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Pending Intents - Part 2

Android  #android 

This is part 2 of two parts pending intent series.

Background

In part 1, we have discussed the need and use of pending intents with an example. We have created PendingIntent and set PendingIntent.FLAG_ONE_SHOT in example but we haven’t discussed anything about creation and flags. These are the topics of this article.

Creating Pending Intents

Pending Intent class provides static methods for creating pending intent of desired type. Like any other intent, we create pending intent for specific component. e.g. activity, service etc.

public static PendingIntent getService(Context context, int requestCode, @NonNull Intent intent, @Flags int flags);

public static PendingIntent getActivity(Context context, int requestCode, Intent intent, @Flags int flags);

public static PendingIntent getBroadcast(Context context, int requestCode, Intent intent, @Flags int flags);

Note: There are other methods too, which you can explore on your own.

Intent FLAGS

From docs,

A PendingIntent itself is simply a reference to a token maintained by the system describing the original data used to retrieve it. This means that, even if its owning application’s process is killed, the PendingIntent itself will remain usable from other processes that have been given it. If the creating application later re-retrieves the same kind of PendingIntent (same operation, same Intent action, data, categories, and components, and same flags), it will receive a PendingIntent representing the same token if that is still valid, and can thus call cancel() to remove it.

From the very first line, it’s clear that Pending Intents are stored somewhere in the system and can be updated later. These Pending Intent Flags help us to achieve this behaviour. Depending on the flag passed to create pending intent we can update or change the behaviour of intent.

Let’s discuss each of them briefly.

FLAG_ONE_SHOT

If a pending intent is created using PendingIntent.FLAG_ONE_SHOT flag; it can be used only once. Any attempt to reuse it will fail (throw exception).

I will create a simple app here.

SampleService - waits for 3 seconds and execute the action attached to pending intent.

public class SampleService extends IntentService {

    public static final String INTENT_KEY = "intent_key";

    public SampleService() {
        super("SampleService");
    }

    @Override
    protected void onHandleIntent(Intent intent) {

        try {
            Thread.sleep(3000); // assume some work

            PendingIntent p = intent.getParcelableExtra(INTENT_KEY);
            log("onHandleIntent[%s]", "sending response...");
            p.send();

        } catch (InterruptedException | PendingIntent.CanceledException e) {
            String msg = e.getMessage();
            if(msg == null) msg = e.getLocalizedMessage();
            log("onHandleIntent[%s]", msg + " intent canceled.");
        }

    } // onHandleIntent

    private void log(String format, Object... args){
        AppUtils.log("SampleService", String.format(format, args));
    } // log

} // SampleService

MainActivity - main activity, it has an init button which starts the service and schedule starting it again after 5 seconds from now.

public class MainActivity extends AppCompatActivity {

    public static final String DATA = "service_data";

    private static final int REQUEST_CODE = 940;


    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
    } // onCreate

    @Override
    protected void onActivityResult(int requestCode, int resultCode, Intent data) {
        super.onActivityResult(requestCode, resultCode, data);
        if (requestCode == REQUEST_CODE && resultCode == RESULT_OK) {
            log("onActivityResult[%s]", data.getStringExtra(DATA));
        }
    } // onActivityResult

    private void log(String format, Object... args) {
        AppUtils.log("MainActivity", String.format(format, args));
    } // log

    public void onInit(View view) {
        Intent base = new Intent(this, ResultActivity.class);
        base.putExtra(ResultActivity.RESULT_ACTIVITY, "first result");

        final PendingIntent pendingIntent = PendingIntent.getActivity(this, REQUEST_CODE, base, PendingIntent.FLAG_ONE_SHOT);
        Intent intent = new Intent(MainActivity.this, SampleService.class);
        intent.putExtra(SampleService.INTENT_KEY, pendingIntent);
        startService(intent);

        new Handler().postAtTime(new Runnable() {
            @Override
            public void run() {
                log("%s", "sending from handler");
                Intent intent = new Intent(MainActivity.this, SampleService.class);
                intent.putExtra(SampleService.INTENT_KEY, pendingIntent);
                startService(intent);

            }
        }, SystemClock.uptimeMillis() + 5000);
    }
} // MainActivity

ResultActivity - activity which will be started from service. It logs the extra data carried with intent.

    public static final String RESULT_ACTIVITY = "result_activity";

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_result);

        if(getIntent().hasExtra(RESULT_ACTIVITY)){
            log("%s", getIntent().getStringExtra(RESULT_ACTIVITY));
        }else {
            log("%s", "no extra");
        }

        finish();
    } // onCreate

    private void log(String format, Object... args){
        AppUtils.log("ResultActivity", String.format(format, args));
    } // log

} // ResultActivity

In this example, we have create pending intent with FLAG_ONE_SHOT

final PendingIntent pendingIntent = PendingIntent.getActivity(this, REQUEST_CODE, base, PendingIntent.FLAG_ONE_SHOT);

When the same intent is passed to starting service in scheduled called in Handler, service throws CanceledException becuase this intent was supposed to be used only once.

Output

D/demo: SampleService -> onHandleIntent[sending response...]
D/demo: ResultActivity -> first result
D/demo: MainActivity -> sending from handler
D/demo: SampleService -> onHandleIntent[sending response...]
D/demo: SampleService -> onHandleIntent - in catch block - [CanceledException intent canceled.]

FLAG_UPDATE_CURRENT

This flag indicates that if intent is already there, update its extras with new intent’s extras otherwise return a new pending intent.

Update onInit method with following code and analyze the result.

    public void onInit(View view) {
        final Intent base = new Intent(this, ResultActivity.class);
        base.putExtra(ResultActivity.RESULT_ACTIVITY, "first result");

        PendingIntent pendingIntent = PendingIntent.getActivity(this, REQUEST_CODE, base, PendingIntent.FLAG_UPDATE_CURRENT);
        log("%s", "pending intent hash [first] - "  + pendingIntent.hashCode());
        Intent intent = new Intent(MainActivity.this, SampleService.class);
        intent.putExtra(SampleService.INTENT_KEY, pendingIntent);
        startService(intent);

        new Handler().postAtTime(new Runnable() {
            @Override
            public void run() {
                log("%s", "sending from handler");
                base.putExtra(ResultActivity.RESULT_ACTIVITY, "updated extras from handler.");
                PendingIntent pendingIntent = PendingIntent.getActivity(MainActivity.this, REQUEST_CODE, base, PendingIntent.FLAG_UPDATE_CURRENT);
                log("%s", "pending intent hash [second] - "  + pendingIntent.hashCode());
                Intent intent = new Intent(MainActivity.this, SampleService.class);
                intent.putExtra(SampleService.INTENT_KEY, pendingIntent);
                startService(intent);

            }
        }, SystemClock.uptimeMillis() + 5000);
    }

Output

D/demo: MainActivity -> pending intent hash [first] - 61346262
D/demo: SampleService -> onHandleIntent[sending response...]
D/demo: ResultActivity -> first result
D/demo: MainActivity -> sending from handler
D/demo: MainActivity -> pending intent hash [second] - 61346262
D/demo: SampleService -> onHandleIntent[sending response...]
D/demo: ResultActivity -> updated extras from handler.

FLAG_CANCEL_CURRENT

It indicates that if described pending intent already exists, cancel it before creating new one. In our example, service waits for 3 seconds before starting new activity. We will update the onInit() method, now it will schedulea new service start after 1 second. It will cancel the previous one (generation canceled exception in the service) and will start a new one.

Analyze the output carefully.

 final Intent base = new Intent(this, ResultActivity.class);
        base.putExtra(ResultActivity.RESULT_ACTIVITY, "first result");

        PendingIntent pendingIntent = PendingIntent.getActivity(this, REQUEST_CODE, base, PendingIntent.FLAG_CANCEL_CURRENT);
        log("%s", "pending intent hash [first] - "  + pendingIntent.hashCode());
        Intent intent = new Intent(MainActivity.this, SampleService.class);
        intent.putExtra(SampleService.INTENT_KEY, pendingIntent);
        startService(intent);

        new Handler().postAtTime(new Runnable() {
            @Override
            public void run() {
                log("%s", "sending from handler");
                base.putExtra(ResultActivity.RESULT_ACTIVITY, "updated extras from handler.");
                PendingIntent pendingIntent = PendingIntent.getActivity(MainActivity.this, REQUEST_CODE, base, PendingIntent.FLAG_CANCEL_CURRENT);
                log("%s", "pending intent hash [second] - "  + pendingIntent.hashCode());
                Intent intent = new Intent(MainActivity.this, SampleService.class);
                intent.putExtra(SampleService.INTENT_KEY, pendingIntent);
                startService(intent);

            }
        }, SystemClock.uptimeMillis() + 1000);

Output

D/demo: MainActivity -> pending intent hash [first] - 61346262
D/demo: MainActivity -> sending from handler
D/demo: MainActivity -> pending intent hash [second] - 66200388
D/demo: SampleService -> onHandleIntent[sending response...]
D/demo: SampleService -> onHandleIntent - in catch block - [CanceledException intent canceled.]
D/demo: SampleService -> onHandleIntent[sending response...]
D/demo: ResultActivity -> updated extras from handler.

FLAG_NO_CREATE

This flag returns null if it does not find any existing pending intent to return.

Update onInit() with this code and see the output.

PendingIntent pendingIntent = PendingIntent.getActivity(this, REQUEST_CODE, base, PendingIntent.FLAG_NO_CREATE);
        
        if(pendingIntent == null){
            log("onInit[%s]", "no intent found.");
            return;
        }

Output

D/demo: MainActivity -> onInit[no intent found.]

FLAG_IMMUTABLE (API >= 23)

From docs,

Flag indicating that the created PendingIntent should be immutable. This means that the additional intent argument passed to the send methods to fill in unpopulated properties of this intent will be ignored.

Note: I haven’t used this flag yet. I have added it here just for completion. You can explore it on your own or I will update it here whenever I get time.

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