Invalid top-level type in JSON write

问题

I'm trying to create a simple JSON object but I still get error and I know what's wrong in my code:

NSString *vCard = [BRContacts getContacts]; // this is just a string, could be nil
NSDictionary *JSONdic = nil;
if (vCard)
{
    JSONdic = [NSDictionary dictionaryWithObjectsAndKeys:@"1",@"status",vCard,@"data", nil];
}
else
{
    JSONdic = [NSDictionary dictionaryWithObjectsAndKeys:@"0",@"status",@"vCard is empty",@"error", nil];
}
NSError *error = nil;
NSData *JSONData = [NSJSONSerialization dataWithJSONObject:JSONdic options:NSJSONWritingPrettyPrinted error:&error];
return [GCDWebServerDataResponse responseWithJSONObject:JSONdata];

The exception is

Invalid top-level type in JSON write

I checked also JSONdic and it's not nil in every case. Any suggestions?

回答1:

I can't say what is the error, because I tried here and worked.

I tried with NSString *vCard = nil and NSString *vCard = @"SOMESTRING", both cases it worked.

NSString *vCard = @"SOMESTRING"; // this is just a string, could be nil
    NSDictionary *JSONdic = nil;
    if (vCard) {
        JSONdic = @{@"status" : @"1", @"data" : vCard};
    } else {
        JSONdic = @{@"status" : @"0", @"error" : @"vCard is empty"};
    }
    NSError *error = nil;
    NSData *JSONData = [NSData data];

if ([NSJSONSerialization isValidJSONObject:JSONdic]) {
    JSONData = [NSJSONSerialization dataWithJSONObject:JSONdic options:NSJSONWritingPrettyPrinted error:&error];
}

Make sure [BRContacts getContacts] returning a NSString, and I just rewrite to a modern syntax the NSDictionary declaration.

回答2:

Ok I solved. It was a problem related to this line:

return [GCDWebServerDataResponse responseWithJSONObject:JSONdata];

this response of GCDWebServer doesn't want a JSON NSData but a NSDictionary: the error is just because responseWithJSONObject process the input for create a JSON object (and I passed a JSON "pre-processed" object). So my error is not related to my initial code so I updated it just now for future reference, I solved using:

return [GCDWebServerDataResponse responseWithJSONObject:JSONdic];

According to the documentation for similar problem be sure to follow this rules:

An object that may be converted to JSON must have the following properties:

The top level object is an NSArray or NSDictionary.

All objects are instances of NSString, NSNumber, NSArray, NSDictionary, or NSNull.

All dictionary keys are instances of NSString.

Numbers are not NaN or infinity.

回答3:

Swift 4: Worth Considering

JSONSerialization.jsonObject(with: data, options: []) as? [String:AnyObject]

instead of

JSONSerialization.data(withJSONObject: data, options: []) as? [String:AnyObject]

来源：https://stackoverflow.com/questions/34205813/invalid-top-level-type-in-json-write

标签

ios

objective-c

json

nsjsonserialization

gcdwebserver