting in background task you have to use shared preferences.

Refer this link to get details about shared preferences.

To pass data to next page you have to use following code :

Intent intent = new Intent( currentActivity.this, NextActivity.class);
intent.putExtra("key", "value");
startActivity(intent);

On nextActivity.java add following code inside onCreate()

Intent currentPageIntent = getIntent();
String strValue = currentPageIntent.getStringExtra("key");

If you are having any other data type than string you have to use other method instead of getStringExtra()

To get id of item clicked, you can use following code :

list.setOnItemClickListener(new OnItemClickListener() {
        @Override
        public void onItemClick(AdapterView<?> parent, View view,
                int position, long id) {
            try {
                JSONArray jsonArray = new JSONArray(jsonData);                  

                if (jsonArray != null) {
                    for (int i = 0; i < jsonArray.length(); i++) {
                        if (i == id) {
                            //Add your code here
                        }
                    }
                }

            } catch (Exception e) {
                e.printStackTrace();
            } finally { }
        }
    });

Note that you have to process jsonData on your own. This is just sample code I used in one of my porjects.