How can I get the application context from an Android Service?

Question

I have an Android service that is running and listening for microphone input. I want it to launch an activity when a certain criteria is met. In order to create an Intent I need the application context. How can I get it?

Intent i = new Intent(ctx, SONR.class);
i.addFlags(Intent.FLAG_ACTIVITY_NEW_TASK);
ctx.startActivity(i);

The above line does not start my activity.

Here is my constructor

public SONRClient(Context c, AudioRecord ar, int buffsize, final AudioManager am) {
    theAudioManager = am;
    theaudiorecord = ar;
    bufferSize = buffsize;
    ctx = c;
    CLIENT_ON = true;
}

Here is my onCreate

@Override
public void onCreate() {
    try {
        // LogFile.MakeLog("\n\nSONRClient CREATED");
        clientStopReceiver = new StopReceiver();
        ctx.registerReceiver(clientStopReceiver, 
            new IntentFilter(SONR.DISCONNECT_ACTION));
        myByteReceiver = new SONRByteReceiver();
        theListener = new MicSerialListener(
            theaudiorecord, bufferSize, myByteReceiver);
        theApplication = getApplication();
    } catch (Exception e) {
        e.printStackTrace();
        ErrorReporter.getInstance().handleException(e);
    }
}

There is myByteReceiver that is listening for signals via audio input. When it finds a matching signal, I want it to launch an activity.

private class SONRByteReceiver implements ByteReceiver {
    private long lastplaytime = 0;
    private long lastmutetime = 0;
    private long lastskiptime = 0;
    private long lastvolutime = 0;
    private long lastbacktime = 0;

    public void receiveByte(int receivedByte) {
        try {
            theKeyEvent = -1;

            if (ismuted) {
                if (receivedByte != MUTE) {
                    volume = 0;
                    ismuted = false;
                }
            }

            switch (receivedByte) {

            case SONR_HOME:
                Log.d(TAG, "HOME");

                Intent i = new Intent(ctx, SONR.class);
                i.addFlags(Intent.FLAG_ACTIVITY_NEW_TASK);
                theApplication.startActivity(i);

                break;
            default:
                Log.d(TAG, "default");
                Log.d(TAG,"RECEIVED " + receivedByte);
                // LogFile.MakeLog("RECEIVED " + receivedByte);
                break;
            }

            if (theKeyEvent >= 0) {
                sendbroadcast();
            }
        } catch (Exception e) {
            e.printStackTrace();
            ErrorReporter.getInstance().handleException(e);
        }
    }
}

Here is the stacktrace

java.lang.NullPointerException
    at com.sonrlabs.test.sonr.SONRClient$SONRByteReceiver.receiveByte(SONRClient.java:320)
    at com.sonrlabs.test.sonr.AudioProcessor.processSample(AudioProcessor.java:145)
    at com.sonrlabs.test.sonr.AudioProcessor.run(AudioProcessor.java:58)

Line 320 is theApplication.startActivity(i);

Could you post the method you call `getApplicationContext` in? — skynet, Nov 29 '11 at 03:46
It would be more helpful if you posted the log of the NullPointerException you are getting. — keno, Nov 29 '11 at 05:39
None of your code seems to assign anything to the ctx variable. Review your code to see where "ctx" is assigned a value and do some print outs around the assignment to see when and if it is ever assigned. — keno, Nov 29 '11 at 14:42
ctx is assigned, in my constructor. i can post that code as well — Sheehan Alam, Nov 29 '11 at 16:12
I also print out the package name from my context. And it does it fine. Problem is in startActivity. Not sure why. — Sheehan Alam, Nov 29 '11 at 16:28
Only other thing I can think of atm is that your SONR activity may not be defined in your manifest. — keno, Nov 29 '11 at 20:41
Can you post the code which calls the SONRClient constructor? It seems you are passing a null value into this constructor. — Matt Accola, Jun 14 '12 at 06:16

score 6 · Answer 1 · edited May 23 '17 at 12:09

6

You can use getApplicationContext() inside your service to get the application context.

Try using

getApplication().startActivity(i);

android start activity from service

edited May 23 '17 at 12:09

Community

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1

answered Nov 29 '11 at 03:36

skynet

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I get a null pointer exception when I try getApplicationContext() – Sheehan Alam Nov 29 '11 at 03:43
I updated my code. I have a reference to the context, but my activity does not show up. Am I doing something wrong? – Sheehan Alam Nov 29 '11 at 03:54
How are you starting the service? Can you edit your question with more complete code from the service, such as which lifecycle methods you try to start the activity in? – skynet Nov 29 '11 at 04:25
1

Try moving `theApplication = getApplication();` to the first line of onCreate – skynet Nov 29 '11 at 12:03
Still get a nullpointerexception for `theApplication.startActivity(i);` – Sheehan Alam Nov 29 '11 at 16:11

Zar E Ahmer · Answer 2 · 2015-07-16T08:36:33.090

5

Every Service has its own Context, just use the that. You don't need to pass a Service an Activity's Context.

No need for activity context in Service.

Intent i = new Intent(ctx, SONR.class);
i.addFlags(Intent.FLAG_ACTIVITY_NEW_TASK);
startActivity(i);

Simply do as you do in Activity

Service and Activity both are subclasses of Context.

edited Jul 16 '15 at 08:36

answered Jul 09 '15 at 12:14

Zar E Ahmer

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score 2 · Answer 3 · edited Jul 30 '12 at 07:33

2

Change this:

Intent i = new Intent(ctx, SONR.class);

to:

Intent i = new Intent(getApplicationContext(),SONR.class);

edited Jul 30 '12 at 07:33

bluish

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answered Nov 29 '11 at 06:34

Rohit

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Impossible, You are getting null pointer exception somewhere else. If your service is running then context cant be null. – Rohit Nov 29 '11 at 09:43
Try to click on this line : at com.sonrlabs.test.sonr.AudioProcessor.processSample(AudioProcessor.java:145) or line above n below that, to find whr u r getting null. – Rohit Nov 30 '11 at 04:20

score 1 · Answer 4 · answered Jan 27 '14 at 13:22

1

getBaseContext() which returns context since every activity extends Context class

answered Jan 27 '14 at 13:22

Vishal Android developer

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score 1 · Answer 5 · edited Jan 12 '16 at 00:15

1

You mustn't call to getApplicationContext() inside its public empty constructor, or it will give you a NullPointerException.

edited Jan 12 '16 at 00:15

JJD

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answered Nov 12 '15 at 15:19

joninx

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Where in the `Service` class is a safe place to call `getApplicationContext()`? – JJD Jan 12 '16 at 00:16
@JJD don't call getApplicationContext(), call to getBaseContext() as Vishal Android Developer wrote. – joninx Jan 12 '16 at 11:45
Still the question remains in which method it is safe to be called. – JJD Jan 12 '16 at 13:57

score 1 · Answer 6 · answered Nov 29 '11 at 04:59

1

You're assertion that you need an application context to start an activity is inaccurate. You can start an activity from any context, including the service, which is a context.

answered Nov 29 '11 at 04:59

dhaag23

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I tried it using just startActivity(), I still get a nullpointerexception. Updated question with more code – Sheehan Alam Nov 29 '11 at 05:12
Show the stack track for the null pointer. It's not because of a null service if you're using it from within that class. – dhaag23 Nov 29 '11 at 16:25
The stacktrace in the question is all that is printed when I am debugging. Any ideas on how to debug further? – Sheehan Alam Nov 29 '11 at 16:28

score 0 · Answer 7 · answered Jul 26 '20 at 13:49

0

There is a not null context only after 'onCreate()' of the Service : getting the context of the service in the constructor is not a good idea (not yet any context), get it with the simple 'getApplicationContext()' in the 'onCreate' method.

answered Jul 26 '20 at 13:49

g910

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score -1 · Answer 8 · answered Nov 28 '16 at 07:10

-1

Just do this to access the Service context

Intent i = new Intent(Service.this, SONR.class);
i.addFlags(Intent.FLAG_ACTIVITY_NEW_TASK);
startActivity(i);

answered Nov 28 '16 at 07:10

DipDro420

1

score -2 · Accepted Answer · answered Dec 02 '11 at 00:01

-2

ctx.getApplicationContext().startActivity(i)

boom.

answered Dec 02 '11 at 00:01

Sheehan Alam

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what is ctx ?? Do you launch the instruction above from the service? – Lisitso Sep 12 '13 at 10:44
@Lisitso `ctx` is a `Context` variable – Feb 12 '14 at 09:27
3

If you already have ctx as Context why get application context and then startActivity? Why not simply ctx.startActivity()? – Ishaan Feb 10 '17 at 13:41

How can I get the application context from an Android Service?

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