Highlight custom listview item when long click

using getActivity() is enough

setListAdapter(new CustomPasswordsList(getActivity(), titles));

You need to override onItemCheckedStateChanged

  public void onItemCheckedStateChanged(ActionMode mode,
            int position, long id, boolean checked) {
        final int checkedCount = getListView().getCheckedItemCount();
        // get checked items count 

Drawing from the samples @

android-sdk-linux/samples/android-17/ApiDemos/src/com/example/android/apis/view/List16

Example : Modify the below according to your needs

public class MainActivity extends ListActivity {
    String[] GENRES = new String[] {
            "Action", "Adventure", "Animation", "Children", "Comedy",
        "Documentary", "Drama",
            "Foreign", "History", "Independent", "Romance", "Sci-Fi",
        "Television", "Thriller"
        };

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        ListView lv = getListView();
        lv.setChoiceMode(ListView.CHOICE_MODE_MULTIPLE_MODAL);
        lv.setMultiChoiceModeListener(new ModeCallback());
        setListAdapter(new ArrayAdapter<String>(this,
                android.R.layout.simple_list_item_activated_1, GENRES));
    }

    @Override
    protected void onPostCreate(Bundle savedInstanceState) {
        super.onPostCreate(savedInstanceState);
        getActionBar().setSubtitle("Long press to start selection");
    }

    private class ModeCallback implements ListView.MultiChoiceModeListener {

        public boolean onCreateActionMode(ActionMode mode, Menu menu) {
            MenuInflater inflater = getMenuInflater();
            inflater.inflate(R.menu.list_select_menu, menu);
            mode.setTitle("Select Items");
            return true;
        }

        public boolean onPrepareActionMode(ActionMode mode, Menu menu) {
            return true;
        }

        public boolean onActionItemClicked(ActionMode mode, MenuItem item) {
            switch (item.getItemId()) {
            case R.id.share:
                Toast.makeText(MainActivity.this, "Shared " + getListView().getCheckedItemCount() +
                        " items", Toast.LENGTH_SHORT).show();
                mode.finish();
                break;
            default:
                Toast.makeText(MainActivity.this, "Clicked " + item.getTitle(),
                        Toast.LENGTH_SHORT).show();
                break;
            }
            return true;
        }

        public void onDestroyActionMode(ActionMode mode) {
        }

        public void onItemCheckedStateChanged(ActionMode mode,
                int position, long id, boolean checked) {
            final int checkedCount = getListView().getCheckedItemCount();
            switch (checkedCount) {
                case 0:
                    mode.setSubtitle(null);
                    break;
                case 1:
                    mode.setSubtitle("One item selected");
                    break;
                default:
                    mode.setSubtitle("" + checkedCount + " items selected");
                    break;
            }
        }

    }
}

list_select_menu.xml

<menu xmlns:android="http://schemas.android.com/apk/res/android">
    <item android:id="@+id/share"
          android:title="share"
          android:icon="@android:drawable/ic_menu_share"
          android:showAsAction="always" />
</menu>

Snap shot

Since you are doubting whether it would work with custom adapter

Edit:

under res/values-v11/styles.xml

<resources>

    <style name="AppTheme" parent="android:Theme.Holo.Light"></style>

    <style name="activated" parent="AppTheme">
        <item name="android:background">?android:attr/activatedBackgroundIndicator</item>
    </style>

</resources>

In the custom layout for the root element add

 style="@style/activated"