Android: How To Get AllowTaskReparenting="true" To Work

I am writing an app that can be launched from another app by receiving an intent with ACTION_VIEW or ACTION_EDIT. For example, it can be opened by viewing an email attachment. The

Solution 1:

Issue:

The trouble is that when you click on the home button and click again on the launch icon of the email app you were using, my activity is killed and any user edits that had been made are lost.

This happens because the email application had set FLAG_ACTIVITY_CLEAR_WHEN_TASK_RESET intent flag while launching your activity. When this flag is set, next time when the task is brought to the foreground, your activity will be finished, so that user returns to the previous activity.

From docs:

This is useful for cases where you have a logical break in your application. For example, an e-mail application may have a command to view an attachment, which launches an image view activity to display it. This activity should be part of the e-mail application's task, since it is a part of the task the user is involved in. However, if the user leaves that task, and later selects the e-mail app from home, we may like them to return to the conversation they were viewing, not the picture attachment, since that is confusing. By setting this flag when launching the image viewer, that viewer and any activities it starts will be removed the next time the user returns to mail.

Solution: Use singleTask launchMode for your activity. The email app will not kill your activity, as the activity belongs to different task now.

If the activity instance is already in the task and an attempt is made to launch the activity again, then a new instance is not created. Instead onNewIntent is called. Here you can prompt the user to save the previous edit if any, before presenting new content.

Solution 2:

As discussed above, the system's default behavior preserves the state of an activity when it is stopped. This way, when users navigate back to a previous activity, its user interface appears the way they left it. However, you can—and should—proactively retain the state of your activities using callback methods, in case the activity is destroyed and must be recreated.

When the system stops one of your activities (such as when a new activity starts or the task moves to the background), the system might destroy that activity completely if it needs to recover system memory. When this happens, information about the activity state is lost. If this happens, the system still knows that the activity has a place in the back stack, but when the activity is brought to the top of the stack the system must recreate it (rather than resume it). In order to avoid losing the user's work, you should proactively retain it by implementing the onSaveInstanceState() callback methods in your activity.

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