Proper way to handle action bar up button?

In your onCreate(Bundle savedInstanceState), do

ActionBar actionBar = getSupportActionBar();
actionBar.setDisplayHomeAsUpEnabled(true);

Then in your onOptionsItemSelected(MenuItem item), do

@Override
public boolean onOptionsItemSelected(MenuItem item) {
    switch (item.getItemId()) {
        case android.R.id.home:
            // go to previous screen when app icon in action bar is clicked
            Intent intent = new Intent(this, PreviousActivity.class);
            intent.addFlags(Intent.FLAG_ACTIVITY_CLEAR_TOP);
            startActivity(intent);
            return true;
    }
    return super.onOptionsItemSelected(item);
}

Have you also tried this (taken from Android website here) :

in the manifest, for each activity X that needs to go to the main activity, add this to the code:

@Override
public boolean onOptionsItemSelected(MenuItem item) {
    switch (item.getItemId()) {
    // Respond to the action bar's Up/Home button
    case android.R.id.home:
        NavUtils.navigateUpFromSameTask(this);
        return true;
    }
    return super.onOptionsItemSelected(item);
}

and this to its manifest xml tag:

<meta-data
android:name="android.support.PARENT_ACTIVITY"
android:value="com.activities.MainActivity" />

if you need to still have the same state on the main activity, use this code instead :

Intent intent = NavUtils.getParentActivityIntent(this); 
intent.setFlags(Intent.FLAG_ACTIVITY_CLEAR_TOP|Intent.FLAG_ACTIVITY_SINGLE_TOP); 
NavUtils.navigateUpTo(this, intent);

if the API is 16 or above, you can add an attribute of parentActivityName with the path to the main activity instead of the metadata .

Found out the root of my problem was a change in the manifest I made a while ago: I added this line:

android:launchMode="singleInstance"

so my main activity wouldn't be relaunched. Changing it to:

android:launchMode="singleTask"

solved my problems, and I was able to remove all the onOptionsItemSelected stuff. I knew there was something wrong, that Android should have been able to handle this better, and I was right. Check the manifest :P

You can Handle Action Bar button by using Code or XML.

Check this code

if you want it programmatically Add this line in onCreate() method

getSupportActionBar().setDisplayHomeAsUpEnabled(true);

And Override this method onSupportNavigateUp()

@Override
public boolean onSupportNavigateUp(){  
finish();  
return true;  
}

OR Non-programmatically you can add meta to manifest file as

<activity android:name="Current Activity"
        android:parentActivityName="Activity you want to open">
    </activity>

Note: Make sure Actionbar is not null.