Swift JSON values

This is one of the worst codes I've ever seen. Almost everything is wrong or a very bad programming habit.

The biggest mistakes are:

• No error handling at all.
• The usage of Foundation (NSArray / NSDictionary) rather than native collection types.
• The usage of multiple string arrays rather than one custom struct / class as data model.
• The forced unwrapping of the values rather than handling the optionals safely.
• The usage of valueForKey rather than dedicated objectForKey or key subscription.

First of all create a struct as data model and one array as data source

struct Schedule {
    let id, subject, course, lecturer, cTime, venue, tDate : String
}

var schedules = [Schedule]()

Assuming all values won't be changed the struct members are declared as constants (let). You get the memberwise initializer for free.

Reading JSON is very easy. There are only two collection types, array ([]) and dictionary ({}).

This JSON is an array of dictionaries ([{ .. }, { ...}]) . All keys and values are strings. The appropriate (native) Swift type is [[String:String]]. The code parses the JSON and assigns an empty string in case one of the keys does not exist.

func downloadJson(with urlString : String) {
    guard let url = URL(string: urlString) else { print("bad URL"); return }
    let task = URLSession.shared.dataTask(with: url) { (data, response, error) in
        if let connectionError = error {
            print(connectionError)
            return
        }
        do {
            if let scheduleArray = try JSONSerialization.jsonObject(with: data!) as? [[String:String]] {
                for item in scheduleArray {
                    self.schedules.append(Schedule(id: item["ID"] ?? "",
                                      subject: item["Subject"] ?? "",
                                      course: item["Course"] ?? "",
                                      lecturer: item["Lecturer"] ?? "",
                                      cTime: item["CTime"] ?? "",
                                      venue: item["Venue"] ?? "",
                                      tDate: item["TDate"] ?? ""))                
                }

                DispatchQueue.main.async {
                    self.tableView.reloadData()
                }
            }
        } catch {
            print(error)
        }
    }
    task.resume()
}

In the table view in cellForRow you can simply write

 let schedule = schedules[indexPath.row]
 aLabel.text = schedule.id
 anotherLabel.text = schedule.subject
 ...

First ignore the JSON contents, and instead, think of it as an array of objects called as course.

[
    {
        "ID": "",
        "Subject": "",
        "Course": "",
        "Lecturer": "",
        "CTime": "",
        "Venue": "",
        "TDate": ""
    },

    ...
]

So first you need to parse your JSON as an array. Let's call it as coursesArray.

if let coursesArray = try? JSONSerialization.jsonObject(with: data!, options: .allowFragments) as? NSArray
{
    for course in CoursesArray
    {
        // course is a json object. So get it into a dictionary so that
        // we can access the values in the course.

        if let courseDict = course as? NSDictionary
        {
            // Now we can print the remaining properties of the course
            let id = courseDict.value(forKey: "ID")
            let subject = courseDict.value(forKey: "Subject")
            let courseName = courseDict.value(forKey: "Course")
            let lecturer = courseDict.value(forKey: "Lecturer")
            let cTime = courseDict.value(forKey: "CTime")
            let venue = courseDict.value(forKey: "Venue")
            let tDate = courseDict.value(forKey: "TDate")

            // Print them, or use them in any way you like now.
        }
    }
}

That should do about the extraction of the data. To be able to use these, you'll need to append them to other arrays, and reload the table. I'm leaving it to you.

Hope this helps.

Try using following code , take json object as [[String:Any]] and loop through all the present dictionaries in It to get all values you require

//Two arrays to store your data and use it as result

    var IDs = [String]()
    var Subjects = [String]()


//Your function

func downloadJsonWithURL() {

        let url = URL(string: urlString)

        URLSession.shared.dataTask(with: (url as? URL)!, completionHandler: {(data, response, error) -> Void in

        if let jsonObj = try? JSONSerialization.jsonObject(with: data!, options: .allowFragments) as?  [[String:Any]] {
            print(jsonObj)

//Loop through all the keys present in the dictionaries inside 
               for key in jsonObj{

//Need to provide required key to check and loop in it  
                let ID = key["ID"]
                let Subject = key["Subject"]

//Append values in Arrays declared above 
                self.IDs.append(ID as! String)

            self.Subjects.append(Subject as! String)


        }


            OperationQueue.main.addOperation({
                self.tableView.reloadData()
            })
        }
    }).resume()
}

In the tutorial the author's data format is dictionary of arrays and each array is of type dictionary so, in the code first author converted json data into NSDictionary then accessed array with actor keyword.

But all this steps are not necessary in your case, because your data is directly in an array of dictionaries. So first convert your data as NSArray and then convert each record of it as NSDictionary as shown in below code snippet.

func downloadJsonWithURL() {
     let url = URL(string: urlString)

    URLSession.shared.dataTask(with: (url as? URL)!, completionHandler: {(data, response, error) -> Void in

    if let jsonObj = try? JSONSerialization.jsonObject(with: data!, options: .allowFragments) as?  [[String:String]] {
        print(jsonObj)

                for student in jsonObj{
                    if let studentDict = student as? [String:String] {
                        if let id = studentDict["ID"] ?? "" {
                            self.idArray.append(id)
                        }
                        if let subject = actorDict["Subject"] ?? "" {
                            self.subArray.append(subject)
                        }
                    }
                }
            OperationQueue.main.addOperation({
                self.tableView.reloadData()
            })
        }
    }).resume()
}