Re: NSDate value set in one method, is inaccessible from another

Okay, those are called instance variables (ivars) or properties, they're not class level.

Here, we've ruled out memory management issues, and global variables issues, so my guess is that the receiver of the messages are not the same, to prove that you have to log self:

NSLog(@"%@ %s", self, __FUNCTION__); the first will call the description method of you class, it will by default print <ClassName MemoryAddress> the second just show the method name, put that log in both methods, if the memory addresses in each calls are different that means you have two instances of your ViewController class and that the one that receive the first message is different from the one that receives the second one.

Remy "Psy" Demarest

Le 19 avr. 2012 à 21:54, The Rhythmic a écrit :

Hi Remy, 

1. I didn't know Objective-C didn't have class-level variables! Thanks for pointing it out!

2. Yes, I've set the project (in Xcode) to do ARC (so, I believe that should take care).

3. Here is the code:

In ViewController.h

....

....

@property (nonatomic, retain) NSDate *historyFromDate;

@property (nonatomic, retain) NSDate *historyToDate;

....

....

-(IBAction) fromDateChosen: (id)sender;

-(void) fetchTheHistory;

-(void) setDates: (NSDate *)date

        withType:(int) type;

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). 

On Thu, Apr 19, 2012 at 11:24 PM, Remy Demarest <email@hidden> wrote:

You have to understand first that "class-level" variables don't exist, if you're defining the variable outside of an ivar block or a method it will be a global, this is evil btw.

Now, if you're not using ARC (Automatic Reference Counting), then your date will be deallocated, trying to accessing it will result in a crash, or just display a broken value if you're lucky.

I suggest to use a static variable if you really want a class-level variable, and I suggest making class-accessors. In any case the code you provide isn't really enough to provide a proper diagnostic, could you send your class implementation with the method implementations?

Remy "Psy" Demarest

Le 19 avr. 2012 à 13:44, The Rhythmic a écrit :

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? 

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