FLAG_ACTIVITY_NEW_TASK clarification needed

问题:

So my problem is:

• I start App1, open Screen1 and then Screen2.
• I press Home, leaving App1 in the background.
• I open App2, start App1.Screen1 with FLAG_ACTIVITY_NEW_TASK, expecting to be on App1.Screen2 in the previously left task. Instead Im on App1.Screen1 and the system called onNewIntent().

When I press back it brings Sceen2 and Screen1 again. I dont use any other intent flags or launch modes.

Could someone explain what's happening??

回答1:

Android has TONS of bugs related to activities and tasks.

Nevertheless, Google changed the behavior of tasks between OS versions and didn't notify the developers, which is the most annoying thing about it.

jakk - If you didn't set any flags on the activities (A or B), than the behavior you are describing is WRONG.

And for all the ones which say that there is no problem with the documentation, try this:

1. Create an application with Activity A (launching activity) & B (with the default launch mode for both).
2. Start the application - a task is created with activity A only.
3. From a button in activity A, launch activity B with a FLAG_ACTIVITY_NEW_TASK.
4. Click the button several times and you'll see that activity B is created multiple times inside the task, which is NOT as the documentation says.

There are more scenarios to prove that the documentation is BAD / WRONG.

回答2:

In your 3rd step when you open App2 and start App1.Screen1 with Intent.FLAG_ACTIVITY_NEW_TASK you need to also set Intent.FLAG_ACTIVITY_SINGLE_TOP to get this to do what you want. It's an Android bug :-(

Be also aware that the behaviour is also a bit broken if you launch your app for the first time from your IDE (IntelliJ, Eclipse), or after installing it via the market (Google Play) or from a browser download. See How to prevent multiple instances of an activity when it is launched with different intents and http://code.google.com/p/android/issues/detail?id=26658

回答3:

Try this. It works for me.

intent.setFlags(Intent.FLAG_ACTIVITY_NEW_TASK |Intent.FLAG_ACTIVITY_CLEAR_TASK);
startActivity(intent);

回答4:

This seems to be in line with the documentation on http://developer.android.com/guide/topics/fundamentals/tasks-and-back-stack.html.

FLAG_ACTIVITY_NEW_TASK is equivalent to launchMode=singleTask and in there I read

However, if an instance of the activity already exists in a separate task, the system routes the intent to the existing instance through a call to its onNewIntent() method, rather than creating a new instance

Starting the activity without FLAG_ACTIVITY_NEW_TASK should give you the expected behavior.

回答5:

   fun isConnectedToInternet(): Boolean {
        val connectivityManager = getSystemService(Context.CONNECTIVITY_SERVICE) as ConnectivityManager
        val activeNetwork = connectivityManager.activeNetworkInfo
        if (activeNetwork != null)
            return activeNetwork.isConnected
        else
            return false
    }

回答6:

The FLAG_ACTIVITY_NEW_TASK places your new activity on a new task stack. I'm going to refer to the activities as A and B.

When you launch the first app, you have a single task with A in it. Task 1 = A

Clicking on the second activity puts B in the task. Task 1 = AB

When you click home you preserve the task. Task 1 = AB (still)

Opening the second app and send the A intent with the new task flag a NEW task will be created with only A on it. Now you have two tasks. Task 1 = AB, Task 2 = A

Unwrapping this arrangement with the back key will result in 2A, 1B, 1A which is what you are seeing. This is the expected result.