如何在没有外部库的情况下解析包含对象列表的对象列表

Posted 2023-04-19

【中文标题】如何在没有外部库的情况下解析包含对象列表的对象列表

【英文标题】：How to parse list of objects with list of objects in it without external libraries

【发布时间】：2021-09-24 04:04:03

【问题描述】：

我在不使用外部库的情况下练习在 Kotlin 中解析 JSON 字符串，当我有一个包含对象列表的对象列表时问题就开始了。 这是我的 JSON

 
   "id":"1",
   "title":"Schedule",
   "weekly_activity":[
      
         "day":"Monday",
         "activity":[
            
               "start":"07:30",
               "end":"",
               "activity_name":"Breakfast"
            ,
            
               "start":"07:30",
               "end":"09:30",
               "activity_name":"Escursion"
            ,
            
               "start":"09:30",
               "end":"11:00",
               "activity_name":"Talk"
            ,
            
               "start":"11:30",
               "end":"15:00",
               "activity_name":"Walk"
            ,
            
               "start":"15:00",
               "end":"16:30",
               "activity_name":"Lunch"
            ,
            
               "start":"Dalle",
               "end":"17:30",
               "activity_name":"Break"
            
         ]
      ,
      
         "day":"Tuesday",
         "activity":[
            
               "start":"07:31",
               "end":"",
               "activity_name":"Breakfast in the forest"
            ,
            
               "start":"07:31",
               "end":"09:31",
               "activity_name":"Walk"
            ,
            
               "start":"09:31",
               "end":"11:01",
               "activity_name":"Escursion"
            ,
            
               "start":"11:31",
               "end":"15:01",
               "activity_name":"Break"
            ,
            
               "start":"15:01",
               "end":"16:31",
               "activity_name":"Lunch"
            ,
            
               "start":"Dalle",
               "end":"17:31",
               "activity_name":"Free time"
            
         ]
      
   ]

这是我解析 JSON 的函数：

 fun parseString (): Scheduler

        val listOfActivity: ArrayList<Activity> = arrayListOf()
        val listOfWeeklyActivity: ArrayList<WeeklyActivity> = arrayListOf()
        val jsonStringScheduler = JSONObject(parseString)


        val id = jsonStringScheduler.getString("id")
        val title = jsonStringScheduler.getString("title")
        val weeklyActivityList =jsonStringScheduler.getJSONArray("weekly_activity")
        weeklyActivityList.let 
            (0 until it.length()).forEach
                val weeklyActivity = weeklyActivityList.getJSONObject(it)
                val day = weeklyActivity.getString("day")
                val activityList = weeklyActivity.getJSONArray("activity")

                activityList.let 
                    (0 until it.length()).forEach
                        val activity = activityList.getJSONObject(it)
                        val start = activity.getString("start")
                        val end = activity.getString("end")
                        val activityName = activity.getString("activity_name")

                        listOfActivity.add(Activity(start, end, activityName))
                    
                
                listOfWeeklyActivity.add(WeeklyActivity(day,listOfActivity))
            
        
        val scheduler = Scheduler(id, title, listOfWeeklyActivity)
        return  scheduler
    

每次我尝试像这样解析时，我的“每周活动”对象都会列出这两个活动，但我需要像 JSON 一样拥有它。

【问题讨论】：

您应该为每个活动列表创建新列表。当您尝试解析第二个“每周活动”时，“listOfActicity”已经包含前一个活动。换句话说，它不是空的。

【参考方案1】：

您的问题是您只创建一次listOfActivity，并且您在每次迭代中都继续修改它。相反，您必须为每个weeklyActivity 创建一个新的listOfActivity。要解决这个问题，您需要将listOfActivity 的声明移动到weeklyActivityList 的循环中，如下所示

fun parseString(): Scheduler 
    // remove this line ---> val listOfActivity: ArrayList<Activity> = arrayListOf()
    ...
    jsonStringScheduler.getJSONArray("weekly_activity")
    weeklyActivityList.let 
        (0 until it.length()).forEach 
            // Create new list of activity for every week here
            val listOfActivity: ArrayList<Activity> = arrayListOf()

            activityList.let 
                (0 until it.length()).forEach 
                    ...
                    listOfActivity.add(Activity(start, end, activityName))
                
            
            // listOfActivity for this week is complete, now add it to listOfWeeklyActivity
            // And for next WeeklyActivity create new listOfActivity 
            listOfWeeklyActivity.add(WeeklyActivity(day, listOfActivity))
        
    
    val scheduler = Scheduler(id, title, listOfWeeklyActivity)
    return scheduler