Develop Reference

NullPointerException in adapter holding viewholders

ElementAdapter class
package com.example.sierendeelementeninbreda;
import android.content.Context;
import android.view.ViewGroup;
import android.util.Log;
import android.view.LayoutInflater;
import android.view.View;
import android.widget.ImageView;
import android.widget.TextView;
import androidx.annotation.NonNull;
import androidx.recyclerview.widget.RecyclerView;
import com.squareup.picasso.Picasso;
import java.util.ArrayList;
import java.util.List;
public class ElementAdapter extends RecyclerView.Adapter<ElementAdapter.ViewHolder> {
private static final String TAG = ElementAdapter.class.getSimpleName();
private List<Element> mElements = new ArrayList<>();
private final ElementOnClickHandler mElementClickHandler;
public ElementAdapter(List<Element> mElements, ElementOnClickHandler mElementClickHandler) {
this.mElements = mElements;
this.mElementClickHandler = mElementClickHandler;
}
#NonNull
#Override
public ElementAdapter.ViewHolder onCreateViewHolder(ViewGroup viewGroup, int viewType) {
Log.v(TAG, "++++++++ onCreateViewHolder - viewGroup-class: " + viewGroup.getClass().getSimpleName());
Log.v(TAG, "++++++++ onCreateViewHolder - viewGroup-resourceName: " + viewGroup.getContext().getResources().getResourceName(viewGroup.getId()));
Log.v(TAG, "++++++++ onCreateViewHolder - viewGroup-resourceEntryName: " + viewGroup.getContext().getResources().getResourceEntryName(viewGroup.getId()));
Context context = viewGroup.getContext();
LayoutInflater inflator = LayoutInflater.from(context);
// create a new view
View elementListItem = inflator.inflate(R.layout.element_item, viewGroup, false);
ElementAdapter.ViewHolder viewHolder = new ViewHolder(elementListItem);
return viewHolder;
}
#Override
public void onBindViewHolder(ViewHolder holder, int position) {
Log.v(TAG, "++++ onBindViewHolder-type: " + holder.getClass().getSimpleName());
holder.title.setText(mElements.get(position).getTitle());
holder.geographicalLocation.setText(mElements.get(position).getGeographicalLocation());
holder.identificationNumber.setText(mElements.get(position).getIdentificationNumber());
Picasso.get()
.load(mElements.get(position).getImage())
.into(holder.image);
}
#Override
public int getItemCount() {
return mElements.size();
}
public class ViewHolder extends RecyclerView.ViewHolder implements View.OnClickListener {
//one drinkItem has 3 views
// Provide a reference to each view in the drinkItem
private ImageView image;
private TextView title;
private TextView geographicalLocation;
private TextView identificationNumber;
public ViewHolder(View listItemView) {
super(listItemView);
title = (TextView) listItemView.findViewById(R.id.element_item_name);
geographicalLocation = (TextView) listItemView.findViewById(R.id.element_Location);
identificationNumber = (TextView) listItemView.findViewById(R.id.element_idNumber);
image = (ImageView) listItemView.findViewById(R.id.element_item_imageview);
// image.setOnClickListener(this);
// name.setOnClickListener(this);
// description.setOnClickListener(this);
// listItemView.setOnClickListener(this);
}
#Override
public void onClick(View view) {
int itemIndex = getAdapterPosition();
mElementClickHandler.onElementClick(view, itemIndex);
}
}
}
NetworkUtils class
package com.example.sierendeelementeninbreda;
import android.os.AsyncTask;
import android.util.Log;
import org.json.JSONArray;
import org.json.JSONException;
import org.json.JSONObject;
import java.io.IOException;
import java.io.InputStream;
import java.net.HttpURLConnection;
import java.net.MalformedURLException;
import java.net.URL;
import java.net.URLConnection;
import java.util.ArrayList;
import java.util.Scanner;
public class NetworkUtils extends AsyncTask<String, Void, String> {
private static final String TAG = NetworkUtils.class.getSimpleName();
private OnElementApiListener listener;
private final static String url = "https://services7.arcgis.com/21GdwfcLrnTpiju8/arcgis/rest/services/Sierende_elementen/FeatureServer/0/query?where=1%3D1&outFields=*&outSR=4326&f=json";
public NetworkUtils(OnElementApiListener listener) {
this.listener = listener;
}
#Override
protected String doInBackground(String... input) {
//De methode begint met een log zodat je kunt zien wat er gebeurt in de run.
Log.d(TAG, "doInBackground was called");
String response = null;
HttpURLConnection httpURLConnection = null;
// ToDo: Url maken op basis van internet adres
try {
URL mUrl = new URL(url);
URLConnection mConnection = mUrl.openConnection();
httpURLConnection = (HttpURLConnection) mConnection;
httpURLConnection.setRequestMethod("GET");
httpURLConnection.setRequestProperty("Content-Type", "application/json");
httpURLConnection.connect();
int responseCode = httpURLConnection.getResponseCode();
if(responseCode != HttpURLConnection.HTTP_OK){
Log.e(TAG, "Aanroep naar de server is mislukt!");
} else {
InputStream in = httpURLConnection.getInputStream();
Scanner scanner = new Scanner(in);
scanner.useDelimiter("\\A");
boolean hasInput = scanner.hasNext();
if (hasInput) {
response = scanner.next();
}
}
Log.d(TAG, response);
} catch (MalformedURLException e) {
e.printStackTrace();
} catch (IOException e) {
e.printStackTrace();
} finally {
if(httpURLConnection != null)
httpURLConnection.disconnect();
}
return response;
}
#Override
protected void onPreExecute() {
super.onPreExecute();
Log.d(TAG, "onPreExecute: ");
}
#Override
protected void onPostExecute(String response) {
super.onPostExecute(response);
Log.i(TAG, "createElementFromJson called");
ArrayList<Element> elements = new ArrayList<>();
if (response == null || response.equals("")) {
Log.e(TAG, "onPostExecute: empty response!");
return;
}
try {
JSONObject jsonResults = new JSONObject(response);
JSONArray elementList = jsonResults.getJSONArray("features");
Log.d(TAG, "onPostExecute: " + jsonResults);
Log.i(TAG, "elementArray length = " + elementList.length());
for(int i = 0; i < elementList.length(); i++) {
JSONObject element = elementList.getJSONObject(i);
//all info
JSONObject elementAttributes = element.getJSONObject("attributes");
String image = elementAttributes.getString("URL");
String title = elementAttributes.getString("AANDUIDINGOBJECT");
String geographicalLocation = elementAttributes.getString("GEOGRAFISCHELIGGING");
String identificationNumber = elementAttributes.getString("IDENTIFICATIE");
Element element_item = new Element(title, geographicalLocation, identificationNumber);
element_item.setImage(image);
elements.add(element_item);
Log.i(TAG, String.valueOf(elements.size()));
}
listener.onElementAvailable(elements);
} catch (JSONException e) {
e.printStackTrace();
}
}
public interface OnElementApiListener {
void onElementAvailable(ArrayList<Element> elements);
}
MainActivity class
package com.example.sierendeelementeninbreda;
import androidx.appcompat.app.AppCompatActivity;
import androidx.recyclerview.widget.LinearLayoutManager;
import androidx.recyclerview.widget.RecyclerView;
import android.content.Context;
import android.os.Bundle;
import android.util.Log;
import android.view.View;
import android.widget.Toast;
import java.util.ArrayList;
public class MainActivity extends AppCompatActivity
implements View.OnClickListener,NetworkUtils.OnElementApiListener,
ElementOnClickHandler{
private static String TAG = MainActivity.class.getName();
private final static String url = "https://services7.arcgis.com/21GdwfcLrnTpiju8/arcgis/rest/services/Sierende_elementen/FeatureServer/0/query?where=1=1&outFields=&outSR=4326&f=json";
private ArrayList<Element> mElementList;
private RecyclerView elementRecyclerView;
private ElementAdapter mElementAdapter;
#Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
elementRecyclerView= findViewById(R.id.recyclerView_element_list);
elementRecyclerView.setLayoutManager(new LinearLayoutManager(this));
mElementAdapter = new ElementAdapter(mElementList,this);
elementRecyclerView.setAdapter(mElementAdapter);
// Start background task
NetworkUtils networkingTask = new NetworkUtils(this);
networkingTask.execute(url);
}
#Override
public void onElementAvailable(ArrayList<Element> elements) {
Log.i(TAG, "elements = " + elements.size());
this.mElementList = new ArrayList<>();
mElementList.clear();
mElementList.addAll(elements);
mElementAdapter.notifyDataSetChanged();
Log.i(TAG, "new elements = " + mElementList.size());
}
#Override
public void onElementClick(View view, int itemIndex) {
Log.v(TAG, "clicked on " + view.getClass().getSimpleName());
int viewId = view.getId();
Context context = this;
String toastMessage = "";
// if (viewId == R.id.product_imageview) {
// toastMessage = "clicked on image of drink item";
// } else if (viewId == R.id.product_item_name || viewId == R.id.product_item_description) {
// toastMessage = "clicked on name or description of drink item";
// } else if (viewId == R.id.product_list_item) {
// toastMessage = "clicked on drink list-item nr: " + itemIndex;
// }
Toast.makeText(context, toastMessage, Toast.LENGTH_LONG)
.show();
}
#Override
public void onClick(View v) {
}
}
Error
D/NetworkUtils: onPreExecute:
D/NetworkUtils: doInBackground was called
D/HostConnection: HostConnection::get() New Host Connection established 0xd4a13c30, tid 27630
D/HostConnection: HostComposition ext ANDROID_EMU_CHECKSUM_HELPER_v1 ANDROID_EMU_native_sync_v2 ANDROID_EMU_native_sync_v3 ANDROID_EMU_native_sync_v4 ANDROID_EMU_dma_v1 ANDROID_EMU_direct_mem ANDROID_EMU_host_composition_v1 ANDROID_EMU_host_composition_v2 ANDROID_EMU_YUV420_888_to_NV21 ANDROID_EMU_YUV_Cache ANDROID_EMU_async_unmap_buffer GL_OES_EGL_image_external_essl3 GL_OES_vertex_array_object GL_KHR_texture_compression_astc_ldr ANDROID_EMU_gles_max_version_3_0
D/AndroidRuntime: Shutting down VM
E/AndroidRuntime: FATAL EXCEPTION: main
Process: com.example.sierendeelementeninbreda, PID: 27595
java.lang.NullPointerException: Attempt to invoke interface method 'int java.util.List.size()' on a null object reference
at com.example.sierendeelementeninbreda.ElementAdapter.getItemCount(ElementAdapter.java:64)
at androidx.recyclerview.widget.RecyclerView.dispatchLayoutStep1(RecyclerView.java:4044)
at androidx.recyclerview.widget.RecyclerView.dispatchLayout(RecyclerView.java:3849)
at androidx.recyclerview.widget.RecyclerView.onLayout(RecyclerView.java:4404)
at android.view.View.layout(View.java:21912)
at android.view.ViewGroup.layout(ViewGroup.java:6260)
That is the error I get when I run the app, I have tried solving this by looking things up but it is not working. The NullPointerException happens in line 64 of my adapter class. The app basically uses an API to get data from a site and then showcases it in a recylerView.

your not init mElementList before passed to adapter so when adapter call size method
will throw null pointer
edit your code here
#Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
elementRecyclerView= findViewById(R.id.recyclerView_element_list);
elementRecyclerView.setLayoutManager(new LinearLayoutManager(this));
// init mElementList here
mElementList = new ArrayList<>();
mElementAdapter = new ElementAdapter(mElementList,this);
elementRecyclerView.setAdapter(mElementAdapter);
// Start background task
NetworkUtils networkingTask = new NetworkUtils(this);
networkingTask.execute(url);
}

It is always better to do null check
#Override
public int getItemCount() {
if(mElements!=null)
return mElements.size();
else return 0
}
and initialize mElements in constructor

Getting json response in log.d but not inside app (code included)

I am trying to use the ProductHunt API to display a list of new posts in a ListView and further expand the list item on click.
On opening the app, the Progress bar appears but after that the app screen stays blank. I think there might be some error in my OnPostExecute method, because when I added a textview to display a string, its getting displayed but my listView is not getting displayed.
I used the standard Apache HttpClient for handling api requests.
I have 4 classes,
MainActivity.java
package com.emoji.apisoup;
/**
* Created by mdhalim on 16/05/16.
*/
import java.io.IOException;
import java.util.ArrayList;
import org.json.JSONArray;
import org.json.JSONException;
import org.json.JSONObject;
import android.app.Activity;
import android.app.ProgressDialog;
import android.content.Intent;
import android.os.AsyncTask;
import android.os.Bundle;
import android.util.Log;
import android.view.View;
import android.widget.AdapterView;
import android.widget.ListView;
import org.apache.http.HttpClientConnection;
import org.apache.http.HttpResponse;
import org.apache.http.auth.AuthScope;
import org.apache.http.auth.UsernamePasswordCredentials;
import org.apache.http.client.ClientProtocolException;
import org.apache.http.client.HttpClient;
import org.apache.http.client.ResponseHandler;
import org.apache.http.client.methods.HttpGet;
import org.apache.http.client.methods.HttpPost;
import org.apache.http.entity.StringEntity;
import org.apache.http.impl.client.BasicResponseHandler;
import org.apache.http.impl.client.DefaultHttpClient;
import org.apache.http.message.BasicHttpResponse;
import org.apache.http.protocol.HTTP;
public class MainActivity extends Activity {
private ListView lvPosts;
private ProductHuntAdapter adapterPosts;
public static final String POST_DETAIL_KEY = "posts";
private ProgressDialog pDialog;
#Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.phunt_main);
String serverURL = "https://api.producthunt.com/v1/posts/";
ArrayList<ProductHuntList> aPosts = new ArrayList<ProductHuntList>();
adapterPosts = new ProductHuntAdapter(MainActivity.this, aPosts);
lvPosts = (ListView) findViewById(R.id.lvPosts);
lvPosts.setOnItemClickListener(new AdapterView.OnItemClickListener() {
#Override
public void onItemClick(AdapterView<?> parent, View view, int position, long id) {
{
Intent i = new Intent(MainActivity.this, ProductHuntDetail.class);
i.putExtra(POST_DETAIL_KEY, adapterPosts.getItem(position));
startActivity(i);
}
}
});
new LongOperation().execute(serverURL);
}
private class LongOperation extends AsyncTask<String, Void, Void> {
private final HttpClient Content = new DefaultHttpClient();
private String Error = null;
#Override
protected void onPreExecute() {
super.onPreExecute();
// Showing progress dialog
pDialog = new ProgressDialog(MainActivity.this);
pDialog.setMessage("Please wait...");
pDialog.setCancelable(false);
pDialog.show();
}
protected Void doInBackground(String... urls){
JSONArray items = null;
try {
HttpGet httpget = new HttpGet(urls[0]);
httpget.setHeader("Accept","application/json");
httpget.setHeader("Content-Type","application/json");
httpget.setHeader("Authorization","Bearer 2587aa878d7334e3c89794a6b73ebffb59a06c23b82cd0f789d2ab72d2417739");
ResponseHandler<String> responseHandler = new BasicResponseHandler();
String jsonStr = Content.execute(httpget, responseHandler);
Log.d("Response: ", "> " + jsonStr);
JSONObject jsonObj = new JSONObject(jsonStr);
items = jsonObj.getJSONArray("posts");
// Parse json array into array of model objects
ArrayList<ProductHuntList> posts = ProductHuntList.fromJson(items);
// Load model objects into the adapter
for (ProductHuntList post : posts) {
adapterPosts.add(post);
}
} catch (JSONException e) {
e.printStackTrace();
} catch (IOException e) {
Error = e.getMessage();
cancel(true);
}
return null;
}
#Override
protected void onPostExecute(Void result) {
super.onPostExecute(result);
// Dismiss the progress dialog
if (pDialog.isShowing())
pDialog.dismiss();
ArrayList<ProductHuntList> aPosts = new ArrayList<ProductHuntList>();
adapterPosts = new ProductHuntAdapter(MainActivity.this, aPosts);
lvPosts.setAdapter(adapterPosts);
}
}
}
ProductHuntList.java containing the JSON Data model and deserializer and a static method for parsing an array of JSON
package com.emoji.apisoup;
import org.json.JSONArray;
import org.json.JSONException;
import org.json.JSONObject;
import java.util.ArrayList;
import java.io.Serializable;
/**
* Created by mdhalim on 18/05/16.
*/
public class ProductHuntList implements Serializable {
private static final long serialVersionUID = -8959832007991513854L;
private String name;
private String tagline;
private String screenshot_url;
private String largePosterUrl;
private String discussion_Url;
private String created_at;
private int votes_count;
public String getNames() {
return name;
}
public String getCreated_at() {
return created_at;
}
public String getScreenshot_url() {
return screenshot_url;
}
public String getDiscussion_Url() {
return discussion_Url;
}
public int getVotes_count() {
return votes_count;
}
public String getLargePosterUrl() {
return largePosterUrl;
}
public String getTagline(){
return tagline;
}
public static ProductHuntList fromJson(JSONObject jsonObject) {
ProductHuntList b = new ProductHuntList();
try {
// Deserialize json into object fields
b.name = jsonObject.getString("name");
b.created_at = jsonObject.getString("created_at");
b.tagline = jsonObject.getString("tagline");
b.screenshot_url = jsonObject.getJSONObject("screenshot_url").getString("300px");
b.largePosterUrl = jsonObject.getJSONObject("screenshot_url").getString("850px");
b.votes_count = jsonObject.getInt("votes_count");
b.discussion_Url = jsonObject.getString("discussion_url");
} catch (JSONException e) {
e.printStackTrace();
return null;
}
// Return new object
return b;
}
public static ArrayList<ProductHuntList> fromJson(JSONArray jsonArray) {
ArrayList<ProductHuntList> posts = new ArrayList<ProductHuntList>(jsonArray.length());
for (int i = 0; i < jsonArray.length(); i++) {
JSONObject productJson = null;
try {
productJson = jsonArray.getJSONObject(i);
} catch (Exception e) {
e.printStackTrace();
continue;
}
ProductHuntList post = ProductHuntList.fromJson(productJson);
if (post != null)
{
posts.add(post);
}
}
return posts;
}
}
ProductHuntAdapter.java this implements the ArrayAdapter
package com.emoji.apisoup;
/**
* Created by mdhalim on 18/05/16.
*/
import android.content.Context;
import android.view.LayoutInflater;
import android.view.View;
import android.view.ViewGroup;
import android.widget.ArrayAdapter;
import android.widget.ImageView;
import android.widget.TextView;
import com.squareup.picasso.Picasso;
import java.util.ArrayList;
/**
* Created by mdhalim on 18/05/16.
*/
public class ProductHuntAdapter extends ArrayAdapter<ProductHuntList> {
public ProductHuntAdapter(Context context, ArrayList<ProductHuntList> aPosts) {
super(context, 0, aPosts);
}
#Override
public View getView(int position, View convertView, ViewGroup parent) {
// Get the data item for this position
ProductHuntList posts = getItem(position);
// Check if an existing view is being reused, otherwise inflate the view
if (convertView == null) {
LayoutInflater inflater = LayoutInflater.from(getContext());
convertView = inflater.inflate(R.layout.item_product_hunt, null);
}
// Lookup view for data population
TextView name = (TextView) convertView.findViewById(R.id.name);
TextView created = (TextView) convertView.findViewById(R.id.created);
TextView tagline = (TextView) convertView.findViewById(R.id.tagline);
ImageView ivPosterImage = (ImageView) convertView.findViewById(R.id.ivPosterImage);
// Populate the data into the template view using the data object
name.setText(posts.getNames());
created.setText("Created On: " + posts.getCreated_at() + "%");
tagline.setText(posts.getTagline());
Picasso.with(getContext()).load(posts.getScreenshot_url()).into(ivPosterImage);
// Return the completed view to render on screen
return convertView;
}
}
and finally, a class implementing the activity for Item Details when a user clicks on any item on the list.
ProductHuntDetail
package com.emoji.apisoup;
/**
* Created by mdhalim on 18/05/16.
*/
import android.annotation.SuppressLint;
import android.app.Activity;
import android.os.Bundle;
import android.text.Html;
import android.widget.ImageView;
import android.widget.TextView;
import com.squareup.picasso.Picasso;
public class ProductHuntDetail extends Activity {
private ImageView ivPosterImage;
private TextView name;
private TextView discusUrl;
private TextView upvotes;
private TextView tagline;
private TextView created;
#Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.product_hunt_detail);
// Fetch views
ivPosterImage = (ImageView) findViewById(R.id.ivPosterImage);
name = (TextView) findViewById(R.id.name);
discusUrl = (TextView) findViewById(R.id.discusUrl);
created = (TextView) findViewById(R.id.created);
upvotes = (TextView) findViewById(R.id.upvotes);
tagline = (TextView) findViewById(R.id.tagline);
// Load movie data
ProductHuntList posts = (ProductHuntList) getIntent().getSerializableExtra(MainActivity.POST_DETAIL_KEY);
loadMovie(posts);
}
// Populate the data for the movie
#SuppressLint("NewApi")
public void loadMovie(ProductHuntList posts) {
// Populate data
name.setText(posts.getNames());
upvotes.setText(Html.fromHtml("<b>Upvotes:</b> " + posts.getVotes_count() + "%"));
created.setText(posts.getCreated_at());
tagline.setText(posts.getTagline());
discusUrl.setText(Html.fromHtml("<b>Discussion Url:</b> " + posts.getDiscussion_Url()));
// R.drawable.large_movie_poster from
// http://content8.flixster.com/movie/11/15/86/11158674_pro.jpg -->
Picasso.with(this).load(posts.getLargePosterUrl()).
placeholder(R.drawable.large_movie_poster).
into(ivPosterImage);
}
}
I have been trying to debug this for hours :/

Your Async task is returning a void.
protected void onPostExecute(Void result) {
super.onPostExecute(result);
// Dismiss the progress dialog
if (pDialog.isShowing())
pDialog.dismiss();
ArrayList<ProductHuntList> aPosts = new ArrayList<ProductHuntList>();
adapterPosts = new ProductHuntAdapter(MainActivity.this, aPosts);
lvPosts.setAdapter(adapterPosts);
}
As far as I can tell from the code, aPosts is empty.
I think your Async task should be -
AsyncTask<String, Void, ProductHuntAdapter>
and remove -
adapterPosts = new ProductHuntAdapter(MainActivity.this, aPosts);
You are creating and updating this in your doInBackground() method already.

I got it!
I didnt need to declare these lines again in my onPostExecute() method
ArrayList<ProductHuntList> aPosts = new ArrayList<ProductHuntList>();
adapterPosts = new ProductHuntAdapter(MainActivity.this, aPosts);
So bascially, my new onPostExecute() method goes like this
protected void onPostExecute(Void result) {
super.onPostExecute(result);
// Dismiss the progress dialog
if (pDialog.isShowing())
pDialog.dismiss();
lvPosts.setAdapter(adapterPosts);
}
I had been trying to find this error for last 2 hours, it was harder since, I wasn't even getting any errors. As soon as I posted it on StackOverFlow, seems like I had a divine intervention.

AsyncTask and MainActivity in separated files

I'm trying to separate my AsyncTask class and MainActivity class by putting them in other files.
Here is my fully-working program:
package com.example.kamilh.pierwsza;
import android.location.Address;
import android.location.Criteria;
import android.location.Geocoder;
import android.location.Location;
import android.location.LocationManager;
import android.os.AsyncTask;
import android.os.Bundle;
import android.support.v7.app.ActionBarActivity;
import android.view.Menu;
import android.view.MenuItem;
import android.view.View;
import android.widget.EditText;
import android.widget.TextView;
import android.widget.Toast;
import java.io.BufferedReader;
import java.io.IOException;
import java.io.InputStreamReader;
import java.net.MalformedURLException;
import java.net.URL;
import java.util.List;
import java.util.Locale;
public class MainActivity extends ActionBarActivity {
String region = null;
#Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
}
#Override
public boolean onCreateOptionsMenu(Menu menu) {
// Inflate the menu; this adds items to the action bar if it is present.
getMenuInflater().inflate(R.menu.menu_main, menu);
return true;
}
#Override
public boolean onOptionsItemSelected(MenuItem item) {
// Handle action bar item clicks here. The action bar will
// automatically handle clicks on the Home/Up button, so long
// as you specify a parent activity in AndroidManifest.xml.
int id = item.getItemId();
//noinspection SimplifiableIfStatement
if (id == R.id.action_settings) {
return true;
}
return super.onOptionsItemSelected(item);
}
private void getRegion()
{
TextView textView = (TextView) findViewById(R.id.textView3);
Criteria cr = new Criteria();
LocationManager lm = (LocationManager) getSystemService(LOCATION_SERVICE);
Location loc = lm.getLastKnownLocation(lm.getBestProvider(cr, true));
double lat = loc.getLatitude();
double lon = loc.getLongitude();
new Region().execute(lat, lon);
textView.setText(region);
}
public void count(View view) throws IOException {
EditText editText = (EditText) findViewById(R.id.editText);
EditText editText2 = (EditText) findViewById(R.id.editText2);
double cost = 5.25;
double petrol = Double.valueOf(editText.getText().toString());
double distance = Double.valueOf(editText2.getText().toString());
double result = Math.round(cost*(distance/100)*petrol);
//textView.setText("The cost of your trip is: "+String.valueOf(result)+" zł");
getRegion();
}
private class Region extends AsyncTask<Double, Void, String> {
#Override
public String doInBackground(Double... params) {
URL url = null;
BufferedReader in = null;
try {
url = new URL("https://maps.googleapis.com/maps/api/geocode/json?latlng="+params[0]+","+params[1]);
} catch (MalformedURLException e) {
e.printStackTrace();
}
try {
if (url != null) {
in = new BufferedReader(new InputStreamReader(url.openStream()));
}
} catch (IOException e) {
e.printStackTrace();
}
String line = null;
String x = null;
for (int i = 0; i<31; i++){
if (in != null) {
try {
line = in.readLine();
} catch (IOException e) {
e.printStackTrace();
}
}
}
return line;
}
#Override
protected void onPostExecute(String result) {
super.onPostExecute(result);
region = result;
}
}
Now, I'd like to be able to clean up a bit my code, so I decided to separate those two classes. I saw this example (above) and I tried to implement this solution in my project, but i failed.
Android: How to run asynctask from different class file?
Here are my MainActivity class:
package com.example.kamilh.pierwsza;
import android.location.Criteria;
import android.location.Location;
import android.location.LocationManager;
import android.os.Bundle;
import android.support.v7.app.ActionBarActivity;
import android.view.Menu;
import android.view.MenuItem;
import android.view.View;
import android.widget.EditText;
import android.widget.TextView;
import java.io.IOException;
public class MainActivity extends ActionBarActivity {
#Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
}
#Override
public boolean onCreateOptionsMenu(Menu menu) {
// Inflate the menu; this adds items to the action bar if it is present.
getMenuInflater().inflate(R.menu.menu_main, menu);
return true;
}
#Override
public boolean onOptionsItemSelected(MenuItem item) {
// Handle action bar item clicks here. The action bar will
// automatically handle clicks on the Home/Up button, so long
// as you specify a parent activity in AndroidManifest.xml.
int id = item.getItemId();
//noinspection SimplifiableIfStatement
if (id == R.id.action_settings) {
return true;
}
return super.onOptionsItemSelected(item);
}
public void getRegion(String result)
{
TextView textView = (TextView) findViewById(R.id.textView3);
textView.setText(result);
}
public void count(View view) throws IOException {
EditText editText = (EditText) findViewById(R.id.editText);
EditText editText2 = (EditText) findViewById(R.id.editText2);
double cost = 5.25;
double petrol = Double.valueOf(editText.getText().toString());
double distance = Double.valueOf(editText2.getText().toString());
double result = Math.round(cost*(distance/100)*petrol);
//textView.setText("The cost of your trip is: "+String.valueOf(result)+" zł");
Criteria cr = new Criteria();
LocationManager lm = (LocationManager) getSystemService(LOCATION_SERVICE);
Location loc = lm.getLastKnownLocation(lm.getBestProvider(cr, true));
double lat = loc.getLatitude();
double lon = loc.getLongitude();
new Region(this).execute(lat, lon);
}
}
Here is my Region class:
package com.example.kamilh.pierwsza;
import android.content.Context;
import android.os.AsyncTask;
import java.io.BufferedReader;
import java.io.IOException;
import java.io.InputStreamReader;
import java.net.MalformedURLException;
import java.net.URL;
/**
* Created by KamilH on 2015-02-19.
*/
class Region extends AsyncTask<Double, Void, String> {
private Context context;
MainActivity activity;
public Region (Context context){
this.context = context;
}
#Override
public String doInBackground(Double... params) {
URL url = null;
BufferedReader in = null;
try {
url = new URL("https://maps.googleapis.com/maps/api/geocode/json?latlng="+params[0]+","+params[1]);
} catch (MalformedURLException e) {
e.printStackTrace();
}
try {
if (url != null) {
in = new BufferedReader(new InputStreamReader(url.openStream()));
}
} catch (IOException e) {
e.printStackTrace();
}
String line = null;
String x = null;
for (int i = 0; i<31; i++){
if (in != null) {
try {
line = in.readLine();
} catch (IOException e) {
e.printStackTrace();
}
}
}
return line;
}
#Override
protected void onPostExecute(String result) {
super.onPostExecute(result);
activity.getRegion(result);
}
}
After I run the app with separated files I get those errors:
02-19 14:42:39.793 13842-13842/com.example.kamilh.pierwsza E/AndroidRuntime﹕ FATAL EXCEPTION: main
Process: com.example.kamilh.pierwsza, PID: 13842
java.lang.NullPointerException
at com.example.kamilh.pierwsza.Region.onPostExecute(Region.java:57)
at com.example.kamilh.pierwsza.Region.onPostExecute(Region.java:15)
at android.os.AsyncTask.finish(AsyncTask.java:632)
at android.os.AsyncTask.access$600(AsyncTask.java:177)
at android.os.AsyncTask$InternalHandler.handleMessage(AsyncTask.java:645)
at android.os.Handler.dispatchMessage(Handler.java:102)
at android.os.Looper.loop(Looper.java:157)
at android.app.ActivityThread.main(ActivityThread.java:5867)
at java.lang.reflect.Method.invokeNative(Native Method)
at java.lang.reflect.Method.invoke(Method.java:515)
at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:858)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:674)
at dalvik.system.NativeStart.main(Native Method)
Could you please, tell me how to fix it?

Change your Region class to this:
package com.example.kamilh.pierwsza;
import android.os.AsyncTask;
import java.io.BufferedReader;
import java.io.IOException;
import java.io.InputStreamReader;
import java.net.MalformedURLException;
import java.net.URL;
/**
* Created by KamilH on 2015-02-19.
*/
class Region extends AsyncTask<Double, Void, String> {
private MainActivity activity;
public Region (MainActivity activity){
this.activity = activity;
}
#Override
public String doInBackground(Double... params) {
URL url = null;
BufferedReader in = null;
try {
url = new URL("https://maps.googleapis.com/maps/api/geocode/json?latlng="+params[0]+","+params[1]);
} catch (MalformedURLException e) {
e.printStackTrace();
}
try {
if (url != null) {
in = new BufferedReader(new InputStreamReader(url.openStream()));
}
} catch (IOException e) {
e.printStackTrace();
}
String line = null;
String x = null;
for (int i = 0; i<31; i++){
if (in != null) {
try {
line = in.readLine();
} catch (IOException e) {
e.printStackTrace();
}
}
}
return line;
}
#Override
protected void onPostExecute(String result) {
super.onPostExecute(result);
activity.getRegion(result);
}
}
Why? Well. You call getRegion on activity in the onPostExecute. But activity is never initialised. And since you want it to call that method in the MainActivity where you did new Region(this), the constructor has to be changed. Since you don't use the Context, we remove that and replace it by MainActivity and make sure it gives the value to the activity field in your class.
Note that an Activity is a subclass of Context. And that this in the activity is the activity and thus a context. Not that you need it here.
It could also be good to look into callback routines. It is what you're doing here, but it can be done by using an interface. And then re-using your code will be easier.

You are not initializing activity in Region constructor, so activity is null when you try to call getRegion in asyncTask postExecute. You should init activity in Region constructor.

Your activity is null
public Region (Context context, MainActivity act){
this.context = context;
this.activity = act;
}

You're getting NullPointerException, because your Region class does not find getRegion() method which is inside your MainActivity.
Provide the activity to the constructor of Region class.

Error org.json.JSONException: Value <html><head><title> Error of type java.lang.String cannot be converted to JSONObject

I have a Android app about Public Transportation, and I have a PHP script that connects to mySQL database. This is the main.java
package com.chera.trans;
import com.chera.trans.R;
import android.os.Bundle;
import android.app.Activity;
import android.content.Intent;
import android.view.Menu;
import android.view.MenuInflater;
import android.view.MenuItem;
public class Main extends Activity {
#Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
}
#Override
public boolean onCreateOptionsMenu(Menu menu) {
MenuInflater inflater = getMenuInflater();
inflater.inflate(R.menu.menu_main, menu);
return true;
}
#Override
public boolean onOptionsItemSelected(MenuItem item) {
switch(item.getItemId()) {
case R.id.traseu2:
Intent traseu2 = new Intent(this, Traseu2.class);
this.startActivity(traseu2);
break;
case R.id.traseu401:
Intent traseu401 = new Intent(this, Traseu401.class);
this.startActivity(traseu401);
break;
default:
return super.onOptionsItemSelected(item);
}
return true;
}
}
And this is the code for Traseu2.java
package com.chera.trans;
import java.io.BufferedReader;
import java.io.IOException;
import java.io.InputStream;
import java.io.InputStreamReader;
import java.util.ArrayList;
import java.util.HashMap;
import java.util.List;
import java.util.Map;
import org.apache.http.HttpResponse;
import org.apache.http.client.ClientProtocolException;
import org.apache.http.client.HttpClient;
import org.apache.http.client.methods.HttpPost;
import org.apache.http.impl.client.DefaultHttpClient;
import org.json.JSONArray;
import org.json.JSONException;
import org.json.JSONObject;
import com.chera.trans.R;
import android.os.AsyncTask;
import android.os.Bundle;
import android.app.Activity;
import android.content.Intent;
import android.view.Menu;
import android.view.MenuInflater;
import android.view.MenuItem;
import android.widget.ListView;
import android.widget.SimpleAdapter;
import android.widget.Toast;
public class Traseu2 extends Activity {
private String jsonResult;
private String url = "http://transploiesti.tk/2.php";
private ListView listView;
#Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.traseu2);
listView = (ListView) findViewById(R.id.listView1);
accessWebService();
}
#Override
public boolean onCreateOptionsMenu(Menu menu) {
MenuInflater inflater = getMenuInflater();
inflater.inflate(R.menu.menu_main, menu);
return true;
}
#Override
public boolean onOptionsItemSelected(MenuItem item) {
switch(item.getItemId()) {
case R.id.traseu2:
Intent traseu2 = new Intent(this, Traseu2.class);
this.startActivity(traseu2);
break;
case R.id.traseu401:
Intent traseu401 = new Intent(this, Traseu401.class);
this.startActivity(traseu401);
break;
default:
return super.onOptionsItemSelected(item);
}
return true;
}
// Async Task to access the web
private class JsonReadTask extends AsyncTask<String, Void, String> {
#Override
protected String doInBackground(String... params) {
HttpClient httpclient = new DefaultHttpClient();
HttpPost httppost = new HttpPost(params[0]);
try {
HttpResponse response = httpclient.execute(httppost);
jsonResult = inputStreamToString(
response.getEntity().getContent()).toString();
}
catch (ClientProtocolException e) {
e.printStackTrace();
} catch (IOException e) {
e.printStackTrace();
}
return null;
}
private StringBuilder inputStreamToString(InputStream is) {
String rLine = "";
StringBuilder answer = new StringBuilder();
BufferedReader rd = new BufferedReader(new InputStreamReader(is));
try {
while ((rLine = rd.readLine()) != null) {
answer.append(rLine);
}
}
catch (IOException e) {
// e.printStackTrace();
Toast.makeText(getApplicationContext(),
"Error..." + e.toString(), Toast.LENGTH_LONG).show();
}
return answer;
}
#Override
protected void onPostExecute(String result) {
ListDrwaer();
}
}// end async task
public void accessWebService() {
JsonReadTask task = new JsonReadTask();
// passes values for the urls string array
task.execute(new String[] { url });
}
// build hash set for list view
public void ListDrwaer() {
List<Map<String, String>> employeeList = new ArrayList<Map<String, String>>();
try {
JSONObject jsonResponse = new JSONObject(jsonResult);
JSONArray jsonMainNode = jsonResponse.optJSONArray("traseudoi");
for (int i = 0; i < jsonMainNode.length(); i++) {
JSONObject jsonChildNode = jsonMainNode.getJSONObject(i);
String name = jsonChildNode.optString("Statie");
String number = jsonChildNode.optString("Oraplecare");
String outPut = "Autobuzul pleaca din " + name + " la ora " + number;
employeeList.add(createEmployee("employees", outPut));
}
} catch (JSONException e) {
Toast.makeText(getApplicationContext(), "Error" + e.toString(),
Toast.LENGTH_SHORT).show();
}
SimpleAdapter simpleAdapter = new SimpleAdapter(this, employeeList,
android.R.layout.simple_list_item_1,
new String[] { "employees" }, new int[] { android.R.id.text1 });
listView.setAdapter(simpleAdapter);
}
private HashMap<String, String> createEmployee(String name, String number) {
HashMap<String, String> employeeNameNo = new HashMap<String, String>();
employeeNameNo.put(name, number);
return employeeNameNo;
}
}
` Why I receive this error when I m running the app? Thanks!

HTML is not JSON, and it can not be parsed into JSONObjects. The top answer for org.json.JSONException: Value <!DOCTYPE of type java.lang.String cannot be converted to JSONObject is pretty good at explaining this further.

ListViewActivity with Custom Adapter doesn' t work

Dear Stackoverflow Comunitiy,
I'd like to have a ListView getting filled by an BackgroundTask.
This is my actual Code
HomeActivity:
package com.example.instaemgnew;
import java.util.ArrayList;
import android.app.ListActivity;
import android.os.Bundle;
import android.util.Log;
import android.view.Menu;
import com.example.instaemgnew.classes.Beitrag;
import com.example.instaemgnew.classes.beitragLoader;
import com.example.instaemgnew.classes.listViewHomeActivitiyAdapter;
public class HomeActivity extends ListActivity {
listViewHomeActivitiyAdapter adapter;
ArrayList<Beitrag> beitraege = new ArrayList<Beitrag>();
#Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_home);
adapter = new listViewHomeActivitiyAdapter(this, beitraege);
setListAdapter(adapter);
Log.e("TestPoint 1", "Adapter Set");
new beitragLoader(this).execute();
}
#Override
public boolean onCreateOptionsMenu(Menu menu) {
// Inflate the menu; this adds items to the action bar if it is present.
getMenuInflater().inflate(R.menu.activity_home, menu);
return true;
}
public void addToListView(Beitrag toAddBeitrag){
beitraege.add(toAddBeitrag);
adapter.notifyDataSetChanged();
}
}
BackgroundTask:
package com.example.instaemgnew.classes;
import java.io.File;
import java.io.FileOutputStream;
import java.io.IOException;
import java.io.InputStream;
import java.net.MalformedURLException;
import java.security.MessageDigest;
import java.security.NoSuchAlgorithmException;
import java.util.ArrayList;
import java.util.List;
import org.apache.http.NameValuePair;
import org.apache.http.message.BasicNameValuePair;
import org.json.JSONArray;
import org.json.JSONException;
import org.json.JSONObject;
import com.example.instaemgnew.HomeActivity;
import android.content.Context;
import android.net.Uri;
import android.os.AsyncTask;
import android.os.Environment;
import android.util.Log;
import android.widget.ArrayAdapter;
public class beitragLoader extends AsyncTask<String, String, String>{
//Array List für die Beiträge
ArrayList<Beitrag> beitraege;
//User Daten
/*mail = userManager.getMail();
grade = String.valueOf(userManager.getGrade());
school = userManager.getSchool();*/
String mail = "simon-frey#gmx.de";
String grade = String.valueOf(334);
String school = "EMG";
//JSONParser
JSONParser jsonParser = new JSONParser();
//ArrayList mit Beitrag Objekten
ArrayList<Beitrag> beitraegeList;
// Onlinedaten
private static final String SERVER_URL = "http://yooui.de/InstaEMGTest/";
private static final String PASSWORD = "8615daf406f7e2b313494f0240";
//Context
private final HomeActivity homeActivity;
//Konstruktor
public beitragLoader(HomeActivity homeActivity){
this.homeActivity = homeActivity;
Log.e("TestPoint 2", "Created beitragLoader");
}
#Override
protected void onPreExecute() {
super.onPreExecute();
//TODO: Test for InternetConnection
Log.e("TestPoint 3", "PreExectute");
}
/**
* getting All products from url
* */
protected String doInBackground(String... args) {
beitraegeList = new ArrayList<Beitrag>();
String SQLUrl = SERVER_URL + "testBeiträgeAbrufen.php";
String token = getMD5Hash("password" + "data");
List<NameValuePair> params = new ArrayList<NameValuePair>();
params.add(new BasicNameValuePair("token", token));
//TODO: params.add(new BasicNameValuePair("page", skipBeitraege))
params.add(new BasicNameValuePair("grade", grade));
params.add(new BasicNameValuePair("school", school));
JSONObject json = jsonParser.makeHttpRequest(SQLUrl, "GET", params);
if (json == null) {
// Server offline
}
Log.e("TestPoint 3,5", "FetchedJSON");
try {
JSONArray beitraege = json.getJSONArray("beitraege");
// looping through All Products
for (int i = 0; i < beitraege.length(); i++) {
Beitrag tempBeitrag = null;
Log.e("TestPoint 3,6", "StartLoop");
JSONObject c = beitraege.getJSONObject(i);
//HDImagesURLList ArrayList
ArrayList<String> HDImagesURLList = new ArrayList<String>();
// Storing each json item in variable
String id = c.getString("ID");
String url = c.getString("url");
String titel = c.getString("titel");
String tags = c.getString("tags");
String onlineDate = c.getString("onlineDate");
Log.e("TestPoint 3,7", "Stored JSON Items");
//Fetching previewImage
try {
Log.e("TestPoint 3,8", "TryImageDownload");
InputStream in = new java.net.URL(url).openStream();
String fileName = "InstaEMG" + String.valueOf(System.currentTimeMillis())+".jpg";
Log.e("imageUri", url);
Log.e("fileName", fileName);
FileOutputStream fileOutput = new FileOutputStream(new File(Environment.getExternalStorageDirectory(),fileName));
byte[] buffer = new byte[1024];
int bufferLength = 0;
while ((bufferLength = in.read(buffer)) > 0 ) {
fileOutput.write(buffer, 0, bufferLength);
Log.e("File Output", String.valueOf(bufferLength));
}
//Fill HDImagesURLList
//TODO
// creating newBeitrag
tempBeitrag = new Beitrag(Integer.parseInt(id), titel, onlineDate, fileName, HDImagesURLList);
// adding Beitrag to ArrayList
beitraegeList.add(tempBeitrag);
Log.e("TestPoint 4", "NewBeitragSet");
} catch (MalformedURLException e) {
Log.e("Exceptrion", "URL Exception");
} catch (IOException e) {
Log.e("Exceptrion", "IO Exception");
}
homeActivity.addToListView(tempBeitrag);
}
} catch (JSONException e) {
// TODO Auto-generated catch block
e.printStackTrace();
} return null;
}
/**
* After completing background Safe to MainActivity
* **/
protected void onPostExecute() {
Log.e("TestPoint 5", "PostExecutre");
// homeActivity.updateListView(beitraegeList);
}
/**
* Methode zum Errechnen eines MD5Hashs
*
* #param string
* String welcher kodiert werden soll
* #return MD5 Hash des Strings, bei Fehler der ursprüngliche String.
*/
private String getMD5Hash(String string) {
try {
MessageDigest md5 = MessageDigest.getInstance("MD5");
md5.update(string.getBytes());
byte[] result = md5.digest();
StringBuffer hexString = new StringBuffer();
for (int i = 0; i < result.length; i++) {
if ((0xff & result[i]) < 0x10) {
hexString.append("0" + Integer.toHexString((0xFF & result[i])));
} else {
hexString.append(Integer.toHexString(0xFF & result[i]));
}
}
string = hexString.toString();
} catch (NoSuchAlgorithmException e1) {
e1.printStackTrace();
}
return string;
};
}
and the BaseAdapter:
package com.example.instaemgnew.classes;
import java.util.ArrayList;
import com.example.instaemgnew.R;
import android.content.Context;
import android.view.LayoutInflater;
import android.view.View;
import android.view.View.OnClickListener;
import android.view.ViewGroup;
import android.widget.ArrayAdapter;
import android.widget.BaseAdapter;
import android.widget.ImageView;
import android.widget.TextView;
public class listViewHomeActivitiyAdapter extends BaseAdapter {
private final Context context;
private ArrayList<Beitrag> beitraege;
private final LayoutInflater layoutInflater;
public listViewHomeActivitiyAdapter(Context context, ArrayList<Beitrag> beitraege) {
super();
this.beitraege = beitraege;
this.context = context;
this.layoutInflater = (LayoutInflater) context.getSystemService(Context.LAYOUT_INFLATER_SERVICE);
}
#Override
public View getView(final int position, View convertView, ViewGroup parent) {
//Allgemeien Layout Vorgaben
LayoutInflater inflater = (LayoutInflater) context
.getSystemService(Context.LAYOUT_INFLATER_SERVICE);
View rowView = inflater.inflate(R.layout.single_beitrag_row_layout, parent, false);
if (convertView == null) {
convertView = layoutInflater.inflate(R.layout.single_beitrag_row_layout, null);
}
//getViews
TextView titelView = (TextView) rowView.findViewById(R.id.beitragTitel);
ImageView beitragImageView = (ImageView) rowView.findViewById(R.id.beitragImg);
/*
* TODO: Tags anzeigen und suchen lassen (Wunschfunktion)
* TextView tagsView = (TextView) rowView.findViewById(R.id.beitragTags);
*/
//setTitel From Object
titelView.setText(beitraege.get(position).getTitel());
//setPreviewImage From Object
beitragImageView.setImageBitmap(beitraege.get(position).getPreviewImage());
//setOnClickListener on PreviewImage for PopOutGallery
beitragImageView.setOnClickListener(new OnClickListener() {
#Override
public void onClick(View v) {
//TODO: PopOut Gallery
}
});
return rowView;
}
#Override
public int getCount() {
return beitraege.size();
}
#Override
public Object getItem(int position) {
return beitraege.get(position);
}
#Override
public long getItemId(int position) {
// TODO Auto-generated method stub
return 0;
}
}
In my opinion the Bug have to be in the BaseAdapter, but I don't know where it could be.
Sincerly and thankful,
Simon

To fill listView in doInBackground you need to use Handler, or runOnUiThread, because this is not UI thread.
homeActivity.runOnUiThread(new Runnable()
{
public void run()
{
homeActivity.addToListView(tempBeitrag);
}});

adapter = new listViewHomeActivitiyAdapter(this, beitraege);
beitraege is not populated with any data.
Edit:
Instead of calling this from doInbackground. Use a Interface as a call back to the activity and then populate listview.
public void addToListView(Beitrag toAddBeitrag){
beitraege.add(toAddBeitrag);
adapter.notifyDataSetChanged();
}
How do I return a boolean from AsyncTask?
Instead of boolen value its arraylist in your case.
Then use the below and set the adapter your listview
adapter = new listViewHomeActivitiyAdapter(this, beitraege);