NSDATA writeToFile crashes without a reason

Question

I am downloading images from a url using NSDATA and saving them to local file system using

NSData *dataForStorage = [NSData dataWithData:UIImagePNGRepresentation(img)];


    BOOL saveResult=[ dataForStorage writeToFile:jpegFilePath options:NSDataWritingAtomic error:&error];
    NSLog(@"Write returned error: %@", [error localizedDescription]);

My app crashes randomly without even giving a message, though some files are saved (again randomly). When I run the app in Debug mode, I frequently see "EXC_BAD_ACCESS" but continuing execution succeeds in saving some of the files.

This code is executed in background from:

[self performSelectorInBackground:@selector(loadImageInBackground:) withObject:arr];

Please suggest.

This is iPad app. Here is the console log: 2011-04-11 16:36:59.784 AJiPadPhotos[5881:7203] *** __NSAutoreleaseNoPool(): Object 0x4e222c0 of class NSHTTPURLResponse autoreleased with no pool in place - just leaking 2011-04-11 16:36:59.784 AJiPadPhotos[5881:7203] *** __NSAutoreleaseNoPool(): Object 0x4b41c80 of class __NSCFData autoreleased with no pool in place - just leaking 2011-04-11 16:36:59.785 AJiPadPhotos[5881:7203] *** __NSAutoreleaseNoPool(): Object 0x4e23ba0 of class NSConcreteData autoreleased with no pool in place - just leaking — Monica Chaturvedi, Apr 11 '11 at 11:09
@Twelve47, it doesn't even reflect the error..no stack trace nothing...any clue where the problem might be? — Monica Chaturvedi, Apr 11 '11 at 11:31
Is jpegFilePath valid? Has it been released already perhaps? — Twelve47, Apr 11 '11 at 11:32

score 2 · Answer 1 · answered Apr 12 '11 at 08:55

2

One of the problems in your code is that your running code in a thread without an autorelease pool but are using functions that would require one. Put the following code into the loadImageInBackground method:

NSAutoreleasePool *pool = [[NSAutoreleasePool alloc] init];

// existing code

[pool drain];

This is probably just one of several problems. For further assistance, we need to see the stack trace of the crash.

answered Apr 12 '11 at 08:55

Codo

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Hello Codo, Thank you for replying. I already have these in place, had just excluded them here for brevity. Anything else that could be done? – Monica Chaturvedi Apr 13 '11 at 05:41
Yes, add the stack trace of the crash to the question. – Codo Apr 13 '11 at 05:58

score 1 · Answer 2 · answered Apr 11 '11 at 12:25

1

Just a wild guess : arr is an autoreleased object, so, sometimes it gets deallocated before your selector gets called. Try using [arr copy] and release it after saving it.

answered Apr 11 '11 at 12:25

Marcelo Alves

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The withObject: parameters in the various performSelector methods are retained for you, so I don't see this as a problem. – Mike Weller Apr 11 '11 at 14:25
Thank you @Marcelo but that didn't help :( Any other idea? – Monica Chaturvedi Apr 12 '11 at 06:11

score 0 · Answer 3 · answered May 18 '11 at 17:59

I was having the EXACT same problem, but it turned out that the problem was something else: my URL was getting release prematurely. In the end this is what I did and it worked:

I made this call:

[self performSelectorInBackground:@selector(downloadData:) withObject:nil];

And this is the method:

// URL - (NSString) URL for file
// filePath - (NSString) save location on device
-(void)download:(NSString *)URL
{
    NSAutoreleasePool *pool = [[NSAutoreleasePool alloc] init];
    NSData *data = [NSData dataWithContentsOfURL:[NSURL URLWithString:URL]];
    [data writeToFile:filePath atomically:YES];
    [pool release];
}

So I think that your download code is correct, but there is some other variable that is getting deallocated early (possibly your path).

Hope this helps! I know the other answers on this page worked for me.

NSDATA writeToFile crashes without a reason

3 Answers3