On 19.04.2012, at 19:43, The Rhythmic wrote: > Am sorry to ask such a trivial question. Am a newbie to Objective-C, & > simply cannot see how to get this working, after having tried several > possible ways & google'd around for it. Please help! > My question is simple. I have a class-level NSDate object, which is > declared outside any method in the class as: > > * NSDate *fromDate;*
There are no "class-level objects" in Objective C. There are only global variables (even if they are declared between @implementation and @end of a class), and instance variables (declared using @property and @synthesize, or declared between the curly brackets of the class. So if you google for "global variable", or "instance variable" you might find better information. But reading on, I think your main confusion is memory management. I presume you have not turned on ARC or the garbage collector, right? > Now, within a method, am setting this value to the date from a DatePicker > as: > > * fromDate = [datePicker date];* "date" does not contain "retain", "copy", "new" or "alloc", so it gives you an object you do not own. Usually an autoreleased object, which stays around until your method returns or thereabouts, but maybe it's just owned by this date picker. fromDate contains the address (think "building number" of one building in a street) of that particular date. Now when your date picker gets destroyed (e.g. you close its window) or when its value changes, the date picker releases the old date (and creates a new one in the case of the change). (Going with a house metaphor, this means it tears down the house whose house number you remembered, and forgets its house number, then goes to build another house containing the new date) Now, the problem is, your fromDate variable still contains the address of the old, destroyed date. So when you later use it in another method, you end up not at a date object, but in a random memory location (an empty building site, if you want). > Soon after the above assignment, I print its value into the log & it works > fine. > > * NSLog(@"From Date: %@", fromDate);* > > Now, when I use NSDate's value in another/different method, the value's > gone! Why is it not persisted across methods in the same class itself? What > can I do for the value to be accessible across methods? Learn about memory management in Objective C, from this article: https://developer.apple.com/library/mac/#documentation/Cocoa/Conceptual/MemoryMgmt/Articles/mmRules.html Cheers, -- Uli Kusterer "The Witnesses of TeachText are everywhere..." http://www.masters-of-the-void.com _______________________________________________ Cocoa-dev mailing list (Cocoa-dev@lists.apple.com) Please do not post admin requests or moderator comments to the list. Contact the moderators at cocoa-dev-admins(at)lists.apple.com Help/Unsubscribe/Update your Subscription: https://lists.apple.com/mailman/options/cocoa-dev/archive%40mail-archive.com This email sent to arch...@mail-archive.com
