问题
I know that there are many posts about this particular error, but none of them are solving my issue and I am new to Android development. As a result of this error, I am unable to see the data in a listView for an app.
The following is my code:
public class JSONBuilderActivity extends ListActivity {
private ProgressDialog pDialog;
//URL to get JSON
private static String url = "http://"";
//JSON Node names
private static final String TAG_CARS = "cars"; //root
private static final String TAG_CARID = "car_id";
JSONArray carid = null; //Initializes JSON array
static String response = null;
//Hashmap for ListView
ArrayList<HashMap<String, String>>caridList;
@Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
ListView lv = getListView();
//Listview on item click listener
lv.setOnItemClickListener(new OnItemClickListener() {
@Override
public void onItemClick(AdapterView<?> parent, View view, int position, long id) {
//Gets values from selected ListItem
String cars = ((TextView) view.findViewById(R.id.cars)).getText().toString();
String car_id = ((TextView) view.findViewById(R.id.car_id)).getText().toString();
Intent in = new Intent(JSONBuilderActivity.this, MainActivity.class);
//getApplicationContext()
//sending data to new activity
in.putExtra("TAG_CARS", cars);
in.putExtra("TAG_CARID", car_id);
startActivity(in);
}
});
//Calls async task to get json
new GetCars().execute();
}
public class ServiceHandler {
public final static int GET = 1;
public final static int POST = 2;
public ServiceHandler() {
}
/**
* Makes service call
* @url - url to make request
* @method - http request method
* */
public String makeServiceCall(String url, int method) {
return this.makeServiceCall(url, method, null);
}
/**
* Makes service call
* @url - url to make request
* @method - http request method
* @params - http request params
* */
public String makeServiceCall(String url, int method,ArrayList<NameValuePair> params) {
try {
DefaultHttpClient httpClient = new DefaultHttpClient();
HttpEntity httpEntity = null;
HttpResponse httpResponse = null;
//Checks http request method type
if (method == POST) {
HttpPost httpPost = new HttpPost(url);
//Adds post params
if (params != null) {
httpPost.setEntity(new UrlEncodedFormEntity(params));
}
httpResponse = httpClient.execute(httpPost);
} else if (method == GET) {
//Appends params to url
if (params != null) {
String paramString = URLEncodedUtils.format(params, "utf-8");
url += "?" + paramString;
}
HttpGet httpGet = new HttpGet(url);
httpResponse = httpClient.execute(httpGet);
}
httpEntity = httpResponse.getEntity();
response = EntityUtils.toString(httpEntity);
} catch (UnsupportedEncodingException e) {
e.printStackTrace();
} catch (ClientProtocolException e) {
e.printStackTrace();
} catch (IOException e) {
e.printStackTrace();
}
return response;
}
}
/*
* Async task class to get json by making HTTP call
*/
private class GetCars extends AsyncTask<Void, Void, Void> {
@Override
protected void onPreExecute() {
super.onPreExecute();
caridList = new ArrayList<HashMap<String, String>>();
//Shows progress dialog
pDialog = new ProgressDialog(JSONBuilderActivity.this);
pDialog.setMessage("Please wait...");
pDialog.setCancelable(false);
pDialog.show();
}
@Override
protected Void doInBackground(Void... arg0) {
//Creates service handler class instance
ServiceHandler sh = new ServiceHandler();
//Makes a request to url and getting response
String jsonStr = sh.makeServiceCall(url, ServiceHandler.GET);
//Prints the json response in the log
Log.d("GetCars response: ", "> " + jsonStr);
//Prints array in app
if (jsonStr != null) {
try {
Log.d("try", "in the try");
JSONObject jsonObj = new JSONObject(jsonStr);
Log.d("jsonObject", "new json Object");
//Gets JSON Array node
carid = jsonObj.getJSONArray(TAG_CARS);
Log.d("json array", "user point array");
int len = carid.length();
Log.d("len", "get array length");
for (int i = 0; i < carid.length(); i++) {
JSONObject c = carid.getJSONObject(i);
String car_id = c.getString(TAG_CARID);
Log.d("car_id", car_id);
//Hashmap for single match
HashMap<String, String> matchGetCars = new HashMap<String, String>();
//Adds each child node to HashMap key => value
matchGetCars.put(TAG_CARID, car_id);
caridList.add(matchGetCars);
}
} catch (JSONException e) {
e.printStackTrace();
}
} else {
Log.e("ServiceHandler", "Couldn't get any data from the url");
}
return null;
}
@Override
protected void onPostExecute(Void result) {
super.onPostExecute(result);
//Dismisses the progress dialog
if (pDialog.isShowing())
pDialog.dismiss();
/**
* Updates parsed JSON data into ListView
* */
ListAdapter adapter = new SimpleAdapter(JSONBuilderActivity.this, caridList, R.layout.list_item,
new String[]{TAG_CARID}, new int[]{R.id.car_id});
setListAdapter(adapter);
Log.v("List parsed", caridList.toString());
}
}
}
I realize that an error is occurring near the following:
if (jsonStr != null) {
try {
Log.d("try", "in the try");
JSONObject jsonObj = new JSONObject(jsonStr);
Log.d("jsonObject", "new json Object");
//Gets JSON Array node
carid = jsonObj.getJSONArray(TAG_CARS);
Log.d("json array", "user point array");
int len = carid.length();
Log.d("len", "get array length");
for (int i = 0; i < carid.length(); i++) {
JSONObject c = carid.getJSONObject(i);
String car_id = c.getString(TAG_CARID);
Log.d("car_id", car_id);
//Hashmap for single match
HashMap<String, String> matchGetCars = new HashMap<String, String>();
//Adds each child node to HashMap key => value
matchGetCars.put(TAG_CARID, car_id);
caridList.add(matchGetCars);
}
} catch (JSONException e) {
e.printStackTrace();
}
} else {
Log.e("ServiceHandler", "Couldn't get any data from the url");
}
return null;
}
Here is the logcat data:
org.json.JSONException: No value for car_id
07-20 15:31:30.424 7567-7677/com.example.justin.myapplication W/System.err﹕ at org.json.JSONObject.get(JSONObject.java:354)
07-20 15:31:30.424 7567-7677/com.example.justin.myapplication W/System.err﹕ at org.json.JSONObject.getString(JSONObject.java:510)
07-20 15:31:30.424 7567-7677/com.example.justin.myapplication W/System.err﹕ at com.example.justin.myapplication.JSONBuilderActivity$GetCars.doInBackground(JSONBuilderActivity.java:202)
07-20 15:31:30.424 7567-7677/com.example.justin.myapplication W/System.err﹕ at com.example.justin.myapplication.JSONBuilderActivity$GetCars.doInBackground(JSONBuilderActivity.java:155)
07-20 15:31:30.431 7567-7677/com.example.justin.myapplication W/System.err﹕ at android.os.AsyncTask$2.call(AsyncTask.java:287)
07-20 15:31:30.431 7567-7677/com.example.justin.myapplication W/System.err﹕ at java.util.concurrent.FutureTask.run(FutureTask.java:234)
07-20 15:31:30.431 7567-7677/com.example.justin.myapplication W/System.err﹕ at android.os.AsyncTask$SerialExecutor$1.run(AsyncTask.java:230)
07-20 15:31:30.431 7567-7677/com.example.justin.myapplication W/System.err﹕ at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1080)
07-20 15:31:30.431 7567-7677/com.example.justin.myapplication W/System.err﹕ at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:573)
07-20 15:31:30.431 7567-7677/com.example.justin.myapplication W/System.err﹕ at java.lang.Thread.run(Thread.java:856)
07-20 15:31:30.455 7567-7567/com.example.justin.myapplication V/List parsed﹕ []
A brief view of what the JSON looks like:
{"cars":[{"id":1,"CarID":"20946"....so on...
I appreciate if any suggestions could be thoroughly explained and demonstrated as to why this error is occurring. Thank you greatly.
回答1:
Replace
private static final String TAG_CARID = "car_id";
with
private static final String TAG_CARID = "CarID";
You JSONArray has key "CarID", whereas you are searching for "car_id".
Hope this helps :)
回答2:
"cars" is jsonArray in the jsonObject. You must get the array first and then extract values from it. I cant give you code example right now, because I am currently on my phone.
来源：https://stackoverflow.com/questions/31525327/jsonexception-no-value-for-android-app