Develop Reference

How properly delete an activity

I've written an android application.
So, this is what happens:
I've got a listview and if the user taps on a specific row the following code in invoked to create an activity:
Intent intent = new Intent();
intent.setClassName( getPackageName(), getPackageName() + ".matchView.MatchViewActivity" );
intent.putExtra("leagueId", leagueId );
startActivity( intent );
Then the activity is started and let's suppose the user return back to the list view by tapping the back button
Now he is again in the Listview and can tap the same cell again such that the same activity is started again.
However, the problem is that when I start the activity and I return back with the back button the (now old) activity is not deallocated. It still runs in the background and if the user again taps on the same cell the same acitvity is started again resulting in the same activity running two, three, four and so on times (depending on how often the user taps).
So if the user taps the back button how do I make sure that the activity I started is properly deleted or ended?

Activity will be deleted automatically (when you return back) by system if you are not holding any reference to it.
Better read about activities and back stack

Answering to your question, if you don't intend anymore to use an Activity, the correct way of ending it is by calling finish().
This tells the Android SO you don't want to use it again, but don't expect it to be finished immediately. Android keeps the references to both instances and Activities (this ones are instances too) in memory a certain time after finished so if the user reopens that Activity within a short amount of time, it's recovered much faster.
If you are worried about the state in which the Activity is reopened, you can force it to be restarted every time it's reopened. You might find more references in the Intent reference page, especially the FLAG_ACTIVITY_CLEAR_TOP flag.

You can define in the manifest how an activity is launched based on the "launchMode", and you can choose from one of four launch modes:
"standard"
"singleTop"
"singleTask"
"singleInstance"
It sounds like you want to use, "singleTask" or "singleInstance", which you can read more about under the "android:launchMode" section here:
http://developer.android.com/guide/topics/manifest/activity-element.html

Add finish(); after starting the new activity to delete the current one.

Remove app completely from memory on exit

I am building an Android app, which starts a service that keeps running in the background. When the user uses the Home button to close one of the activities (which communicate with the service), and then navigates to the app again, they get the last activity. This is correct behaviour.
However, when I explicitly stop the service (via an option in the menu), the app should "Quit". Currently, that works like this:
stopService(new Intent(this, MyService.class));
finish();
// just go to to the home screen, as it is intended in Android
Intent intent = new Intent(Intent.ACTION_MAIN);
intent.addCategory(Intent.CATEGORY_HOME);
intent.setFlags(Intent.FLAG_ACTIVITY_NEW_TASK);
startActivity(intent);
and that works fine. But when I now navigate to the app again, it starts the previously opened Activity. What I want is that it starts the starting activity again (the launcher).
How could I accomplish that?

System.exit(0);
But you should have only one Activity in stack.

If you look at the description of android:excludeFromRecents it says:
Whether or not the task initiated by this activity should be excluded from the list of recently used applications ("recent apps").
isn't this what you are looking for ? Once the user hits exit, this app won't be in the recently used apps and hence will be completely removed from memory ? :)

I think that removing 'the app completely from memory on exit' is not the issue. Even if you stop your service the process is likely to remain in memory - that is the systems' decision.
You want an explicit, custom behaviour - user chooses your 'exit' option from menu --> next app launch starts at main activity - so you will need to handle this explicitly.
The default behaviour is that the user returns to their last activity when they re-launch. So they only return to the main activity if they exit by 'backing out' through your activities. Your use of an 'exit' menu option is non-standard (not to say it is bad).
One option would be to do the backing out through your activities yourself. Perhaps now you are just finishing the current activity and you should instead finish all the activities in the back stack.
Another option is that you could save a flag, and when the UI is launched again you could read that flag and launch the appropriate activity (but again be careful with the backstack). The easiest way to set that flag is probably by overriding onSaveInstanceState(Bundle) and then reading the bundle in onCreate (or use sharedpreferences).

Have you tried setting the clearTaskOnLaunch to true for your main activity (in your manifest).
From the documentation:
When the value is "true", every time users start the task again, they are brought to its root activity regardless of what they were last doing in the task and regardless of whether they used the Back or Home button to leave it.
This seems to describe what you want to do. I have never tried this personally, but it seems worth investigating for your purpose.

How to launch the activity of this case?

I have 3 activities in my app.
Home -> List -> Detail
When I am in Detail activity, I want to have a home button that will redirect me to Home activity and close the other activities. Then, I tried this code:
Intent intent = new Intent(this, HomeActivity.class);
intent.addFlags(Intent.FLAG_ACTIVITY_CLEAR_TOP);
startActivity(intent);
since the FLAG_ACTIVITY_CLEAR_TOP is:
If set, and the activity being launched is already running in the
current task, then instead of launching a new instance of that
activity, all of the other activities on top of it will be closed and
this Intent will be delivered to the (now on top) old activity as a
new Intent.
I got what I want, but then it still goes to onCreate. Is there any way to launch the home and not going to its onCreate?

Your thinking and Android's are not yet fully compatible. ;)
When you "launch the home", that means it's going to be launched, and that means it's going to be created.
You can, however, use Activity.startActivityForResult() to start List and Detail. Your "home" button then will finish your Detail Activity. In the onActivityResult callback of List, you'll just pass through using Activity.finish(), and in onActivityResult of Home you'll just catch the event and know that you're now back.

You cannot control the Activity life cycle. It's up to Android to decide which activities to keep running and which to close. This means that when an Activity loses focus, it is not necessarily destroyed or closed, but might simply lost focus and keep running, but might also not. This is up to Android; you cannot control this behavior.
If you want to recover an Activity in a given state, you have to save all needed data and restore it in onCreate().

How can i manage my activities and finish them properly?

I am new in android and I have total 6-7 activities in my application. I want to know how can I manage my activities properly means when I move to the A->B->C->D like that. Then how can I move that the stack of these activities not created.
On moving from one activity to the other I am using the below code:
Intent intent=new Intent(current.this,next.class);
startActivityForResult(intent, 0);
And now if I want to move back on the earlier activity I used the code as:
Intent start = new Intent(current.this,next.class);
startActivity(start);
finishActivity(0);

Is there a special reason that you don't want to use the activity stack and let the activities handle themselves?
The Android system has done a very good job with the activity lifecycle. It allows you to start an Activity from different places without confusing the user because the back button will bring the user back to a different activity.
If you don't have a very good reason to not use the Android guideline try to stick to the way the system is doing it. Every other thing will only give you problems.
You are starting activities for a result but how I understand you you will never return to them.
You can start an Activity and after that just finish the current Activity. That way the activity will not be put on the back stack. Now you need to listen for back button pushes and create the activities that you want to bring the user to.
If you want to move from Activity A to D like going to the start/home screen of you app you do the following:
Intent goBackToA = new Intent(context, StdActivity.class);
goBackToA.setFlags(Intent.FLAG_ACTIVITY_CLEAR_TOP);
startActivity(goBackToA);
The flag FLAG_ACTIVITY_CLEAR_TOP will tell the system that if the backstack contains an instance of the Activity this activity will be shown and all activity that are between the current activity and the target activity are removed from the backstack. This allows you to go back to a home activity without creating huge loops that the user can move through with the back button.

To move back to the previous activity you don't have to create a new intent, you can simply call this.finish() on the one that should dissapear.

To move back to the previous activity you don't have to create a new intent, you can simply call this.finish() on the one that should dissapeear or you can press Back button to see the previous Activity .

whenever you want to navigate from one class to another use this code, may be this help you to navigate the Activity,
Intent nextpage = new Intent(CurrentActivity.this,NextActivity.class);
startActivity(nextpage);
this.finish();

android, starting and exiting activities

I have not really understood the handling of activities and the stack.
I have 3 activities, A - a splashcreen, B- a menu and C another Activity. I start the splash and exits it after a while when the menu is started.
In code I handle them all like this:
startActivity(new Intent(this, ContactInfoMenu.class));
finish();
Now, if I start the app and goes A-B-C, when I hit "Back" in C screen I jump back to B-the menu. Another "Back" exits the application, just like I want.
BUT .. if I go A-B-C-B-C - the "Back" button in C screen exits the whole app instead of getting me back to the B screen?
Why is that? It does like that in all my "subscreens", I can only enter them once, if I enter them a second time the "Back" button exits the app. And I have not tried to catch the "Back" action anywhere? Shouldn't I always call "finish()" when I start a new activity?
Regards

Finish is good for leaving the current activity and going back to the previous one. Otherwise, try to avoid calling finish() if you can help it.
There are a set of flags that you can pass when you start an activity that do a better job of determining how that activity behaves on the stack. These include:
FLAG_ACTIVITY_NO_HISTORY - your activity will not remain on the stack after another activity covers it.
FLAG_ACTIVITY_CLEAR_TOP - a good way to pop off a bunch of activities when you need to "go back" to a certain activity.
Many of these flags can be set in the manifest. Reading up on them will give you a better idea about "The Android Way".

Basically, You don't need to call finish() every time you go to another activity. If system is low on memory it will close your activity instance by itself.

finish() is more often used when yor are inserting some information in one page and then moving on to some other page. In that case, you might need to fininsh your first activity.
But in case where you need to shuffle between views, you must not use a finish() function, because it will cause the whole application to finish.
Try using back button of your own in your views to shift between activities, where you can move to any other activity of your application or even to the Main Screen.