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How to get Activity/getWindow() from services java class?

I'm trying to run a function that requires passing it a screen capture. When I run this from the main activity, I can run the code like this:
SendScreenFunction(getWindow().getDecorView().getRootView(), getApplicationContext());
I'm not trying to call this function from a service and I can't access the getWindow() function because it requires an activity (which isn't available in the service). I was looking around online and someone suggested a function to get the activity so I can use the function. My current code looks like this:
public class ASTasks extends Service {
// This method run only one time. At the first time of service created and running
#Override
public void onCreate() {
HandlerThread thread = new HandlerThread("ServiceStartArguments",
Process.THREAD_PRIORITY_BACKGROUND);
thread.start();
Log.d("onCreate()", "After service created");
}
#Override
public int onStartCommand(Intent intent, int flags, int startId) {
Toast.makeText(this, "Entered Timer!", Toast.LENGTH_SHORT).show();
Activity main_activity = getActivity(getApplicationContext());
try {
Log.i("Services", "Before crash");
SendScreenFunction(main_activity.getWindow().getDecorView().getRootView(), getApplicationContext());
Log.i("Services", "After crash");
} catch (IOException e) {
e.printStackTrace();
}
return START_STICKY;
}
#Override
public IBinder onBind(Intent intent) {
// We don't provide binding
return null;
}
public void SendScreenFunction(View view, Context context){
// Function goes here
}
public static Activity getActivity(Context context) {
if (context == null) return null;
if (context instanceof Activity) return (Activity) context;
if (context instanceof ContextWrapper) return getActivity(((ContextWrapper)context).getBaseContext());
return null;
}
}
Unfortunately, that solution doesn't seem to work and it's crashing. The Logcat error is shown below:
Process: com.example.ASservice:remote, PID: 15966
java.lang.RuntimeException: Unable to start service com.example.ASservice.ASTasks#6e7fed5 with Intent { cmp=com.example.ASservice/.ASTasks }: java.lang.NullPointerException: Attempt to invoke virtual method 'android.view.Window android.app.Activity.getWindow()' on a null object reference
at android.app.ActivityThread.handleServiceArgs(ActivityThread.java:5110)
at android.app.ActivityThread.access$2100(ActivityThread.java:310)
at android.app.ActivityThread$H.handleMessage(ActivityThread.java:2319)
at android.os.Handler.dispatchMessage(Handler.java:106)
at android.os.Looper.loopOnce(Looper.java:226)
at android.os.Looper.loop(Looper.java:313)
at android.app.ActivityThread.main(ActivityThread.java:8680)
at java.lang.reflect.Method.invoke(Native Method)
at com.android.internal.os.RuntimeInit$MethodAndArgsCaller.run(RuntimeInit.java:567)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:1135)
Caused by: java.lang.NullPointerException: Attempt to invoke virtual method 'android.view.Window android.app.Activity.getWindow()' on a null object reference
at com.example.ASservice.ASTasks.onStartCommand(ASTasks.java:41)
at android.app.ActivityThread.handleServiceArgs(ActivityThread.java:5092)
at android.app.ActivityThread.access$2100(ActivityThread.java:310) 
at android.app.ActivityThread$H.handleMessage(ActivityThread.java:2319) 
at android.os.Handler.dispatchMessage(Handler.java:106) 
at android.os.Looper.loopOnce(Looper.java:226) 
at android.os.Looper.loop(Looper.java:313) 
at android.app.ActivityThread.main(ActivityThread.java:8680) 
at java.lang.reflect.Method.invoke(Native Method) 
at com.android.internal.os.RuntimeInit$MethodAndArgsCaller.run(RuntimeInit.java:567) 
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:1135) 
Any ideas on the best way to take the screen capture from within the service (or even a way to pass a flag back to main to process it there)?
Any suggestions would be greatly appreciated. Thanks!

How to move reusable functionalities to a generic class and invoke another activity from there?

I am new to Android development and I am facing an issue in invoking an activity from a generic class where I have a reusable function.
I have MainActivity where I need to check if the application has Network connectivity and then check if the user is already signed in.
If the user is signed in I need to open the Rate activity otherwise I will open the Login activity.
I thought I can keep the logic that checks the Network connectivity and shows the popup reusable and move it to a Global class as below
public class Global extends AppCompatActivity {
public static boolean hasConnectivity = false;
public static boolean userSignedIn = false;
String TAG = "Debug Log - Helper";
Context context;
#Override
public void onCreate(Bundle savedInstanceState){
super.onCreate(savedInstanceState);
context = this;
}
private void networkConnectionErrorDialog(final Context context, final Class targetClass){
Log.d(TAG, "Show Alert Dialog");
new AlertDialog.Builder(context)
.setTitle(R.string.connection_error_title)
.setMessage(R.string.connection_error_message)
.setIcon(R.drawable.warning)
.setPositiveButton(
R.string.try_again,
new DialogInterface.OnClickListener() {
#Override
public void onClick(DialogInterface dialog, int which) {
Log.d(TAG, "Trying Again");
isNetworkAvailable(context, targetClass);
}
}).show();
}
protected void isNetworkAvailable(Context context, Class targetClass) {
if(NetworkUtil.isConnected(context)){
Log.d(TAG, "Has connectivity");
if(targetClass != null){
Log.d(TAG, targetClass.toString());
Intent targetIntent = new Intent(context, targetClass);
startActivity(targetIntent);
}
hasConnectivity = true;
return;
}else{
Log.d(TAG, "Has no connectivity");
hasConnectivity = false;
networkConnectionErrorDialog(context, targetClass);
}
}
}
I pass in the targetClass as Login.class or Rate.class (based on user signed in state) from the MainActivity where isNetworkAvailable() is invoked.
I am getting the following error. Could someone help me fix the issue and help me understand if my approach needs improvement?
java.lang.RuntimeException: Unable to resume activity {com.solitontech.dayatsoliton/com.solitontech.dayatsoliton.MainActivity}: java.lang.NullPointerException: Attempt to invoke virtual method 'android.app.ActivityThread$ApplicationThread android.app.ActivityThread.getApplicationThread()' on a null object reference
at android.app.ActivityThread.performResumeActivity(ActivityThread.java:3581)
at android.app.ActivityThread.handleResumeActivity(ActivityThread.java:3621)
at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2862)
at android.app.ActivityThread.-wrap11(Unknown Source:0)
at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1589)
at android.os.Handler.dispatchMessage(Handler.java:106)
at android.os.Looper.loop(Looper.java:164)
at android.app.ActivityThread.main(ActivityThread.java:6494)
at java.lang.reflect.Method.invoke(Native Method)
at com.android.internal.os.RuntimeInit$MethodAndArgsCaller.run(RuntimeInit.java:438)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:807)
Caused by: java.lang.NullPointerException: Attempt to invoke virtual method 'android.app.ActivityThread$ApplicationThread android.app.ActivityThread.getApplicationThread()' on a null object reference
at android.app.Activity.startActivityForResult(Activity.java:4488)
at android.support.v4.app.BaseFragmentActivityJB.startActivityForResult(BaseFragmentActivityJB.java:50)
at android.support.v4.app.FragmentActivity.startActivityForResult(FragmentActivity.java:79)
at android.app.Activity.startActivityForResult(Activity.java:4445)
at android.support.v4.app.FragmentActivity.startActivityForResult(FragmentActivity.java:859)
at android.app.Activity.startActivity(Activity.java:4806)
at android.app.Activity.startActivity(Activity.java:4774)
at com.solitontech.dayatsoliton.Global.isNetworkAvailable(Global.java:50)
at com.solitontech.dayatsoliton.MainActivity.onResume(MainActivity.java:68)
at android.app.Instrumentation.callActivityOnResume(Instrumentation.java:1355)
at android.app.Activity.performResume(Activity.java:7117)
at android.app.ActivityThread.performResumeActivity(ActivityThread.java:3556)

It looks like your application is experiencing a null pointer exception in your activity's onResume method. If you had called startActivityForResult, make sure that the data in
#Override
protected void onActivityResult(int requestCode, int resultCode, Intent data)
{..}
is non null before processing it.
As for your question about starting an activity from your helper class Global, you can define a function like this.
private static void goToActivity(Context context, Class<?> activityClass){
Intent intent = new Intent(context, activityClass);
context.startActivity(intent);
}
You can call this method as below.
goToActivity(context,TargetActivity.class);
Good luck.

Intent targetIntent = new Intent(context, targetClass);
startActivity(targetIntent);
above code is wrong. You should pass your current activity and target activity here.
Intent intent = new Intent(CurrentActivity.this, TargetingActivity.class);
startActivity(intent);
As a example :
If you want to start ActivtyB form ActivtyA
Intent intent = new Intent(ActivityA.this, ActivityD.class);
startActivity(intent);
1st try to correct this error. then you can find some others.

Call a Context within a class for a different activity

I am checking for SEND_SMS permission within a class:
public class SendSms extends Activity{
int requestPerm;
private void checkPermissionSms(){
if(ContextCompat.checkSelfPermission(, Manifest.permission.SEND_SMS)
!= PackageManager.PERMISSION_GRANTED){
ActivityCompat.requestPermissions(this, new String[]{Manifest.permission.SEND_SMS},
requestPerm); //If we don't have the permission, request it here
}
}
But at checkSelPermission, it needs a context but I'm not sure what context it needs(not even too sure what Context for checkSelfPermission)
I am following:
https://developer.android.com/training/permissions/requesting.html#java
The above method is called like so:
public static void sendSms(String message){
// Intent calledSendSMS = getIntent();
//String message = calledSendSMS.getStringExtra(Intent.EXTRA_TEXT);
// PendingIntent pi = PendingIntent.getActivity(this,0, new Intent(this,SendSms.class),0);
SendSms checkPerm = new SendSms();
SmsManager sendTheMessage = SmsManager.getDefault();
String phoneNumber = "5556";
checkPerm.checkPermissionSms();
sendTheMessage.sendTextMessage(phoneNumber, null,message,null,null);
}
And this Method is called from another activity.
I did put in "this" but then I get the following error:
Caused by: java.lang.NullPointerException: Attempt to invoke virtual method 'int android.content.Context.checkPermission(java.lang.String, int, int)' on a null object reference
at android.content.ContextWrapper.checkPermission(ContextWrapper.java:724)
at android.support.v4.content.ContextCompat.checkSelfPermission(ContextCompat.java:430)
at com.example.android.footysortit.SendSms.checkPermissionSms(SendSms.java:17)
Really all I want to do is check for permission and request it if needed.
Edit: If I add the check permissions within an actual activity and use "this" it works just fine.
So how do I get it to pass the activity data?

Change this:
SendSms checkPerm = new SendSms();
To:
SendSms checkPerm = new SendSms(this);
SendSms class - you need to create constuctor of the class
public class SendSms extends Activity {
private Activity mActivity;
private int requestPerm;
public SendSms(Activity mActivity) {
this.mActivity = mActivity;
}
private void checkPermissionSms() {
if (ContextCompat.checkSelfPermission(mActivity, Manifest.permission.SEND_SMS) != PackageManager.PERMISSION_GRANTED) {
ActivityCompat.requestPermissions(this, new String[]{Manifest.permission.SEND_SMS}, requestPerm);
//If we don't have the permission, request it here
}
}
}

Context for intent in onpostexecute is not null but getting null exception

I've been stumped with this problem for two days now. I've checked this forum and other forums but can't get a question or answer close enough to my problem.
Basically I'm trying to execute an intent to open an activity from a non-activities onpostexecute, I'm sending the context (MainActivty.this) and string from a onMarkerClick function that is in a method in the MainActivity. This is going to a constructor in the non-activity which has the parameters for context and the string.
The issue is that I'm getting a null exception, but after debugging, the context is not null, it has the value of MainActivity, but when the intent is executed it returns a null exception. I've also tried many variations eg. Activity, getApplicationContext, this.context, (classname).context, (classname).this and tried a global context to no avail. The odd thing is I put the intent into an if statement if(context != null) and it passes through and it executes the intent which in turn gives me null exception which doesn't make sense. I know I'm new to android if anyone has any other suggestions on opening the activity that would be great thanks very much.
E/AndroidRuntime: FATAL EXCEPTION: main
Process: com.example.quantusapps.joggertest, PID: 12253
java.lang.NullPointerException: Attempt to invoke virtual method 'java.lang.String android.content.Context.getPackageName()' on a null object reference
at android.content.ContextWrapper.getPackageName(ContextWrapper.java:131)
at android.content.ComponentName.(ComponentName.java:77)
at android.content.Intent.(Intent.java:4029)
at com.example.quantusapps.joggertest.BusCoachTramInfo.onPostExecute(BusCoachTramInfo.java:131)
at com.example.quantusapps.joggertest.BusCoachTramInfo.onPostExecute(BusCoachTramInfo.java:25)
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:155)
at android.app.ActivityThread.main(ActivityThread.java:5696)
at java.lang.reflect.Method.invoke(Native Method)
at java.lang.reflect.Method.invoke(Method.java:372)
at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:1028)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:823)<
This is the Mainactivity Method with onMarkerClick
mGoogleMap.setOnMarkerClickListener(new GoogleMap.OnMarkerClickListener() {
#Override
public boolean onMarkerClick(Marker marker) {
String bctID = bctExtraMarkerInfo.get(marker.getId());
BusCoachTramInfo busCoachTramInfo = new BusCoachTramInfo(bctID, MainActivity.this);
busCoachTramInfo.execute(bctID);
return false;
}
});
This is the non-activity constructor.
Context context;
BusCoachTramInfo(String busstopID, Context context) {
this.context = context;
naptanIdUrl = "https://api.tfl.gov.uk/StopPoint/" + busstopID + "/Arrivals?app_key=" + tfl_API_KEY + "&app_id=9c0b3009";
}
This is where the null exception is happening.
#Override
protected void onPostExecute(TreeMap<Integer, String[]> Map) {
super.onPostExecute(Map);
Intent i = new Intent(context, BusArrivalTime.class);
context.startActivity(i);

One way to get things done is implementing the AsyncTask as part of a method which takes an instance of MainActivity as a parameter. The AsyncTask on the other hand would work with a WeakReference:
void doExecuteBusCoachTramInfo(final String busstopID, MainActivity activity){
final WeakReference<MainActivity> wrActivity = new WeakReference<MainActivity>(MainActivity.this);
new AsyncTask<Void, Void, TreeMap<Integer, String[]>>(){
#Override
protected TreeMap<Integer, String[]> doInBackground(Void... params)
{
// your code from BusCoachTramInfo here
}
#Override
protected void onPostExecute(TreeMap<Integer, String[]> integerTreeMap)
{
// get back to the original Activity if possible:
MainActivity activity = wrActivity.get();
if (activity != null){
Intent i = new Intent(activity, BusArrivalTime.class);
activity.startActivity(i);
}
}
}.execute();
}
This method may be part of MainActivity, but it can just as well belong to some other class.

Android Retrofit "Attempt to invoke virtual method on a null object reference"

Hi first of all i searched some similar questions like mine but unfortunately i couldn't find the similarity of my code to them so please here me out
I have a Main Activity Class
public class MainActivity extends AppCompatActivity {
public ProgressDialog loading;
public String[] itemer;
#Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
RetrofitHandler handler = new RetrofitHandler();
handler.getContacts(MainActivity.this);
}
public void getter(String[] response, int size) {
String[] itemer;
itemer = new String[size];
if (response != null) {
itemer = response;
Toast.makeText(MainActivity.this, itemer[0], Toast.LENGTH_SHORT).show();
}
}
And a Handler for my result
public class RetrofitHandler {
public String[] item;
public static final String ROOT_URL = "http://api.androidhive.info";
public List<Contacts> contacts;
// final MainActivity main = new MainActivity();
public void getContacts(final Context context) {
final ProgressDialog loading = ProgressDialog.show(context, "Fetching Data", "Please wait...", false, false);
RestAdapter adapter = new RestAdapter.Builder().setEndpoint(ROOT_URL).build();
ContactsAPI api = adapter.create(ContactsAPI.class);
api.getContacts(new Callback<Contacts>() {
#Override
public void success(Contacts contacts, Response response) {
loading.dismiss();
MainActivity update = new MainActivity();
List<Contact> contactList = contacts.getContacts();
item = new String[contactList.size()];
int size = contactList.size();
for (int i = 0; i < contactList.size(); i++) {
item[i] = contactList.get(i).getName();
}
update.getter(item, size);
}
#Override
public void failure(RetrofitError error) {
Toast.makeText(context, "Error Occured", Toast.LENGTH_LONG).show();
}
});
}
But I get an error on my response in the main activity here is my log
java.lang.NullPointerException: Attempt to invoke virtual method 'android.content.res.Resources android.content.Context.getResources()' on a null object reference
at android.content.ContextWrapper.getResources(ContextWrapper.java:87)
at android.view.ContextThemeWrapper.getResources(ContextThemeWrapper.java:81)
at android.support.v7.app.AppCompatActivity.getResources(AppCompatActivity.java:542)
at android.widget.Toast.<init>(Toast.java:102)
at android.widget.Toast.makeText(Toast.java:259)
at com.exist.kelvs.retrofit2.MainActivity.getter(MainActivity.java:55)
at com.exist.kelvs.retrofit2.RetrofitHandler$1.success(RetrofitHandler.java:41)
at com.exist.kelvs.retrofit2.RetrofitHandler$1.success(RetrofitHandler.java:28)
at retrofit.CallbackRunnable$1.run(CallbackRunnable.java:45)
at android.os.Handler.handleCallback(Handler.java:739)
at android.os.Handler.dispatchMessage(Handler.java:95)
at android.os.Looper.loop(Looper.java:148)
at android.app.ActivityThread.main(ActivityThread.java:5417)
at java.lang.reflect.Method.invoke(Native Method)
at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:726)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:616)
I maked sure that the handler item where not null tested it with toast but when i pass it to getter it gives me the error where did i do wrong? :(

MainActivity update = new MainActivity();
Never instantiate activities with new. They are not initialized to be useful.
Instead, you can pass your activity as a reference where needed. Change
public void getContacts(final Context context)
to e.g.
public void getContacts(final MainActivity mainActivity)
and use mainActivity where you need an activity Context (such as with Dialogs) and when you need to invoke a method on MainActivity.
Note that generally passing activity references to async operations can be prone to significant memory leaks, and you need to take activity lifecycle into account - the activity might not be active when the async operation finishes.

try to delete the toast in your main activity or replace Mainactivity.this to getApplicationContext() .
from :
Toast.makeText(MainActivity.this, itemer[0], Toast.LENGTH_SHORT).show();
to :
Toast.makeText(getApplicationContext(), itemer[0], Toast.LENGTH_SHORT).show();