I have two buttons on my application. One button starts a new Game (lets say solitair).
When ever this button is pressed it will always start a new game
My problem is that I would like a second button to go back to the game that has already started if the user clicks back.
How do I go about recalling that activity that has already been created
Thanks
I assume that the game is from a third party. As I see it you don't even need second button. Just click the first one again and you will get back to the game.
If the game intercepts Back it may intentionally destroy it's state so there is no way to jump back to the place that you were before hitting Back.
You have to save the state of the activity
onSaveInstanceState() and onRestoreInstanceState() are used to handle the activity state
onSaveInstanceState() method gets called for an activity when user leaves the activity. Note this method is only called when activity is present in the History state and user can come back to the activity.
onRestoreInstanceState() restores the state of the views.
see the following link
How to manage activity state
You have to read manual about activity stack
Your application can has more than one task and more than one activity back stack
Related
I know that in Android, if stuff is idle for a while, the operating system will devour things to free up memory.
So if I have a first Activity, and I invoke a second Activity by using an Intent, and then invoke a third Activity using yet another Intent, I can use the back button to go back to the previous Activities.
But let's say I stay on the third Activity, and let the phone idle for a while until the OS decides to devour my app for memory. If I open the app again, will I have lost the stack I have formed from my Intents? Will I still be in the third Activity with the ability to press Back and go to Activity 2, then Activity 1?
The OS will handle how long a particular Activity stays "active" in memory. However, the "stack" shouldn't change, regardless of whether an activity is "active" or not. This is where the Bundle comes in handy and the methods: "onSaveInstanceState()" and "onRestoreInstanceState()".
Implementing these methods properly is the difference of the activity reappearing on the screen in an empty state vs. with its previous state maintained.
Some documentation on Recreating an Activity
The backstack stays intact for the task in hand. It will always stay in task and whenever the user presses the back button, it will go through the back stack like popping the last item. However, not all the activities in the stack are in the foreground. Usually, only the last item put into the back stack (the top of the stack) is in the foreground and if there are multiple apps/tasks open this may not even be true. Here is a great diagram to show this.
Now, lets say a user opens a task with a couple of activities in its back stack. The top activity is in the foreground and is running normally, but to preserve memory the other activities were destroyed. So now when the user presses the back button, the task knows what activity was in the back stack and knows it is now destroyed. So, it will recreate it following the Activities lifecycle and any data that was in it will be lost. One way to preserve it (mentioned by original answer) is using the onSaveInstanceState() and onRestoreInstanceState(), which save things in a bundle that Android preserves for the user so data can be saved. All of this information can be found in the docs. To answer your question more clearly, yes you will be in the activity you think you would be in, but you can treat it as a new instance of that activity and to recover the data from before to display it in the same way, you should use bundle and implement the methods aforementioned.
The home screen of my app needs to have different behavior when the app is being launched from outside the app versus when a back navigation occurs. For example, imagine an Android Twitter client which on launch tries to get your updated feed but when you click on an item to hit its detail page and hit back, the screen doesn't reload new feeds but is instead where you left from.
So far I've tried looking at the calling package property but this hasn't helped since it seems to be null both when app is launched by the user for the first time or when I hit back from a detail page.
When user launches it first time, onCreate() then onresume() will be called for sure. When navigating back and getting your activity from backstack, just onResume will be called.
Also if you activity has singleTop set, then you can look into onNewIntent() which will be called when you navigate back to your activity from other screens.
So, the solution I can suggest you is to set singleTop for your activity. Then while navigating back using onNewIntent(). For 1st time launch onCreate() will be called.
Sorry if I could not understand your question well..
Let's say we have a default, empty activity with default behaviour, launched with default intent flags. User presses back button on the device. The activity disappear... but how, actually?
Is pressing back button behaving the same way like finish()?
Is the activity immedietely destroyed (onDestroy is called)?
Is the activity guaranteed to be destroyed, but not immedietely?
Is there any chance the activity won't be destroyed and this instance will be reused when this activity is launched in the future? (so only onPause and onStop -> onStart and onResume are called?)
I'm looking for a reliable answer, so please do not answer if you are not absolutely sure what happens here.
http://developer.android.com/training/basics/activity-lifecycle/recreating.html
This is a subchapter from the official Android documentation that addresses your question. It is a subchapter of the topic Managing the Activity Lifecycle, which can be read here:
http://developer.android.com/training/basics/activity-lifecycle/index.html
It is definitely worth reading the whole chapter to get to know the details about Androids Activity behaviour. But the subchapter ( first link ) is the relevant part to this question.
you use should look into this try this
and please tell specific what you wish to do with back button for your default activities ......
When you press back, (if not intercepted by anything like the keyboard, fragment, activity, etc) the OS (via ActivityManager probably) will try to show the user the previous activity in your current task (again, ignoring fragments' back stack).
If there is no such activity, the task will be terminated and you'll go to the previous task - the home screen most of the times or some other application that might have launched your app.
You'll get onDestroy called soon (it depends on how long it takes to start the next activity but on a good phone it should be under 100-200ms).
Your activity instance won't be reused after onFinish. This happens before the activity is destroyed so if you need another activity of the same type, the OS will create another instance.
When the user presses the BACK key, the current activity is popped from the top of the stack (the activity is guaranteed to be destroyed, but not immediately, may be when the system resources are low) and the previous activity resumes (the previous state of its UI is restored).
Which actions does the back button/back key on Android trigger?
Definitly onDestroy() is called .....There are a few scenarios in which your activity is destroyed due to normal app behavior, such as when the user presses the Back button or your activity signals its own destruction by calling finish().
As Android newbie I started to wonder about the Activity lifecycle. I'm having an Activity that loads a list of Persons and displays them. Upon the click of a Person I want to open another Activity showing the details of that Person. I'm currently doing this by creating an Intent on the "PersonDetailActivity" which I then start. So far so good. On the PersonDetail page I would like to have a menu action to go back to the Person list. I again applied the same technique, meaning an Intent that brings me back to the PersonListActivity.
Now I started to wonder what returning to the PersonListActivity means. Will a new instance get created and will I have to reload the persons that it displays in the list? Can you come back to the same instance, avoiding having to reload the list again? Do you then have to pass a pointer to yourself via the intent to the other Activity?
So when will and Activity be re-instantiated and when will it not. Any hints or suggestions are more than welcome. Maybe there are some patterns to be applied for these back and forth menu actions that I'm not yet aware of.
Thanks,
Vincent
Yes,,. Call finish() in second Activity instead of starting new Activity..
There is basically something called Activity stack which stores all Activities in the order they were started.. so if start new Actvity , that sits on top of the stack and preveous one gets below it.. when you call finish the Activity is poped out..
if you don't want to call finish() correct waht ever you were doing then add flag ACTIVITY_CLEAR_TOP in manifest for the 1st Activity..
Basically if you just call the finish() method on your PersonDetailActivity
PersonDetailActivity.this.finish();
it will activate the onResume() method from the Activity that is on the top of the finished one, which here would be your PersonsActivity. You can specify in your onResume() method what you want to perform when turning back there.
My Android Application has only one activity called MainActivity. When I press the back-button and run my application again, the previous activity will be destroyed. Now I want to know that is it possible to save the exact previous activity?
Thank you
Pressing the back key kills your current activity. A user would not expect it to be saved as there is no way to go "Forward" .
You can save the important parts of your activity in SharedPreferences or a database when you press back and restore it to its previous state when the activity next starts which would give the impression that it was "saved"
Activities are created in a stack, when you create A from B then B is now at the top of the stack, when you press the back button you are telling android that the top level of the stack (current activity) is no longer needed and it gets removed.
You will have to save state yourself and restore it if that's what you need to do when B is recreated.
one way you can use sharedpreferences for saving state of TextView,EditView ...etc.and resigning again when activity recreated.
Thanks.maybe helpful :-)