Android: Detect when an activity returns to the previous activity

Question

I have activity A with a listView, a user clicks on any item which starts Activity B. Depending on what the user does in activity B may change the listView on activity A.

So my question:

How can I tell activity A that it was resumed when the user returns to it from activity B?

I want to be able to signal a refresh of the listView in activity A when it is returned to.

Thanks!

Answer 1

Using startActivityForResult is the most elegant way to do it. OnResume will happen every time you close and open up the app, which will use a bit more resources, especially if you're refreshing a lot of data.

Declare the request code as a constant at the top of your activity:

public static final int OPEN_NEW_ACTIVITY = 123456;

Put this where you start the new activity:

Intent intent = new Intent(this, NewActivity.class);
startActivityForResult(intent, OPEN_NEW_ACTIVITY);

Do something when the activity is finished. Documentation suggests that you use resultCode, but depending on the situation, your result can either be RESULT_OK or RESULT_CANCELED when the button is pressed. So I would leave it out.

@Override
protected void onActivityResult(int requestCode, int resultCode, Intent data) {
    if (requestCode == OPEN_NEW_ACTIVITY) {
        // Refresh your ListView here
        // ....
    }
}

For some reason, I had trouble when putting this in a Fragment. So you will have to put it in the Activity.

Answer 2

You can add the code to refresh listview in the onResume() of Activity A.

@Override
protected void onResume() {
    super.onResume();
    //Code to refresh listview
}

Answer 3

I have another way to do this, which might come handy in some situations - I keep private Bundle variable, let's call it state, and when I start an activity I put a string that says which activity I started:

state.putString("startedActivity", "A");
Intent intent = new Intent(this, ActivityA.class);
startActivity(intent);

I store the state bundle to persevere device changes (rotation etc.):

@Override
public void onSaveInstanceState(Bundle savedInstanceState) {
    super.onSaveInstanceState(savedInstanceState);
    savedInstanceState.putAll(state);
}

In onCreate I load the state:

@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    if (savedInstanceState == null) {
        savedInstanceState = new Bundle();
    }
    state = savedInstanceState;
}

Then in onResume method, I can check, whether I was just at some Activity. Note that I remove the string from the state immediately, so it doesn't show up again at rotation change etc.

public void onResume() {
    super.onResume();
    if (state.getString(STARTED_ACTIVITY, null) != null) {
        // we just came from another activity!
        state.putString(STARTED_ACTIVITY, null); // clear the state
        // do whatever you need
    }
}

Answer 4

Use startActivityForResult to launch B activity. And check the data from activity B, on activity A s onActivityResult() method. Use notifyDataSetChanged for the listView to update contents.