Notifications --- Preserving Navigation when Starting an Activity

When you start an Activity from a notification, you must preserve the user's expected navigation experience. Clicking Back should take the user back through the application's normal work flow to the Home screen, and clicking Recents should show the Activity as a separate task. To preserve the navigation experience, you should start the Activity in a fresh task. How you set up the PendingIntent to give you a fresh task depends on the nature of the Activity you're starting. There are two general situations:

Regular activity

You're starting an Activity that's part of the application's normal workflow. In this situation, set up the PendingIntent to start a fresh task, and provide the PendingIntent with a back stack that reproduces the application's normal Back behavior.

Notifications from the Gmail app demonstrate this. When you click a notification for a single email message, you see the message itself. Touching Back takes you backwards through Gmail to the Home screen, just as if you had entered Gmail from the Home screen rather than entering it from a notification.

This happens regardless of the application you were in when you touched the notification. For example, if you're in Gmail composing a message, and you click a notification for a single email, you go immediately to that email. Touching Back takes you to the inbox and then the Home screen, rather than taking you to the message you were composing.

Special activity

The user only sees this Activity if it's started from a notification. In a sense, the Activity extends the notification by providing information that would be hard to display in the notification itself. For this situation, set up the PendingIntent to start in a fresh task. There's no need to create a back stack, though, because the started Activity isn't part of the application's activity flow. Clicking Back will still take the user to the Home screen.

Setting up a regular activity PendingIntent

To set up a PendingIntent that starts a direct entry Activity, follow these steps:

1. Define your application's Activity hierarchy in the manifest.
   1. Add support for Android 4.0.3 and earlier. To do this, specify the parent of the Activity you're starting by adding a <meta-data> element as the child of the <activity>.

      For this element, set android:name="android.support.PARENT_ACTIVITY". Set android:value="<parent_activity_name>" where <parent_activity_name> is the value of android:name for the parent <activity> element. See the following XML for an example.

   2. Also add support for Android 4.1 and later. To do this, add the android:parentActivityName attribute to the <activity> element of the Activity you're starting.

   The final XML should look like this:

   <activity
       android:name=".MainActivity"
       android:label="@string/app_name" >
       <intent-filter>
           <action android:name="android.intent.action.MAIN" />
           <category android:name="android.intent.category.LAUNCHER" />
       </intent-filter>
   </activity>
   <activity
       android:name=".ResultActivity"
       android:parentActivityName=".MainActivity">
       <meta-data
           android:name="android.support.PARENT_ACTIVITY"
           android:value=".MainActivity"/>
   </activity>

   
   
   
2. Create a back stack based on the Intent that starts the Activity:
   1. Create the Intent to start the Activity.
   2. Create a stack builder by calling TaskStackBuilder.create().
   3. Add the back stack to the stack builder by calling addParentStack(). For each Activity in the hierarchy you've defined in the manifest, the back stack contains an Intent object that starts the Activity. This method also adds flags that start the stack in a fresh task.

      Note: Although the argument to addParentStack() is a reference to the started Activity, the method call doesn't add the Intent that starts the Activity. Instead, that's taken care of in the next step.

   4. Add the Intent that starts the Activity from the notification, by calling addNextIntent(). Pass the Intent you created in the first step as the argument to addNextIntent().
   5. If you need to, add arguments to Intent objects on the stack by calling TaskStackBuilder.editIntentAt(). This is sometimes necessary to ensure that the target Activity displays meaningful data when the user navigates to it using Back.
   6. Get a PendingIntent for this back stack by calling getPendingIntent(). You can then use this PendingIntent as the argument tosetContentIntent().

The following code snippet demonstrates the process:

...
Intent resultIntent = new Intent(this, ResultActivity.class);
TaskStackBuilder stackBuilder = TaskStackBuilder.create(this);
// Adds the back stack
stackBuilder.addParentStack(ResultActivity.class);
// Adds the Intent to the top of the stack
stackBuilder.addNextIntent(resultIntent);
// Gets a PendingIntent containing the entire back stack
PendingIntent resultPendingIntent =
        stackBuilder.getPendingIntent(0, PendingIntent.FLAG_UPDATE_CURRENT);
...
NotificationCompat.Builder builder = new NotificationCompat.Builder(this);
builder.setContentIntent(resultPendingIntent);
NotificationManager mNotificationManager =
    (NotificationManager) getSystemService(Context.NOTIFICATION_SERVICE);
mNotificationManager.notify(id, builder.build());

Setting up a special activity PendingIntent

The following section describes how to set up a special activity PendingIntent.

A special Activity doesn't need a back stack, so you don't have to define its Activity hierarchy in the manifest, and you don't have to calladdParentStack() to build a back stack. Instead, use the manifest to set up the Activity task options, and create the PendingIntent by callinggetActivity():

1. In your manifest, add the following attributes to the <activity> element for the Activity

   android:name="activityclass"

   The activity's fully-qualified class name.

   android:taskAffinity=""

   Combined with the FLAG_ACTIVITY_NEW_TASK flag that you set in code, this ensures that this Activity doesn't go into the application's default task. Any existing tasks that have the application's default affinity are not affected.

   android:excludeFromRecents="true"

   Excludes the new task from Recents, so that the user can't accidentally navigate back to it.

   This snippet shows the element:

   <activity
       android:name=".ResultActivity"
   ...
       android:launchMode="singleTask"
       android:taskAffinity=""
       android:excludeFromRecents="true">
   </activity>
   ...

   
   
   
2. Build and issue the notification:
   1. Create an Intent that starts the Activity.
   2. Set the Activity to start in a new, empty task by calling setFlags() with the flags FLAG_ACTIVITY_NEW_TASK andFLAG_ACTIVITY_CLEAR_TASK.
   3. Set any other options you need for the Intent.
   4. Create a PendingIntent from the Intent by calling getActivity(). You can then use this PendingIntent as the argument tosetContentIntent().

   The following code snippet demonstrates the process:

   // Instantiate a Builder object.
   NotificationCompat.Builder builder = new NotificationCompat.Builder(this);
   // Creates an Intent for the Activity
   Intent notifyIntent =
           new Intent(this, ResultActivity.class);
   // Sets the Activity to start in a new, empty task
   notifyIntent.setFlags(Intent.FLAG_ACTIVITY_NEW_TASK
                           | Intent.FLAG_ACTIVITY_CLEAR_TASK);
   // Creates the PendingIntent
   PendingIntent notifyPendingIntent =
           PendingIntent.getActivity(
           this,
           0,
           notifyIntent,
           PendingIntent.FLAG_UPDATE_CURRENT
   );
   
   // Puts the PendingIntent into the notification builder
   builder.setContentIntent(notifyPendingIntent);
   // Notifications are issued by sending them to the
   // NotificationManager system service.
   NotificationManager mNotificationManager =
       (NotificationManager) getSystemService(Context.NOTIFICATION_SERVICE);
   // Builds an anonymous Notification object from the builder, and
   // passes it to the NotificationManager
   mNotificationManager.notify(id, builder.build());
   

   
   
   
   
   From:https://developer.android.com/guide/topics/ui/notifiers/notifications.html#NotificationResponse