How to parse unknown json data type in swift 2

Question

While fetching data from api I can get response either array of products or dictionary with error for e.g.

If everything went right api sends array of products as:

[
"Product1":
{
name = "someting",
price = 100,
discount = 10%,
images = [image1,image2]
},
"Product2":
{
name = "someting",
price = 100,
discount = 10%,
images = [image1,image2]
}
]

But if some error occur it sends dictionary with error message and code as:

{
error_message = "message"
error_code = 202
}

I am using this code to convert JSON data to array:

do {
   let jsonDict = try NSJSONSerialization.JSONObjectWithData(data!, options: NSJSONReadingOptions.MutableContainers)  as! NSArray{
                //Some code....
  } catch let error as NSError {
    print("JSON Error: \(error.localizedDescription)")    
 }

but if I get error as dictionary it crash.

Problems: 1. How to know whether received data is an array or dictionary ? 2. Some time even key or value can be missing so checking for value it becomes very lengthy code like:

if let productsArray = jsonObject as? NSArray{
    if let product1 = productsArray[0] as? NSDictionary{
        if let imagesArray = product1["image"] as? NSArray{
            if let imageUrl = imagesArray[0] as? String{
                //Code ....
            }
        }
    }
}

I read about guard keyword to reduce if condition but I don't have clear idea how to use here.

How are you getting the JSON? - are you able to see the http response status code? — Fred Faust
– Fred Faust, Commented Mar 6, 2016 at 20:03
@thefredelement Yes,I can get response error code it is send by my server specific to any product like trying to get unavailable product detail. — Sunil Sharma
– Sunil Sharma, Commented Mar 6, 2016 at 20:08
I would recommend downloading the SwiftyJSON library from Github, so you dont need to have 10 levels of nested if-let's — Oscar Apeland
– Oscar Apeland, Commented Mar 7, 2016 at 15:57

Sebastian P. · Accepted Answer · 2016-03-07 16:41:00Z

3

Problem 1: For try catch , add an if let for casting the object as NSDictionary or NSArray like :

 do {
    let jsonObject = try NSJSONSerialization.JSONObjectWithData(data!, options: NSJSONReadingOptions.MutableContainers) 
    if let jsonDict = jsonObject as? NSDictionary {
       // Do smthg.
    } 
    if let jsonArray = jsonObject as? NSArray {
      // Do smthg. 
    }
 }catch {
 //...
 }

For Problem 2: I think guard won't help you . It needs smthg like return / break in its else statement. If you don't want to throw your methods if one of your values isn't available you have to use this lengthy if let code style. Maybe in your case best practice would be setting up a Data Model for Product with optional properties.

Class product {
 var name:String?
 var image:[NSData]? // maybe UIImage or smthg.
 var price:Int?
 var discount:Int?

  init(jsonDic:NSDictionary){
// if it's not there it would be nil
  self.name = jsonDic["name"] as? String 
  self.image = jsonDic["image"] as? NSArray
  self.discount = jsonDic["discount"] as? Int
  self.price = jsonDic["price"] as? Int
  }
}

Now you can load those models with your data without the if let etc.. But if you wanna read those values you have to use the if let for checkin if its not nil. For init in your case it should be something like this: Add this into the if let statement of the do catch block ( ... as? NSArray // DO smthg. )

for item in jsonArray {
  guard let jsonDic = item as? NSDictionary else { return }
 // if you dont know every key you can just iterate through this dictionary
    for (_,value) in jsonDic {
      guard let jsonDicValues = value as? NSDictionary else { return }
      productArray.append(Product(jsonDic: jsonDicValues) 
    }
}

As i said , know you got the whole if let stuff when reading from the model an not when writing ( reading the json )

edited Mar 7, 2016 at 16:41

answered Mar 6, 2016 at 20:24

Sebastian P.

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5 Comments

Sunil Sharma Over a year ago

Ok, I got sol for problem1 by little modification like putting else before second if let that helps me to execute either dictionary or array part

Sebastian P. Over a year ago

Yeah , okay it's quite the same, bcz both can't get true ( not nil )

Sunil Sharma Over a year ago

It will helpful for me if u give e.g while storing data in Data model product because even by using data model I have to through checks

Sunil Sharma Over a year ago

I am not getting clear idea how use of Data model will decrease checks

Sebastian P. Over a year ago

It won't decrease it but it will give you a more readable structure . I'll try to give you a better example . but sorry I'll do this tomorrow

Fred Faust · Accepted Answer · 2016-03-06 20:18:21Z

You have a few things going on here, one, I would analyze your server's http response status code and only attempt to process data if you received a status code indicating you will have good data

// In practical scenarios, this may be a range
if statusCode != 200 {
// Handle a scenario where you don't have good data.
return
}

Secondly, I'd guard against the response, it looks like you have named it "data" like so:

guard let receivedData = data else {
return 
}

From this point on, you can use the receivedData constant.

Here'd I'd attempt to use NSJSONSeralization, like you do, but by casting it into a Swift dictionary, like so:

if let responseDictionary = try? NSJSONSerialization.JSONObjectWithData(data!, options: NSJSONReadingOptions.MutableContainers) as? [String:AnyObject] {

// Here you can try to access keys on the response
// You can try things like
let products = responseDictionary?["products"] as? [[String:AnyObject]]

 for product in products {

     let productName = product["name"] as? String

     if productName == nil {
     continue
     }

     let newProduct = Product(name: productName)
     // Do something with newly processed data

 } 

}

I tried to be general and also show you a guard example.

B25Dec · Accepted Answer · 2020-02-26 14:47:19Z

first of all I recommend using SwiftyJSON pod or the class straight into your Xcode, it works like a charm and you won't need to cast things down to figure whether you have a string or a dictionary or whatever. It is gold.

Once you've got your JSON, you can use this recursive function I created that does exactly what you need. It turns any Json into a dictionary. I mostly use it to save data into Firebase, without having to parse everything.

After you have imported SwiftyJSON into your project and added import SwiftyJSON to your Swift file you can:

    //JSON is created using the awesome SwiftyJSON pod
    func json2dic(_ j: JSON) -> [String:AnyObject] {
        var post = [String:AnyObject]()
        for (key, object) in j {
            post[key] = object.stringValue as AnyObject
            if object.stringValue == "" {
                post[key] = json2dic(object) as AnyObject
            }
        }
        return post
    }


    let json = JSON(value) // Value is the json structure you received from API.
    var myDictionary = [String:AnyObject]()
    myDictionary = json2dic(json)

Maulik Bhuptani · Accepted Answer · 2016-03-06 20:09:53Z

0

You can catch the class of your response. If your response is kind of class dictionary, assign it as dictionary else if your response is kind of class array, assign it to array. Good luck.

answered Mar 6, 2016 at 20:09

Maulik Bhuptani

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1 Comment

Sunil Sharma Over a year ago

I know how to do in Objective-C but I don't in swift

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