This is my code:
i.putExtra(Intent.EXTRA_NOT_UNKNOWN_SOURCE, true);
i.setDataAndType(Uri.parse(FileUtil.getPublicDir(Environment.DIRECTORY_DOWNLOADS).concat("/Vertretungsplan.apk")), "application/vnd.android.package-archive");
i.setFlags(Intent.FLAG_ACTIVITY_CLEAR_TASK | Intent.FLAG_ACTIVITY_NEW_TASK); i.addFlags(Intent.FLAG_GRANT_READ_URI_PERMISSION);
However, when I start the activity, the Package Installer won't show as "open with".