accessing class file crashes when scrolling starts (UIScrollview)

Question

hopefully someone will be able to help me. I have a UIScrollView on my page. The .h file has set the UIscrollviewdelegate.

I have a class file called "Picture.h / Picture.m".

- (id)initWithName:(NSString *)aName filename:(NSString *)aFilename {
    self.name = aName;
    self.filename = aFilename;
    return self; 
}

In this class file, I simply set a couple of strings. I load an array with object of this picture class, for example

Picture *image2 = [[Picture alloc] initWithName:@"Apple" filename:@"apple.png"];
[pictureArray addObject: image2];
[image2 release];

Within my viewController, I call this class and assign is as such

Picture *thisPicture = (Picture *)[appDelegate.pictureArray objectAtIndex:0];
view2image.image = [UIImage imageNamed:[NSString stringWithFormat:@"%@", thisPicture.filename]];

The above works fine. The image is set to what ever I put, example, "apple.png". However, when I tried to set this in the - (void) scrollViewDidScroll:(UIScrollView *) method within my viewController, I get a bad exec error and the app crashes.

Yet, if I had an array of filenames (so not storing my class object in the array) and access objectAtIndex:0 in the scrollViewDidScroll - it works fine.

So, this code is OK

nextImageView.image = [UIImage imageNamed: [NSString stringWithFormat:@"%@", [appDelegate.pictureCardsArray objectAtIndex:0]]];

but this crashes

Picture *image3 = (Picture *)[appDelegate.pictureArray objectAtIndex:0];
nextImageView.image = [UIImage imageNamed:[NSString stringWithFormat:@"%@", image3.filename]];

Interestingly though, if I don't try to access the element of image3 (eg image3.filename) it doesn't crash. This is useless though! Also, if I disable the delegate = self for the uiscrollview, then this code works, but none of the scrolling actions are fired. I came across this post (http://stackoverflow.com/questions/1734720/uiscrollview-on-a-uiviewcontroller) when searching for the solution, but cannot see where I might be releasing the viewController early. To be safe, nothing is getting released (yet!)

Hopefully someone might be able to shed some light on it!!

[edit]Just adding in the full class files][/edit]

Picture.h

#import <UIKit/UIKit.h>

@interface Picture : NSObject {
    NSString *name;
    NSString *filename;
}

@property (nonatomic, copy) NSString *name;
@property (nonatomic, copy) NSString *filename;

- (id)initWithName:(NSString *)aName filename:(NSString *)aFilename;

@end

Picture.m

#import "Picture.h"

@implementation Picture
@synthesize name, filename;

- (id)initWithName:(NSString *)aName filename:(NSString *)aFilename {

    self.name = aName;
    self.filename = aFilename;
    return self;

}

@end

How did you define the properties of the class? retaining the name / fileName or not? — Antwan van Houdt
so it turns out that it was the (nonatomic, copy) that was the problem. I have changed to (nonatomic, retain) and that works perfectly. Thanks for the heads up! — Matt Facer
ah yeah, you should only use copy if you really need another instance of an object, for instance when they are likely going to be changed in the future ( array from mutablearray etc. ) — Antwan van Houdt

Matt Facer Matt Facer · Accepted Answer · 2011-05-09T21:18:13

Just for completeness... the solution was as Antwen Van Houdt said - I changed copy to retain and it worked fine.

#import <UIKit/UIKit.h>

@interface Picture : NSObject {
    NSString *name;
    NSString *filename;
}

@property (nonatomic, retain) NSString *name;
@property (nonatomic, retain) NSString *filename;

- (id)initWithName:(NSString *)aName filename:(NSString *)aFilename;

@end

accessing class file crashes when scrolling starts (UIScrollview)

1 Answers