I have an annoying issue with the foreground dispatch behavior. Sometimes instead of calling onNewIntent(), it completely recreates the activity, which breaks the app's workflow.
My concrete situation: Activity A is the MainActivity, which uses the foreground dispatch. Everything works as it should. However, in my activity B, which is launched from the browser (VIEW action), the foreground dispatch doesn't work under some circumstances anymore.
The workflow:
I start the MainActivity, switch to the browser (without closing
the MainActivity), launch activity B and attach my NFC device --> it
creates a new activity B.
I start the MainActivity and close it again. After that I switch
to the browser, launch activity B and attach my NFC device -->
everything works with onNewIntent()
The code is correct, e.g. if I attach the NFC device in the first scenario twice, it works as it should at the second time, but not at the first time. In the MainActivity and activity B I definitively call the disableForegroundDispatch() method in the activity's onPause() method.
Is there a solution for my specific problem? For me it sounds like a bug.
Edit:
public void resume(Activity targetActivity) {
if (nfc != null && nfc.isEnabled()) {
// nfc is the default NFC adapter and never null on my devices
Intent intent = new Intent(targetActivity, targetActivity.getClass()).addFlags(Intent.FLAG_ACTIVITY_SINGLE_TOP);
PendingIntent pendingIntent = PendingIntent.getActivity(targetActivity, 0, intent, 0);
nfc.enableForegroundDispatch(targetActivity, pendingIntent, null, new String[][] { new String[] { IsoDep.class.getName() } });
}
}
public void pause(Activity targetActivity) {
if (nfc != null && nfc.isEnabled()) {
nfc.disableForegroundDispatch(targetActivity);
}
}
These methods are called in the corresponding methods in each activity. Thanks for the help!
Solution: After a very long research I finally found the issue. Logcat printed:
startActivity called from non-Activity context; forcing Intent.FLAG_ACTIVITY_NEW_TASK for: Intent
I found other issues at Stackoverflow, where people had have the same issue with the NotificationManager, but all the hints didn't help me. Adding the flag singleTask to my activity B did the trick for me, but to be honest I don't understand it, because the context is always an activity.
I removed all the code from the MainActivity and the first scenario still didn't work. I romved the MainActivity from the manifest and after that everything was fine. Maybe it is a problem, that an app instance is running and activity B is launched from the browser? I don't know.
Anyway, thanks for the help NFC guy!
The IntentFilter[] that you pass to enableForegroundDispatch is empty. So your NFC intent probably arrive at your Activity due to the IntentFilter(s) in the manifest file. This explains the behaviour you observe, as an NFC intent always creates a new instance when delivered this way.
Add something like this instead to your code for enabling foreground dispatch:
IntentFilter[] iFilters = new IntentFilter[2];
iFilters[0] = new IntentFilter();
iFilters[0].addAction("android.nfc.action.TECH_DISCOVERED");
iFilters[1] = new IntentFilter();
iFilters[1].addAction("android.nfc.action.TAG_DISCOVERED");
iFilters[1].addCategory(Intent.CATEGORY_DEFAULT);
And pass that as parameter to enableForegroundDispatch.
UPDATE:
I recently learned more about this specific problem. It is caused by the way Android determines in which task a new Activity should be launched. I don't know or understand the specific details of how that works, but the effect is that:
When Activity B is launched from the Browser, it is created in the Browser's task
When the NFC intent arrives, the system determines that a new Activity B is to be created in Activity A's task
Because of 2., the SINGLE_TOP is not ignored: there is only one instance of Activity B at the top of A's task. When Activity A is closed, it's task has disappeared, so Activity B will always be created in the Browser's task, as you have observed.
You may feel that this is an Android bug in this case (I do, I think), but this behaviour of how to create activities in which task is so fundamental to Android that many apps rely on it. So it is very unlikely that this will ever change.
Possible work-around: declare Activity B with launchMode "singleTask" (or "singleInstance"). Then a new (3rd) task will be created when B is launched.
I guess your workflow is as follow : Main --> Detect tag --> Reader Activity --> Writer activity Detect tag --> Write tag
This problem seems to arise when your writer activity (the one with foreground enabled, I suppose that's for writing purposes) belongs to an Activity Stack (e.g. a Task) that was called from a previous tag discovery.
In particular, it doesn't arise if your workflow is as follow :
Main Writer activity Detect tag --> Write tag
My workaround is to call the writer activity in a new task to begin with.
In the activity that laucnhes the writer, just add the new task flag in the intent that starts the writer.
startActivity(new Intent(this,MyTagWriterActivity.class).addFlags(Intent.FLAG_ACTIVITY_NEW_TASK));
Main --> Detect tag --> Reader Activity -NEW_TASK-> Writer activity Detect tag --> Write tag
It does mess with the activity history, but makes the writer activity more predictable.
Related
I have an android application which has two activities let's say A and B where A is the launcher activity. For activity A I registered an intent-filter which opens application for a specific URL. I want to have always a single task for my application in current running apps. To solve this problem I tried different combinations for launchMode attributes:
A singleTop, B standard but when I access app via intent URL I have two applications in current running apps
A singleTask B standard but every time when I open the app, it starts with activity A even the apps was already opened with activity B (in this case I want to resume the app)
A singleTask B singleTask the behavior is like A singleTask B standard
I want that my app to have the same behavior like for example gmail, always to have maximum one instance in current running apps, when I open it and there is already an instance in background, to resume it and if I open the app via intent filter I want to process the intent and provide content accordingly (for example gmail is in background and I receive a new mail notification after I click it, the android keep one instance for gmail and displays the new mail).
I use Samsung Galaxy Note 4 with Android 6.0
Problem solved
I found a solution for my problem, maybe it is not the best but it works. Firstly I added a new Activity to catch the intent filter which has launchMode = "SingleTask" and in its onCreate method I posted an event to kill all existing activities.
#Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
if ("android.intent.action.VIEW".equals(getIntent().getAction())) {
// This Activity is started using an external app (eg: Gmail)
// So start the app from the beginning
// (redirecting to Activity A)
Intent mainIntent = getIntent(); // Copy the Intent used to launch me
// Launch the real root Activity (launch Intent)
mainIntent.setClass(this, StartActivity.class);
// Post an event to kill all existing activities
// To do this i use Guava
PubSub.getInstance().post(new KillActivityEvent());
startActivity(mainIntent);
finish();
} else {
// The activity wasn't started by an external app
finish();
}
}
My app and activity is in my list of recent apps when I receive a notification. When I click on the notification, I want the intent of the notification to be honored. In my case I want to restart the activity (brute force) and pass in the new intent: so, finish then re-create. I am reading about such tags as FLAG_ACTIVITY_NEW_TASK and FLAG_ACTIVITY_SINGLE_TOP but I don't understand them enough to know how to force a "finish then re-create` of my activity. And, oh, the activity in question is MainActivity.
The snippet inside GcmListenerService uses
intent.addFlags(Intent.FLAG_ACTIVITY_CLEAR_TOP);
for sending the notification intent
Alternatively
If I go with onNewIntent things get complicated because there maybe DialogFragments being displayed, etc. And I would have to clear everything. That is why finish then re-create seem like the simplest solution to me.
Intent flag FLAG_ACTIVITY_CLEAR_TOP should produce the desired behavior. The documentation for Tasks and Back Stack says this in the section for Using Intent Flags:
If the launch mode of the designated activity is "standard", it too is
removed from the stack and a new instance is launched in its place to
handle the incoming intent. That's because a new instance is always
created for a new intent when the launch mode is "standard".
The documentation for FLAG_ACTIVITY_CLEAR_TOP describes the same behavior in more detail.
What happens when you click on an app's launch icon?
Is a new intent always sent, or is the result sometimes the same as resuming a task from recent tasks?
If an intent is sent, when does it get sent to the onCreate() method of a new activity instance and when does it get routed through onNewIntent() of an existing activity?
Let's suppose the intent gets routed through onNewIntent() of an existing activity in the task. Which activity does it get sent to? The one nearest the top or the one nearest the root? Will it always get sent to an instance of the application's launch activity or can it sometimes get sent to an activity with the same affinity as the root? Can it ever get sent to an activity which does not share the same affinity as the root?
Finally, how is this all affected by the various launch modes (standard, single top, single instance, single task) of the activities in the task?
If there is anyone out there who understands all this, please help me!
What happens when you click on an app's launch icon?
Launcher apps calls startActivity with an intent [action = Intent.ACTION_MAIN, category = Intent.CATEGORY_LAUNCHER and flag = Intent.FLAG_ACTIVITY_NEW_TASK].
Regarding Intent.FLAG_ACTIVITY_NEW_TASK, from docs:
When using this flag, if a task is already running for the activity
you are now starting, then a new activity will not be started;
instead, the current task will simply be brought to the front of the
screen with the state it was last in.
onNewIntent basics:
onNewIntent is delivered only when activity has set either singleTask, singleInstance launch modes. It is also delivered if activity has set singleTop launch mode or the intent to start the activity has set the flag FLAG_ACTIVITY_SINGLE_TOP and the activity instance is already at the top of the target task. It means an attempt was made to launch a new instance of activity, instead the existing instance itself need to handle the intent.
Here is the response to your queries:
Is a new intent always sent, or is the result sometimes the same as
resuming a task from recent tasks?
If the task is already running, it is brought to foreground. In case FLAG_ACTIVITY_CLEAR_WHEN_TASK_RESET flag was used to launch a activity and latter the task is brought to foreground, then the activity is killed. 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.
-
If an intent is sent, when does it get sent to the onCreate() method
of a new activity instance and when does it get routed through
onNewIntent() of an existing activity?
onCreate is called while creating a new instance of activity. onNewIntent is called if already an activity instance exists and no new instance need to be created, as in case of singleInstance, singleTask and conditionally singleTop (as described above).
Let's suppose the intent gets routed through onNewIntent() of an
existing activity in the task. Which activity does it get sent to? The
one nearest the top or the one nearest the root? Will it always get
sent to an instance of the application's launch activity or can it
sometimes get sent to an activity with the same affinity as the root?
Can it ever get sent to an activity which does not share the same
affinity as the root?
In case of singleTask and singleInstance it has to be root of the task. In case of singleTop it has to be top activity of the task.
Finally, how is this all affected by the various launch modes
(standard, single top, single instance, single task) of the activities
in the task?
I hope the explanation provided till now, answers it.
Update 1:
Here is the Launcher code which adds the flags to intent:
void processShortcut(Intent intent) {
....
Intent mainIntent = new Intent(Intent.ACTION_MAIN, null);
mainIntent.addCategory(Intent.CATEGORY_LAUNCHER);
....
}
void startActivitySafely(Intent intent) {
intent.addFlags(Intent.FLAG_ACTIVITY_NEW_TASK);
...
startActivity(intent);
}
Your best bet is to read through the Developer docs here: http://developer.android.com/training/basics/activity-lifecycle/index.html
There is a flow chart in the first lesson(http://developer.android.com/images/training/basics/basic-lifecycle.png) which provides an excellent graphical representation of the Android activity life-cycle.
My app, running in background, at some point displays activity to purposefully interrupt user's flow. My activity starts a new task, which appears in "Recent Tasks" lists while being in foreground. Is there any way it could be prevented? Setting android:excludeFromRecents does not work - activity is not presented anymore in "Recent Tasks" only after is has been paused.
Manifest looks like:
<activity
android:name="com.example.recenttasks.MainActivity"
android:excludeFromRecents="true">
</activity>
and activity is started this way:
#Override
public void onReceive(Context context, Intent intent) {
Intent i = new Intent(context, MainActivity.class);
i.setFlags(Intent.FLAG_ACTIVITY_NEW_TASK);
context.startActivity(i);
}
The key thing you mentioned is
appears in "Recent Tasks" lists while being in foreground
I think you can't change that behavior. I just tested on my app and the same thing happens. If I press the "recent tasks" button while having my activity in the foreground, it appears listed there. The moment I move out of it to another activity or to my phone's main screen, the activity is not listed anymore.
I also tested this on the built-in DeskClock app that comes with recent Android versions and the same behavior is present there when a new alarm is triggered. Note that the AlarmAlertFullscreen activity of that app has the same parameters you mentioned in your question.
I'm not sure you can circumvent this or why you would need to in the first place since the activity is not listed anymore once it loses the focus.
you are defined it in manifest that is enough but it is not coming..
ok..try add this flag also to your Intnet and start the Activity..
intnet.addFlags(Intent.FLAG_ACTIVITY_EXCLUDE_FROM_RECENTS);
Should the user be able to return to it? (Meaning if it shows and user clicks recents, have they lost their chance to see the hidden activity or should it still be there?)
If they cannot return to it anyway then the best action would be to finish() the activity onPause(). This will mean that as long as you have used android:excludeFromRecents and android:noHistory="true", there will be no item in recents.
If however you do wish to return to the 'interruption' activity (but do not want a recents entry) you could consider still finishing the activity onPause - but also recording a preference flag (something like IS_INTERSTITIAL). Your other activities can then check this preference in onResume and, if it is true, send an Intent to restart the Interstitial instead - To the user it will just appear they are resuming the app in the same state as they left it (interstitial)
Edit: If the screen needs to stay (rather than be re-instantiated) it may be possible to use a DialogFragment, although then you must worry about configuration changes. There is one hack you could try (explained in this answer) -
Set your label empty By using android:label="" your recent task is excluded. however this is a definite hack which may produce inconsistent results (as I haven't tested it to be sure)
I have an application that uses Urban Airship for push notification. When a notification arrives and the user clicks on it, activity A in my application should open and do something.
I've installed the BroadcastReceiver as is shown in the docs, and it's almost working.
When my app is in the foreground I don't let the user see the notification at all, and just handle it automatically.
When my app is not running at all, the activity opens up just fine.
When my app is in the background (which always happens when A is the top activity), a second instance of Activity A is created.
This is, of course, a problem. I don't want two A activities, I just want one of them. Here's the relevant BroadcastReceiver code:
#Override
public void onReceive(Context ctx, Intent intent)
{
Log.i(tag, "Push notification received: " + intent.toString());
String action = intent.getAction();
int notificationId = intent.getIntExtra(PushManager.EXTRA_NOTIFICATION_ID, -1);
if(action.equals(PushManager.ACTION_NOTIFICATION_OPENED))
{
Intent intentActivity = new Intent(ctx, ActivityA.class);
intentActivity.setFlags(Intent.FLAG_ACTIVITY_NEW_TASK);
UAirship.shared().getApplicationContext().startActivity((intentActivity);
}
}
UPDATE:
I tried to bypass this bug by calling System.exit(0) when the user presses Back on Activity A. The process ended, but then it was restarted immediately! My BroadcastReceiver is not called again in the second instance. What's happening?
UPDATE 2:
#codeMagic asked for more information about the app and activity A.
This app lets its user review certain items and comment on them. Activity A is started when the app is launched. If the user's session isn't valid any more, a Login activity is started. Once the user logs in, activity A becomes active again. A only has a "No items to review" message and a "Try now" button.
When the user logs in, the server starts sending push notifications whenever a new item is available for review. When the app gets the notification, activity A accesses the server and gets the next item to review. The item is shown in activity B. Once the review is submitted to the server, activity B finishes and activity A is again the top activity.
The server knows when a user is reviewing an item (because activity A fetched it), and doesn't send push notifications until the review is submitted - meaning a notification can't come if the user isn't logged in or if the user is viewing activity B.
While I agree there is a subtle race condition here, it is not causing the problem I'm seeing - in testing I am 100% positive there's no race condition - the push notification is only sent after Activity A becomes active again.
The solution was to add a launchMode='singleTask' to the activity in AndroidManifest.xml . As a result, instead of a new activity, onNewIntent of the same activity instance is called.
You can use one of several Intent Flags. FLAG_ACTIVITY_REORDER_TO_FRONT being one of them. This will bring the Activity to the front of the stack if it is already in the stack and if not then it will create a new instance. I believe you will still need FLAG_ACTIVITY_NEW_TASK if you aren't calling it from an Activity
Intent.FLAG_ACTIVITY_CLEAR_TOP should also work. But this will clear any other Activities on the stack. It just depends on what other functionality you need. Look through the Intent Flags and see which of these will work best for you
There are multiple scenarios when this could happen. One of them can be handled this way. Please see my answer here: https://stackoverflow.com/a/44117025/2959575
Ok, two notes on this :
You can register a broadcast receiver via the manifest so it is independent of any parts of your app. and use a Singleton pattern (keep a static reference to your activity somewhere in your app) that way you can check if their is an activity viewing or not and process accordingly.
// your activity A
#Override
public void onCreate(Bundle bundle) {
super.onCreate(bundle);
myActivityReference = this;
}
public void onPause() {
super.onPause();
if (isFinishing()) {
myActivityReference = null;
}
}
or you can keep everything as it is and use activity lunching modes flags in your manifest such as singleTop, singleInstance ... etc. take a look here android activity lunch modes