JSON to Array conversion

Question

I'm trying to convert a JSON string to an array. The JSON string is:

[
  {
    "field_value" : "28 Aug 2017",
    "field_data_type_combo_value" : "",
    "field_data_type_category_id" : "1",
    "form_id" : "19",
    "field_id" : "133",
    "message_unique_id" : "7941501245582800298",
    "field_data_type_combo_id" : "0",
    "field_data_type_id" : "1"
  },
  {
    "field_value" : "",
    "field_data_type_combo_value" : "",
    "field_data_type_category_id" : "9",
    "form_id" : "19",
    "field_id" : "134",
    "message_unique_id" : "7941501245582714588",
    "field_data_type_combo_id" : "0",
    "field_data_type_id" : "26"
  },
  {
    "field_value" : "hk",
    "field_data_type_combo_value" : "",
    "field_data_type_category_id" : "6",
    "form_id" : "19",
    "field_id" : "135",
    "message_unique_id" : "7941501245582699681",
    "field_data_type_combo_id" : "0",
    "field_data_type_id" : "17"
  }
]

and my conversion code is

if let data = text.data(using: .utf8) {
    do {
        return try JSONSerialization.jsonObject(with: data, options: .mutableContainers)  as? [String : AnyObject]
    } catch {
        print(error.localizedDescription)
    }
}

The conversion result is always nil. I also checked that JSON string in Online JSON Viewer and the string is correct. Please help me guys.

Why do you pass .mutableContainers but assign the result to an immutable constant? — vadian
– vadian, Commented Jul 29, 2017 at 8:04

gnasher729 · Accepted Answer · 2017-07-29 08:07:27Z

1

You explicitely write in your call:

as? [String: AnyObject]

In other words, you ask Swift to take whatever JSON returned, check that it is a dictionary with String keys, and either return that dictionary or nil. Since your data is an array and not a dictionary, it returns nil. Exactly what you asked for, but not what you wanted.

What you are expecting is an array of dictionaries, not a dictionary. You should also use Any instead of AnyObject. So convert it using

as? [[String: Any]]

The outer [] means it is an array, the inner [String: Any] means the items in the array must be dictionaries with String keys and Any values.

And why are you using .mutableContainers? If you have a good reason that you can explain then use it. If you don't and just copied the code from somewhere then remove it.

answered Jul 29, 2017 at 8:07

gnasher729

53k5 gold badges83 silver badges106 bronze badges

Sign up to request clarification or add additional context in comments.

Comments

luk2302 · Accepted Answer · 2017-07-28 20:23:25Z

1

That json isn't a dictionary on the top level but an array. You can see that from the [ ... ], it would be a dictionary if it was { ... }. Fix your code using the corresponding cast:

return try JSONSerialization.jsonObject(with: data, options: .mutableContainers)  as? [AnyObject]

answered Jul 28, 2017 at 20:23

luk2302

57.5k24 gold badges108 silver badges151 bronze badges

3 Comments

Test Test Over a year ago

thanks bro. working fine now.. why im getting value as Optional(value)

luk2302 Over a year ago

@TestTest because of the as?, try to wrap it in an if let ...

Test Test Over a year ago

good bro.. thanks for helping.. i used as? String. working fine now.

Collectives™ on Stack Overflow

JSON to Array conversion

2 Answers 2

Comments

3 Comments

Your Answer

Hot Network Questions

Collectives™ on Stack Overflow

2 Answers 2

Comments

3 Comments

Your Answer

Sign up or log in

Post as a guest

Related