How to detect if came back from child activity?

Question

How can I detect if an activity came to focus after pressing the back button from a child activity, and how can I execute some code at that time?

Answer 1

The method you're looking for may be the onResume method you can implements in your mother class ;). You must know that the onResume is also called the first time you launch any activity. Look at the lifecycle of an activity : http://developer.android.com/images/activity_lifecycle.png

Regards,

Answer 2

js's answer is right, but here is some debugged code.

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

public static final int OPEN_NEW_ACTIVITY = 12345;

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) {
        // Execute your code on back here
        // ....
    }
}

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

Answer 3

One possibility would be to start your child activity with startActivityForResult() and implement onActivityResult() which will be called when you return from the child activity.

Answer 4

You can also override both the onBackPressed() method and the onOptionsItemSelected() method and put some logic there. For example I put this into my BaseActivity which all the other Activities extends from:

@Override
public void onBackPressed() {
    // your logic
    super.onBackPressed();
}

@Override
public boolean onOptionsItemSelected(MenuItem item) {
    if (item.getItemId() == android.R.id.home) {
        // your logic
    }
    return super.onOptionsItemSelected(item);
}