Objective c NSMutableDictionary与“一起崩溃”；发送到不可变对象的变异消息“；

我有一个类，它的属性是

NSMutableDictionary

：

@interface Alibi : NSObject <NSCopying>
@property (nonatomic, copy) NSMutableDictionary * alibiDetails;
@end

和复制方法：

- (Alibi *)copyWithZone:(NSZone *)zone
{
    Alibi *theCopy = [[Alibi alloc] init];
    theCopy.alibiDetails = [self.alibiDetails mutableCopy];    
    return theCopy;
}

当我试图调用

setObject:ForKey:

时，我得到一个运行时错误

mutating方法，该方法被发送到不可变对象

我在视图控制器中将

Alibi

对象声明为

@property（copy，nonatomic）Alibi*theAlibi在
viewDidLoad
中

崩溃的线路是：

NSString * recipient;
recipient = @"Boss";
[self.theAlibi.alibiDetails setObject:recipient forKey:@"Recipient"];

请让我知道我做错了什么。我正在为iPhone上的iOS 5编写代码。
您有一个“copy”属性，这意味着-您的NSMutableDictionary将调用-copy方法，并在分配给合成实例变量之前返回一个常规NSDictionary。提供有关解决此问题的一些选项的信息。
为了完成此线程，我将在下面包括我修订的
不在场证明类，这是我所要求的。如果有人注意到任何内存泄漏或其他问题，我们将不胜感激

@implementation Alibi

NSMutableDictionary *_details;

- (Alibi *)init
{
    self = [super init];
    _details = [NSMutableDictionary dictionary];
    return self;
}

- (NSMutableDictionary *)copyDetails
{
    return [_details mutableCopy];
}

- (NSMutableDictionary *)setDetails:(NSMutableDictionary *)value
{
    _details = value;
    return value;
}

- (void)addDetail:(id)value forKey:(id)key
{
    [_details setObject:value forKey:key];
}

- (id)getDetailForKey:(id)key
{
    return [_details objectForKey:key];
}

- (Alibi *)copyWithZone:(NSZone *)zone
{
    Alibi *theCopy = [[Alibi alloc] init];

    theCopy.serverId = [self.serverId copyWithZone:zone];
    theCopy.user = [self.user copyWithZone:zone];
    theCopy.startTime = [self.startTime copyWithZone:zone];
    theCopy.endTime = [self.endTime copyWithZone:zone];
    [theCopy setDetails:[self copyDetails]];

    return theCopy;
}

@end

@implementation Alibi

NSMutableDictionary *_details;

- (Alibi *)init
{
    self = [super init];
    _details = [NSMutableDictionary dictionary];
    return self;
}

- (NSMutableDictionary *)copyDetails
{
    return [_details mutableCopy];
}

- (NSMutableDictionary *)setDetails:(NSMutableDictionary *)value
{
    _details = value;
    return value;
}

- (void)addDetail:(id)value forKey:(id)key
{
    [_details setObject:value forKey:key];
}

- (id)getDetailForKey:(id)key
{
    return [_details objectForKey:key];
}

- (Alibi *)copyWithZone:(NSZone *)zone
{
    Alibi *theCopy = [[Alibi alloc] init];

    theCopy.serverId = [self.serverId copyWithZone:zone];
    theCopy.user = [self.user copyWithZone:zone];
    theCopy.startTime = [self.startTime copyWithZone:zone];
    theCopy.endTime = [self.endTime copyWithZone:zone];
    [theCopy setDetails:[self copyDetails]];

    return theCopy;
}

@end