Encoded nsstring becomes invalid, "normal" nsstring remains - iphone

Question

I'm running into a problem with a string that contains encoded characters. Specifically, if the string has encoded characters it eventually becomes invalid while a "normal" string will not.
in the .h file:
#interface DirViewController : TTThumbsViewController
<UIActionSheetDelegate,UINavigationControllerDelegate,UIImagePickerControllerDelegate>
{
NSString *sourceFolder;
NSString *encodedSourceFolder;
}
#property (nonatomic, retain) NSString *sourceFolder;
#property (nonatomic, retain) NSString *encodedSourceFolder;
in the .m file:
- (id)initWithFolder:(NSString*)folder query:(NSDictionary*)query {
if (self = [super init]) {
sourceFolder = folder;
}
return self;
}
Up to now everything seems to run as expected. In viewDidLoad I have the following:
sourceFolderCopy = [self urlEncodeValue:(sourceFolder)];
//I also have this button, which I'll refer to later:
UIBarButtonItem *importButton = [[UIBarButtonItem alloc] initWithTitle:#"Import/Export" style:UIBarButtonItemStyleBordered
target:self
action:#selector(importFiles:)];
self.navigationItem.rightBarButtonItem = importButton;
Which uses the following method to encode the string (if it has characters I want encoded):
- (NSString *)urlEncodeValue:(NSString *)str {
NSString *result = (NSString *) CFURLCreateStringByAddingPercentEscapes (kCFAllocatorDefault, (CFStringRef)str, NULL, CFSTR(":/?#[]#!$&’()*+,;="), kCFStringEncodingUTF8);
return [result autorelease];
}
If I NSLog result, I get the expected values. If the string has characters like a white space, I get a string with encoding. If the string doesn't have any characters that need to be encoded, it just gives me the original string.
I have a button on the nav bar which begins an image import process by opening an action sheet. Once the method for the action sheet starts, my string is invalid - but only if it contains encoded characters. If it is just a "normal" string, everything is fine and acts as expected. Am I off on my encoding? At first I thought it might be a memory problem but I can't figure out why that would affect only encoded strings.
Here's where the action sheet is defined (and the first place I can see the encoded string becoming invalid) the NSLog statements are where it crashes:
- (IBAction)importFiles:(id)sender {
NSLog(#"logging encodedSF from import files:");
NSLog(#"%#",encodedSourceFolder);//crashes right here
NSLog(#"%#",sourceFolder);
if (shouldNavigate == NO)
{
NSString *msg = nil;
msg = #"It is not possible to import or export images while in image selection mode.";
UIAlertView *alert = [[UIAlertView alloc]
initWithTitle:#"Unable to Import/Export"
message:msg
delegate:self
cancelButtonTitle:#"OK"
otherButtonTitles:nil];
[alert show];
[alert release];
[msg release];
}
else{
UIActionSheet *actionSheet = [[UIActionSheet alloc]
initWithTitle:#"What would you like to do?"
delegate:self
cancelButtonTitle:#"Cancel"
destructiveButtonTitle:nil
otherButtonTitles:#"Import Photos (Picker)", #"Export Photos", nil, nil];
[actionSheet showInView:self.view];
[actionSheet release];
}
}
I don't get any crash errors going to the console. By using breakpoints I was able to see that the encodedSourceFolder is invalid in the action sheet method.

Answer 1

You should copy your passed in folder string in your initWithFolder:query: method like this or create a new string with:
- (id)initWithFolder:(NSString*)folder query:(NSDictionary*)query {
if (self = [super init]) {
sourceFolder = [folder copy];
}
return self;
}
Otherwise your string gets autoreleased elsewhere.

Answer 2

Do not use retain for NSString properties. Use copy:
#property (nonatomic, copy) NSString *sourceFolder;
There are several questions/answers here that explain this further, such as Chris Hanson's response at:
NSString property: copy or retain?