ActionBar SearchView not fully expanding in landscape mode

Did you try something like that?

editView.setOnKeyListener(new OnKeyListener() {
    private boolean extended = false;

    @Override
    public boolean onKey(View v, int keyCode, KeyEvent event) {
        if (!extended && event.getAction() == KeyEvent.ACTION_DOWN) {
            extended = true;
            LayoutParams lp = v.getLayoutParams();
            lp.width = LayoutParams.MATCH_PARENT;
        }

        return false;
    }

});

MenuItemCompat's SearchView has a property named maxWidth.

    final MenuItem searchItem = menu.findItem(R.id.action_search);
    final SearchView searchView = (SearchView) MenuItemCompat.getActionView(searchItem);
    searchView.setMaxWidth(xxx);

use screen width instead of xxx offcourse