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android studion giving error on disableWebView() in android studio

I am trying to use BackgroundMode.disableWebViewOptimizations(); in my ionic app but when i launch the app in the android studio then i am getting this error
E/AndroidRuntime: FATAL EXCEPTION: main
Process: com.siloc.users, PID: 6275
java.lang.NullPointerException: Attempt to invoke interface method 'android.view.View org.apache.cordova.CordovaWebViewEngine.getView()' on a null object reference
at de.appplant.cordova.plugin.background.BackgroundModeExt$1.lambda$run$0$BackgroundModeExt$1(BackgroundModeExt.java:169)
at de.appplant.cordova.plugin.background.-$$Lambda$BackgroundModeExt$1$ENae6xHnDD7pQOdOSwld6cT0QNo.run(Unknown Source:2)
at android.os.Handler.handleCallback(Handler.java:883)
at android.os.Handler.dispatchMessage(Handler.java:100)
at android.os.Looper.loop(Looper.java:230)
at android.app.ActivityThread.main(ActivityThread.java:7880)
at java.lang.reflect.Method.invoke(Native Method)
at com.android.internal.os.RuntimeInit$MethodAndArgsCaller.run(RuntimeInit.java:526)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:1034)
E/NetdClient: querySockNetidForUid nid:0, uid:10357, command.cmdId:11, id:0
This is the function in BackgroundModeExt.java file
private void disableWebViewOptimizations() {
Thread thread = new Thread(){
public void run() {
try {
Thread.sleep(1000);
getApp().runOnUiThread(() -> {
View view = webView.getEngine().getView();
try {
Class.forName("org.crosswalk.engine.XWalkCordovaView")
.getMethod("onShow")
.invoke(view);
} catch (Exception e){
view.dispatchWindowVisibilityChanged(View.VISIBLE);
}
});
} catch (InterruptedException e) {
// do nothing
}
}
};
thread.start();
}
iS there any way i can solve this problem?

Change line: View view = webView.getEngine().getView(); to View view = webView.getView();

Download task throws exception with no internet

I have an app that downloads the current unix timestamp from the internet. The code for the download task is as follows.
public class DownloadTask extends AsyncTask<String, Void, String> {
#Override
protected String doInBackground(String... urls) {
String result = "";
URL url;
HttpURLConnection urlConnection = null;
try {
url = new URL(urls[0]);
urlConnection = (HttpURLConnection) url.openConnection();
InputStream in = urlConnection.getInputStream();
InputStreamReader reader = new InputStreamReader(in);
int data = reader.read();
while (data != -1) {
char current = (char) data;
result += current;
data = reader.read();
}
return result;
} catch (Exception e) {
e.printStackTrace();
Toast.makeText(SplashActivity.this, "you aint got no internet man", Toast.LENGTH_SHORT).show();
}
return null;
}
I run this code in onCreate
DownloadTask task = new DownloadTask();
String result = null;
try {
result = task.execute("http://www.currenttimestamp.com/").get();
Pattern p = Pattern.compile("current_time = (.*?);");
Matcher m = p.matcher(result);
m.find();
String unixTime = (m.group(1));
timeStamp = Integer.parseInt(unixTime);
endTimeMaths = endTime/1000;
} catch (InterruptedException e) {
e.printStackTrace();
Toast.makeText(SplashActivity.this, "you aint got no internet man", Toast.LENGTH_SHORT).show();
} catch (ExecutionException e) {
e.printStackTrace();
Toast.makeText(SplashActivity.this, "you aint got no internet man", Toast.LENGTH_SHORT).show();
}
timeDelta = timeStamp-endTimeMaths;
Log.i("TimeDelta", timeDelta+"");
//If dem boys cheatin
if (timeDelta < 1){
Toast.makeText(SplashActivity.this, "You cheatin boi?", Toast.LENGTH_SHORT).show();
reward=false;
} else if (timeDelta >= 300){
reward = true;
Toast.makeText(SplashActivity.this, "Here is your reward for being gone", Toast.LENGTH_SHORT).show();
}
}
The Exception is as follows
09-04 21:26:42.853 8459-8493/com.firefluxentertainment.retroclicker E/AndroidRuntime: FATAL EXCEPTION: AsyncTask #1
Process: com.firefluxentertainment.retroclicker, PID: 8459
java.lang.RuntimeException: An error occurred while executing doInBackground()
at android.os.AsyncTask$3.done(AsyncTask.java:318)
at java.util.concurrent.FutureTask.finishCompletion(FutureTask.java:354)
at java.util.concurrent.FutureTask.setException(FutureTask.java:223)
at java.util.concurrent.FutureTask.run(FutureTask.java:242)
at android.os.AsyncTask$SerialExecutor$1.run(AsyncTask.java:243)
at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1133)
at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:607)
at java.lang.Thread.run(Thread.java:761)
Caused by: java.lang.RuntimeException: Can't create handler inside thread that has not called Looper.prepare()
at android.os.Handler.<init>(Handler.java:200)
at android.os.Handler.<init>(Handler.java:114)
at android.widget.Toast$TN.<init>(Toast.java:346)
at android.widget.Toast.<init>(Toast.java:101)
at android.widget.Toast.makeText(Toast.java:260)
at com.firefluxentertainment.retroclicker.SplashActivity$DownloadTask.doInBackground(SplashActivity.java:155)
at com.firefluxentertainment.retroclicker.SplashActivity$DownloadTask.doInBackground(SplashActivity.java:119)
at android.os.AsyncTask$2.call(AsyncTask.java:304)
at java.util.concurrent.FutureTask.run(FutureTask.java:237)
at android.os.AsyncTask$SerialExecutor$1.run(AsyncTask.java:243) 
at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1133) 
at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:607) 
at java.lang.Thread.run(Thread.java:761)
Since all the code is in try catch braces I have no idea why it would be crashing. Any help is very much appreciated!

This is because you are trying to show toast in a non-UI thread. There are multiple solutions to your problem :
Create a handler in the Activity and pass it along to DownloadTask. Simply send a message in Handler and show the toast.
Another solution is to send the context in DownloadTask and show the toast as
context.runOnUIThread(new Runnable() {
public void run(){
Toast.showToast("your message here")
}
)
You can send the result of your task in onPostExecute() and show Toast there.

Exception in doinbackground()

I have activity A and B. Both of them have AsyncTasks that connect to the web and fetch some JSON. I get an error that I can't quite replicate always, but I'm not sure what I'm doing wrong. I get the error when I press the back button from activity B to A to Homescreen.
protected Void doInBackground(Void... params) {
synchronized (this) {
if (img_flag == 1) {
System.out.println("entered into doinback1");
UploadImage();
System.out.println("entered into doinback2");
}
if (offlineast_flag == 0) {
System.out.println("entered into doinback3");
UpdateAsset_webService();
System.out.println("entered into doinback4");
ServiceRequest _autoupdate = new ServiceRequest();
_autoupdate.cat_sync(Update_asset.this, _companyId, _usrid,
access_id, profile_id, catid_db);
System.out.println("entered into doinback5");
}
if (img_flag == 2) {
System.out.println("entered into doinback6");
UploadImageOffline();
} else {
System.out.println("entered into doinback7");
loading_dialog.dismiss();
System.out.println("entered into doinback8");
}
}
return null;
}
// Update the progress
protected void onProgressUpdate(Integer... values) {
}
// after executing the code in the thread
protected void onPostExecute(Void result) {
onback();
loading_dialog.dismiss();
img_flag = 0;
Toast.makeText(getApplicationContext(),
"Your asset updated successfully.", Toast.LENGTH_LONG)
.show();
}
This is my Logcat:
java.lang.RuntimeException: An error occured while executing doInBackground()
at android.os.AsyncTask$3.done(AsyncTask.java:300)
at java.util.concurrent.Futuenter code herereTask.finishCompletion(FutureTask.java:355)
at java.util.concurrent.FutureTask.setException(FutureTask.java:222)
at java.util.concurrent.FutureTask.run(FutureTask.java:242)
at android.os.AsyncTask$SerialExecutor$1.run(AsyncTask.java:231)
at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1112)
at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:587)
at java.lang.Thread.run(Thread.java:841)
Caused by: java.lang.NullPointerException
at com.kodology.assetbin.Update_asset.UpdateAsset_webService(Update_asset.java:1733)
at com.kodology.assetbin.Update_asset$LoadViewTask.doInBackground(Update_asset.java:2239)
at com.kodology.assetbin.Update_asset$LoadViewTask.doInBackground(Update_asset.java:1)
at android.os.AsyncTask$2.call(AsyncTask.java:288)
at java.util.concurrent.FutureTask.run(FutureTask.java:237)
... 4 more

NullPointerException on onPostExecute method

I’m having a navigation drawer for my app that contains a menu with which I can navigate between the fragments. The first fragment that i get after the app lunch is the Home which contains a listView and a footer attached in the bottom (is just for the test). The problem is when I lunch the Home fragment for the first time nothing happen and its work very well, but when I change the fragments from the navigation drawer and trying to get back the home fragment the app crash. The error log show me a null pointer Exception. Thes is my code detail
onCreateView method
#Override
public View onCreateView(LayoutInflater inflater, ViewGroup container,
Bundle savedInstanceState) {
if (v != null) {
ViewGroup parent = (ViewGroup) v.getParent();
if (parent != null)
parent.removeView(v);
}
try {
v = inflater.inflate(R.layout.fragment_homes, container, false);
listView = (ListView) v.findViewById(R.id.homeList);
l = new HomeListAdapter(this, homeList);
if(l == null)
Log.i("tag","null");
listView.setAdapter(l);
} catch (InflateException e) {
}
return v;
}
onPostExecute method
#Override
protected void onPostExecute(final String res) {
/*try {
jObj = new JSONArray(res);
} catch (JSONException e) {
e.printStackTrace();
}*/
/* JSONArray j = null;
try {
j = new JSONArray(res);
} catch (JSONException e) {
e.printStackTrace();
}*/
// Parsing json
for (int i = 0; i < 5; i++) {
//JSONObject obj = j.getJSONObject(i);
Home home = new Home();
//String photoNews = java.net.URLDecoder.decode(obj.getString("photonews"), "UTF-8");
home.setNomC("Karim Ennassiri");
home.setPhotoP("http://i1239.photobucket.com/albums/ff509/FestusMANAFEST/iker-casillas20Wallpaper__yvt2.jpg");
home.setPhotoAr("http://voyage-essaouira-maroc.com/upload/apostrophe_image_(13).jpg");
home.setText("Chlada V2.0 Edition");
home.setNbrSick("5");
home.setNbrComm("8");
home.setNbrShare("0");
homeList.add(home);
}
l.notifyDataSetChanged();
//pDialog.hide();
}
The error log
10-10 09:31:30.884 2447-2447/com.example.user.unchained E/AndroidRuntime﹕ FATAL EXCEPTION: main
Process: com.example.user.unchained, PID: 2447
java.lang.NullPointerException
at com.example.user.unchained.HomesActivity$PlaceholderFragment$FeedsTask.onPostExecute(HomesActivity.java:375)
at com.example.user.unchained.HomesActivity$PlaceholderFragment$FeedsTask.onPostExecute(HomesActivity.java:277)
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:136)
at android.app.ActivityThread.main(ActivityThread.java:5017)
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:779)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:595)
at dalvik.system.NativeStart.main(Native Method)
And this is exactly the line that cause the error : l.notifyDataSetChanged();. I notice that the error is just in the case when i'm trying to display the fragment for the secode time.
So any help please ? Thanks !

You need to use this in doInBackground.
#Override
protected Void doInBackground(void... ) {
try {
for (int i = 0; i < 5; i++) {
//JSONObject obj = j.getJSONObject(i);
Home home = new Home();
//String photoNews = java.net.URLDecoder.decode(obj.getString("photonews"), "UTF-8");
home.setNomC("Karim Ennassiri");
home.setPhotoP("http://i1239.photobucket.com/albums/ff509/FestusMANAFEST/iker-casillas20Wallpaper__yvt2.jpg");
home.setPhotoAr("http://voyage-essaouira-maroc.com/upload/apostrophe_image_(13).jpg");
home.setText("Chlada V2.0 Edition"); //give some other name in getter setter for setText in Home.java. It makes not to understand whether you are using setText for textview assigning.
home.setNbrSick("5");
home.setNbrComm("8");
home.setNbrShare("0");
homeList.add(home);
}
postExecute is used to display UI. don't perform heavy operation like parsing in PostExecute.

RSS AsyncTask - ArrayAdapter is undefined

I am creating an RSS reader application for android 4.0+. I have put the reader code in AsyncTask because of the NetworkOnMainThreadException. The code almost works fine, however one line has an error. This is my code:
Java code:
private class PostTask extends AsyncTask<String, Integer, String> {
#Override
protected void onPreExecute() {
super.onPreExecute();
}
#Override
protected String doInBackground(String... params) {
String url=params[0];
headlines = new ArrayList();
links = new ArrayList();
//Download and parse xml feed
headlines = new ArrayList();
links = new ArrayList();
try {
URL url1 = new URL("http://feeds.pcworld.com/pcworld/latestnews");
XmlPullParserFactory factory = XmlPullParserFactory.newInstance();
factory.setNamespaceAware(false);
XmlPullParser xpp = factory.newPullParser();
// We will get the XML from an input stream
xpp.setInput(getInputStream(url1), "UTF_8");
/* We will parse the XML content looking for the "<title>" tag which appears inside the "<item>" tag.
* However, we should take in consideration that the rss feed name also is enclosed in a "<title>" tag.
* As we know, every feed begins with these lines: "<channel><title>Feed_Name</title>...."
* so we should skip the "<title>" tag which is a child of "<channel>" tag,
* and take in consideration only "<title>" tag which is a child of "<item>"
*
* In order to achieve this, we will make use of a boolean variable.
*/
boolean insideItem = false;
// Returns the type of current event: START_TAG, END_TAG, etc..
int eventType = xpp.getEventType();
while (eventType != XmlPullParser.END_DOCUMENT) {
if (eventType == XmlPullParser.START_TAG) {
if (xpp.getName().equalsIgnoreCase("item")) {
insideItem = true;
} else if (xpp.getName().equalsIgnoreCase("title")) {
if (insideItem)
headlines.add(xpp.nextText()); //extract the headline
} else if (xpp.getName().equalsIgnoreCase("link")) {
if (insideItem)
links.add(xpp.nextText()); //extract the link of article
}
}else if(eventType==XmlPullParser.END_TAG && xpp.getName().equalsIgnoreCase("item")){
insideItem=false;
}
eventType = xpp.next(); //move to next element
}
} catch (MalformedURLException e) {
e.printStackTrace();
} catch (XmlPullParserException e) {
e.printStackTrace();
} catch (IOException e) {
e.printStackTrace();
}
return "Feed parsed!";
}
#Override
protected void onProgressUpdate(Integer... values) {
super.onProgressUpdate(values);
}
#Override
protected void onPostExecute(String result) {
super.onPostExecute(result);
// Binding data
ArrayAdapter adapter = new ArrayAdapter(this,
android.R.layout.simple_list_item_1, headlines);
setListAdapter(adapter);
}
}
in this code snippet i get an error:
#Override
protected void onPostExecute(String result) {
super.onPostExecute(result);
// Binding data
ArrayAdapter adapter = new ArrayAdapter(this,
android.R.layout.simple_list_item_1, headlines);
setListAdapter(adapter);
}
Error: The constructor ArrayAdapter(MainActivity.PostTask, int, List) is undefined.
Logcat:
01-26 20:55:53.811: E/AndroidRuntime(1830): FATAL EXCEPTION: AsyncTask #1
01-26 20:55:53.811: E/AndroidRuntime(1830): java.lang.RuntimeException: An error occured while executing doInBackground()
01-26 20:55:53.811: E/AndroidRuntime(1830): at android.os.AsyncTask$3.done(AsyncTask.java:278)
01-26 20:55:53.811: E/AndroidRuntime(1830): at java.util.concurrent.FutureTask$Sync.innerSetException(FutureTask.java:273)
01-26 20:55:53.811: E/AndroidRuntime(1830): at java.util.concurrent.FutureTask.setException(FutureTask.java:124)
01-26 20:55:53.811: E/AndroidRuntime(1830): at java.util.concurrent.FutureTask$Sync.innerRun(FutureTask.java:307)
01-26 20:55:53.811: E/AndroidRuntime(1830): at java.util.concurrent.FutureTask.run(FutureTask.java:137)
01-26 20:55:53.811: E/AndroidRuntime(1830): at android.os.AsyncTask$SerialExecutor$1.run(AsyncTask.java:208)
01-26 20:55:53.811: E/AndroidRuntime(1830): at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1076)
01-26 20:55:53.811: E/AndroidRuntime(1830): at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:569)
01-26 20:55:53.811: E/AndroidRuntime(1830): at java.lang.Thread.run(Thread.java:856)
01-26 20:55:53.811: E/AndroidRuntime(1830): Caused by: java.lang.IllegalArgumentException
01-26 20:55:53.811: E/AndroidRuntime(1830): at org.kxml2.io.KXmlParser.setInput(KXmlParser.java:1615)
01-26 20:55:53.811: E/AndroidRuntime(1830): at com.mysoftware.mysoftwareos.mobile.MainActivity$PostTask.doInBackground(MainActivity.java:343)
01-26 20:55:53.811: E/AndroidRuntime(1830): at com.mysoftware.mysoftwareos.mobile.MainActivity$PostTask.doInBackground(MainActivity.java:1)
01-26 20:55:53.811: E/AndroidRuntime(1830): at android.os.AsyncTask$2.call(AsyncTask.java:264)
01-26 20:55:53.811: E/AndroidRuntime(1830): at java.util.concurrent.FutureTask$Sync.innerRun(FutureTask.java:305)
01-26 20:55:53.811: E/AndroidRuntime(1830): ... 5 more
Could anyone please look into my problem and come up with a solution? Or tell me if i should do anything different? Thanks a lot!

Change it to:
ArrayAdapter adapter = new ArrayAdapter(MainActivity.this,
android.R.layout.simple_list_item_1, headlines);
this refers to the AsyncTask, so you have to explicitly reference MainActivity's this.

use Activity Context instead of AsyncTask to Create ArrayAdapter inside onPostExecute method as :
ArrayAdapter<String> adapter =
new ArrayAdapter<String>(Your_Current_Activity.this,
android.R.layout.simple_list_item_1, headlines);
setListAdapter(adapter);
EDIT :
after log posted also change
xpp.setInput(getInputStream(url1), "UTF_8");
to
xpp.setInput(url1.openConnection().getInputStream(), "UTF_8");