Develop Reference

Difference between launching app from recents and home screen

I have ActivityA as launcher activity.
From ActivityA I open -> ActivityB. I put the app in background.
When I open the app from recents the app is resumed with ActivityB.
When I open the app from homescreen, the app is resumed with ActivityA without calling onCreate(), just onResume().
Why is ActivityB cleared from stack when I open the app from homescreen, even if onCreate() from ActivityA is never called, and how to fix this?
Manifest file looks like this:
ActivityA:
<activity-alias
android:name=".Launcher"
android:label="#string/app_name"
android:targetActivity="path.ActivityA">
<intent-filter>
<action android:name="android.intent.action.MAIN" />
<category android:name="android.intent.category.LAUNCHER" />
</intent-filter>
</activity-alias>
<activity
android:name=".path.ActivityA"
android:launchMode="singleTask"
android:screenOrientation="sensorPortrait"
android:theme="#style/BlackIntroTheme"
android:windowSoftInputMode="adjustPan">
<nav-graph android:value="#navigation/graph1" />
<nav-graph android:value="#navigation/graph2" />
<nav-graph android:value="#navigation/graph3" />
<nav-graph android:value="#navigation/graph4" />
</activity>
ActivityB:
<activity
android:name=".path.ActivityB"
android:launchMode="singleTask"
android:screenOrientation="sensorPortrait"
android:windowSoftInputMode="adjustPan" />

this is how Activity stacking works, some nice example of all launchModes in HERE, more complex info in DOCs
in short - Activity with singleTask started (again) will clear all on-top-of-it Activities. you have your first MAIN Activity declared with this launchMode, so every icon click on devices launcher will clear your Activities stack. you can track this by overriding onNewIntent method. picking from recents just brings all your Activities stack to front, with last opened on top ofc.
consider removing launchMode (is this necessary line for you?) or set it as standard (default)
android:launchMode="standard"

IllegalArgumentException: setTaskFromReuseOrCreateNewTask

I have the next crash when I try to launch an Activity:
2019-10-24 15:12:29.887 4245-4296/fr.zapotec.eliodroid.tv E/AndroidRuntime: FATAL EXCEPTION: Thread-6
Process: fr.zapotec.eliodroid.tv, PID: 4245
java.lang.IllegalArgumentException: setTaskFromReuseOrCreateNewTask: task=TaskRecord{6e69142 #1643 A=fr.zapotec.eliodroid.tv U=0 StackId=1 sz=3} is in a different stack (1) than the parent of r=ActivityRecord{8062424 u0 fr.zapotec.eliodroid.tv/fr.zapotec.eliodroid.SplashActivity t1644} (0)
at android.os.Parcel.readException(Parcel.java:1955)
at android.os.Parcel.readException(Parcel.java:1897)
at android.app.IActivityManager$Stub$Proxy.startActivities(IActivityManager.java:6812)
at android.app.Instrumentation.execStartActivitiesAsUser(Instrumentation.java:1677)
at android.app.Instrumentation.execStartActivities(Instrumentation.java:1632)
at android.app.ContextImpl.startActivities(ContextImpl.java:910)
at android.app.ContextImpl.startActivities(ContextImpl.java:884)
at android.content.ContextWrapper.startActivities(ContextWrapper.java:399)
at fr.zapotec.eliodroid.utils.LaunchActivityUtils.launchTVLastProgram(LaunchActivityUtils.java:22)
at fr.zapotec.eliodroid.standby.StandbyManager.launchAction(StandbyManager.java:253)
at fr.zapotec.eliodroid.standby.StandbyManager.onEventReceived(StandbyManager.java:141)
at fr.zapotec.eliodroid.handset.HandsetEventDispatcherImpl.handleKeyPress(HandsetEventDispatcherImpl.java:229)
at fr.zapotec.eliodroid.handset.HandsetEventDispatcherImpl.handleKeyPress(HandsetEventDispatcherImpl.java:204)
at fr.zapotec.eliodroid.handset.HandsetEventDispatcherImpl.onMessageReceived(HandsetEventDispatcherImpl.java:165)
at fr.zapotec.handsetbluetooth.HandsetManagerImpl.dispatchMessage(HandsetManagerImpl.java:49)
at fr.zapotec.handsetbluetooth.MessageManager.onNewMessageReceived(MessageManager.java:119)
at fr.zapotec.handsetbluetooth.HandsetThread.listenAndWrite(HandsetThread.java:126)
at fr.zapotec.handsetbluetooth.HandsetThread.run(HandsetThread.java:56)
This is the Manifest file:
<activity
android:launchMode="singleTask"
android:name=".SplashActivity"
android:noHistory="true"
android:theme="#style/SplashTheme">
<intent-filter>
<action android:name="android.intent.action.MAIN" />
<category android:name="android.intent.category.LAUNCHER" />
<category android:name="android.intent.category.HOME" />
<category android:name="android.intent.category.DEFAULT" />
<category android:name="android.intent.category.LEANBACK_LAUNCHER" />
</intent-filter>
</activity>
<activity
android:launchMode="singleTask"
android:noHistory="true"
android:name=".StandbyActivity"/>
<activity
android:launchMode="singleTask"
android:name=".main.SimpleMainActivity"/>
<activity
android:launchMode="singleTask"
android:name=".main.InstallActivity"/>
I need the Activity 'SimpleMainActivity' to be one only instance (that's why the 'singleTask')
This Activity can be launched due to Bluetooth events (triggered by a bluetooth device) or due to a given timing in a very specific situation.
The method which launches the Activity is:
startActivity(new Intent(context, MainActivity.class).addFlags(Intent.FLAG_ACTIVITY_NEW_TASK | Intent.FLAG_ACTIVITY_CLEAR_TASK));
I have the crash when trying to launch the Activity from the 2 different sources almost at the same time.
Anyone knows how to solve this problem without removing the 'singleTask' from my Activity?
For information, my application is the "Default launcher", so "SplashActivity" maybe be launched if system needs to show the launcher. The SplashActivity only shows a splash screen and launches the first activity (SimpleMainActivity.class)

What will likely work is to use a launchMode of singleTop instead and set the flags FLAG_ACTIVITY_NEW_TASK and FLAG_ACTIVITY_CLEAR_TOP. The docs do recommend this for activities launched by notifications.

Android: Recents starts incorrect activity

I am developing an android app which has 2 methodes of starting.
One is the normal way by pressing the app icon on the phone.
The other method is with a deep link from a website.
The deeplink also sends some data which the app needs to do some "stuff". However this should only be done once.
When the deeplink activity is finished it start the main activity. However when I press back (on the device) and open the app from recents it opens the deeplink activity again.
I could exclude the deeplink activity from the recents in the manifest. This also excludes the mainactivity from the recent apps, this should not be the case.
How do I prevent the deeplink activity from beeing started from the recent apps?
My Manifest:
<activity
android:name="MainActivity"
android:label="#string/app_name"
android:screenOrientation="portrait"
android:launchMode="singleTask"
android:theme="#style/AppTheme">
</activity>
<activity
android:name="DeeplinkActivity"
android:label="#string/app_name"
android:noHistory="true"
android:screenOrientation="portrait"
android:launchMode="singleTask"
android:theme="#style/AppTheme">
<intent-filter>
<action android:name="android.intent.action.VIEW" />
<category android:name="android.intent.category.DEFAULT" />
<category android:name="android.intent.category.BROWSABLE" />
<data android:scheme="app_name" android:host="test" />
</intent-filter>
<intent-filter>
<action android:name="android.intent.action.VIEW" />
<category android:name="android.intent.category.DEFAULT" />
<category android:name="android.intent.category.BROWSABLE" />
<data android:host="test" android:path="/" android:scheme="app_name" />
</intent-filter>
</activity>
To switch to the MainActivity I do the following:
Intent intent = new Intent(this, MainActivity.class);
intent.addFlags(Intent.FLAG_ACTIVITY_REORDER_TO_FRONT);
intent.addFlags(Intent.FLAG_ACTIVITY_CLEAR_TASK);
intent.addFlags(Intent.FLAG_ACTIVITY_NEW_TASK);
startActivity(intent);
EDIT:
This post was marked as duplicate with: Android: Starting app from 'recent applications' starts it with the last set of extras used in an intent
However that post is regarding the same activity. I want to change the root activity so when I start the app from recents it does not start the DeeplinkActivity. Yes as a workaround I could check the Intent.FLAG_ACTIVITY_LAUNCHED_FROM_HISTORY flag. But then every time the user starts the app from recents the DeeplinkActivity is opened whilst it is not needed anymore.
Setting and or clearing aditional intent values does not seem to work.
I use information from the getIntent().getData()
If you still feel as if this is a duplicate please explain.

Your problem is that both DeepLinkActivity and MainActivity are in the same task, so when the user selects the app from the list of recent tasks, Android will either bring an existing task to the foreground, or if there is no existing task (with live/active activities in it), start the Activity that was the root Activity in the most recent task. You can't predict which Activity will be the root Activity, since the task could be started with either DeepLinkActivity or MainActivity, depending on which one the user chose first.
You really need to have 2 separate tasks to do this. One task will have your DeepLinkActivity in it, and this task should be excluded from the "recent task list". The other task will have your MainActivity in it.
I assume that MainActivity has the <intent-filter> with ACTION=MAIN and CATEGORY=LAUNCHER, even though your posted manifest does not show this.
Your manifest should look like this:
<activity
android:name="MainActivity"
android:label="#string/app_name"
android:screenOrientation="portrait"
android:theme="#style/AppTheme">
<intent-filter>
<action android:name="android.intent.action.MAIN" />
<category android:name="android.intent.category.LAUNCHER" />
</intent-filter>
</activity>
<activity
android:name="DeeplinkActivity"
android:label="#string/app_name"
android:noHistory="true"
android:screenOrientation="portrait"
android:taskAffinity=""
android:excludeFromRecents="true"
android:theme="#style/AppTheme">
<intent-filter>
<action android:name="android.intent.action.VIEW" />
<category android:name="android.intent.category.DEFAULT" />
<category android:name="android.intent.category.BROWSABLE" />
<data android:scheme="app_name" android:host="test" />
</intent-filter>
<intent-filter>
<action android:name="android.intent.action.VIEW" />
<category android:name="android.intent.category.DEFAULT" />
<category android:name="android.intent.category.BROWSABLE" />
<data android:host="test" android:path="/" android:scheme="app_name" />
</intent-filter>
</activity>
You definitely do not need launchMode="singleTask" for MainActivity and you probably don't need it for DeepLinkActivity either (that depends on what else you do with this).
Specifying taskAffinity="" ensures that DeepLinkActivity is not launched into the same task as MainActivity, and allows you to launch MainActivity from DeepLinkActivity in a separate task. NOTE: Without specifying taskAffinity, both activities will end up in the same task, even though you specify launchMode="singleTask" for both of them.
Specifying excludeFromRecents="true" on DeepLinkActivity tells Android that the task with DeepLinkActivity as its root activity should not appear in the list of recent tasks.
When you launch MainActivity from DeepLinkActivity, you should do this:
Intent intent = new Intent(this, MainActivity.class);
intent.addFlags(Intent.FLAG_ACTIVITY_CLEAR_TASK);
intent.addFlags(Intent.FLAG_ACTIVITY_NEW_TASK);
startActivity(intent);
and make sure that you call finish() on DeepLinkActivity.
If necessary you can also add noHistory="true" to DeepLinkActivity, but I don't think it is necessary. If the user is in DeepLinkActivity and gets an incoming phone call, after the phone call is ended, DeepLinkActivity should be displayed. If you specify noHistory="true", DeepLinkActivity would be finished immediately when the user accepts the incoming phone call.
Let me know if this is clear and works for you.

singleTask activity not loading properly

I have an activity 'A' defined in Manifest like below:
<activity
android:name=".A"
android:launchMode="singleTask"
android:screenOrientation="portrait">
<intent-filter>
<action android:name="android.intent.action.MAIN" />
<category android:name="android.intent.category.LAUNCHER" />
</intent-filter>
</activity>
When I launch my APP, that activity is always loaded from the start. It wont start from my prev activity.
When I remove android:launchMode, then it works as I expect.

Since you set android:launchMode="singleTask", the activity A will always be the root of your activities.
From DOCS:
In contrast, "singleTask" and "singleInstance" activities can only begin a task. They are always at the root of the activity stack. Moreover, the device can hold only one instance of the activity at a time — only one such task.
Default mode is standard. So, when you remove android:launchMode="singleTask", your APP returns to standard launch mode.
That's why if you app is always starting Activity A.

If you would like to start a different Activity on launch replace that in the xml name attribute that contains LAUNCHER
<activity
android:name=".ActivityB"
android:launchMode="singleTask"
android:screenOrientation="portrait"
>
<intent-filter>
<action android:name="android.intent.action.MAIN" />
<category android:name="android.intent.category.LAUNCHER" />
</intent-filter>
</activity>
Where Activity B is an alternate activity.

launchMode="singleTask" does not create a new task

I have 2 activities: Activity A and Activity B. Activity A's launch mode is standard, and Activity B's launch mode is singleTask.
<activity
android:name=".AActivity"
android:label="#string/app_name"
android:launchMode="standard">
<intent-filter>
<action android:name="android.intent.action.MAIN" />
<category android:name="android.intent.category.LAUNCHER" />
</intent-filter>
<intent-filter>
<action android:name="android.intent.action.VIEW" />
<data android:scheme="dd"></data>
<data android:host="a"></data>
<category android:name="android.intent.category.DEFAULT" />
<category android:name="android.intent.category.BROWSABLE" />
</intent-filter>
</activity>
<activity
android:name=".BActivity"
android:label="#string/app_name"
android:launchMode="singleTask">
<intent-filter>
<action android:name="android.intent.action.VIEW" />
<data android:scheme="dd"></data>
<data android:host="b"></data>
<category android:name="android.intent.category.DEFAULT" />
<category android:name="android.intent.category.BROWSABLE" />
</intent-filter>
</activity>
I launch the app, and the launcher Activity A starts. Then i press Home Button and return to home screen of the phone. Then i launch browser app and type the following:
dd://b
to open Activity B. The system navigates to my App and starts activity B on top of activity A. At this point if i press back button, activity B is popped and i see activity A.
This is not what i expected because the android documentation states:
For singleTask activities, the system creates a new task and instantiates the activity at the root of the new task. 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. Only one instance of the activity can exist at a time.
What i understand from these sentences is, in my case since an instance of Activity B does not exist, a new task should have been launched and it should have had only Activity B at its stack(Another instance of my app should still exist in a separate task and it should have Activity A in its stack). Then if i press back while i was at Activity B, since it is the only activity in the backstack, it is popped out and the system returns to the browser.
Why this is not the case? How does android system know that my app is open and navigates to it and starts activity B on top of existing app stack instead of launching another instance of my app and letting two instances of my app have their own stacks? What does it mean to instantiate activity in a new task? Can anyone explain?
Thanks.

In addition to the accepted answer, I found an explanation to this problem. As android documentation states:
The affinity indicates which task an activity prefers to belong to. By default, all the activities from the same application have an affinity for each other. So, by default, all activities in the same application prefer to be in the same task which belongs to that app(The app that has the Activity B). However, you can modify the default affinity for an activity.
So, if your app is running, and you start an activity, which has launchMode:singleTask attribute, unless you explicitly state taskAffinity attribute, it starts the activity in the same task. But if you explicitly state an affinity in your manifest:
<activity
android:name=".BActivity"
android:label="#string/app_name"
android:taskAffinity=""
android:launchMode="singleTask">
</activity>
then it starts the activity in a new task.
You can see which activity belongs to which task by the following adb command:
adb shell dumpsys activity
and also, to better understand launchMode concept, you can see the following app in the Google Play: https://play.google.com/store/apps/details?id=com.novoda.demos.activitylaunchmode

You said that your app navigate to B in passing by A.
So, i think you have two stack. In the first, you have only A, in the second you have only B. If you press back, then B is popped and disapeared but A exists and is showing because A in behind B even if A and B are in separate stack.
If you want that B pop and then you return to home, try to call "finish()" after call B from A