Question

I’m having a problem in a usually very simple quest, I want to create a custom class containing an integer, a NSString and a NSDate. However, in my example I only use a NSString to show my problem when storing objects.

This is my class header:
#import

@interface MyClass : NSObject <NSCoding> {
    NSString * myString;
}
@property (retain) NSString * myString;
@end

and my body:

#import "MyClass.h"

@implementation MyClass
@synthesize myString;

- (id)initWithCoder:(NSCoder *)coder {
    self = [super init];
    if (self) {
        myString = [coder decodeObjectForKey:@"myString"];
    }
    return self;
}
- (id)init {
    self = [super init];
    if (self) {
        myString = @"Hi";
    }
    return self;
}

- (void)encodeWithCoder:(NSCoder *)aCoder{
    [aCoder encodeObject: myString forKey:@"myString"];
}

- (void)dealloc {
    myString = nil;
    [super dealloc];
}
@end

My ViewController contains two buttons called Create and Read, as well as a UILabel called label.

#import <UIKit/UIKit.h>
@interface UserDefaultsTestViewController : UIViewController {

    IBOutlet UILabel *label;
}
- (IBAction)pushCreate;
- (IBAction)pushLoad;
@end

I will only show the functions I’ve edited here:

#import "UserDefaultsTestViewController.h"
#import "MyClass.h"
- (IBAction)pushCreate {
    MyClass * myClass = [[MyClass alloc] init];
    NSData * data = [NSKeyedArchiver archivedDataWithRootObject:myClass];
    NSUserDefaults * defaults = [NSUserDefaults standardUserDefaults];
    [defaults setObject:data forKey:@"Test"];
    [myClass release];
}

- (IBAction)pushLoad {
    NSUserDefaults * defaults = [NSUserDefaults standardUserDefaults];
    NSData * atchive = [defaults objectForKey:@"Test"];
    MyClass * myClass = [NSKeyedUnarchiver unarchiveObjectWithData:atchive];
    label.text = myClass.myString;
}

However, if I run my code, I get either a EXC_BAD_ACCESS error or it displays it correctly the first time and crashes when doing it a second time, again with the same error.
What am I doing wrong?

Answer 1

You want to do:

self.myString = @"Hi";

Or:

myString = @"Hi";
[myString retain];

Likewise, your dealloc should have:

self.myString = nil;

or

[myString release];