I am learning iOS dev and have a crashing MapKit app. Need help understanding this crash log

I am working on and app called whereami from the "BNR Guide to iOS programming" chapter 5. I have the app working and left it on my phone to show the wife and family I am learning stuff. It is exhibiting a regular crashing behavior though. Here is what happens....

When you first open app and run it it does fine, If you hit home and then open it again within just a few minutes it does fine, If you leave it in the background then reopen more than a few minutes (say like 5 or more) later it crashes. You can then reopen it then and it does fine but the pattern repeats.

I have double checked all my code with the book and looked on the errata page but can't figure out what could be wrong. The Xcode organizer shows logs for all the crashes but I don't know how to read that yet. I was starting to wonder if since this is just a learning project app, not meant for real use, maybe it is missing something that makes it multitask/background/reopen??? correctly? I am using Xcode 4.1 on Lion with iPhone 4 running iOS 4.3.4. I would be grateful for any assistance anyone can offer.

Here is what I think is the relevant part of the crash log:

Incident Identifier: 352B538C-75BB-4BDF-9C2B-EC9613CE1B44
CrashReporter Key:   5896ed7851b999169919cab30c69940f74ed6b0c
Hardware Model:      iPhone3,1
Process:         WhereAmI [775]
Path:            /var/mobile/Applications/DB57A854-01F8-460F-B8CD-38B8FC50FBAF/WhereAmI.app/WhereAmI
Identifier:      WhereAmI
Version:         ??? (???)
Code Type:       ARM (Native)
Parent Process:  launchd [1]

Date/Time:       2011-07-23 18:47:19.093 -0400
OS Version:      iPhone OS 4.3.4 (8K2)
Report Version:  104

Exception Type:  EXC_CRASH (SIGABRT)
Exception Codes: 0x00000000, 0x00000000
Crashed Thread:  0

Thread 0 name:  Dispatch queue: com.apple.main-thread
Thread 0 Crashed:
0   libsystem_kernel.dylib          0x356d8a1c __pthread_kill + 8
1   libsystem_c.dylib               0x34d543b4 pthread_kill + 52
2   libsystem_c.dylib               0x34d4cbf8 abort + 72
3   libstdc++.6.dylib               0x35434a64 __gnu_cxx::__verbose_terminate_handler() + 376
4   libobjc.A.dylib                 0x35fdd06c _objc_terminate + 104
5   libstdc++.6.dylib               0x35432e36 __cxxabiv1::__terminate(void (*)()) + 46
6   libstdc++.6.dylib               0x35432e8a std::terminate() + 10
7   libstdc++.6.dylib               0x35432f5a __cxa_throw + 78
8   libobjc.A.dylib                 0x35fdbc84 objc_exception_throw + 64
9   CoreFoundation                  0x3504d3c6 -[NSException raise] + 2
10  MapKit                          0x3389bcb2 -[MKMapView setRegion:animated:] + 318
11  WhereAmI                        0x000029cc -[WhereAmIAppDelegate mapView:didUpdateUserLocation:] (WhereAmIAppDelegate.m:52)
12  MapKit                          0x338a11b6 -[MKMapView(UserPositioningInternal) resetUserLocation] + 142
13  MapKit                          0x338a074e -[MKMapView(UserPositioningInternal) locationManagerDidReset:] + 22
14  CoreFoundation                  0x34fbaefc -[NSObject(NSObject) performSelector:withObject:] + 16
15  CoreFoundation                  0x34ff82f2 -[NSArray makeObjectsPerformSelector:withObject:] + 394
16  MapKit                          0x33893802 -[MKLocationManager _reportLocationStatus:] + 34
17  MapKit                          0x338937ce -[MKLocationManager _reportLocationReset] + 14
18  MapKit                          0x33894d24 -[MKLocationManager reset] + 88
19  MapKit                          0x338770a2 -[MKLocationManager applicationResumed:] + 62
20  Foundation                      0x30fa017c _nsnote_callback + 136
21  CoreFoundation                  0x3501c208 __CFXNotificationPost_old + 396
22  CoreFoundation                  0x34fb6ee4 _CFXNotificationPostNotification + 112
23  Foundation                      0x30f9d5cc -[NSNotificationCenter postNotificationName:object:userInfo:] + 64
24  UIKit                           0x3640f720 -[UIApplication _handleApplicationResumeEvent:] + 900
25  UIKit                           0x362b9e20 -[UIApplication handleEvent:withNewEvent:] + 2724
26  UIKit                           0x362b920e -[UIApplication sendEvent:] + 38
27  UIKit                           0x362b8c4c _UIApplicationHandleEvent + 5084
28  GraphicsServices                0x35827e70 PurpleEventCallback + 660
29  GraphicsServices          开发者_如何学Go      0x35827efa PurpleEventSignalCallback + 10
30  CoreFoundation                  0x35024a72 __CFRUNLOOP_IS_CALLING_OUT_TO_A_SOURCE0_PERFORM_FUNCTION__ + 6
31  CoreFoundation                  0x35026758 __CFRunLoopDoSources0 + 376
32  CoreFoundation                  0x350274e4 __CFRunLoopRun + 224
33  CoreFoundation                  0x34fb7ebc CFRunLoopRunSpecific + 224
34  CoreFoundation                  0x34fb7dc4 CFRunLoopRunInMode + 52
35  GraphicsServices                0x35827418 GSEventRunModal + 108
36  GraphicsServices                0x358274c4 GSEventRun + 56
37  UIKit                           0x362e3d62 -[UIApplication _run] + 398
38  UIKit                           0x362e1800 UIApplicationMain + 664
39  WhereAmI                        0x000027c0 main (main.m:14)
40  WhereAmI                        0x00002768 start + 32

I am very new at this but I am guessing that the last function called is here:

8   libobjc.A.dylib                 0x35fdbc84 objc_exception_throw + 64
9   CoreFoundation                  0x3504d3c6 -[NSException raise] + 2
10  MapKit                          0x3389bcb2 -[MKMapView setRegion:animated:] + 318
11  WhereAmI                        0x000029cc -[WhereAmIAppDelegate mapView:didUpdateUserLocation:] (WhereAmIAppDelegate.m:52)

the method code from WhereAmIAppDelegate.m is here:

- (void)mapView:(MKMapView *)mapView didUpdateUserLocation:(MKUserLocation *)userLocation{
    // Zoom in on user here
    CLLocationCoordinate2D loc = [userLocation coordinate];
    MKCoordinateRegion region = MKCoordinateRegionMakeWithDistance(loc, 250, 250);
    [worldView setRegion:region animated:YES];

}

I ran into this problem with the 3rd edition of the book and saw it was answered in the book's 2nd edition forums, but not here. The problem is that the WhereAmIAppDelegate receives an invalid location when the app returns from running in the background for more than 5-10 minutes. Not sure why this happens, but this is how I fixed it:

- (void)mapView:(MKMapView *)mapView 
    didUpdateUserLocation:(MKUserLocation *)userLocation
{
    // Here we are... but how do we actually zoom?
    CLLocationCoordinate2D loc = [userLocation coordinate];
    if(CLLocationCoordinate2DIsValid(loc))
    {
        MKCoordinateRegion region = MKCoordinateRegionMakeWithDistance(loc, 320, 480);
        [worldView setRegion:region animated:YES];
    }
}

Sorry to "necro" an old thread, but I thought this might help somebody looking for help. By the way, I'm using Xcode 4.3.2 and iOS 5.1.

try checking if the region has some value. Also change 250 to 250.0. Give me some feedback. :)