NSDate value not accessible across methods - nsdate

Question

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;
Now, within a method, am setting this value to the date from a DatePicker as:
fromDate = [datePicker date];
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?
Thanks for your reply.
Hi Remy,
I didn't know Objective-C didn't have class-level variables! Thanks for pointing it out!
Yes, I've set the project (in Xcode) to do ARC (so, I believe that should take care).
Here is the code:
In ViewController.h
....
....
#property (nonatomic, retain) NSDate *historyFromDate;
#property (nonatomic, retain) NSDate *historyToDate;
....
....
-(IBAction) fromDateChosen: (id)sender;
-(void) fetchTheHistory;
In ViewController.m
...
...
#synthesize historyFromDate;
#synthesize historyToDate;
....
....
-(IBAction) fromDateChosen: (id)sender {
NSString *buttonTitle = #"I've chosen the 'FROM' date";
if ([[buttonDateChosen currentTitle] isEqualToString:buttonTitle]) {
NSLog(#"User has chosen the 'From' date");
NSDateFormatter *dateFormatter = [[NSDateFormatter alloc] init];
[dateFormatter setDateStyle:NSDateFormatterMediumStyle];
[dateFormatter setTimeStyle:NSDateFormatterMediumStyle];
// Get the chosen date value
NSDate *fromDate = [datePicker date];
historyFromDate = fromDate;
// Set the 'to' date label to reflect the user's choice
labelFromDate.text = [dateFormatter stringFromDate:historyFromDate];
NSLog(#"'From' Date Chosen:%#", historyFromDate);
//[dateFormatter stringFromDate:[datePicker date]]);
[self fetchTheMoodHistory];
}
}
...
...
...
-(void) fetchTheHistory {
NSLog(#"Calling fetchTheHistory for the period from %#", historyFromDate);
...
...
}
...
...
fromDateChosen gets called after the user chooses a date form a Date Picker object in the UI.
Within the method 'fromDateChosen', when I print the historyFromDate, the value is correct.
But, when I print it in fetchTheHistory method, the value shows the current date/time (not the one the user chose).

Answer 1

The date property of UIDatePicker is retained by that class, and will be accessible as long as the date picker itself is in scope and valid (not been released). You are storing this date value in a variable, but not retaining it yourself, so when the date picker goes out of scope you lose the value. As a quick fix, do this instead;
fromDate = [[datePicker date] retain];
Now, this is not the best approach, you really should be making the date a property of whatever class is using this information.

Answer 2

Try put the fromDate variable under class scope, e.g:
#implementation ViewController
{
NSDate *fromDate;
}