How to use the installer._flatpak function in installer

GObject.idle_add(task.info_ready_callback, task)
            return

        task = InstallerTask(pkginfo, self, ready_callback)

        if self.pkginfo_is_installed(pkginfo):
            # It's not installed, so assume we're installing
            task.type = UNINSTALL_TASK
        else:
            task.type = INSTALL_TASK

        if pkginfo.pkg_hash.startswith("a"):
            _apt.select_packages(task)
        else:
            _flatpak.select_packages(task)

def generate_uncached_pkginfos(self, cache):
        """
        Flatpaks installed from .flatpakref files may not actually be in the saved
        pkginfo cache, specifically, if they're added from no-enumerate-marked remotes.
        This gets run at startup to collect and generate their info.
        """
        if self.have_flatpak:
            _flatpak.generate_uncached_pkginfos(cache)

def _generate_cache(self):
        cache = {}
        sections = {}
        flatpak_remote_infos = {}

        if self.have_flatpak:
            cache, flatpak_remote_infos = _flatpak.process_full_flatpak_installation(cache)

        cache, sections = _apt.process_full_apt_cache(cache)

        return cache, sections, flatpak_remote_infos

def find_pkginfo(self, string, pkg_type=None):
        if pkg_type in (None, "a"):
            pkginfo = _apt.find_pkginfo(self, string)

            if pkginfo != None:
                return pkginfo

        if self.have_flatpak:
            if pkg_type in (None, "f"):
                pkginfo = _flatpak.find_pkginfo(self, string)

                if pkginfo != None:
                    return pkginfo

        return None

def list_flatpak_remotes(self):
        """
        Returns a list of FlatpakRemoteInfos.  The remote_name can be used to match
        with PkgInfo.remote and the title is for display.
        """
        if self.have_flatpak:
            return _flatpak.list_remotes()
        else:
            return []

def get_pkginfo_from_ref_file(self, file, ready_callback):
        """
        Accepts a GFile to a .flatpakref on a local path.  If the flatpak's remote
        has not been previously added to the system installation, this also adds
        it and downloads Appstream info as well, before calling ready_callback with
        the created (or existing) PkgInfo as an argument.
        """
        if self.have_flatpak:
            _flatpak.get_pkginfo_from_file(self.cache, file, ready_callback)

def pkginfo_is_installed(self, pkginfo):
        """
        Returns whether or not a given package is currently installed.  This uses
        the AptCache or the FlatpakInstallation to check.
        """
        if self.inited:
            if pkginfo.pkg_hash.startswith("a"):
                return _apt.pkginfo_is_installed(pkginfo)
            elif self.have_flatpak and pkginfo.pkg_hash.startswith("f"):
                return _flatpak.pkginfo_is_installed(pkginfo)

        return False