Why does my activity calls onCreate if opened from notification

Question

I am building an Android app which should just open the app once its notifications are clicked.

    private void createNotificationChannel() {
        // Create the NotificationChannel, but only on API 26+ because
        // the NotificationChannel class is new and not in the support library
        // Gets an instance of the NotificationManager service
        mNotificationManager = NotificationManagerCompat.from(this);
        if (Build.VERSION.SDK_INT >= Build.VERSION_CODES.O) {
            CharSequence name = getString(R.string.channel_name);
            String description = getString(R.string.channel_description);
            int importance = NotificationManager.IMPORTANCE_DEFAULT;
            NotificationChannel channel = new NotificationChannel("ALERTS", name, importance);
            channel.setDescription(description);
            // Register the channel with the system; you can't change the importance
            // or other notification behaviors after this
            mNotificationManager.createNotificationChannel(channel);
        }
    }

    public void showNotification(String Title, String info, int id){   
        // Create an Intent for the activity you want to start
        Intent resultIntent = new Intent(this, MainActivity.class);
        // Create the TaskStackBuilder and add the intent, which inflates the back stack
        TaskStackBuilder stackBuilder = TaskStackBuilder.create(this);
        stackBuilder.addNextIntentWithParentStack(resultIntent);
        // Get the PendingIntent containing the entire back stack
        PendingIntent resultPendingIntent =
                stackBuilder.getPendingIntent(0,
                        PendingIntent.FLAG_UPDATE_CURRENT);


        NotificationCompat.Builder builder =
                new NotificationCompat.Builder(MainActivity.this, "ALERTS")
                .setSmallIcon(R.drawable.notification_icon)
                .setContentTitle(Title)
                .setContentText(info)
                // Set the intent that will fire when the user taps the notification
                .setContentIntent(resultPendingIntent);


        mNotificationManager.notify(mNotificationId, builder.build());
    }

I followed this guide: https://developer.android.com/training/notify-user/navigation

The notifications display correctly and once I click them it takes me to MainActivity, but it restarts MainActivity. Why does this happen and how can I make it to just open it as if opened from onResume?

[EDIT] added my XML structure

<?xml version="1.0" encoding="utf-8"?>
<manifest xmlns:android="http://schemas.android.com/apk/res/android"
    package="com.company.example">
    
    <application
        android:allowBackup="true"
        android:icon="@mipmap/ic_launcher"
        android:label="@string/app_name"
        android:roundIcon="@mipmap/ic_launcher_round"
        android:supportsRtl="true"
        android:screenOrientation="sensorPortrait"
        android:theme="@style/AppTheme">
        <meta-data
            android:name="com.google.android.gms.ads.APPLICATION_ID"
            android:value="..."/>
        <activity
            android:name=".MainActivity"
            android:label="@string/app_name"
            android:windowSoftInputMode="adjustPan"
            android:launchMode="singleTop"
            android:exported="true">
            <intent-filter>
                <action android:name="android.intent.action.MAIN" />
                <category android:name="android.intent.category.LAUNCHER" />
            </intent-filter>
        </activity>
        <activity
            android:name=".Settings"
            android:label="Settings"
            android:exported="false"
            android:parentActivityName=".MainActivity"
            android:theme="@style/AppTheme.NoActionBar">
        </activity>
        <service
            android:name="com.company.example.DeviceService"
            android:permission="android.permission.BIND_MIDI_DEVICE_SERVICE"
            android:exported="false">
            <intent-filter>
                <action android:name="android.media.midi.MidiDeviceService" />
            </intent-filter>

            <meta-data
                android:name="android.media.midi.MidiDeviceService"
                android:resource="@xml/device_info" />
        </service>

    </application>

</manifest>

score 1 · Accepted Answer · answered Jul 06 '22 at 15:40

I changed my showNotification to this

public void showNotification(String Title, String info){
    int mNotificationId = 1;

    final Intent notificationIntent = new Intent(MainActivity.this, MainActivity.class);
    notificationIntent.setAction(Intent.ACTION_MAIN);
    notificationIntent.addCategory(Intent.CATEGORY_LAUNCHER);
    notificationIntent.addFlags(Intent.FLAG_ACTIVITY_NEW_TASK);

    PendingIntent pendingIntent = PendingIntent.getActivity(MainActivity.this, 0, notificationIntent, 0);

    NotificationCompat.Builder builder =
            new NotificationCompat.Builder(MainActivity.this, "ALERTS")
            .setSmallIcon(R.drawable.notification_icon)
            .setContentTitle(Title)
            .setContentText(info)
            // Set the intent that will fire when the user taps the notification
            .setAutoCancel(true)
            .setContentIntent(pendingIntent);



     mNotificationManager.notify(mNotificationId, builder.build());
   
}

And also added singleTop in the Manifest like @Maurice Lam suggested. Now it seems to be working correctly.

Thanks for the solution. It seems to work for me even without notificationIntent.addFlags(Intent.FLAG_ACTIVITY_NEW_TASK); — JiriB, Apr 23 '23 at 13:15

score 0 · Answer 2 · answered Jul 01 '22 at 18:14

You can use the singleTop launch mode to get the behavior you want.

From https://developer.android.com/guide/components/activities/tasks-and-back-stack:

If an instance of the activity already exists at the top of the current task, the system routes the intent to that instance through a call to its onNewIntent() method, rather than creating a new instance of the activity. The activity can be instantiated multiple times, each instance can belong to different tasks, and one task can have multiple instances (but only if the activity at the top of the back stack is not an existing instance of the activity).

For example, suppose a task's back stack consists of root activity A with activities B, C, and D on top (the stack is A-B-C-D; D is on top). An intent arrives for an activity of type D. If D has the default "standard" launch mode, a new instance of the class is launched and the stack becomes A-B-C-D-D. However, if D's launch mode is "singleTop", the existing instance of D receives the intent through onNewIntent(), because it's at the top of the stack—the stack remains A-B-C-D. However, if an intent arrives for an activity of type B, then a new instance of B is added to the stack, even if its launch mode is "singleTop".

I cant seem to get this to work. I added launchmode="singleTop" to my mainAcitivity xml (which is my launch activity). I also added the override onNewIntent and let it print something but it never printed it and the activity is still calling onCreate upon opening from a notification. — aWiseMan, Jul 04 '22 at 14:01
Interesting... from my research I think that is because you are using `TaskStackBuilder` for your intent. According to https://stackoverflow.com/a/42678747/2921519 it always recreates the back stack and restarts the activity rather than trying to start a new one. Maybe you can try creating a pending intent from `PendingIntent.getActivity()` instead? — Maurice Lam, Jul 06 '22 at 02:19

Why does my activity calls onCreate if opened from notification

2 Answers2