I have a rather specific question about JSON parsing in Android.
I have a requirement to download a single JSON array containing information in the format shown below, the number of JSON objects in the array is variable. I need to retrieve all the JSON values in the array so each JSON value has to be stored as an android list named after the common JSON keys because there are many instances of each, e.g. a list for placenames keys [place1,place2,place3 = placename list], a list for questions key, etc. A caveat to this is I cannot use an android array to store these JSON key values since each time my app runs this download task I don't know how many JSON objects will be in the single array. Users can submit as much as they want at any time to the database.
[
{
"placename": "place1",
"latitude": "50",
"longitude": "-0.5",
"question": "place1 existed when?",
"answer1": "1800",
"answer2": "1900",
"answer3": "1950",
"answer4": "2000",
"correctanswer": "1900"
},
{
"placename": "place2",
"latitude": "51",
"longitude": "-0.5",
"question": "place2 existed when?",
"answer1": "800",
"answer2": "1000",
"answer3": "1200",
"answer4": "1400",
"correctanswer": "800"
},
{
"placename": "place3",
"latitude": "52",
"longitude": "-1",
"question": "place 3 was established when?",
"answer1": "2001",
"answer2": "2005",
"answer3": "2007",
"answer4": "2009",
"correctanswer": "2009"
}
]
Below is my code for mainactivity which I managed to get working but had a derp moment and realised I'd simply gone through and parsed out the values for each JSON key in each object as a single string value for each JSON key. Since the loop iterates it merely overwrites at each stage - the placename string is "place1", then "place2", then "place3" by the end of the loop, rather than ["place1","place2", "place3"] which is what I want. My question now is how would I go about parsing the JSONArray to extract all instances of each JSON value and output as a string list for each JSON key, the length of the list is determined by the number of Objects?
I've already got the template for a string list that stores all the JSON key values (commented out in the below code) but I'm not sure how to fill that String list from the JSON parsing process.
I've had a good look around and couldn't find anything specifically about JSON Array to Android List so help would be greatly appreciated. I'd also like to know if there is a way of maintaining association between each list (e.g. questions & answers for specific placenames) if I bundle the data out to different activities (e.g. q&a to a quiz and placenames/lat/lon to GPS). Can I do this by referencing the same index in the list? Or would I need to store these lists in local storage? an SQL lite database?
Thanks for your time and sorry for the overwhelmingly long post!
public class MainActivity extends Activity {
// The JSON REST Service I will pull from
static String dlquiz = "http://www.example.php";
// Will hold the values I pull from the JSON
//static List<String> placename = new ArrayList<String>();
static String placename = "";
static String latitude = "";
static String longitude = "";
static String question = "";
static String answer1 = "";
static String answer2 = "";
static String answer3 = "";
static String answer4 = "";
static String correctanswer = "";
@Override
public void onCreate(Bundle savedInstanceState) {
// Get any saved data
super.onCreate(savedInstanceState);
// Point to the name for the layout xml file used
setContentView(R.layout.main);
// Call for doInBackground() in MyAsyncTask to be executed
new MyAsyncTask().execute();
}
// Use AsyncTask if you need to perform background tasks, but also need
// to change components on the GUI. Put the background operations in
// doInBackground. Put the GUI manipulation code in onPostExecute
private class MyAsyncTask extends AsyncTask<String, String, String> {
protected String doInBackground(String... arg0) {
// HTTP Client that supports streaming uploads and downloads
DefaultHttpClient httpclient = new DefaultHttpClient(new BasicHttpParams());
// Define that I want to use the POST method to grab data from
// the provided URL
HttpPost httppost = new HttpPost(dlquiz);
// Web service used is defined
httppost.setHeader("Content-type", "application/json");
// Used to read data from the URL
InputStream inputStream = null;
// Will hold the whole all the data gathered from the URL
String result = null;
try {
// Get a response if any from the web service
HttpResponse response = httpclient.execute(httppost);
// The content from the requested URL along with headers, etc.
HttpEntity entity = response.getEntity();
// Get the main content from the URL
inputStream = entity.getContent();
// JSON is UTF-8 by default
// BufferedReader reads data from the InputStream until the Buffer is full
BufferedReader reader = new BufferedReader(new InputStreamReader(inputStream, "UTF-8"), 8);
// Will store the data
StringBuilder theStringBuilder = new StringBuilder();
String line = null;
// Read in the data from the Buffer untilnothing is left
while ((line = reader.readLine()) != null)
{
// Add data from the buffer to the StringBuilder
theStringBuilder.append(line + "\n");
}
// Store the complete data in result
result = theStringBuilder.toString();
} catch (Exception e) {
e.printStackTrace();
}
finally {
// Close the InputStream when you're done with it
try{if(inputStream != null)inputStream.close();}
catch(Exception e){}
}
//Log.v("JSONParser RESULT ", result);
try {
JSONArray array = new JSONArray(result);
for(int i = 0; i < array.length(); i++)
{
JSONObject obj = array.getJSONObject(i);
//now, get whatever value you need from the object:
placename = obj.getString("placename");
latitude = obj.getString("latitude");
longitude = obj.getString("longitude");
question = obj.getString("question");
answer1 = obj.getString("answer1");
answer2 = obj.getString("answer2");
answer3 = obj.getString("answer3");
answer4 = obj.getString("answer4");
correctanswer = obj.getString("correctanswer");
}
} catch (JSONException e){
e.printStackTrace();
}
return result;
}
protected void onPostExecute(String result){
// Gain access so I can change the TextViews
TextView line1 = (TextView)findViewById(R.id.line1);
TextView line2 = (TextView)findViewById(R.id.line2);
TextView line3 = (TextView)findViewById(R.id.line3);
// Change the values for all the TextViews
line1.setText("Place Name: " + placename);
line2.setText("Question: " + question);
line3.setText("Correct Answer: " + correctanswer);
}
}
}
