Develop Reference

How to resume an existing task in its current state

My application has two activities A and B. A is the root of the task, and is the one that is launched from the launch icon. B can be started from A.
As well as starting A from the launch icon, it is possible to launch A by clicking on a file in another application, e.g. clicking on an email attachment or a file in Drive. I have done this by adding actions and categories to the intent filter in the manifest file.
I want to make it so that when A is launched from another application, instead of creating a new task I want the existing task to resume in the same state it was in before. This could be activity A or B, wherever the user happened to be before they pressed home.
I have tried all kinds of launch modes and intent flags but nothing seems to work.

Broadcast an intent that's identical to the launcher intent in your manifest:
Intent intent = new Intent(context, MainActivity.class);
intent.setFlags(Intent.FLAG_ACTIVITY_NEW_TASK);
intent.setAction(Intent.ACTION_MAIN);
intent.addCategory(Intent.CATEGORY_LAUNCHER);
I don't know why, but this raises the existing task instead of starting a new one. By contrast, a launcher intent obtained the "official" way will actually start a new task:
Intent intent = context.getPackageManager()
.getLaunchIntentForPackage(context.getPackageName());

change launchmode to singletask. and listening onNewIntent()

reopen app from background

When user press "Home Button" my app go to Background, but is still running. I need bring my app to front again. For example i've this code:
Context ctx=getApplicationContext();
Intent i =ctx.getPackageManager().getLaunchIntentForPackage("com.example.test");
ctx.startActivity(i);
but this code is to open app in different activity, there are a method or something to do this "correctly"?

You can simulate the "launching" of the app the same way that Android launches the app when the user selects it from the list of available apps. If the user starts an application that is already running, Android just brings the existing task to the foreground (which is what you want). Do it like this:
Intent intent = new Intent(context, SplashScreen.class);
intent.addFlags(Intent.FLAG_ACTIVITY_NEW_TASK); // You need this if starting
// the activity from a service
intent.setAction(Intent.ACTION_MAIN);
intent.addCategory(Intent.CATEGORY_LAUNCHER);
startActivity(intent);
(Source: https://stackoverflow.com/a/12075313/3529926)

You can set this flag to your intent
intent.setFlags(Intent.FLAG_ACTIVITY_CLEAR_TOP | Intent.FLAG_ACTIVITY_SINGLE_TOP);
and set the launch mode of your activity to single task in manifest (add this is your activity tags):
android:launchMode="singleTask"

Closing an android application programatically in android

I have a application that has two activities
Activity1
Activity2
Now i start Activity1 and move to Activity2 now i want to close the application at a moment
If i use finish() i am able to close only Activity2 and not
Activity1
What i want to do ::
i want my application to quit(close all activities and go to
homescreen)
But i don't want my apk to be removed from android system itself
How can i achieve this ?
{Edit}
I used the code(Activity2 has a fragment which launched a dialog on
"ok" condition in positive condition i am performing this condition below)
I am able to launch the previous activity but it is not canceled, its
just reloaded
Intent intent = new Intent(getActivity(), SplashActivity.class);
intent.setFlags(Intent.FLAG_ACTIVITY_CLEAR_TASK);
startActivity(intent);
getActivity().finish();

You need to make your Activity2 as "top task" with a Flag when you call it as follows:
Intent intent = new Intent(Activity1.this, Activity2.class);
intent.setFlags(Intent.FLAG_ACTIVITY_CLEAR_TASK);
startActivity(intent);
See the Reference:
If set in an Intent passed to Context.startActivity(), this flag will cause any existing task that would be associated with the activity to be cleared before the activity is started. That is, the activity becomes the new root of an otherwise empty task, and any old activities are finished.
Then, call finish() in your Activity2. This should do the trick.

There is a way to kill your application process, but it is not recommended
this.finish();
Process.killProcess(Process.myPid());
This will kill your application and releases all the memory associated with it.
Note: Assuming your app has a single process id

Do like this
Intent intent = new Intent(Activity1.this, Activity2.class);
startActivity(intent);
Activity1.this.finish();

Intent intObj=new Intent(this, Homescree.class);
intObj.setFlags(Intent.FLAG_ACTIVITY_CLEAR_TOP |
Intent.FLAG_ACTIVITY_CLEAR_TASK |
Intent.FLAG_ACTIVITY_NEW_TASK);
startActivity(intObj);

Clearing all activities in android

I have 4 Activities 1.Home,2.B,3.C and 4.D. Whenever I start Home from Activity D I want to finish all other activities. I Used this code, but when I press back button from Home it brings me to the previous activity. What I did wrong here.?
Intent intent = new Intent(getApplicationContext(), Home.class);
intent.addFlags(Intent.FLAG_ACTIVITY_CLEAR_TOP);
startActivity(intent)

You can try this,
Intent intent = new Intent(getApplicationContext(), Home.class);
intent.addFlags(Intent.FLAG_ACTIVITY_CLEAR_TOP);
intent.addFlags(Intent.FLAG_ACTIVITY_NEW_TASK);
startActivity(intent);
Note: As described in FLAG_ACTIVITY_CLEAR_TOP documentation
This launch mode can also be used to good effect in conjunction with FLAG_ACTIVITY_NEW_TASK: if used to start the root activity of a task, it will bring any currently running instance of that task to the foreground, and then clear it to its root state. This is especially useful, for example, when launching an activity from the notification manager.

intent.addFlags(Intent.FLAG_ACTIVITY_CLEAR_TOP);
This will work only for activities which are still in the activity stack. I believe you are finishing the Home Activity when going to B. So that CLEARTOP won't work.
Now try something like this.
You need to set an Extra with intent Of "D" to Home. Then you have to check the Intent extra in Home, call finish() if the extra matching
Intent intent = new Intent(contxt, Home.class);
intent.putExtra("urString",defaultvalue);
intent.addFlags(Intent.FLAG_ACTIVITY_CLEAR_TOP);
startActivity(intent);
// Checking the intent extra at "HOME"
if(getIntent().hasExtra("urString")){
// manage your own way
finish();
}

In manifest.xml file set android:nohistroy="true" for all the activities

Start / Resume Task Back Stack from Notification as Recent Apps Switching

My application has two activities A and B. A is the root activity and set with singleTop launchMode. B is started from A, i.e. the task stack is (A->B)
I add a status notification to launch the application as long press Home button. The notification intent point to activity A.
When the task stack is (A) only, the intent invokes onNewIntent() from existing A, as expected.
When the task stack is (A->B), the intent create new activity A. But what I wants is resume task (A->B) as switch recent apps by long press Home button.
Is the problem caused by incorrect launch mode used? or any flags need to be added to the notification intent?
Thanks.

You can use the following from your notification manager:
Intent intent = new Intent(context, ActivityA.class);
intent.setAction(Intent.ACTION_MAIN);
intent.addCategory(Intent.CATEGORY_LAUNCHER);
context.startActivity(intent);
Make sure that your ActivityA is not launched with FLAG_ACTIVITY_NEW_TASK.