public static List<Map<String, Object>> getZonesList(Context context) {
final Locale locale = Locale.getDefault();
final Date now = new Date();
// The display name chosen for each zone entry depends on whether the zone is one associated
// with the country of the user's chosen locale. For "local" zones we prefer the "long name"
// (e.g. "Europe/London" -> "British Summer Time" for people in the UK). For "non-local"
// zones we prefer the exemplar location (e.g. "Europe/London" -> "London" for English
// speakers from outside the UK). This heuristic is based on the fact that people are
// typically familiar with their local timezones and exemplar locations don't always match
// modern-day expectations for people living in the country covered. Large countries like
// China that mostly use a single timezone (olson id: "Asia/Shanghai") may not live near
// "Shanghai" and prefer the long name over the exemplar location. The only time we don't
// follow this policy for local zones is when Android supplies multiple olson IDs to choose
// from and the use of a zone's long name leads to ambiguity. For example, at the time of
// writing Android lists 5 olson ids for Australia which collapse to 2 different zone names
// in winter but 4 different zone names in summer. The ambiguity leads to the users
// selecting the wrong olson ids.
// Get the list of olson ids to display to the user.
List<String> olsonIdsToDisplay = readTimezonesToDisplay(context);
// Create a lookup of local zone IDs.
Set<String> localZoneIds = new TreeSet<String>();
for (String olsonId : TimeZoneNames.forLocale(locale)) {
localZoneIds.add(olsonId);
}
// Work out whether the long names for the local entries that we would show by default would
// be ambiguous.
Set<String> localZoneNames = new TreeSet<String>();
boolean localLongNamesAreAmbiguous = false;
for (String olsonId : olsonIdsToDisplay) {
if (localZoneIds.contains(olsonId)) {
TimeZone tz = TimeZone.getTimeZone(olsonId);
String zoneLongName = getZoneLongName(locale, tz, now);
boolean longNameIsUnique = localZoneNames.add(zoneLongName);
if (!longNameIsUnique) {
localLongNamesAreAmbiguous = true;
break;
}
}
}
// Generate the list of zone entries to return.
List<Map<String, Object>> zones = new ArrayList<Map<String, Object>>();
for (String olsonId : olsonIdsToDisplay) {
final TimeZone tz = TimeZone.getTimeZone(olsonId);
// Exemplar location display is the default. The only time we intend to display the long
// name is when the olsonId is local AND long names are not ambiguous.
boolean isLocalZoneId = localZoneIds.contains(olsonId);
boolean preferLongName = isLocalZoneId && !localLongNamesAreAmbiguous;
String displayName = getZoneDisplayName(locale, tz, now, preferLongName);
String gmtOffsetString = getGmtOffsetString(locale, tz, now);
int offsetMillis = tz.getOffset(now.getTime());
Map<String, Object> displayEntry =
createDisplayEntry(tz, gmtOffsetString, displayName, offsetMillis);
zones.add(displayEntry);
}
return zones;
}
