Question

A simple test —

- (void)viewDidLoad
{
    [super viewDidLoad];

    date2 = [NSDate dateWithTimeIntervalSinceNow:3];
    myTimer = [NSTimer scheduledTimerWithTimeInterval:1
                                                   target:self
                                         selector:@selector(timerFires)
                                                 userInfo:nil
                                                  repeats:YES];

}

- (void)timerFires{
    date1 = [NSDate date];
    NSTimeInterval timeBetween = [date1 timeIntervalSinceDate:date2];
    NSLog(@"follow: %f", timeBetween);  
}

It cause an “EXC_BAD_ACCESS” error in “timerFires”

Thread 1: Program received signal: "EXC_BAD_ACCESS".

I have declared ‘date1’ ‘date2’ and ‘myTimer’ in .h file.

It seems -(void)timerFires cannot got the value of ‘date2’.
Could you help me fix it please!

Answer 1

i’m guessing that your date variables are not staying around because you’ve never explicitly retained them. [NSDate dateWithTimeIntervalSinceNow:3] returns an autoreleased object. are you declaring the date instance variables as properties that are retained and synthesizing their getters and setters? for example, in your interface file:

@interface MyClass {
   NSDate *date1;
   NSDate *date2;
}

@property (nonatomic, retain) NSDate *date1;
@property (nonatomic, retain) NSDate *date2;

then in your implementation file:

@implementation
@synthesize date1, date2

then you should access them using self so they are properly retained:

self.date2 = [NSDate dateWithTimeIntervalSinceNow:3];