So here in Java I've written a typical class, to send json to a rest server. (I'll include the whole class below for clarity.) So that's a file "Fetcher.java"
Now for the callback you need an interface. The interface is trivial, just one function with a string.
public interface FetcherInterface {
public void fetcherDone(String result);
}
Annoyingly you need a whole file for that, "FetcherInterface.java"
So this interface is nothing but "one callback with a string". Often all you need is just "one callback with no arguments".
In fact ........ are there some sort of standard interfaces I can use, or something like that?
It seems kind of annoying to have to put in a whole interface for such a simple "standard" interface.
What's the deal on this? What's the javaly solution?
It seems you CAN NOT put it in the same file:
Perhaps I misunderstand something there. If you could put it in the same file, that would be convenient at least.
(Lambdas are not yet practically available. Anyway, sometimes you want an interface.)
Just for clarity, here's how you call the class
JSONObject j = new JSONObject();
try {
j.put("height", 2.1);
j.put("width", 2.5);
j.put("command", "blah");
} catch (JSONException e) {
e.printStackTrace();
}
new Fetcher("mobile/login", j, new FetcherInterface() {
#Override
public void fetcherDone(String result) {
Log.d("DEV","all done");
doSomething(result);
}
}
).execute();
or indeed
public class HappyClass extends Activity implements FetcherInterface {
...
private void someCall() {
JSONObject j = new JSONObject();
try {
j.put("height", 2.1);
j.put("width", 2.5);
j.put("command", "blah");
} catch (JSONException e) {
e.printStackTrace();
}
new Fetcher("mobile/data", j, this).execute();
devBlank();
}
#Override
public void fetcherDone(String result) {
Log.d("DEV","all done" +result);
doSomething(result);
}
Here's the whole class... Fetcher.java file
public class Fetcher extends AsyncTask<Void, Void, String> {
private String urlTail;
private JSONObject jsonToSend;
private FetcherInterface callback;
// initializer...
Fetcher(String ut, JSONObject toSend, FetcherInterface cb) {
urlTail = ut;
jsonToSend = toSend;
callback = cb;
}
#Override
protected String doInBackground(Void... params) {
HttpURLConnection urlConnection = null; // declare outside try, to close in finally
BufferedReader reader = null; // declare outside try, to close in finally
String rawJsonResultString = null;
String json = jsonToSend.toString();
Log.d("DEV","the json string in Fetcher is " +json);
try {
URL url = new URL("https://falcon.totalfsm.com/" + urlTail);
Log.d("DEV","the full URL in Fetcher is " +url);
// open a json-in-the-body type of connection.......
urlConnection = (HttpURLConnection) url.openConnection();
urlConnection.setRequestMethod("POST");
urlConnection.setRequestProperty("Content-Type", "application/json; charset=UTF-8");
urlConnection.setDoOutput(true);
urlConnection.setDoInput(true);
urlConnection.setConnectTimeout(5000);
// urlConnection.setDoOutput(false); // can be important?
urlConnection.connect();
OutputStream os = urlConnection.getOutputStream();
os.write(json.getBytes("UTF-8"));
os.close();
// annoyingly, you have to choose normal versus error stream...
InputStream inputStream;
int status = urlConnection.getResponseCode();
if (status != HttpURLConnection.HTTP_OK)
inputStream = urlConnection.getErrorStream();
else
inputStream = urlConnection.getInputStream();
if (inputStream == null) { // nothing to do.
return null;
}
StringBuffer buffer = new StringBuffer();
reader = new BufferedReader(new InputStreamReader(inputStream));
String line;
while ((line = reader.readLine()) != null) { // adding newlines makes debugging easier
buffer.append(line + "\n");
}
if (buffer.length() == 0) { // stream was empty
return null;
}
rawJsonResultString = buffer.toString();
return rawJsonResultString;
} catch (IOException e) {
Log.e("PlaceholderFragment", "Error ", e);
return null;
} finally{
if (urlConnection != null) {
urlConnection.disconnect();
}
if (reader != null) {
try {
reader.close();
} catch (final IOException e) {
Log.e("PlaceholderFragment", "Error closing stream", e);
}
}
}
}
#Override
protected void onPostExecute(String s) {
super.onPostExecute(s);
Log.d("DEV", "Fetcher done");
if (s==null) {
Log.d("DEV","applying anti-null measures in Fetcher!");
s = "message from app communications layer: 'null' returned from servers for that call at " +urlTail;
}
callback.fetcherDone(s);
}
}
I feel bad answering my own question, but as there were no other answers this info may be helpful.
DaveNewton and Rowtang have supplied the exact answers here:
(Point 1) If you want a genuinely public interface, it goes in its own file. That's how Java works. There's no alternative.
(Point 2) Normally, use protected interface and declare the interface inside the class. It can then be used throughout the app.
So...
public class Fetcher extends AsyncTask<Void, Void, String> {
protected interface FetcherInterface {
public void fetcherDone(String result);
}
private String urlTail;
private JSONObject jsonToSend;
private FetcherInterface callback;
Fetcher(String ut, JSONObject toSend, FetcherInterface cb) {
urlTail = ut;
jsonToSend = toSend;
callback = cb;
}
#Override
protected String doInBackground(Void... params) {
....
(c# programmers would maybe call it "IFetcher".)
Related
I had wrote a code which use a parse to catch some data from a JSON file but i don't know what kind of structure is better between the sparse array or the array map for memorise these data ?
I had used a array map but I don't know if it's too wasted on so little data data.
public class MainActivity extends AppCompatActivity {
private ProgressDialog pd;
private String TAG = MainActivity.class.getSimpleName();
public ArrayMap<Integer, ValoriDiSueg> ArrayDati = new ArrayMap<>();
Button buttonProg;
TextView textViewProg;
#Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
buttonProg = (Button) findViewById(R.id.button);
textViewProg = (TextView) findViewById(R.id.textView);
buttonProg.setOnClickListener(new View.OnClickListener() {
#Override
public void onClick(View v) {
new JsonCLASS().execute("https://samples.openweathermap.org/data/2.5/weather?q=London,uk&appid=b6907d289e10d714a6e88b30761fae22");
}
});
}
private class JsonCLASS extends AsyncTask<String, String, String> {
#Override
protected void onPreExecute() {
super.onPreExecute();
pd = new ProgressDialog(MainActivity.this);
pd.setMessage("Please wait");
pd.setCancelable(false);
pd.show();
}
#Override
protected String doInBackground(String... params) {
HttpURLConnection connection = null;
BufferedReader reader = null;
try {
URL url = new URL(params[0]);
connection = (HttpURLConnection) url.openConnection();
connection.connect();
InputStream stream = connection.getInputStream();
reader = new BufferedReader(new InputStreamReader(stream));
StringBuffer buffer = new StringBuffer();
String line = "";
while ((line = reader.readLine()) != null) {
buffer.append(line + "\n");
Log.d("Response: ", "> " + line); //here u ll get whole response...... :-)
}
return buffer.toString();
} catch (MalformedURLException e) {
e.printStackTrace();
} catch (IOException e) {
e.printStackTrace();
} finally {
if (connection != null) {
connection.disconnect();
}
try {
if (reader != null) {
reader.close();
}
} catch (IOException e) {
e.printStackTrace();
}
}
return null;
}
The parse of these data
#Override
protected void onPostExecute(String result) {
super.onPostExecute(result);
try {
JSONObject jsonObject = new JSONObject(result);
JSONArray Arr = new JSONArray(jsonObject.getString("weather"));
for (int i = 0; i < Arr.length(); i++){
JSONObject jsonPart = Arr.getJSONObject(i);
ArrayDati.put(i,new ValoriDiSueg( jsonPart.getString("main"), jsonPart.getString("description")));
//ArrayDati.put(i,new ValoriDiSueg("description : "+ jsonPart.getString("description")));
textViewProg.setText(textViewProg.getText()+"main : "+ ArrayDati.get(i).Main +"\n"+textViewProg.getText()+"description : "+ ArrayDati.get(i).Description );
}
} catch (Exception e ){
e.printStackTrace();
}
if (pd.isShowing()) {
pd.dismiss();
}
}
}
}
And I created a class:
public class ValoriDiSueg {
String Main;
String Description;
public ValoriDiSueg(String main, String description) {
this.Main = main;
this.Description = description;
}
}
any suggestions??
In simple:
If your key is int or long, you should use SparseArray, SparseLongArray as it will not boxing/un-boxing the key value when operates. Also, it provides similar classes for int/long values as long as the key is int/long.
If you key is not int nor long, such as an object or String, you should use ArrayMap instead as it will handle the conflicts of key hashes.
There are no much performance and memory usage difference between these two class as they are all requires O(log n) to search and O(n) to insert/delete (in most cases).
I am storing the data that I parsed from the JSON that is returned by my API request into the Firebase database.
submitButton.setOnClickListener(new View.OnClickListener() {
#Override
public void onClick(View v) {
String APIURL = "https://api.github.com/users/" + idInput.getText().toString();
String repoURL = "https://api.github.com/users/" + idInput.getText().toString() + "/repos";
new JSONTask().execute(APIURL);
//new JSONTask().execute(repoURL);
String parsedUserID = idInput.getText().toString();
SM.sendDataToProfile(parsedUserID);
viewPager.setCurrentItem(1);
//addUser(parsedUserID);
}
});
When the button is clicked, it calls a new JSONTask (asynctask) on the APIURL.
JSONTask
public class JSONTask extends AsyncTask<String, String, String> {
#Override
// Any non-UI thread process is running in this method. After completion, it sends the result to OnPostExecute
protected String doInBackground(String... params) {
HttpURLConnection connection = null;
BufferedReader reader = null;
try {
// Pass in a String and convert to URL
URL url = new URL(params[0]);
connection = (HttpURLConnection) url.openConnection();
connection.connect();
InputStream stream = connection.getInputStream();
// Reads the data line by line
reader = new BufferedReader(new InputStreamReader(stream));
StringBuffer strBuffer = new StringBuffer();
String line = "";
while ((line = reader.readLine()) != null) {
strBuffer.append(line);
}
// If we are able to get the data do below :
String retreivedJson = strBuffer.toString();
return retreivedJson;
// When we are not able to retreive the Data
} catch (MalformedURLException e) {
e.printStackTrace();
} catch (IOException e) {
e.printStackTrace();
} finally {
if (connection != null) {
// close both connection and the reader
connection.disconnect();
}
try {
if (reader != null) {
reader.close();
}
} catch (IOException e) {
e.printStackTrace();
}
}
return null;
}
And it does parsing in another function.
My question is, as you can see on my setOnClickListener, I tried to make two JSONTask on two different URLs because the first URL gives me the information of the user and the second URL (repoURL) gives me the information of the user's repositories. I tried to fetch the repo info of the user and store it into the DB, but it seems like this is a wrong approach.
What is a right way to call two separate AsyncTasks on two different URLs?
EDIT
private void addUserRepo(final String githubID, final String[] repoList) {
DatabaseReference users = databaseReference.child("users");
users.addListenerForSingleValueEvent(new ValueEventListener() {
#Override
public void onDataChange(DataSnapshot dataSnapshot) {
List list = new ArrayList<String>(Arrays.asList(repoList));
databaseReference.child("users").child(githubID).child("Repos").setValue(list);
}
#Override
public void onCancelled(DatabaseError databaseError) {
}
});
}
Using data parsed from
public void formatJSONArray(String results){
try {
JSONArray jsonArray = new JSONArray(results);
RepoInfo[] repoList = new RepoInfo[jsonArray.length()];
for(int i = 0; i < jsonArray.length(); i++){
JSONObject jsonObject=jsonArray.getJSONObject(i);
if(jsonObject.optString("name") != null) {
repoList[i].setRepoName(jsonObject.getString("name"));
//repoNameList.add(jsonObject.getString("name"));
}
if(jsonObject.optString("description") != null) {
repoList[i].setDescription(jsonObject.getString("description"));
//descriptionList.add(jsonObject.getString("description"));
}
if(jsonObject.optJSONObject("owner") != null){
JSONObject ownerObject=jsonObject.getJSONObject("owner");
if(ownerObject.optString("login")!=null) {
repoList[i].setOwner(ownerObject.getString("login"));
//userNameList.add(ownerObject.getString("login"));
}
}
}
} catch (JSONException jsonException){
}
}
The response of two different URLs will surely not be similar. So you need different parse methods for them.
One lazy way would be to use two different AsyncTasks subclasses for two different urls.
Another way would be to store a flag inside the asynctask indicating whether it is dealing with user or repo.
public class JSONTask extends AsyncTask <String , String , String> {
boolean fetchingRepo;
#Override
protected String doInBackground (String... params) {
fetchingRepo = params[0].endsWith("/repos");
//other statements
}
Now inside onPostExecute:
if(fetchingRepo){
//parse one way
} else {
//parse another way
}
I am new to android and am completely puzzled by AsyncTasks. I need to create a leaderboard which will pull global leaderboard scores from a server.
I have posted below the two methods that were created in the LeaderboardsFragment which are used to access and display the scores - getGlobalScores and readStream.
I am unsure of how to use these in the AsyncTask - mostly how and what parameters to pass to the AsyncTask - most of the tutorials I have been looking at do not deal with 2D arrays. Any hints would be really appreciated, I am really having trouble understanding the literature surrounding this.
package uk.ni.appidemic.whackamole;
import java.io.BufferedReader;
public class LeaderboardsFragment extends Fragment {
AssetStore AS;
private TextView TopScores;
private String[][] global_scores = new String[10][3];
#Override
public View onCreateView(LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState) {
View rootView = inflater.inflate(R.layout.fragment_leaderboards, container, false);
//Go and get the asset store from the activity
AS = WhackAMoleActivity.getAssetManager();
TopScores = (TextView) rootView.findViewById(R.id.leaderboards);
// Extract and display the top score text view from the preferences
displayLocalScores();
// this method is used to send a highscore to the server (name and score)
// this method may get pulled out to the gameloop as its the only place it should be used in the final game
// but this can be used for testing purposes atm (Server needs to be on)
// sendScoreGlobal("porter", 1001);
//async Get global scores from the server and display them - new thread
new AsyncOperation().execute();
...................
public void getGlobalScores() {
//gets global score in HTML format to be parsed
StrictMode.ThreadPolicy policy = new StrictMode.ThreadPolicy.Builder().permitAll().build();
StrictMode.setThreadPolicy(policy);
try {
URL url = new URL("http://62........./high_scores");
HttpURLConnection con = (HttpURLConnection) url.openConnection();
readStream(con.getInputStream());
} catch (Exception e) {
e.printStackTrace();
}
}
/gets the data and stores the global scores in a 2d array
//it then displays to screen
public void readStream(InputStream in) {
BufferedReader reader = null;
try {
StringBuilder htmlIn = new StringBuilder();
StringBuilder globalScoreBuilder = new StringBuilder();
htmlIn.append("");
reader = new BufferedReader(new InputStreamReader(in));
String line = "";
while ((line = reader.readLine()) != null) {
htmlIn.append(line);
}
// String to be scanned to find the pattern.
String html = htmlIn.toString();
String regexPattern = "<td align=\"left\" style=\"padding-left:10px;\">(\\d+?)</td>|<td align=\"right\" style=\"padding-right:10px;\">(\\w+?)</td>";
// Create a Pattern object
Pattern patternObject = Pattern.compile(regexPattern);
// Now create matcher object.
Matcher matcherObject = patternObject.matcher(html);
Log.d(getActivity().getResources().getString(R.string.LOG_TAG), "Trying to find regex matches");
TopScores.append("\n");
int nextFreePointer = 0;
int rowCount = 0;
while (matcherObject.find()) {
if (matcherObject.group(1) != null) {
Log.d(getActivity().getResources().getString(R.string.LOG_TAG), "Regex match : " + matcherObject.group(1));
globalScoreBuilder.append(matcherObject.group(1) + " ");
global_scores[rowCount][nextFreePointer] = matcherObject.group(1);
nextFreePointer++;
}
if (matcherObject.group(2) != null) {
Log.d(getActivity().getResources().getString(R.string.LOG_TAG), "Regex match : " + matcherObject.group(2));
globalScoreBuilder.append(matcherObject.group(2) + " ");
global_scores[rowCount][nextFreePointer] = matcherObject.group(2);
nextFreePointer++;
}
if (nextFreePointer > 2) {
nextFreePointer = 0;
rowCount++;
}
globalScoreBuilder.append("\n");
}
StringBuilder sb = new StringBuilder();
String lineSeparator = System.getProperty("line.separator");
for (String[] row : global_scores) {
sb.append(Arrays.toString(row)).append(lineSeparator);
}
String text = sb.toString();
TopScores.append("Global Top 10 Scores\n");
TopScores.append(text);
} catch (IOException e) {
e.printStackTrace();
} finally {
if (reader != null) {
try {
reader.close();
} catch (IOException e) {
e.printStackTrace();
}
}
}
}
public class AsyncOperation extends AsyncTask<String, Void, Void>{
protected void onPreExecute(){
}//end of onPreExecute
#Override
protected Void doInBackground(Void... values) {
}//doinBackground
protected void onProgressUpdate(Void... values){
}//onProgressUpdate
protected void onPostExecute(Void... result){
}//end of onPostExecute
}//end of AsyncOperation inner class
}//end of Leaderboards class
You should fetch your game score through a WebService class that extentds AsynTask. Below is my class that I am using in order to fetch remote data safely.
CODE:
public class WebServiceRestTask extends AsyncTask<HttpUriRequest, Void, Object> {
private static final String TAG = "WebServiceRestTask";
private AbstractHttpClient mClient;
private WeakReference<WebServiceRestCallback> mCallback;
private int ws_task;
public WebServiceRestTask(int ws_task) {
this(new DefaultHttpClient(), ws_task);
}
public WebServiceRestTask(AbstractHttpClient client, int task_number) {
mClient = client;
this.ws_task = task_number;
}
public interface WebServiceRestCallback {
public void onRequestSuccess(String response);
public void onRequestError(Exception error);
}
public void setResponseCallback(WebServiceRestCallback callback) {
mCallback = new WeakReference<WebServiceRestCallback>(callback);
}
#Override
protected Object doInBackground(HttpUriRequest... params) {
try {
HttpUriRequest request = params[0];
HttpResponse serverResponse = mClient.execute(request);
BasicResponseHandler handler = new BasicResponseHandler();
String response = handler.handleResponse(serverResponse);
return response + ws_task;
} catch (Exception e) {
Log.w(TAG, e);
return e;
}
}
#Override
protected void onPostExecute(Object result) {
if (mCallback != null && mCallback.get() != null) {
if (result instanceof String) {
mCallback.get().onRequestSuccess((String) result);
} else if (result instanceof Exception) {
mCallback.get().onRequestError((Exception) result);
} else {
mCallback.get().onRequestError(
new IOException("Unknown Error Contacting Host"));
}
}
}
}
Not at my workstation but think something like this should work.
public class AsyncOperation extends AsyncTask<String, Void, Void>{
private String[][] global_scores = new String[10][3];
protected void onPreExecute(){
// optionally show loading indicator
TopScores.append("\n");
}//end of onPreExecute
#Override
protected Void doInBackground(Void... values) {
try {
URL url = new URL("http://62........./high_scores");
HttpURLConnection con = (HttpURLConnection) url.openConnection();
readStream(con.getInputStream());
} catch (Exception e) {
e.printStackTrace();
}
}//doinBackground
protected void onProgressUpdate(Void... values){
}//onProgressUpdate
protected void onPostExecute(Void... result){
// optionally hide loading indicator
StringBuilder sb = new StringBuilder();
String lineSeparator = System.getProperty("line.separator");
for (String[] row : global_scores) {
sb.append(Arrays.toString(row)).append(lineSeparator);
}
String text = sb.toString();
TopScores.append("Global Top 10 Scores\n");
TopScores.append(text);
}//end of onPostExecute
private void readStream(InputStream in) {
BufferedReader reader = null;
try {
StringBuilder htmlIn = new StringBuilder();
StringBuilder globalScoreBuilder = new StringBuilder();
htmlIn.append("");
reader = new BufferedReader(new InputStreamReader(in));
String line = "";
while ((line = reader.readLine()) != null) {
htmlIn.append(line);
}
// String to be scanned to find the pattern.
String html = htmlIn.toString();
String regexPattern = "<td align=\"left\" style=\"padding-left:10px;\">(\\d+?)</td>|<td align=\"right\" style=\"padding-right:10px;\">(\\w+?)</td>";
// Create a Pattern object
Pattern patternObject = Pattern.compile(regexPattern);
// Now create matcher object.
Matcher matcherObject = patternObject.matcher(html);
Log.d(getActivity().getResources().getString(R.string.LOG_TAG), "Trying to find regex matches");
int nextFreePointer = 0;
int rowCount = 0;
while (matcherObject.find()) {
if (matcherObject.group(1) != null) {
Log.d(getActivity().getResources().getString(R.string.LOG_TAG), "Regex match : " + matcherObject.group(1));
globalScoreBuilder.append(matcherObject.group(1) + " ");
global_scores[rowCount][nextFreePointer] = matcherObject.group(1);
nextFreePointer++;
}
if (matcherObject.group(2) != null) {
Log.d(getActivity().getResources().getString(R.string.LOG_TAG), "Regex match : " + matcherObject.group(2));
globalScoreBuilder.append(matcherObject.group(2) + " ");
global_scores[rowCount][nextFreePointer] = matcherObject.group(2);
nextFreePointer++;
}
if (nextFreePointer > 2) {
nextFreePointer = 0;
rowCount++;
}
globalScoreBuilder.append("\n");
}
} catch (IOException e) {
e.printStackTrace();
} finally {
if (reader != null) {
try {
reader.close();
} catch (IOException e) {
e.printStackTrace();
}
}
}
}
}//end of AsyncOperation inner class
I am currently working with the tab host and fragment. Currently I set fragment a to download json A and fragment B to download json B , the problem is when I switch fragment, the fragment A onPostExecute function will fall into the fragment B one , is there any way to fix this?
Thanks
Tab host:
tabHost = (FragmentTabHost) findViewById(R.id.tabhost);
tabHost.setup(this, getSupportFragmentManager(), R.id.tabcontent);
tabHost.addTab(
tabHost.newTabSpec("Home").setIndicator("",
res.getDrawable(R.drawable.btn_about)), Home.class,
null);
tabHost.addTab(
tabHost.newTabSpec("About").setIndicator("",
res.getDrawable(R.drawable.btn_about)), About.class,
null);
The async task
public class JSONReader {
public static final String TAG = "JSONReader";
public ArrayList<Record> records;
public Record myRecordObj;
public ArrayList<GalleryImage> images;
public String url;
public int failCount = 0; // retry twice
public Context ctx;
public String readCase;
public JSONReader(String _url, Context _ctx , String _readCase) {
url = _url;
ctx = _ctx;
readCase = _readCase;
}
public void getJSON() {
new JSONDownload().execute(url);
}
private class JSONDownload extends AsyncTask<String, Void, JSONObject> {
// TODO Auto-generated method stub
StringBuilder builder = new StringBuilder();
String temp = "";
String json = ""; // json content
InputStream input = null;
OutputStream output = null;
HttpURLConnection connection = null;
#Override
protected JSONObject doInBackground(String... params) {
// TODO Auto-generated method stub
try {
Log.d(TAG, "Start reading: " + url);
URL url = new URL(params[0]);
connection = (HttpURLConnection) url.openConnection();
connection.connect();
if (connection.getResponseCode() != HttpURLConnection.HTTP_OK)
return null;
// return "Server returned HTTP " + connection.getResponseCode()
// + " " + connection.getResponseMessage();
input = connection.getInputStream();
BufferedReader reader = new BufferedReader(
new InputStreamReader(input));
while ((temp = reader.readLine()) != null) {
builder.append(temp);
}
json = builder.toString();
} catch (Exception e) {
return null;
} finally {
try {
if (input != null)
input.close();
if (output != null)
output.close();
} catch (IOException ignored) {
}
if (connection != null)
connection.disconnect();
}
try {
return new JSONObject(json);
} catch (JSONException e) {
e.printStackTrace();
return null;
}
}
#Override
protected void onPostExecute(JSONObject result) {
// TODO Auto-generated method stub
super.onPostExecute(result);
onJSONDownloaded(result);
}
}
public void onJSONDownloaded(JSONObject result) {
// TODO Auto-generated method stub
if (result != null) {
failCount = 0;
if (readCase.equals("leaderBoard")){
records = new ArrayList<Record>();
try {
JSONObject myRecord = result.getJSONObject("myRecord");
if (myRecord != null) {
myRecordObj = new Record(myRecord.getString("pic"),myRecord.getString("name"),myRecord.getString("score"));
}
JSONArray topRecords = result.getJSONArray("topRecord");
for (int i = 0; i < topRecords.length(); i++) {
JSONObject topRecord = topRecords.getJSONObject(i);
String topName = topRecord.getString("name");
String topPic = topRecord.getString("pic");
String topScore = topRecord.getString("score");
records.add(new Record(topPic, topName, topScore));
}
} catch (JSONException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
((LeaderBoardDetail)ctx).setData(records,myRecordObj);
} else if (readCase.equals("galleryList")){
images = new ArrayList<GalleryImage>();
try {
JSONArray imageList = result.getJSONArray("images");
for (int i = 0; i < imageList.length(); i++) {
JSONObject image = imageList.getJSONObject(i);
images.add(new GalleryImage(image.getString("url"),image.getString("thumbUrl"),image.getString("category"),image.getString("userPic"),image.getString("name")));
}
} catch (JSONException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
//exception
if (((FragmentActivity) ctx).getSupportFragmentManager().findFragmentById(R.id.tabcontent).getTag().equals("Gallery")) {
PhotoGallery galleryFragment = (PhotoGallery) ((FragmentActivity) ctx).getSupportFragmentManager().findFragmentById(R.id.tabcontent);
galleryFragment.setData(images);
}
}
} else {
if (failCount <= 1) { // check global_conf twice if fail
failCount++;
Log.d(TAG, "No of retry" + failCount);
new JSONDownload().execute(url); // Retry download json
} else {
failCount = 0;
}
}
}
}
I used it in my app this way which works for me and answer is a bit similar to another answer but few additions and more detail. Hope it help you too.
NOTE: This is just a idea, u need to try, it may vary as per your app architect.
At your activity make the task object global [make sure set task obj null once task is finish]
JSDownload js = null;
public void getJSON() {
if(js != null && js.getStatus() == AsyncTask.Status.RUNNING)
{
js.cancel(true);
if(js.isCancelled())
{
js = new JSONDownload();
js.execute(url);
}
else
{
js = new JSONDownload();
js.execute(url);
}
}
At the Async class side....[make sure u take care null result # onpostExcute]
class JSONDownload extends AsyncTask<String, Void, JSONObject>
{
protected JSONObject doInBackground(String... params) {
// TODO Auto-generated method stub
try {
if(!this.isCancelled())
{
//make http connection ..
URL url = new URL(params[0]);
connection = (HttpURLConnection) url.openConnection();
connection.connect();
//as we are in steps in bg check iscancel .. again
//if its a loop here we call break; and return null once only..
if(this.isCancelled())
return null;
// connection status check and get buffer etc .. code here
if(this.isCancelled())
return null;
//read data
return data;
}
} catch (Exception e) {
return null;
}
}
#Override
protected void onCancelled(){
// If you write your own implementation, do not call super.onCancelled(result).
}
}
Use the global async task variable
LongOperation LongOperationOdeme = new LongOperation();
and set:
LongOperationOdeme.cancel(true);
This will stop any async task running at that moment, it's what the back button does
If you are not looking for a simplest answer but for a maybe more interesting and elegant, have a peek at this article, especially if you find functional programming interesting.
It's easier than it looks, i was almost unfamiliar to FP before this article but it covers common problems related to AsyncTask and asynchronicity in Android in general, so I got the gist and consider to use Observables instead of AsyncTask in the future projects myself. It is RxJava and it can solve your problem gracefully: "The fromFragment call transforms the given source observable in such a way that events will only be emitted to the fragment if it’s still alive and attached to its host activity."
One more citation form the article: "What if the user decides to back out of the Activity that triggered the task, and we are holding on to a stale reference. This not only creates a substantial memory leak, but is also worthless because meanwhile it has been detached from the application window. A problem that everyone is well aware of."
This the most bizarre problem I have ever seen. I get "No product available" although there are products in my database.
Here my service:
public class AllProductsService {
private String URL = "xxxx";
Gson gson;
public AllProductsService(int page) {
gson = new Gson();
URL = URL + "?page=" + Integer.toString(page);
}
private InputStream sendRequest(URL url) throws Exception {
try {
HttpURLConnection urlConnection = (HttpURLConnection) url.openConnection();
urlConnection.connect();
if (urlConnection.getResponseCode() == HttpURLConnection.HTTP_OK) {
return urlConnection.getInputStream();
}
} catch (Exception e) {
throw new Exception("");
}
return null;
}
public List<Product> getProducts() {
try {
InputStream inputStream = sendRequest(new URL(URL));
if(inputStream != null) {
InputStreamReader reader = new InputStreamReader(inputStream);
return gson.fromJson(reader, new TypeToken<List<Product>>(){}.getType());
}
}
catch (Exception e) {
}
return null;
}
}
And my AsyncTask class:
private class AllProductsTask extends AsyncTask<Void, Void, List<Product>> {
#Override
protected void onPreExecute() {
setSupportProgressBarIndeterminateVisibility(true);
}
#Override
protected List<Product> doInBackground(Void... params) {
AllProductsService allProductsService = new AllProductsService(current_page);
List<Product> liste = allProductsService.getProducts();
if (liste != null && liste.size() >= 1)
return liste;
return new ArrayList<Product>();
}
protected void onPostExecute(java.util.List<Product> result) {
setSupportProgressBarIndeterminateVisibility(false);
if (result.isEmpty() && isInternetPresent && current_page < 2) {
Crouton.makeText(MainActivity.this, "No product available!", Style.ALERT).show();
}
//populate adapter
}
}
When I call the URL from the browser, results are displayed correctly. I also try with a different URL with the same code and it works fine. I don't know why.
I think problem is; you are returning the
new ArrayList<Product>();
in doInBackground() of Asynctask which is null. You should return the liste here. or place the return new ArrayList<Product>(); in else condition
I found the solution: just have to remove the slash at the end of the URL. Thank you #trevor-e. Knowing the HTTP code status help me.