问题
Is it possible to deserialize an NSString of JSON into objects via RestKit? I checked the API list here and could not find something that would serve for this purpose. The closest I could find are the various parser classes that return NSDictionary after parsing the input. I assume RestKit uses these parsers after downloading the response so my thinking is that the functionality is available somewhere in RestKit but not exposed publicly.
If I am not missing anything and this functionality is not exposed, what would be the alternatives? Two obvious ones do not look very promising: Get the resulting NSDictionary and try to deserialize myself (effectively reimplementing RestKit) or try to dive into RestKit source and see if this can be somehow exposed (looks tedious and error prone).
Thanks in advance for any help.
PS: The idea is that a string property on a deserialized object is actually the JSON representation of another set of objects (embedded JSON in a sense) and it is deserialized on demand during runtime.
回答1:
Pretty "simple":
NSString *stringJSON;
...
RKJSONParserJSONKit *parser;
NSError *error= nil;
parser= [[[RKJSONParserJSONKit alloc] init] autorelease];
MyManagedObject *target;
target= [MyManagedObject object];
NSDictionary *objectAsDictionary;
RKObjectMapper* mapper;
objectAsDictionary= [parser objectFromString:stringJSON error:&error];
mapper = [RKObjectMapper mapperWithObject:objectAsDictionary
mappingProvider:[RKObjectManager sharedManager].mappingProvider];
mapper.targetObject = target;
RKObjectMappingResult* result = [mapper performMapping];
NSLog(@"%@", [result asObject]);
回答2:
As of RestKit 0.20.0-pre2
NSString* JSONString = @"{ \"name\": \"The name\", \"number\": 12345}";
NSString* MIMEType = @"application/json";
NSError* error;
NSData *data = [JSONString dataUsingEncoding:NSUTF8StringEncoding];
id parsedData = [RKMIMETypeSerialization objectFromData:data MIMEType:MIMEType error:&error];
if (parsedData == nil && error) {
// Parser error...
}
AppUser *appUser = [[AppUser alloc] init];
NSDictionary *mappingsDictionary = @{ @"someKeyPath": someMapping };
RKMapperOperation *mapper = [[RKMapperOperation alloc] initWithRepresentation:parsedData mappingsDictionary:mappingsDictionary];
mapper.targetObject = appUser;
NSError *mappingError = nil;
BOOL isMapped = [mapper execute:&mappingError];
if (isMapped && !mappingError) {
// Yay! Mapping finished successfully
NSLog(@"mapper: %@", [mapper representation]);
NSLog(@"firstname is %@", appUser.firstName);
}
回答3:
This works for Restkit 0.21.0:
NSString* jsonFilePath = [[NSBundle mainBundle] pathForResource:@"fileName"
ofType:@"json"];
NSString* JSONString = [NSString stringWithContentsOfFile:jsonFilePath
encoding:NSUTF8StringEncoding
error:NULL];
NSError* error;
NSData *data = [JSONString dataUsingEncoding:NSUTF8StringEncoding];
id parsedData = [RKMIMETypeSerialization objectFromData:data MIMEType:RKMIMETypeJSON error:&error];
if (parsedData == nil && error) {
// Parser error...
}
//_objectManager is RKObjectManager instance
NSMutableDictionary *mappingsDictionary = [[NSMutableDictionary alloc] init];
for (RKResponseDescriptor *descriptor in _objectManager.responseDescriptors) {
[mappingsDictionary setObject:descriptor.mapping forKey:descriptor.keyPath];
}
RKMapperOperation *mapper = [[RKMapperOperation alloc] initWithRepresentation:parsedData mappingsDictionary:mappingsDictionary];
NSError *mappingError = nil;
BOOL isMapped = [mapper execute:&mappingError];
if (isMapped && !mappingError) {
NSLog(@"result %@",[mapper mappingResult]);
}
回答4:
This works for Restkit 0.20, using Core Data Entities. It is based in the solution given by @innerself
NSString* jsonFilePath = [[NSBundle mainBundle] pathForResource:@"info-base"
ofType:@"json"];
NSString* JSONString = [NSString stringWithContentsOfFile:jsonFilePath
encoding:NSUTF8StringEncoding
error:NULL];
NSError *error = nil;
NSData *data = [JSONString dataUsingEncoding:NSUTF8StringEncoding];
id parsedData = [RKMIMETypeSerialization objectFromData:data MIMEType:RKMIMETypeJSON error:&error];
if (parsedData == nil && error) {
// Parser error...
NSLog(@"parse error");
}
//_objectManager is RKObjectManager instance
NSMutableDictionary *mappingsDictionary = [[NSMutableDictionary alloc] init];
for (RKResponseDescriptor *descriptor in [RKObjectManager sharedManager].responseDescriptors) {
[mappingsDictionary setObject:descriptor.mapping forKey:descriptor.keyPath];
}
RKManagedObjectMappingOperationDataSource *datasource = [[RKManagedObjectMappingOperationDataSource alloc]
initWithManagedObjectContext:[RKManagedObjectStore defaultStore].persistentStoreManagedObjectContext
cache:[RKManagedObjectStore defaultStore].managedObjectCache];
RKMapperOperation *mapper = [[RKMapperOperation alloc] initWithRepresentation:parsedData
mappingsDictionary:mappingsDictionary];
[mapper setMappingOperationDataSource:datasource];
NSError *mappingError = nil;
BOOL isMapped = [mapper execute:&mappingError];
if (isMapped && !mappingError) {
// data is in [mapper mappingResult]
}
回答5:
You can see how RestKit does this internally in the RKManagedObjectResponseMapperOperation class.
There are three stages of this operation.
The first is to parse the JSON string into NSDictionarys, NSArrays, etc. This is the easiest part.
id parsedData = [RKMIMETypeSerialization objectFromData:data
MIMEType:RKMIMETypeJSON
error:error];
Next you need to run a mapping operation to convert this data into your NSManagedObjects. This is a bit more involved.
__block NSError *blockError = nil;
__block RKMappingResult *mappingResult = nil;
NSOperationQueue *operationQueue = [[NSOperationQueue alloc] init];
operationQueue.maxConcurrentOperationCount = 1;
[[RKObjectManager sharedManager].managedObjectStore.persistentStoreManagedObjectContext performBlockAndWait:^{
Remember to replace this dictionary with your own mappings. The key [NSNull null] maps this object from the root.
NSDictionary *mappings = @{[NSNull null]: [jotOfflineRequestStatus mapping]};
RKMapperOperation *mapper = [[RKMapperOperation alloc] initWithRepresentation:parsedData
mappingsDictionary:mappings];
RKManagedObjectMappingOperationDataSource *dataSource = [[RKManagedObjectMappingOperationDataSource alloc]
initWithManagedObjectContext:[RKManagedObjectStore defaultStore].persistentStoreManagedObjectContext
cache:[RKManagedObjectStore defaultStore].managedObjectCache];
dataSource.operationQueue = operationQueue;
dataSource.parentOperation = mapper;
mapper.mappingOperationDataSource = dataSource;
[mapper start];
blockError = mapper.error;
mappingResult = mapper.mappingResult;
}];
You now need to run the tasks that have been put into the operationQueue we created. It is at this stage that connections to existing NSManagedObjects are made.
if ([operationQueue operationCount]) {
[operationQueue waitUntilAllOperationsAreFinished];
}
回答6:
A more iOS 5+ oriented answer:
NSString* JSONString = jsonString;
NSString* MIMEType = @"application/json";
NSError* error = nil;
id<RKParser> parser = [[RKParserRegistry sharedRegistry] parserForMIMEType:MIMEType];
id parsedData = [parser objectFromString:JSONString error:&error];
if (parsedData == nil && error) {
NSLog(@"ERROR: JSON parsing error");
}
RKObjectMappingProvider* mappingProvider = [RKObjectManager sharedManager].mappingProvider;
RKObjectMapper* mapper = [RKObjectMapper mapperWithObject:parsedData mappingProvider:mappingProvider];
RKObjectMappingResult* result = [mapper performMapping];
if (result) {
NSArray *resultArray = result.asCollection;
MyObject *object = [resultArray lastObject];
NSLog(@"My Object: %@", object);
}
回答7:
For Restkit 0.22, You can use this code. This returns an RKMappingResult wherein you can enumerate the objects after mapping using the property .array.
- (RKMappingResult *)mapJSONStringWithString:(NSString *)jsonString
{
RKMappingResult *result = nil;
NSError* error;
NSData *data = [jsonString dataUsingEncoding:NSUTF8StringEncoding];
id parsedData = [RKMIMETypeSerialization objectFromData:data MIMEType:RKMIMETypeJSON error:&error];
if (parsedData == nil && error) {
NSLog(@"json mapping error");
}
NSDictionary *mappingsDictionary = @{@"":[CustomMappingClass getMappingForUsers]};
ObjectClass *obj = [ObjectClass new];
RKMapperOperation *mapper = [[RKMapperOperation alloc] initWithRepresentation:parsedData mappingsDictionary:mappingsDictionary];
NSError *mappingError = nil;
mapper.targetObject = obj;
BOOL isMapped = [mapper execute:&mappingError];
if (isMapped && !mappingError) {
result = [mapper mappingResult];
}
return result;
}
回答8:
Is this not what you're looking for? http://restkit.org/api/0.10.0/Classes/RKJSONParserJSONKit.html
回答9:
Judging by the views without any answers, it seems this facility does not exist in RestKit yet. Instead of spending more time trying to figure out how to do the mapping, I wrote my own mapper using the output of JsonKit parser and removed the dependency on RestKit (used the builtin classes for network activity). Right now my mapper is not generic (it has a few dependencies on how the objects are laid out and their names in json) but it works for the purposes of the project. I might come back later and turn it into a more generic object mapping library later on.
EDIT: This was selected answer because there was no other answer as of this answer's date (Jan 21, 2012). Since then, I stopped working on iOS and never visited this question again. Now I am selecting Ludovic's answer because of another user's comment and the upvotes for that answer.
来源：https://stackoverflow.com/questions/8873607/deserializing-local-nsstring-of-json-into-objects-via-restkit-no-network-downlo