In 2019r3 Xojo added something that a lot of people have been asking for for a very long time. A way for a class that exposes events to know IF an instance implements the event. <\/p>\n\n\n\n
Its literally called IsEventImplemented (see http:\/\/feedback.xojo.com\/case\/58342<\/a>)<\/p>\n\n\n\n But it remains undocumented<\/a><\/p>\n\n\n\n Previously if you wrote a class that could have some default behaviour IF an instance did not implemnent the event to alter the behaviour you had no way to know if you should operate in whatever way was the default or not.<\/p>\n\n\n\n You could never have your superclass do something like<\/p>\n\n\n\n In this case its not so bad and you could probably just use RaiseEvent without any impact. But if you wanted to do something more, like know if you should use a default color or not you had a much more difficult task<\/p>\n\n\n\n But now with IsEventImplemented we could know<\/p>\n\n\n\nIf IsEventImplemented(\"Action\") then\n \/\/ call the instance' code\n raiseEvent Action\nelse\n \/\/ do nothing\nend if<\/code><\/pre>\n\n\n\n\/\/ if we had an event ChooseColor that instances could implement or not\n\ndefaultBackGroundColor = raiseEvent ChooseColor\n\n\/\/ if setColor IS implemented we'd get a color \n\/\/ if setColor is NOT implemented we still get a color - its just all 0's\n\/\/ and we have no way to know which is the case \n<\/code><\/pre>\n\n\n\n\/\/ if we had an event ChooseColor that instances could implement or not\n\nif IsEventImplemented(\"ChooseColor\") then\n defaultBackGroundColor = raiseEvent ChooseColor\nelse\n defaultBackgroundColor = &cFF00FF \/\/ or whatever\nend if\n\n\/\/ now we can use defaultBackgroundColor knowing whether \n\/\/ it did or did not come from the instance<\/code><\/pre>\n\n\n\n