在Objective-c的NSDictionary中创建带有“ Struct”的地图？

Question

我想创建一个NSMutableDictionary，其中有一个整数映射到strucuter（struct）。 例：

int nVar = 1;
typedef struct 
{
  NSString *pstrName;
}sSampleStruct;
sSampleStruct *sObject = {@"test"};
NSMutableDictioary *pSampleMap = [[NSMutableDictioary allo] init];
[pSampleMap setObject:sObject forKey:[[nsnumber alloc] initwithint:nVar];

这就是我要做什么？ 但是由于struct不是对象，因此它会发出警告吗？ 我可以用任何方法创建带有结构的字典。 还是通过其他方式创建具有结构的地图？

请尽快回复.....

谢谢Pradeep。

Answer 1

看一下NSValue ：

[pSampleMap setObject:[NSValue value:&sObject withObjCType:@encode(sSampleStruct)] forKey:[NSNumber numberWithInt:nInt]];

另外，您在[[NSNumber alloc] initWithInt:nVar]中发生内存泄漏，并且由于Objective-C区分大小写，因此您的代码甚至无法编译。

Answer 2

您说对了，因为NSDictionary中的键和值都必须是对象。 您正在寻找的是NSValue 。

从文档 ：

NSValue对象是单个C或Objective-C数据项的简单容器。 它可以容纳任何标量类型，例如int，float和char，以及指针，结构和对象id。 此类的目的是允许将此类数据类型的项目添加到集合中，例如NSArray和NSSet实例，它们要求它们的元素成为对象。 NSValue对象始终是不可变的。

有点像（稍微清理一下代码）：

typedef struct 
{
    NSString *pstrName;
} sSampleStruct;

// Changed sObject to non-pointer so it can be initialized with a literal
sSampleStruct sObject = {@"test"};

// Corrected spelling of NSMutableDictionary
NSMutableDictionary *pSampleMap = [[NSMutableDictionary alloc] init];

// Changed to [NSNumber numberWithInt:] to avoid leaking memory
// Corrected spelling and capitalization of NSNumber
[pSampleMap setObject:[NSValue valueWithPointer:&sObject] 
               forKey:[NSNumber numberWithInt:nVar]];

Answer 3

您可以使用NSData来包装您的结构。 以下是我的解决方案，它对我的​​工作：

// this is complex structure SIO2Object. Use you custom initialization instead of this 
SIO2object *el = ( SIO2object * )sio2ResourceGetObject(sio2->_SIO2resource, @"User/11/..." );

NSMutableDictionary *elements = [NSMutableDictionary dictionary];
NSData *elData = [NSData dataWithBytes:&el length:sizeof(el)];
[elements setObject:elData forKey:@"first"];

SIO2object *newEl = nil;
NSData *newData = [elements objectForKey:@"first"];
[newData getBytes:&newEl];
//there newEl is equal to el 

Answer 4

您可以使用NSDictionary，但是这些功能仅可通过CF接口使用：

/* define our custom key callbacks */
CFDictionaryKeyCallBacks keyCallbacks;

keyCallbacks.version = 0; /* default */
keyCallbacks.retain = 0; /* no retain performed */
keyCallbacks.release = 0; /* no release performed */
keyCallbacks.copyDescription = 0; /* potentially applicable */
keyCallbacks.equal = 0; /* potentially applicable */
keyCallbacks.hash = 0; /* potentially applicable */

/* note: if you prefer to use NSNumber for keys,
    then you should use the default key callbacks.
    this illustrates what you could do if you wanted to use int keys.
*/

/* define our custom value callbacks */
CFDictionaryValueCallBacks valueCallbacks;
/* see per-field comments at keyCallbacks */
valueCallbacks.version = 0;
valueCallbacks.retain = 0;
valueCallbacks.release = 0;
valueCallbacks.copyDescription = 0;
valueCallbacks.equal = 0;

CFAllocatorRef allocator = kCFAllocatorDefault;
CFIndex capacity = 0; /* no hint in this example - resizes as needed */

NSMutableDictionary * myNewDictionary = (NSMutableDictionary*)
   CFDictionaryCreateMutable(allocator, capacity, &keyCallbacks, &valueCallbacks);

/*
for insertions/values/keys:
  - use a pointer to the key/value if the value is larger than a pointer.
    this may require dynamic memory allocation and use of reference counting
    since the keys/values must live in memory as long as the dictionary exists
*/

Answer 5

或者如果您熟悉c ++：

std::map<sSampleStruct,int> myDictionary;