UITableView Swift/JSON 的嵌套结构

Question

I need to display topic and description in a UITableView.

struct Topics: Decodable {

let subtopics: [subTopic]

    struct subTopic: Decodable {
     
      var topic = ""
      var description = ""

    }
}

The data for the TableView is fetched with a URL post request and assigned inside a do/try/catch block.

let Topics = Topics()

excerpt from URLRequest:

 self.Topics =  try JSONDecoder().decode(Topics.self, from: data)                  

 func tableView(_ tableView: UITableView, cellForRowAt indexPath: IndexPath) -> UITableViewCell {
        
        let cell = tableView.dequeueReusableCell(withIdentifier: "topicCell") as! topicCell

var subTopic = Topics?.subtopics[indexPath.row]

cell.topicLabel?.text = subTopic.topic
cell.descriptionTextView?.text = subTopic.description


return cell 
}


func tableView(_ tableView: UITableView, numberOfRowsInSection section: Int) -> Int {

  return Topics?.subtopics.count
}

Sample JSON:

{"subtopics":[{"topic":"Computer Science", "description":"beginner course"},{"topic":"Data Analysis", "description":"beginner course"}]}

Answer 1

You give the the variable the same name as the struct.

let Topics = Topics()

Don't do that. It is confusing and can cause unexpected behavior. There is a reason for the naming convention to name variables lowercase and structs/classes uppercase.

For less confusion name the top object different for example

struct Response: Decodable {
    
    let subtopics: [SubTopic]
    
    struct SubTopic: Decodable {
        
        let topic, description : String
        
    }
}

The default values (and var iables) in SubTopic make no sense.

My next recommendation is to omit the top object and declare the data source array

var subTopics = [Response.SubTopic]()

and assign

let response = try JSONDecoder().decode(Response.self, from: data)
self.subTopics = response.subtopics

This will clean up the table view code and gets rid of the ugly optionals

 func tableView(_ tableView: UITableView, cellForRowAt indexPath: IndexPath) -> UITableViewCell {
        
    let cell = tableView.dequeueReusableCell(withIdentifier: "topicCell") as! topicCell

    let subTopic = subTopics[indexPath.row]
    cell.topicLabel?.text = subTopic.topic
    cell.descriptionTextView?.text = subTopic.description

    return cell 
}


func tableView(_ tableView: UITableView, numberOfRowsInSection section: Int) -> Int {
    return subTopics.count
}