Develop Reference

My current code takes a JSON response, parses it, then displays the value to an activity, all in one function. How do I separate them into threads?

(note: I'm using the Android Volley library for the network connection)
public class PostureActivity extends AppCompatActivity {
private static final String LOG_TAG = PostureActivity.class.getName();
private static final String EMB_URL = "https://api.thingspeak.com/channels/xxxxxxx/feed/last.json?round=1";
#Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
}
#Override
protected void onResume() {
super.onResume();
connect(); // call at the start
final Handler handler = new Handler();
Runnable scrape = new Runnable() {
#Override
public void run() {
connect(); // call every x ms
handler.postDelayed(this, 3000);
}
};
handler.postDelayed(scrape, 3000);
}
private void connect() {
MySingleton.getInstance(this.getApplicationContext()).getRequestQueue();
JsonObjectRequest collectData = new JsonObjectRequest(
Request.Method.GET, // HTTP method
EMB_URL, // URL string that returns the desired JSON // TODO: change appropriate url
null, // optional JSON to send as request
response -> { // retrieved data
try {
JSONObject myResponse = new JSONObject(response.toString());
// TODO: cast to double to show the average
String ultrasonic = myResponse.getString("field1");
String flex1 = myResponse.getString("field2");
String flex2 = myResponse.getString("field3");
TextView neck = findViewById(R.id.neck_number);
TextView back = findViewById(R.id.back_number);
TextView butt = findViewById(R.id.butt_number);
neck.setText(ultrasonic);
back.setText(flex1);
butt.setText(flex2);
} catch (JSONException e) { // what if response is null?
e.printStackTrace();
Toast.makeText(getApplicationContext(), "Response values are empty.", Toast.LENGTH_LONG).show();
finishAffinity();
finishAndRemoveTask();
}
},
error -> { // retrieved error/failure
error.printStackTrace();
Toast.makeText(getApplicationContext(), "Could not connect to website.", Toast.LENGTH_LONG).show();
finishAffinity();
finishAndRemoveTask();
}
);
MySingleton.getInstance(this).addToRequestQueue(collectData);
}
As you can see, connect() essentially retrieves, parses, and displays the data, and I run it via a handler. How do split the code so that this entire function doesn't simply populate the UI thread? I'm not very familiar with handler/loopers or java threads outside of async tasks, so I was hoping that I could be pointed in the right direction as to how to optimize the function better.

How to make UI methods wait for an asynctask?

I have two arrays (groupIDs, groupNames) I need to fill with variables received from certain URLs which is done inside a subclass extending AsyncTask as otherwise, it results in a NetworkOnMainThreadException error. Problem is I need to make sure those two arrays are filled before initRecyclerView(); is called in UI thread.
How can I make sure my code waits for async to finish before executing initRecyclerView();?
public class GroupPage extends AppCompatActivity {
private static final String TAG = "RecycleViewAdapter";
private ArrayList<Integer> groupIDs = new ArrayList<>();
private ArrayList<String> groupNames = new ArrayList<>();
private class groupPageConnect extends AsyncTask {
#Override
protected Object doInBackground(Object... arg0) {
try{
System.out.println("Testing 1 - Send Http GET request");
getGroups();
} catch (Exception e) {
System.err.println("Oops!");
e.printStackTrace();
}
return null;
}
}
private void getGroups() throws Exception{
String url = "http://obsco.me/obsco/api/v1.0/users/12345671";
URL obj = new URL(url);
HttpURLConnection con = (HttpURLConnection) obj.openConnection();
con.setRequestMethod("GET");
con.setRequestProperty("User-Agent", "Mozilla/5.0");
int responseCode = con.getResponseCode();
System.out.println("Response Code for IDs: " + responseCode);
BufferedReader in = new BufferedReader(new InputStreamReader(con.getInputStream()));
String inputLine;
StringBuffer response = new StringBuffer();
while ((inputLine = in.readLine()) != null) {
response.append(inputLine);
}
in.close();
JSONObject reader = new JSONObject(response.toString());
JSONArray allContainingArray = reader.getJSONArray("users");
JSONObject userJSON = (JSONObject) allContainingArray.get(0);
JSONArray temp = userJSON.getJSONArray("groups");
Log.d(TAG, "initializing");
for (int x = 0; x < temp.length(); x++){
//System.out.println(temp.getJSONObject(x).getInt("id"));
groupIDs.add(temp.getJSONObject(x).getInt("id"));
System.out.println(groupIDs.size() );
System.out.println(groupIDs.get(x));
//groupNames.add("Dummy");
url = "http://obsco.me/obsco/api/v1.0/groupname/" + groupIDs.get(x);
System.out.println("ar1");
obj = new URL(url);
System.out.println("ar2");
con = (HttpURLConnection) obj.openConnection();
con.setRequestMethod("GET");
con.setRequestProperty("User-Agent", "Mozilla/5.0");
responseCode = con.getResponseCode();
System.out.println("Response Code for IDs: " + responseCode);
in = new BufferedReader(new InputStreamReader(con.getInputStream()));
response = new StringBuffer();
while ((inputLine = in.readLine()) != null) {
response.append(inputLine);
}
in.close();
reader = new JSONObject(response.toString());
System.out.println(reader.getString("name"));
groupNames.add(reader.getString("name"));
}
}
#Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_group_page);
Log.d(TAG, "started");
try {
groupPageInit();
} catch (Exception e) {
e.printStackTrace();
}
}
private void groupPageInit() throws Exception{
new groupPageConnect().execute();
initRecyclerView();
}
private void initRecyclerView(){
Log.d(TAG, "initializingRecyclerView");
RecyclerView recyclerView = findViewById(R.id.recycler_view);
RecyclerViewAdapter adapter = new RecyclerViewAdapter( this, groupIDs, groupNames);
recyclerView.setAdapter(adapter);
recyclerView.setLayoutManager( new LinearLayoutManager( this));
}
}

After getGroups() you can use runOnUiThread().
Example:
getGroups();
runOnUiThread(new Runnable() {
#Override
public void run() {
// Logic that you want to execute on main thread
initRecyclerView();
}
});

Call initRecyclerView() method on onPostExecute(result)method. An asynchronous task is defined by a computation that runs on a background thread and whose result is published on the UI thread. An asynchronous task is defined by 4 steps, called onPreExecute, doInBackground, onProgressUpdate and onPostExecute.onPostExecute(Result) invoked on the UI thread after the background computation finishes.
private class groupPageConnect extends AsyncTask<Object,void,String> {
#Override
protected Object doInBackground(Object... arg0) {
//put your code here
}
#Override
protected void onPostExecute(String result) {
//call what you want to update
initRecyclerView();
// dismiss progress dialog here
// into onPostExecute() but that is upto you
}
#Override
protected void onPreExecute() {
// start progress dialog here
}
#Override
protected void onProgressUpdate(Void... values) {
// progress update here}
}
}

You can override onPostExecute.
onPostExecute(Result), invoked on the UI thread after the background computation finishes. The result of the background computation is passed to this step as a parameter.task goes through 4 steps
Please pay attention that loading of data from network through AsyncTask may be cause of memory leaks .

Android - My onPostExecute in AsyncTask is not getting called

So I have been trying to fetch JSON objects in my Django REST Framework API. The algorithm for this called within the onPostExecute of my AsyncTask but it seems that it is not being called as when I debug it doesn't go there. Nothing fatal seems to be appearing in my logcat except that there is nothing in my array that should contain data from the DRF API.
I have two activities that calls my AsyncTask from my WSAdapter class. One is for logging in and the other is for listing all posts once logged in.
The logging in works just fine but listing the posts doesn't.
My code is below:
Posts.java
public class Posts extends AppCompatActivity {
TextView postsSect;
Button postsDoneBtn;
WSAdapter.SendAPIRequests PostsHelper;
StringBuilder postsBuffer = new StringBuilder();
#Override
protected void onResume(){
super.onResume();
PostsDetails postDetailsHelper = new PostsDetails();
postDetailsHelper.ListPosts();
}
#Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_posts);
PostsDetails postDetailsHelper = new PostsDetails();
postsDoneBtn = (Button) findViewById(R.id.PostsDoneButton);
postDetailsHelper.callPostDetails("192.168.0.18:8000/api");
postDetailsHelper.ListPosts();
postDetailsHelper.postDetailsCalled('n');
postsDoneBtn.setOnClickListener(new View.OnClickListener() {
#Override
public void onClick(View v) {
startActivity(new Intent(Posts.this, MainActivity.class));
}
});
}
public class PostsDetails {
//String post_title, post_content;
ArrayList<Integer> post_id = new ArrayList<Integer>();
ArrayList<String> post_title = new ArrayList<String>();
ArrayList<String> post_content = new ArrayList<String>();
boolean isPDCalled;
// sets if Post details are called
boolean postDetailsCalled(char called) {
if (called == 'y'){
return true;
}
return false;
}
// checks if postsDetails functions are called for AsyncTask
boolean getIsPDCalled(){
return isPDCalled;
}
// calls the execute for AsyncTask
private void callPostDetails(String theurl){
PostsHelper = new WSAdapter.SendAPIRequests();
// sets if post details are called
postDetailsCalled('y');
// executes AsyncTask
PostsHelper.execute(theurl);
}
// sets values for the posts arrays
public void setPost(int p_id, String p_title, String p_content) {
post_id.add(p_id);
post_title.add(p_title);
post_content.add(p_content);
}
// Lists the posts from the database
public void ListPosts() {
/////////// add functionality if a post was deleted and was clicked
postsSect = (TextView) findViewById(R.id.PostsSection);
postsSect.setText(post_title.get(post_title.size()) + "\n");
for (int i = post_id.size() - 1; i > 0; i--)
{
postsSect.append(post_title.get(i));
}
}
}
}
WSAdapter.java
public class WSAdapter extends AppCompatActivity {
#Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
}
static public class SendAPIRequests extends AsyncTask<String, String, String> {
// Add a pre-execute thing
#Override
protected String doInBackground(String... params) {
Log.e("TAG", params[0]);
Log.e("TAG", params[1]);
String data = "";
HttpURLConnection httpURLConnection = null;
try {
// Sets up connection to the URL (params[0] from .execute in "login")
httpURLConnection = (HttpURLConnection) new URL(params[0]).openConnection();
// Sets the request method for the URL
httpURLConnection.setRequestMethod("POST");
// Tells the URL that I am sending a POST request body
httpURLConnection.setDoOutput(true);
// To write primitive Java data types to an output stream in a portable way
DataOutputStream wr = new DataOutputStream(httpURLConnection.getOutputStream());
// Writes out a byte to the underlying output stream of the data posted from .execute function
wr.writeBytes("postData=" + params[1]);
// Flushes the postData to the output stream
wr.flush();
wr.close();
// Representing the input stream
InputStream in = httpURLConnection.getInputStream();
// Preparing input stream bytes to be decoded to charset
InputStreamReader inputStreamReader = new InputStreamReader(in);
StringBuilder dataBuffer = new StringBuilder();
// Translates input stream bytes to charset
int inputStreamData = inputStreamReader.read();
while (inputStreamData != -1) {
char current = (char) inputStreamData;
inputStreamData = inputStreamReader.read();
// concatenates data characters from input stream
dataBuffer.append(current);
}
data = dataBuffer.toString();
} catch (Exception e) {
e.printStackTrace();
} finally {
// Disconnects socket after using
if (httpURLConnection != null) {
httpURLConnection.disconnect();
}
}
Log.e("TAG", data);
return data;
}
#Override
protected void onPostExecute(String result) {
super.onPostExecute(result);
// expecting a response code fro my server upon receiving the POST data
Log.e("TAG", result);
Posts.PostsDetails postsHelper = new Posts().new PostsDetails();
// For posts
try {
if (postsHelper.getIsPDCalled()){
JSONObject pJObj = new JSONObject(result);
JSONArray pJObjArray = pJObj.getJSONArray("posts");
for (int i = 0; i < pJObjArray.length(); i++) {
JSONObject pJObj_data = pJObjArray.getJSONObject(i);
postsHelper.setPost(pJObj_data.getInt("id"), "post_title", "post_content");
}
}
} catch (JSONException e) {
//Toast.makeText(JSonActivity.this, e.toString(), Toast.LENGTH_LONG).show();
Log.d("Json","Exception = "+e.toString());
}
}
}
}
Login.java
public class Login extends AppCompatActivity {
Button LoginButton;
EditText uUserName, uPassWord;
WSAdapter.SendAPIRequests AuthHelper;
#Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_login);
//SetupHomeBtn = (ImageButton) findViewById(R.id.SetupHomeBtn);
LoginButton = (Button) findViewById(R.id.LoginButton);
uUserName = (EditText) findViewById(R.id.LoginUserBox);
uPassWord = (EditText) findViewById(R.id.LoginPassBox);
//AuthHelper = new WSAdapter().new SendDeviceDetails();
// Moves user to the main page after validation
LoginButton.setOnClickListener(new View.OnClickListener() {
#Override
public void onClick(View v) {
// gets the username and password from the EditText
String strUserName = uUserName.getText().toString();
String strPassWord = uPassWord.getText().toString();
// API url duh
String APIUrl = "http://192.168.0.18:8000/token-auth/";
// If the user is authenticated, then transfer to the MainActivity page
if (APIAuthentication(strUserName, strPassWord, APIUrl)){
startActivity(new Intent(Login.this, Posts.class));
}
}
});
}
private boolean APIAuthentication(String un, String pw, String url){
// when it wasn't static -> AuthHelper = new WSAdapter().new SendAPIRequests();
AuthHelper = new WSAdapter.SendAPIRequests();
JSONObject postData = new JSONObject();
try {
// Attempt to input info to the Django API
postData.put("username", un);
postData.put("password", pw);
// Putting the data to be posted in the Django API
AuthHelper.execute(url, postData.toString());
return true;
} catch (JSONException e) {
e.printStackTrace();
}
return false;
}
}
I was expecting my onPostExecute to be called and store data for my posts arrays.

Okay this is a nice example of async tasks. The problem here is when you call an async task then the code below will continue to execute even when the async task hasn't finished. So what happens in your case:
You fetch the posts and then ask to display them on the exact moment that the async function is still getting the posts. So of course the List is empty.
You can fix this by using the await keyword. This keyword stops the rest of your code from executing until that line has been executed. So change:
postDetailsHelper.callPostDetails("192.168.0.18:8000/api");
to:
await postDetailsHelper.callPostDetails("192.168.0.18:8000/api");
Now the reason that the login does work is because you call that function within the if statement. If you would store the return value of that function in a boolean first then it wouldn't work either.

Getting HttpURLConnection data back to List View Adapter

This is driving me crazy. I was forced by android to create a thread so that it did not lock the main thread. Now I want to get that data back to the ListView Adapter that I created. I googled the error but it is not clear how to adapt this code. Thanks to any help you can give
public class Detail extends AppCompatActivity
{
ListView list;
ListViewAdapter listviewadapter;
List<CData> lstData = new ArrayList<CData>();
#Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.listview_main);
list = (ListView) findViewById(R.id.listview);
listviewadapter = new ListViewAdapter(this, R.layout.listview_item, lstData);
list.setAdapter(listviewadapter);
// these work
CData d1 = new CData("test1", "data1", "a");
lstData.add(d1);
CData d2 = new CData("test2", "data2", "a");
lstData.add(d2);
Thread thread = new Thread(new Runnable(){
#Override
public void run(){
try {
URL url = new URL("http://testserver.com/getdata.php");
HttpURLConnection connection = (HttpURLConnection) url.openConnection();
connection.setRequestMethod("GET");
connection.connect();
InputStream inStream = null;
inStream = connection.getInputStream();
BufferedReader bReader = new BufferedReader(new InputStreamReader(inStream));
String temp, response = "";
while ((temp = bReader.readLine()) != null) {
response += temp;
}
// this is not working
CData d4 = new CData("test3", response, "a");
lstData.add(d4);
listviewadapter.notifyDataSetChanged();
// this prints out to the log window
System.out.println("---------------yesss--------" + response);
// this does not work
listviewadapter.notifyDataSetChanged();
// this does not work either
listviewadapter.clear();
listviewadapter.addAll(lstData);
listviewadapter.notifyDataSetChanged();
}
catch(Exception ex)
{
System.out.println("generic ex" + ex.toString());
}
}
});
thread.start();
CData d3 = new CData("test4", "data4", "a");
lstData.add(d3);
Error
CalledFromWrongThreadException: Only the original thread that created a view hierarchy can touch its views.

First of all don't use threads for network request.
Either use AsyncTask or Http libraries like Retrofit or volley etc libraries. Because they provide batter implementation of Http web request and handling mechanism.
From your code this can be solution
runOnUiThread(new Runnable() {
#Override
public void run() {
//UI updates
// this does not work either
listviewadapter.clear();
listviewadapter.addAll(lstData);
listviewadapter.notifyDataSetChanged();
}
});

Make your d4 variable global.
After your catch statement :-
runOnUiThread(new Runnable() {
#Override
public void run() {
lstData.add(d4);
listviewadapter.clear();
listviewadapter.addAll(lstData);
listviewadapter.notifyDataSetChanged();
}
}

you should update UI on UI thread like this
runOnUiThread(new Runnable() {
#Override
public void run() {
//stuff that updates ui
listviewadapter.clear();
listviewadapter.addAll(lstData);
listviewadapter.notifyDataSetChanged();
}
});

Listview jump to top when adding new item

i am making application that have scroll listener that add data from multiple URL
but when i scroll the list jump to first position and than load the URL i know that the adapter in my a sync task get executed every time i load new URL task when i load new item but i don't know how to fix it
public class jsontask extends AsyncTask<String, String, List<newsmodel>> {
#Override
protected List<newsmodel> doInBackground(String... params) {
BufferedReader reader = null;
HttpURLConnection connection = null;
try {
URL url = new URL(params[0]);
connection = (HttpURLConnection) url.openConnection();
if (connectiondetector.isConnected()) {
connection.addRequestProperty("Cache-Control", "max-age=0");
} else {
moviemodelList.addAll((List<newsmodel>) cacheThis.readObject(
technology.this, fileName));
}
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);
}
String finaljson = buffer.toString();
JSONObject parentobject = new JSONObject(finaljson);
JSONArray parentarray = parentobject.getJSONArray("articles");
for (int i = 0; i < parentarray.length(); i++) {
JSONObject finalobject = parentarray.getJSONObject(i);
newsmodel newsmodel = new newsmodel();
newsmodel.setAuthor(finalobject.getString("author"));
if (finalobject.isNull("author")) {
}
newsmodel.setDescription(finalobject.getString("description"));
newsmodel.setTitle(finalobject.getString("title"));
newsmodel.setImage(finalobject.getString("urlToImage"));
newsmodel.setUrl(finalobject.getString("url"));
newsmodel.setPublishedAt(finalobject.getString("publishedAt"));
cacheThis.writeObject(technology.this, fileName, moviemodelList);
moviemodelList.add(newsmodel);
}
return moviemodelList;
} catch (MalformedURLException e) {
e.printStackTrace();
return moviemodelList;
} catch (IOException e) {
e.printStackTrace();
return moviemodelList;
} catch (JSONException e) {
} catch (ClassNotFoundException e) {
e.printStackTrace();
} finally {
if (connection != null) {
}
try {
if (reader != null) {
reader.read();
}
} catch (IOException e) {
e.printStackTrace();
}
}
return moviemodelList;
}
#Override
protected void onPostExecute(List<newsmodel> result) {
super.onPostExecute(result);
newsadapter adapter = new newsadapter(getApplicationContext(), R.layout.row, result);
lvnews.setAdapter(adapter);
}
}
public class newsadapter extends ArrayAdapter {
private List<newsmodel> moviemodelList;
private int resource;
private LayoutInflater inflater;
public newsadapter(Context context, int resource, List<newsmodel> objects) {
super(context, resource, objects);
moviemodelList = objects;
this.resource = resource;
inflater = (LayoutInflater) getSystemService(LAYOUT_INFLATER_SERVICE);
}`
and this is how i excute my a sync task
protected void onStart() {
super.onStart();
getSupportActionBar().setDisplayHomeAsUpEnabled(true);
moviemodelList.clear();
new jsontask().execute("https://newsapi.org/v1/articles?source=engadget&sortBy=top&apiKey=ade8f00a634b4825a028837ec107afae");
lvnews.setOnScrollListener(new EndlessScrollListener() {
#Override
public boolean onLoadMore(int page, int totalItemsCount) {
new jsontask().execute("url1");
new jsontask().execute("url2");
new jsontask().execute("url3");
new jsontask().execute("url4");
new jsontask().execute("url5");
new jsontask().execute("url6");
return false;
}
});
}

Remove these lines from onPostExecute
newsadapter adapter = new newsadapter(getApplicationContext(), R.layout.row, result);
lvnews.setAdapter(adapter);
You are setting adapter eveytime after executing doInBackground. You need to do it only once. You can do it in onCreate
The basic methods used in an android AsyncTask class are defined below
:
doInBackground() : This method contains the code which needs to be executed in background. In this method we can send results multiple
times to the UI thread by publishProgress() method. To notify that the
background processing has been completed we just need to use the
return statements
onPreExecute() : This method contains the code which is executed before the background processing starts
onPostExecute() : This method is called after doInBackground method completes processing. Result from doInBackground is passed to
this method
onProgressUpdate() : This method receives progress updates from doInBackground method, which is published via publishProgress method,
and this method can use this progress update to update the UI thread
Please refer this link to know how Async task

After getting first url response call for second new jsontask().execute("url2"); then call for third, fourth and so on.
Make a common code to reuse it again and again.
try this link : http://www.devexchanges.info/2015/03/android-listview-dynamically-load-more.html