I have a FragmentActivity. Within its onPause function, I would like to differentiate
Home button pressed
Back button pressed
Launching a new activity (This will cause the fragment activity's onPause being called)
For back button pressed case, I know I can differentiate it by using this.isFinishing() == true.
However, how about launching a new activity case?
I know perhaps I can set a flag before launching the new activity, and reset the flag, at the end of onPause function. But, it doesn't sound elegant to me. Is there any better and robust way?
You can create a singleton class that tracks when your activities start/resume/pause/stop. Make a base Activity class that calls the singleton in each of its lifecycle callbacks.
If you look at the order of the callbacks when transitioning between activities, you should see this:
Pause Activity A
Create Activity B
Start Activity B
Resume Activity B
Stop Activity A
When your singleton gets called from Activity A's onStop(), you can check if there was a call from onResume() from another Activity (which clearly belongs to your app). If there wasn't, you know the user has changed apps or gone back to the home screen.
As for the back button press, you can check isFinishing(), or override Activity.onBackPressed() and do your bookkeeping there.
Related
I launch main activity, change some settings in UI, press back button and then reopen the activity. onCreate() is called again and activity is back to default state. Why is this?
I would expect only onResume() to be called since I have this in Manifest:
android:launchMode="singleInstance"
Try using moveTaskToBack(true); in onBackPressed() to make your current activity hide instead of destroying, so you can reopen it again
#Override
public void onBackPresses(){
moveTaskToBack(true);
}
I launch main activity, change some settings in UI, press back button and then reopen the activity. onCreate() is called again and activity is back to default state. Why is this?
This is expected behavior of activity life cycle. When you press back button then activity get destroyed, it will start from onCreate method.
This is because when you press back, it destroyes the activity.
I think that what you want is to keep the state when you come back to this activity, not really to have one instance of it. So you should save the information you need and then restore them in onCreate.
Single instance only means (if I remember it well) that if you launch multiple activities without finishing them, the ones that have singleInstance will go back to front when you will call startActivity() and will not call onCreate. But this means you can't have this behavior by pressing back.
Maybe you can override onBackPressed and start another activity (the one you should go back to) instead of calling super.onBackPressed(). this should do what you want but if think it will be kind of difficult to manage.
By the way remember that Activities might be killed by the system itself, so you should not rely on the fact that your activity as not been killed
I wrote an Android app with several Activities and a Main Activity. When I go from the Main Activity to lets say Activity B, I want to "pause" the Main Activity, when the back button is pressed it should go back and reactivate the Main Activity instead of calling onCreate().
This shall work with all Activities, so if I click on a button to start Activity B, it shall also reactivate the old Activity B instead of creating a new state with onCreate().
How can I realize this?
PS: I already tried it with parcelable, but this do only work, if I close the application or something unexpected happens.
It's always possible that the first activity may be destroyed when you start another activity. It will be recreated when you go back to it. Every app should be written with this possibility in mind. To make sure your activities can handle being destroyed and recreated, turn on the "don't keep activities" developer option.
It is by default in Android. If you Start Activity B from Activity A then activity A goes in stopped state. Below methods will be called of Activity A
onPause()
onStop()
When you tap on Back key on Activity B. Below methods of Activity A will be called.
onRestart()
onStart()
onResume()
For reactivating Activity B, you can set Activity B launch mode as singleInstance. This will make sure that only single instance of Activity B will be created. onCreate will be not be called again. onNewIntent will be called when that activity is reactivated.
Refer: http://developer.android.com/guide/topics/manifest/activity-element.html#lmode
Activities live in stack order. Each activity has its life cycle. When you close an activity (Activity B in your example) it eventually reaches onDestroy() method and removed from the stack order. It is by default in Android and there's nothing you can do about it.
What you can do is rewrite the onStop() method in Activity B and save some activity data (like text in EditText, for example) in SharedPreferences - read here. Then in your onCreate() method you can call for SharedPreferences, check if it's not empty and restore the text in the EditText by pulling appropriate value by key.
I am new going for the android.I am working on an app in which I have two activities let say A and B.
In activity A I have a list view of some items.I have a button in activity A which takes me to activity B.In activity B I have a seek-bar.
I am using the seek-bar to filter the result of activity A.
I have two buttons in activity B cancel and filter.
After adjusting seek-bar if user clicking filter button than it takes user to activity A and showing filter results.
User can play between activity A and activity B.
Now three different scenario are there for coming back from activity B to A.
By pressing filter button
By pressing cancel button
By pressing phone's back button
After adjusting seek-bar if user pressing filter button then activity A is re ordering and showing filter results. Here I want to save the instance of activity B. so that from activity A if user again going in activity B then I can show the previous state of activity B.(I am able to do this)
In second scenario if user adjusting the seek-bar again and pressing cancel button then Activity A is reordering.Here I do not want to save the instance of activity B and if user again going in activity B from activity A then I want to show the previous state of activity B.(I am not getting how to do this ??)
In Third scenario if user adjusting the seek-bar again and pressing phone's back button then Activity A is reordering but now if user again going in activity B from activity A then activity B is restarting that I do not want, here also I want to show the previous state of activity B.(I am not getting how to do this also ??)
I am stuck with this problem.
Thank you so much in advance.
You must consider each of the cases and manage the activity lifecycle accordingly. You did this just fine, the problem is how to manage it. So, the first step is to study this:
activity and lifecycles
After understanding how the lifecycle of activities is handled by the android os you're on your way: Manage the life of your second activity so that state is mantained by overriding the onPause method (which is called when your activity is no longer in the front of the application) or finish the activity if you don't want to save the state (effectively calling the onStop method.
I would solve this in this way:
in activity A i call the activity B with a startActivityForResult. This way, when the activity B is finished, it's state is not mantained. So, call finish() inside activity B to return to activity A without saving it's state.
When wanting to save the state of activity b, call the activity A so that the onPause method gets called and the state saved.
Hope this clarifies it for you.
What activity state is called when another activity, in the same application, is launched, and then the backpress button is clicked to navigate back to it?
What lifecylce method is called during the proccess of going back to the previous activity?
onPause() is called in Activity A when it launches Activity B. After the back button is called in Activity B, onResume() is called in Activity A.
What lifecylce method is called during the proccess of going back to
the previous activity?
According to the docs: onPause(), onStop(), and possibly onDestroy(). In addition to the lifecycle documentation, you might want to read the docs on Tasks and Back Stack.
Is there any way to tell whether an Activity is being resumed (i.e. onResume is called) from the home screen/launcher?
For example, if I have an Application with two activities, A and B.
Scenario 1:
Some user action on Activity A will invoke Activity B, bringing it into the foreground - moving Activity A into the background. As Activity A moves into the background, it goes through onPause() and onStop(). The user (now on Activity B) either finishes the Activity or hits the "back" button, bringing Activity A back to the foreground, causing an onRestart(), onStart(), onResume() sequence.
Scenario 2:
If the user hits the "home" button while Activity A is in the foreground and then re-invokes the Application from the launcher, it goes through the same lifecycle as in Scenario 1. I.e. User hits the "home" button. Activity goes through onPause() and onStop(). User launches the application again, causing Activity A go come back into the foreground, again going through the same onRestart(), onStart(), onResume() sequence as in Scenario 1.
As far as I can tell, the Activity has no way of knowing how it was resumed, it just knows it is being brought back into view. In fact, I have a feeling that there isn't really as much of a concept of an "Application" in Android - in the sense of something that has a single entry and exit point.
in Scenario 2, your activity will get an onNewIntent call, with the launcher intent passed to it.
You could capture the back button press on Activity B and pass an extra value to Activity A. If there is an extra value then the activity was resumed from pressing back on Activity B, if there is no extra value then the Activity was resumed from being hidden.
Could Acitivity A use startActivityForResult() to start Activity B and use onActivityResult() to detect that Activity B finished?
So the straightforward answer to the initial question is probably: no. Launching an activity from the home screen through an icon, or resuming it from the recents screen can not be observed from the intent it is (re)started/resumed with.
Depending on what you are trying to achieve there are some approaches though:
what #superfell suggested:
Check for whether the onNewIntent-method is called on your activity to decide if it was restarted from the launcher. As a precondition you need to set your activity to singleTask/singleTop launchMode in your Manifest:
android:launchMode="singleTask"
depending on what you're trying to achieve, this might be enough! But additionally you might have to deal with what happens when the user presses the back button. Default behavior is to finish & destroy your activity. Thus a brand new copy of it would be launched when it gets selected from the recents screen. Though onNewIntent would not be called, everything would be rebuilt from scratch. If you need to prevent this you can use:
override fun onBackPressed() {
moveTaskToBack(true)
}
finally when you navigate "back" from an activity you launched yourself onNewIntent will also not be called. If you further need to distinguish why your activity is resumed, you might want to start the 2nd activity with startActivityForResult so the onActivityResult is called when you get resumed.
Launcher activity & Intent extra
A completely different approach would be to have a "launcher" activity in your manifest that directly calls your "main" activity and finishes itself. When calling your main activity you can put an intent extra that allows your main activity to distinguish if it was just launched for the first time, or not. As the extra would be present on further onResumes, make sure to overwrite it the first time you "consume" it:
override fun onResume() {
super.onResume()
val firstLaunch = intent.getBooleanExtra(FIRST_LAUNCH, false)
intent.putExtra(FIRST_LAUNCH, false)
if (firstLaunch) {
// do something
}
}
and when starting from your "launcher" activity:
intent.putExtra(FIRST_LAUNCH, true)
startActivity(intent)