循环遍历 NSDictionary 从属性列表中读入证明很麻烦

Question

大家好，我正在从一个如下结构的 plist 中读取：

如您所见，这是一个 plist包含不同类型（C，Visitor）的注释信息。我可以很好地显示每种注释类型，但我试图循环遍历所有类型并立即在地图视图上显示所有注释。这是代码：

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];
  }
 }

这是我运行程序时的控制台输出：

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";
}

因此它正确地循环第一个 NSDictionary，但在即将开始循环下一个时崩溃。我尝试将 NSDictionary 更改为 NSMutableDictionary 但结果是相同的。因此，当我在表视图中选择“所有许可”行时，它会挂起几分之一秒（不切换到地图视图），然后崩溃，而不会生成错误。

如果有人不介意在这里帮助我，我将不胜感激。提前致谢！

编辑： 这是堆栈跟踪（在下面的注释中描述）：

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'

但是，我在 for 循环中释放了 PermitDict（第二个 [permitDict release] 未注释），所以我不知道为什么它抱怨 NSDictionary 是不可变的。正如你所看到的，permitDict 是 NSMutableDictionary 类型，所以我不明白为什么它会给我这个错误。

Answer 1

该代码崩溃的主要原因有两个。

首先，for循环内的这一行：

[rootOfPermitDataPlistDict release];

销毁当前正在循环的对象。将其移至最后 - 在 if ([self title]... 语句的右大括号之后。

以下两行：

[permitDict release];

第二，应删除 不要释放permitDict，因为您正在使用dictionaryWithDictionary 创建它，它返回一个自动释放的对象，

通过这两个更改，代码应该运行。

---

However, there are a few other problems:

• 您分配+init annotationsArray 但从未释放它（内存泄漏）。在遍历该数组的 for 循环之后释放它（当前有第二个 [permitDict release];）。
• 您分配+ init annotationContainerDict，但随后仅使用该变量作为对annotationsArray中对象的引用（因此放弃分配的内存 - 内存泄漏）。不必费心对annotationContainerDict 进行alloc+init，只需声明它即可。将 NSDictionary *annotationContainerDict = [[NSDictionary alloc] init]; 更改为 NSDictionary *annotationContainerDict;。
• 您正在使用 == 比较字符串。使用 isEqualToString: 代替，如下所示：
  if ([[self title] isEqualToString:@"All Permits"])...。有关为什么应使用 isEqualToString 的说明，请参阅此问题 和这个问题。
• 这里并不是一个真正严重的问题，但没有必要使用dictionaryWithDictionary，从而复制 rootOfPermitDataPlistDict 中已有的内容。您可以使用 PermitDict 作为嵌入字典的速记引用，如下所示：NSMutableDictionary *permitDict = [rootOfPermitDataPlistDict objectForKey:key];。
• 与annotationsArray相同的一点：你不需要分配+初始化一个新数组。该数组已位于 rootOfPermitDataPlistDict 中。只需像这样获取对它的引用：NSArray *annotationsArray = [permitDict objectForKey:@"annotations"];。如果您决定这样做，请不要释放annotationsArray。

内存管理编程指南解释了所有内容这个详细。

Answer 2

首先，您的代码存在很多问题，但除非这是性能关键的代码，否则您将每秒循环数百次（这可能会创建许多自动释放的对象），否则使用 alloc] init] 方法只会使代码更难遵循。 （因为您必须在心里仔细考虑并不断平衡分配与释放）。不要误会我的意思，理解保留和释放等很重要，但这就是我解决问题的方式。

请记住，一切尽在您的掌控之中。让你的停车注释类能够“自己思考”一点。在下面的示例中，我添加了一个 -(id)initWithDictionary: ，这样您的其他类就不必坐在那里并完成一一设置键的所有繁重工作。 （有一些虚构的部分，我假设你会填补空白......

NSString * const PPAnnotationsKey   = @"annotations";
NSString * const PPTitleKey         = @"title";
NSString * const PPSubtitleKey      = @"subtitle";
NSString * const PPLatitudeKey      = @"latitude";
NSString * const PPLongitudeKey     = @"longitude";

NSLog(@"loadAnnotations");
NSString *plistPath = [[NSBundle mainBundle] pathForResource:@"PermitData" ofType:@"plist"]; // autoreleased
NSDictionary *permitDictionary = [NSDictionary dictionaryWithContentsOfFile:plistPath]; // autoreleased
if ([[self title] isEqualToString:@"All Permits"]) {
    for (NSString *parkingGroup in permitDictionary) {
        NSLog(@"parkingGroup == %@", parkingGroup);
        NSArray *annotations = [parkingGroup objectForKey:PPAnnotationsKey];
        for (NSDictionary *entry in annotations) {
            PPParkingAnnotation *annotation = [PPParkingAnnotation parkingAnnotationWithDictionary:entry]; // autoreleased
            if (annotation) {
            // assuming here that mapView's addAnnotation: will retain the
            // annotation
            [mapView addAnnotation:annotation]; 
            }
        }
    }
}

@interface PPParkingAnnotation : NSObject <MKAnnotation> {
    CLLocationCoordinate2D   coordinate;
    NSString                *title;
    NSString                *subtitle;
}
+ (id)parkingAnnotationWithDictionary:(NSDictionary *)dictionary;
- (id)initWithDictionary:(NSDictionary *)dictionary;

@properties...
@end

@implementation PPParkingAnnotation

+ (id)parkingAnnotationWithDictionary:(NSDictionary *)dictionary {
    return [[[[self class] alloc] initWithDictionary:dictionary] autorelease];
}

- (id)initWithDictionary:(NSDictionary *)dictionary {
    [self setTitle:[dictionary objectForKey:PPTitleKey]];
    [self setSubtitle:[dictionary objectForKey:PPTitleKey]];
    // and so on.
}