Android Activity Stack Manipulation

Question

I have activity A and B. A is the activity that loads when the app is launched and when they click a button a new intent is made to go to activity B. When I click a button in B I want to put activity A on the top of the stack so when I click the activity A button again it loads my onResume() for activity B instead of my onCreate().

How would I do this?

Answer 1

You could use intent flags to achieve this

FLAG_ACTIVITY_CLEAR_TOP is the best option here. 

As per the developer site

If the activity being started 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 are destroyed and this intent is delivered to the resumed instance of the activity (now on top), through onNewIntent()).

Example of how you set FLAG_ACTIVITY_CLEAR_TOP

  findViewById(R.id.button2).setOnClickListener(new View.OnClickListener() {
        @Override
        public void onClick(View v) {
            Intent i = new Intent(Main3Activity.this, Main2Activity.class);
            i.putExtra("HELLO","HI");
            i.setFlags(Intent.FLAG_ACTIVITY_CLEAR_TOP|
                    Intent.FLAG_ACTIVITY_SINGLE_TOP);
            startActivity(i);
        }
    });

In receiving activity

  @Override
    protected void onNewIntent(Intent intent) {
        super.onNewIntent(intent);
        Toast.makeText(getApplicationContext(), intent.getExtras().get("HELLO").toString(), Toast.LENGTH_SHORT).show();

    }