Develop Reference

What is context when a BroadcastReceiver is called?

I know this is a broad question, but this might be any average android developer's question. In a BroadcastReceiver, what is the context parameter passed through onReceive() method?
public class MyReceiver extends BroadcastReceiver {
#Override
public void onReceive(Context context, Intent intent) {
}
}
I just know we have 3 main types of context: Activity, Service, Application.

Initially Context represents environment data and it is used to create application specific resource.
for example, if you create a new object for a class with "this" keyword as its context, that object was resource for that specific class and not for others.
context was also used to share system resources like layoutInflater, NotificationManager and so on.
In Broadcast receiver, context refers to the activity or class in which the broadcast receiver is running. if your "MainActivity" sends a broadcast then the context would have something like the following "com.example.MainActivity"

Android Change a variable in service from other app

the title says all, I need to change the variable of my service from a activity in my other app , what to finalize the service or not, this is possible?
I found the Message object , but I do not quite understand

The simplest solution would be to implement a BroadcastReceiver. Your Service listens for the Broadcast and the other App sends the Broadcast.
Example Reciever:
public class MyReceiver extends BroadcastReceiver {
#Override
public void onReceive(Context context, Intent intent) {
// Get bundle from intent and use it to set your Variable in your Service
}
}
Example Broadcaster (courtesy of Vogella):
Intent intent = new Intent();
intent.setAction("de.vogella.android.mybroadcast");
sendBroadcast(intent);

Why would LocalBroadcastManager not work instead of Context.registerReceiver?

I had to implement a feature to this app which consists of an Activity and a Service working on the background (it implements Service, not IntentService).
I went through a few tutorials on the Internet that are supposed to work, and they all use LocalBroadcastManager, which by the way is the recommended by Android:
If you don't need to send broadcasts across applications, consider
using this class with LocalBroadcastManager instead of the more
general facilities described below.
I literally lost a day to find out the problem why it wouldn't work for me: it only works if I use Context.sendBroadcast(). and Context.registerReceiver() instead of the LocalBroadcastManager methods.
Now my app is working, but I feel I am going against the best practices, and I don't know why.
Any ideas why it could be happening?
EDIT:
After I wrote this question I went further on the problem. LocalBroadcastManager works through a Singleton, as we should call LocalBroadcastManager.getInstance(this).method(). I logged both instances (in the Activity and in the Service) and they have different memory addresses.
Now I came to another question, shouldn't a Service have the same Context as the Activity that called it? From this article a Service runs on the Main Thread, hence I'd think the Context would be
the same.
Any thoughts on that? (sorry for the long post)
Code samples:
MyService
public class MyService extends Service {
...
// When an event is triggered, sends a broadcast
Intent myIntent = new Intent(MainActivity.MY_INTENT);
myIntent.putExtra("myMsg","msg");
sendBroadcast(myIntent);
// Previously I was trying:
// LocalBroadcastManager.getInstance(getApplicationContext()).sendBroadcast(myIntent);
}
MyActivity
public class MainActivity {
...
private BroadcastReceiver messageReceiver = new BroadcastReceiver() {
#Override
public void onReceive(Context context, Intent intent) {
Log.d("onReceive", "received!");
// TODO something
}
};
#Override
protected void onResume() {
super.onResume();
registerReceiver(messageReceiver, new IntentFilter(MY_INTENT));
// Previously I was trying:
// LocalBroadcastManager.getInstance(getApplicationContext()).registerReceiver(messageReceiver, new IntentFilter(MY_INTENT));
}
}

I've never used LocalBroadcastManager, but it sounds like you have to register your receiver on there (i.e. lbm.registerReceiver(...), not mycontext.registerReceiver(...)). Are you doing that?
Now I came to another question, shouldn't a Service have the same Context as the Activity that called it? From this article a Service runs on the Main Thread, hence I'd think the Context would be the same.
The Context class is not related to threads. In fact, both Service and Activity are (indirect) subclasses of Context -- so they're their own Contexts! That's why you can use "this" as a Context.
But regardless of which context you send into LocalBroadcastManager.getInstance(), you should be getting the exact same LBM instance out. I can't think of any reason that you wouldn't -- except if you're running the Activity and Service in different processes?

Declaration:
private BroadcastReceiver receiver;
Initialization:
receiver = new BroadcastReceiver()
{
#Override
public void onReceive(Context context, Intent intent)
{
//todo
}
};
Registration:
LocalBroadcastManager.getInstance(context).registerReceiver(receiver, new IntentFilter("RECEIVER_FILTER"));
context can be any type of Context, you can use the application context.
Unregister:
LocalBroadcastManager.getInstance(context).unregisterReceiver(receiver);
Broadcast:
Intent intent = new Intent("RECEIVER_FILTER");
intent.putExtra("EXTRA", someExtra);
LocalBroadcastManager.getInstance(context).sendBroadcast(intent);

check out if your Service and Activity are run in different process, LocalBroadcastManager can't apply in different process.(you should see it in AndroidManifest.xml file)

AlarmManager - Am I doing it right?

I had setup AlarmManager in my MainActivity class.
A class called AlarmReceiver gets fired up for every set interval of time.
I have to perform an operation when that class is fired up. That code is in in another class Parsing.java
Now in AlarmReceiver.java, I'm doing this :
public class AlarmReceiver extends BroadcastReceiver {
#Override
public void onReceive(Context context, Intent intent) {
Parsing obj = new Parsing(context);
obj.execute();
}
}
I cannot write the code directly in AlarmReceiver.java, because AlarmReceiver.java is already extending BroadcastReceiverand my code which is Parsing.java is extending another class.
So, I'm creating an object for Parsing class and calling that method.
Is my approach correct?
I'll furnish further information in case needed.
Please let me know if my approach is correct?
Thanks in advance!
EDIT:
Parsing.java
public class Parsing extends AsyncTask<Void, Void, Void> {
//some code
}

Starting an AsyncTask from a BroadcastReceiver is wrong for two reasons:
1. The thread on which onReceive() runs is terminated after the method returns, effectively ending any long-running task which may have been started from there. To quote the official docs:
A BroadcastReceiver object is only valid for the duration of the
call to onReceive(Context, Intent). Once your code returns from this
function, the system considers the object to be finished and no longer
active ..... anything that requires asynchronous operation is not
available, because you will need to return from the function to handle
the asynchronous operation, but at that point the BroadcastReceiver
is no longer active and thus the system is free to kill its process
before the asynchronous operation completes.
2. The Context instance that onReceive() provides is not the same as
the Context of an Activity or Service, i.e. Activity.this or
Service.this. You need that proper Context for performing many of
the common useful operations that we usually do from an Activity or
Service. So, for example, the correct way to start a Service in
onReceive() is:
#Override
public void onReceive(Context context, Intent intent) {
Intent i = new Intent(context.getApplicationContext(), ParsingService.class);
context.getApplicationContext().startService(i);
}
and not
#Override
public void onReceive(Context context, Intent intent) {
Intent i = new Intent(context, ParsingService.class);
context.startService(i);
}

I don't know how you wrote your Parsing.java, it looks fine but remember this
This method is always called within the main thread of its process, unless you explicitly asked for it to be scheduled on a different thread using registerReceiver. When it runs on the main thread you should never perform long-running operations in it (there is a timeout of 10 seconds that the system allows before considering the receiver to be blocked and a candidate to be killed). You cannot launch a popup dialog in your implementation of onReceive()
To me, i think it's a better way to handle this is calling another service inside onReceive method, like this
#Override
public void onReceive(Context context, Intent intent) {
Intent i = new Intent(context, ParsingService.class);
context.startService(i);
}

How to execute methods from a running service from broadcast?

on a broadcast I want to call a non static method from Service XYZ. The Service is start by the receiver on boot.
Has someone a idea to run methods from this running service?
One solution in this forum is to make the method static and use a singleton pattern to execute. But is there another method? Maybe with a binder?
//EDIT for example i have the following clases:
public class MyService extends Service{
.....
public void method(){
//TODO
}
}
public class MyBroadcastReceiver extends BroadcastReceiver{
.....
public void onReceive(Context context, Intent intent) {
String intentAction=intent.getAction();
if(intentAction.equals(Intent.ACTION_BOOT_COMPLETED)){
//start service
Intent serviceIntent = new Intent(context, MyService.class);
context.startService(serviceIntent);
}
else{
//TODO call method() in MyService
}
}
how can i call the method method()? I know that i can cast with context.getSystemService() system services. But how can i get my own service object?
greetings

You can add an action string to your intent using setAction in the intent that launches the Service. In your service's onStartcommand you can extract the intent's action, and based off that you can execute the method in your service.
You will always send commands to your service using startService this will not launch your service twice. It will either get started once, or the new intent is sent to the service.
So, in your on boot completed section you should set the intent action to whatever you want, and start the service - you can remove the else block completely.
In your Service implement the onStartCommand, extract the intent's action, and based off that action you can just execute your method.