+////////////////////////////////////////////////////////////////////////////////
+#pragma mark SUUpdater Delegate
+
+- (nullable NSString*)feedURLStringForUpdater:(SUUpdater*)updater
+{
+ // Record whether this user ever used the beta appcast feed.
+ NSUserDefaults* defaults = [NSUserDefaults standardUserDefaults];
+ NSURL* feedURL = [NSURL URLWithString:[[[NSBundle mainBundle] infoDictionary] objectForKey:@"SUFeedURL"]];
+
+ BOOL usesUnstable = [defaults boolForKey:kPrefUnstableVersionCast] ||
+ [[feedURL absoluteString] hasSuffix:kAppcastUnstable];
+ [defaults setBool:usesUnstable forKey:kPrefUnstableVersionCast];
+
+ if (!usesUnstable)
+ return nil;
+
+ feedURL = [[feedURL URLByDeletingLastPathComponent] URLByAppendingPathComponent:kAppcastUnstable];
+ return [feedURL absoluteString];
+}
+