Looping Through an NSDictionary Read in From Property List Prooving Troublesome

Ey guys, I am reading in from a plist structured like so:

property list

As you can see, it is a plist that contains annotation information of different types(C,Visitor). I can display each annotation type just fine, but I am attempting to loop through all types and display all annotations on the map view at once. Here is the code:

NSLog(@"loadAnnotations");
NSString *plistPath = [[NSBundle mainBundle] pathForResource:@"PermitData" ofType:@"plist"];
NSDictionary *rootOfPermitDataPlistDict = [[NSDictionary alloc] initWithContentsOfFile:plistPath];
// NSMutableDictionary *permitDict = [[NSMutableDictionary alloc] init];
 if ([self title] == @"All Permits") {
  for (id key in rootOfPermitDataPlistDict) {
   NSLog(@"key:%@",key);

   //[key retain];
   NSMutableDictionary *permitDict = [NSDictionary dictionaryWithDictionary:[rootOfPermitDataPlistDict objectForKey:key]];
   //[key release];

   //array containing annotation information: latitude, longitude, title, subtitle(see PermitData.plist)
   NSArray *annotationsArray = [[NSArray alloc] initWithArray:[permitDict objectForKey:@"annotations"]];
   [permitDict release];
   [rootOfPermitDataPlistDict release];

   CLLocationCoordinate2D workingCoordinate;
   NSDictionary *annotationContainerDict = [[NSDictionary alloc] init];
   //loop through annotations array, creating parking annotations filled with the information found in the plist
   for(annotationContainerDict in annotationsArray){
    NSLog(@"%@",annotationContainerDict);

    ParkingAnnotation *parkingAnnot = [[ParkingAnnotation alloc] init];
    workingCoordinate.latitude = [[annotationContainerDict objectForKey:@"latitude"] doubleValue];
    workingCoordinate.longitude = [[annotationContainerDict objectForKey:@"longitude"] doubleValue];
    [parkingAnnot setCoordinate:workingCoordinate];
    [parkingAnnot setTitle:[annotationContainerDict objectForKey:@"title"]];
    [parkingAnnot setSubtitle:[annotationContainerDict objectForKey:@"subtitle"]];
    if ([parkingAnnot title] == @"C Parking") [parkingAnnot setAnnotationType:annotationTypeC];
    else if ([parkingAnnot title] == @"Visitor Parking") [parkingAnnot setAnnotationType:annotationTypeVisitor];
    [mapView addAnnotation:parkingAnnot];
    [parkingAnnot release];
   }
   [permitDict release];
  }
 }

And this is the console output when I run the program:

2010-11-25 03:25:28.020 Parking[38918:207] All Permits
2010-11-25 03:25:28.021 Parking[38918:207] loadAnnotations
2010-11-25 03:25:28.021 Parking[38918:207] key:C
2010-11-25 03:25:28.021 Parking[38918:207] {
    latitude = "38.545301";
    longitude = "-121.754066";
    subtitle = "VP 17";
    title = "C Parking";
}
2010-11-25 03:25:28.022 Parking[38918:207] {
    latitude = "38.544831";
    longitude = "-121.754785";
    subtitle = "VP 16";
    title = "C Parking";
}
2010-11-25 03:25:28.022 Parking[38918:207] {
    latitude = "38.544781";
    longitude = "-121.755729";
    subtitle = "VP 22";
    title = "C Parking";
}
2010-11-25 03:25:28.022 Parking[38918:207] {
    latitude = "38.544412";
    longitude = "-121.752489";
    subtitle = "VP 15";
    title = "C Parking";
}

So it loops through the first NSDictionary properly, but crashes when it is about to begin looping through the next one. And I have tried changing NSDictionary to NSMutableDictionary but the result is the same. So when I select the "All Permits" row in the table view, it hangs for a fraction of a second(without switching to the map view), and then crashes, without generating an error.

If anyone wouldn't mind helping me out here, I would greatly appreciate it. Thanks in advance!

EDIT: Here is the stack trace(described in comments below):

2010-11-25 20:28:08.141 Parking[39400:207] All Permits
2010-11-25 20:28:08.142 Parking[39400:207] loadAnnotations
2010-11-25 20:28:08.142 Parking[39400:207] key:C
2010-11-25 20:28:08.143 Parking[39400:207] {
    latitude = "38.545301";
    longitude = "-121.754066";
    subtitle = "VP 17";
    title = "C Parking";
}
2010-11-25 20:28:08.143 Parking[39400:207] {
    latitude = "38.544831";
    longitude = "-121.754785";
    subtitle = "VP 16";
    title = "C Parking";
}
2010-11-25 20:28:08.143 Parking[39400:207] {
    latitude = "38.544781";
    longitude = "-121.755729";
    subtitle = "VP 22";
    title = "C Parking";
}
2010-11-25 20:28:08.144 Parking[39400:207] {
    latitude = "38.544412";
    longitude = "-121.752489";
    subtitle = "VP 15";
    title = "C Parking";
}
2010-11-25 20:28:08.145 Parking[39400:207] *** Terminating app due to uncaught exception 'NSGenericException', reason: '*** Collection <__NSCFDictionary: 0x6d5fd80> was mutated while being enumerated.<CFBasicHash 0x6d5fd80 [0x2667380]>{type = mutable dict, count = 1,
entries =>
    0 : <0x7380> = <NSKeyValueContainerClass: Original class: ParkingAnnotation, Notifying class: NSKVONotifying_ParkingAnnotation>
}
'
*** Call stack at first throw:
(
    0   CoreFoundation                      0x025fdb99 __exceptionPreprocess + 185
    1   libobjc.A.dylib                     0x0274d40e objc_exception_throw + 47
    2   CoreFoundation                      0x025fd659 __NSFastEnumerationMutationHandler + 377
    3   Parking                             0x00002e93 -[ParkingMapViewController loadAnnotations] + 364
    4   Parking                             0x00002caf -[ParkingMapViewController viewDidLoad] + 117
    5   UIKit                               0x0036a5ca -[UIViewController view] + 179
    6   UIKit                               0x003689f4 -[UIViewController contentScrollView] + 42
    7   UIKit                               0x003787e2 -[UINavigationController _computeAndApplyScrollContentInsetDeltaForViewController:] + 48
    8   UIKit                               0x00376ea3 -[UINavigationController _layoutViewController:] + 43
    9   UIKit                               0x00378067 -[UINavigationController _startTransition:fromViewController:toViewController:] + 326
    10  UIKit                               0x00372ccd -[UINavigationController _startDeferredTransitionIfNeeded] + 266
    11  UIKit                               0x00379d8b -[UINavigationController pushViewController:transition:forceImmediate:] + 876
    12  UIKit                               0x00372b67 -[UINavigationController pushViewController:animated:] + 62
    13  Parking                             0x00002914 -[PermitListViewController tableView:didSelectRowAtIndexPath:] + 307
    14  UIKit                               0x00333a48 -[UITableView _selectRowAtIndexPath:animated:scrollPosition:notifyDelegate:] + 1140
    15  UIKit                               0x0032a32e -[UITableView _userSelectRowAtIndexPath:] + 219
    16  Foundation                          0x0003f21a __NSFireDelayedPerform + 441
    17  CoreFoundation                      0x025def73 __CFRUNLOOP_IS_CALLING_OUT_TO_A_TIMER_CALLBACK_FUNCTION__ + 19
    18  CoreFoundation                      0x025e05b4 __CFRunLoopDoTimer + 1364
    19  CoreFoundation                      0x0253cdd9 __CFRunLoopRun + 1817
    20  CoreFoundation                      0x0253c350 CFRunLoopRunSpecific + 208
    21  CoreFoundation                      0x0253c271 CFRunLoopRunInMode + 97
    22  GraphicsServices                    0x02edc00c GSEventRunModal + 217
    23  GraphicsServices                    0x02edc0d1 GSEventRun + 115
    24  UIKit                               0x002ceaf2 UIApplicationMain + 1160
    25  Parking                             0x00001e08 main + 102
    26  Parking                             0x00001d99 start + 53
)
terminate called after throwing an instance of 'NSException'

However, I am releasing permitDict within the for loop(second [permitDict release] was left uncommented), so I don't know why it is complaining about the NSDictionary being immutable. As you can see, the permitDict is of type NSMutableDictionary, so I am lost as to why it is giving me this error.

Solution

The code is crashing for two main reasons.

First, this line which is inside the for-loop:

[rootOfPermitDataPlistDict release];

destroys the very object that you're currently looping through. Move it to the very end--after the closing brace of the if ([self title]... statement.

Second, the two lines that say:

[permitDict release];

should be removed. Do not release permitDict because you are creating it using dictionaryWithDictionary which returns an autoreleased object.

With those two changes, the code should run.

However, there are a few other problems:

You alloc+init annotationsArray but never release it (memory leak). Release it after the for-loop that goes through that array (where you currently have the second [permitDict release];).
You alloc+init annotationContainerDict but then use the variable only as a reference to the objects in the annotationsArray (and so abandoning the allocated memory--memory leak). Don't bother doing alloc+init on annotationContainerDict, just declare it. Change NSDictionary *annotationContainerDict = [[NSDictionary alloc] init]; to just NSDictionary *annotationContainerDict;.
You are comparing strings using ==. Use isEqualToString: instead like this:
if ([[self title] isEqualToString:@"All Permits"]).... For an explanation of why you should use isEqualToString, see this question and this question.
Not really a serious problem here but it is unnecessary to use dictionaryWithDictionary and thus duplicating what's already there in rootOfPermitDataPlistDict. You could just use permitDict as a shorthand reference to the embedded dictionary like this: NSMutableDictionary *permitDict = [rootOfPermitDataPlistDict objectForKey:key];.
Same point with annotationsArray: you don't need to alloc+init a new array. The array is already in rootOfPermitDataPlistDict. Just get a reference to it like this: NSArray *annotationsArray = [permitDict objectForKey:@"annotations"];. Do not release annotationsArray if you decide to do it this way.

The Memory Management Programming Guide explains all this in detail.