Several lines of code, that blows my mind (or NSString “out of scope” dilemma..)

[Squatch]

Hey, everyone!
I'm totally confused with this small "out of scope" thing.
So here is some code to describe my situation:

Simple iphone view-based application.

View controller header:

#import <UIKit/UIKit.h>

@interface global_nsstring_testViewController : UIViewController {
	UIImageView*	image_view;
	NSString*		image_name;
}

@property (nonatomic,retain) UIImageView*	image_view;
@property (nonatomic,retain) NSString*		image_name;

- (void) fadeView:(UIImageView*)View andThenChangeImageTo:(NSString*)Name;
- (void) switchImageAfterFade;

@end

View controller .m:

#import "global_nsstring_testViewController.h"
@implementation global_nsstring_testViewController
@synthesize image_view, image_name;

- (void) viewDidLoad {
	image_view = [[UIImageView alloc] initWithImage:[UIImage imageWithContentsOfFile:[[NSBundle mainBundle] pathForResource:@"image1.png" ofType:nil]]];
	
//     ## Block 1 ##	
//	NSString* name = @"image2.png";
//	[self fadeView:image_view andThenChangeImageTo:name];

//	## Block 2 ##
//	NSString* name = [NSString stringWithFormat:@"image%d.png",2];
//	[self fadeView:image_view andThenChangeImageTo:name];
	
	[self.view addSubview:image_view];
	[super viewDidLoad];
}

- (void)touchesBegan:(NSSet *)touches withEvent:(UIEvent *)event {
//  ## Block 3 ##
//	NSString* name = @"image2.png";
//	[self fadeView:image_view andThenChangeImageTo:name];

//  ## Block 4 ##
//	NSString* name = [NSString stringWithFormat:@"image%d.png",2];
//	[self fadeView:image_view andThenChangeImageTo:name];
}

- (void) fadeView:(UIImageView*)View andThenChangeImageTo:(NSString*)Name {
	image_name = Name;
	image_view = View; // ## Point 1 ##
	
	[UIView beginAnimations:nil context:nil];
	[UIView setAnimationDuration:1];
	[UIView setAnimationDelegate:self];
	[UIView setAnimationDidStopSelector:@selector(switchImageAfterFade)];
	View.alpha = 0.3;
	[UIView commitAnimations];
}

- (void) switchImageAfterFade {
	UIImage* image = [UIImage imageWithContentsOfFile:[[NSBundle mainBundle] pathForResource:image_name ofType:nil]]; // ## Point 2 ##
	[image_view setImage:image];
}

- (void) dealloc {
	[image_view removeFromSuperview];
	[image_view release];
    [super dealloc];
}

@end

With uncommented #Block 4# I get “out of scope” message from debugger on image_name var at #Point 1#. And therefore I get EXC_BAD_ACCESS at #Point 2#.

However with uncommented #Block 3# or #Block 1# instead of #Block 4# everything works fine, so I suppose this is all about NSString...

I've tried to use NSMutableString, but without any success either.

So if anyone could tell me, what I do wrong or how to fix it, I would be greatly appreciate.


Another strange thing, that I don't get:

If to uncomment #Block 2# and not to use any breakpoints, it won't crash, but image will disappear. But if I set a breakpoint at #Point 2#, it will crash with EXC_BAD_ACCESS after just one step.

Additional information.
xCode version: 3.2.3

[QuantumDoja]

Lets try and break this down to it's basics, ie, does this work?:

@interface global_nsstring_testViewController : UIViewController
{
NSString*		ImageName;
}

@property (nonatomic,retain) NSString*		ImageName;
-(void)Start
-(void)DoSomething(NSString*)new_Name;

@implementation global_nsstring_testViewController
{

- (NSString*) ImageName {	
    return ImageName;
}
- (void) setImageName: (NSString*) newValue {
    [ImageName autorelease];
    ImageName = [newValue retain];
}

-(void)Start
{
NSString* name = @"image2.png";
[self DoSomething:name];
}
-(void)DoSomething(NSString*)new_Name
{
ImageName = new_Name;
//can we get here?
}
}

It would also be great to get your full backtrace, just type backtrace in the console when it crashes.

[Squatch]

Originally Posted by QuantumDoja

It would also be great to get your full backtrace, just type backtrace in the console when it crashes.

Here is a backtrace:

#0  0x30d654f4 in objc_msgSend ()
#1  0x321c621a in CFStringGetCharactersPtr ()
#2  0x321c8c2e in CFStringGetFileSystemRepresentation ()
#3  0x321da3b2 in _CFFindBundleResources ()
#4  0x321d53b6 in CFBundleCopyResourceURL ()
#5  0x30c4b000 in -[NSBundle pathForResource:ofType:] ()
#6  0x00003574 in -[global_nsstring_testViewController switchImageAfterFade] (self=0x13b370, _cmd=0x3db7) at /Users/Squatch/Documents/global_nsstring_test/Classes/global_nsstring_testViewController.m:43
#7  0x34b7b268 in -[UIViewAnimationState sendDelegateAnimationDidStop:finished:] ()
#8  0x34b7b100 in -[UIViewAnimationState animationDidStop:finished:] ()
#9  0x31c8c960 in run_animation_callbacks ()
#10 0x31c8c750 in CA::timer_callback ()
#11 0x3223525c in __CFRUNLOOP_IS_CALLING_OUT_TO_A_TIMER_CALLBACK_FUNCTION__ ()
#12 0x3223796c in __CFRunLoopDoTimer ()
#13 0x322383f0 in __CFRunLoopRun ()
#14 0x321df0c2 in CFRunLoopRunSpecific ()
#15 0x321defd0 in CFRunLoopRunInMode ()
#16 0x3390ff90 in GSEventRunModal ()
#17 0x34b0ab48 in -[UIApplication _run] ()
#18 0x34b08fc0 in UIApplicationMain ()
#19 0x00002f7c in main (argc=1, argv=0x2ffff4ac) at /Users/Squatch/Documents/global_nsstring_test/main.m:14

Your sample works fine, no matter where i call [self Start]
( in a viewDidLoad or touchesBegan )
or how init name
( NSString* name = [NSString stringWithFormat:@"image%d.png",2]; )
or just
( NSString* name = @"image1.png"; )

Thanks for a quick reply.

UPDATE: Here is the solution: link

[RLScott]

The property image_view is never initialized. It is only set to itself, which is still nil. Also, if you have defined image_view and image_name as properties, then you should always set them with their synthesized setters, as in

Self.image_name = ...