JSONSerialization Invalid type in JSON write (_SwiftValue)

Question

Why does the following code give me the error:

Invalid type in JSON write (_SwiftValue).

The error is thrown on this line:

urlRequest.httpBody = try JSONSerialization.data(withJSONObject: parameters)

Full code:

let parameters:Parameters = ["resource":[
        [
            "appUserCode":uuidString,
            "productNFCode": self.nfCode!,
            "status":code,
            "applicationKey":appDelegate.api_key
        ]
        ]
    ]
    do {

        urlRequest.httpBody = try JSONSerialization.data(withJSONObject: parameters)
    } catch {
        // No-op
    }

If I am getting it right, your `"status"` key contains `code` value which is of type `Enum`, then this error will occur. Change code to `code.rawValue`. — Vijay Kharage, Mar 03 '20 at 12:05

KrishnaCA · Accepted Answer · 2017-03-07T19:00:59.873

76

If your problem is still not resolved by the answer given here. I believe one of your objects inside the parameters might not be an instance of NSString, NSNumber, NSArray, NSDictionary, or NSNull. As given in the documentation for JSONSerialization class:

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.

Other rules may apply. Calling isValidJSONObject(_:) or attempting a conversion are the definitive ways to tell if a given object can be converted to JSON data.

So, please check if any of the objects in your parameters object doesn't satisfy the above constraints.

edited Mar 07 '17 at 19:00

answered Nov 05 '16 at 10:33

KrishnaCA

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Every key value is fine in my case still I am getting this error @KrishnaCA – Mansuu.... Dec 12 '17 at 08:02
@Mansuu.... please check if one if your strings are optional as given below – KrishnaCA Dec 12 '17 at 09:11
how do I convert my codable class object into a valid JSON object? – Nishad Arora Sep 08 '20 at 14:00

score 55 · Answer 2 · answered Sep 15 '16 at 23:19

55

I had this problem and it was because one of my strings was Optional. It was trying to serialize a value like: "Optional(\"string value\")"

Instead of "string value"

answered Sep 15 '16 at 23:19

ddiego

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1

Me too, just had to make my parameters String instead of String?. – Gagege Sep 22 '16 at 19:40
8

What do u do when you have to have a null value in your JSON? According to [http://www.json.org/](http://www.json.org/), a JSON can hold null values. – rudenudedude Oct 08 '16 at 06:54
Solved my problem too. I thought it was first NSNull() values with Swift 3 but it only came from an Optional string. – jfgrang Nov 08 '16 at 17:01
rudenudedude something like this works for me let params: [String: Any] = ["someValue": [ "someNestedValueKey": min ?? NSNull(), ] ] – Walter Martin Vargas-Pena Mar 06 '17 at 19:49

score 24 · Answer 3 · answered Jul 12 '17 at 04:21

24

Just in case anyone is still having problems and is using Enums, another cause may be if you are passing an Enum value and not it's rawValue.

Example:

enum Status: String {
  case open
  case closed
}

instead of passing the enum:

params = ["status": Status.open]

pass

params = ["status": Status.open.rawValue]

answered Jul 12 '17 at 04:21

gmogames

2,993
1
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40

3

Had exactly this! Thanks :) – jeff-h Jul 02 '19 at 09:47

score 17 · Answer 4 · answered May 02 '19 at 02:10

17

You can call this method too and see if your parameter can be converted to a JSON object, this will return a Bool.

let checker = JSONSerialization.isValidJSONObject(parameters)

answered May 02 '19 at 02:10

Waner A. Peña Sánchez

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9

score 7 · Answer 5 · answered May 20 '19 at 16:28

7

In my case I accidentally added an object to the Parameters dictionary instead of a string

answered May 20 '19 at 16:28

Dan Precup

95
1
4

Tamás Sengel · Answer 6 · 2018-02-20T13:54:23.860

3

If you're using SwiftyJSON to access a JSON object, it's important to use the dictionaryObject property of the JSON (instead of using dictionaryValue, dictionary or nothing at all), because you will get this error (or a variation of it) otherwise. For example:

guard let jsonDict = json.dictionaryObject else {
    return
}

let jsonData = try JSONSerialization.data(withJSONObject: jsonDict, options: [])

edited Feb 20 '18 at 13:54

answered Feb 20 '18 at 13:39

Tamás Sengel

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You sir, are a legend. Please know that. – linus_hologram Dec 07 '19 at 17:29

score 2 · Answer 7 · answered Apr 24 '19 at 10:13

2

I got this error when used a Set that is linked with Foundation NSSet.

let myArray = Array(mySet)

answered Apr 24 '19 at 10:13

yoAlex5

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score 1 · Answer 8 · answered Sep 18 '20 at 19:34

Had the same problem and error as you! FINALLY found the issue...

My code:

params = [
    "gender": request.gender.first ?? "",
    "age": 15
]

Problem: Even though request.gender.first ?? "" returns a string, its a type of String.Element, which ANY JSONEncoder or JSONSerialization cannot encode (and is not in the list of types it can handle, according to documentation).

Solution:

params = [
    "gender": request.gender.first?.description ?? "",
    "age": 15
]

Typically, just make sure its a string or an appropriate number the Encoders can handle...

score 0 · Answer 9 · edited Jan 27 '19 at 19:52

You should convert NSObject to NSDictionary at first

Try this to convert to NSDictionary.

#import <objc/runtime.h>

//Add this utility method in your class.
+ (NSDictionary *)dictionaryWithPropertiesOfObject:(id)obj {
    NSMutableDictionary *dict = [NSMutableDictionary dictionary];

    unsigned count;
    objc_property_t *properties = class_copyPropertyList([obj class], &count);

    for (int i = 0; i < count; i++) {
        NSString *key = [NSString stringWithUTF8String:property_getName(properties[i])];
        [dict setObject:[obj valueForKey:key] ? [obj valueForKey:key] : @"" forKey:key];
    }

    free(properties);

    return [NSDictionary dictionaryWithDictionary:dict];
}

Then call this:

NSData *jsonData = [NSJSONSerialization dataWithJSONObject:dic options:0 error:&err];
NSString *jsonString = [[NSString alloc] initWithData:jsonData encoding:NSUTF8StringEncoding];

score 0 · Answer 10 · answered Jun 05 '20 at 16:44

I was getting this runtime error because my dictionary was like this:

var dictionary: [AnyHashable: Any] = [:]
let elapsedTime = Date.timeIntervalSince(oldDate)
dictionary["elapsedTime"] = elapsedTime

Can you tell me what the problem is? _{^{hover your mouse on the box below to see answer!}}

elapsedTime's type is Function it's not TimeInterval. I needed to change Date. to Date(). ie use the instance method rather than the static method. When you're dictionary values are Any then this sort of issue doesn't get found until a runtime error where it can't serialize the dictionary to a JSON string...

JSONSerialization Invalid type in JSON write (_SwiftValue)

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