Android - Is it possible to determine if an activity was started from another task?

Question

This is pretty elaborate, so I'll try and be as clear as possible. Currently, my application needs to reload some data when it is launched. I am loading this data in the onCreate/onRestart methods of my main activity. However, I need to be careful to not reload the data if the user never leaves the current task.

For instance, if I need to start the in-built Contacts application from my main activity to select a contact, then my main activity will pause/stop while I am selecting a new contact. When I return to my main activity, onRestart will be called. In this case, because I have never left the Application's task, I do not want to reload the data. This means some check needs to be included here to determine if the user has come straight back from the Contacts app without ever leaving it.

Otherwise, if the user exits the Contacts app while it was open and re-launched the app from the launcher menu (or recent apps list, etc) - I want to close the Contacts app and reload the data when the Main activity's onRestart method is called.

Is there a way to do this without using any user-frightening permissions (e.g. GET_TASKS). I have been stuck on this problem for a long time now so any help would be GREATLY appreciated :)

Tyvm, B. Campbell

Answer 1

I learned a lot from the Android docs:

Tasks and Back Stack

Navigation with Back and Up

Application Structure

Here is some highlight:

A task is a collection of activities that users interact with when performing a certain job. The activities are arranged in a stack (the "back stack"), in the order in which each activity is opened.

When the current activity starts another, the new activity is pushed on the top of the stack and takes focus. The previous activity remains in the stack, but is stopped. When an activity stops, the system retains the current state of its user interface. When the user presses the Back button, the current activity is popped from the top of the stack (the activity is destroyed) and the previous activity resumes (the previous state of its UI is restored). Activities in the stack are never rearranged, only pushed and popped from the stack—pushed onto the stack when started by the current activity and popped off when the user leaves it using the Back button.

It means when your application pick up a contact, the activity stack in the task might be:

| Activity A in Contacts |

| Activity B in Your App |

| Activity C in other app|

When the user leaves a task by pressing the Home button, the current activity is stopped and its task goes into the background. The system retains the state of every activity in the task. If the user later resumes the task by selecting the launcher icon that began the task, the task comes to the foreground and resumes the activity at the top of the stack.

Even if the user exits the Contacts app while it was open and re-launched the app from the launcher menu or recent app list, the activity stack is still like the one we see above. The only possibility that may make your acitity start from another task is another app(might be a launcher app) that start the main activity in a new task by startActivity flags, which is a rare case. In this rare case, you can simply check the uid of the app who start your activity by Binder.getCallinguid() to differentiate it.

EDIT based on comments:

You may check if activity was opened from history by FLAG_ACTIVITY_LAUNCHED_FROM_HISTORY:

if ((getIntent().getFlags() & Intent.FLAG_ACTIVITY_LAUNCHED_FROM_HISTORY) != 0){

}else{

}

You can also look into:

android:excludeFromRecents if you don't want your app start from recent apps

android:finishOnTaskLaunch

android:stateNotNeeded

Answer 2

If the data you are loading related to the application life-cycle not to a specific activity, you can load it in application class, so it will not be reloaded again unless your application task is killed.