Android Question JSON parsing crash when map is not present

[SCIS]

Hi,

I'm trying to parse a JSON from Facebook which contains information about different events, like parties or festivals. I started out with the code from the online JSON Parse Tool which helped a lot.
Most of the events have their information in the JSON like this (this is just a sample with the information changed for privacy reasons, the lay-out has stayed exactly the same):

{
  "events": {
    "data": [
      {
        "name": "Birthday Party",
        "place": {
          "name": "A Friend's House",
          "location": {
            "city": "Antwerp",
            "country": "Belgium",
            "latitude": 51.2605159,
            "longitude": 4.217295,
            "street": "streetname of my house",
            "zip": "2000"
          },
          "id": "012345678901234"
        },
       "id": "012345678901234"",
        "rsvp_status": "unsure"
      },
      {
        "name": "Brother's Wedding",
        "place": {
          "name": "A park",
          "location": {
            "city": "Antwerp",
            "country": "Belgium",
            "latitude": 51.2605159,
            "longitude": 4.217295,
            "street": "streetname of the park",
            "zip": "2000"
          },
          "id": "012345678901234"
        },
       "id": "012345678901234"",
        "rsvp_status": "attending"
      }
     ],
    },
    "id": "012345678901234"
}

Here is part of the B4A code which puts the JSON's information into a list:

Dim parser As JSONParser
parser.Initialize(File.ReadString(File.DirAssets, "file.json"))
Dim root As Map = parser.NextObject
Dim UserId As String = ""
If root.Get("id") <> Null Then UserId = root.Get("id")

Log("User Id: " & UserId)
Dim events As Map = root.Get("events")
Dim data As List = events.Get("data")
Dim i As Int = 0
For Each coldata As Map In data

Dim rsvp_status As String
If coldata.Get("rsvp_status") <> Null Then rsvp_status = coldata.Get("rsvp_status")
EventArray(i).EventStatus = rsvp_status
Log("Status: " & rsvp_status)

Dim name As String
If coldata.Get("name") <> Null Then name = coldata.Get("name")
EventArray(i).EventName = name
Log("Name: " & name)

Dim place As Map
If coldata.Get("place") <> Null Then place = coldata.Get("place")

Dim location As Map
If place.Get("location") <> Null Then location = place.Get("location")

Dim latitude As Double
If location.Get("latitude") <> Null Then latitude = location.Get("latitude")
EventArray(i).EventLocationlatitude = latitude
Log("Latitude: " & latitude)

Dim longitude As Double
If location.Get("longitude") <> Null Then longitude = location.Get("longitude")
EventArray(i).EventLocationLongitude = longitude
Log("Longitude: " & longitude)


i = i + 1
Next

This works fine. I used to do just

latitude = location.Get("latitude")

Sometimes events don't have a longitude - latitude included so I've found the way to solve this is by doing:

If location.Get("latitude") <> Null Then latitude = location.Get("latitude")

This solves the errors on most points where events don't have a specific location set but they do have a "location name" set by the organiser, it's just not an actual place recognised by Facebook so they don't include a place ID and no longitude, latitude or other information.

I've done this with all the elements of the JSON, so if for some reason an event wouldn't have a name it still should not give any problems.

Now, here comes the actual problem: There's some events that don't have any location at all, which looks like this in JSON:

 {
        "name": "event",
        "id": "012345678901234",
        "rsvp_status": "unsure"
  },

My program can handle a value not being present, but if a complete map is not there it crashes (I hope I understand the whole JSON naming a bit, and if not I hope you'll get what I mean)
I've tried using the same way as above, with If () <> Null, but that doesn't fix it.
I also read somewhere else to use .GetDefault("location","") but same as above.

Is there a way to have B4A also check if the map is present before trying to navigate to it? I think that would fix the problem I have. I've searched around but if this has been said somewhere, I don't seem to know the right search terms to find that thread

Thanks for taking the time to read my question, I hope to get answer from this great community soon!

 

[Erel]

You can use Map.ContainsKey to check whether a specific key exists.

 

[SCIS]

So in this case the it's not a "map" but a "key", that would be why I couldn't find any answers. Thanks a lot Erel!

 

[DonManfred]

So in this case the it's not a "map" but a "key"

it is a key in the map.

 

[SCIS]

it is a key in the map.

Oh, ok. I find it complicated to remember what is what, this is the first time I use JSON, so thanks! It seems to work now, for anyone interested I'll put the part of the code that's fixed it here

Dim place As Map
If coldata.ContainsKey("place") Then
    place = coldata.Get("place")
    Dim location As Map
    If place.ContainsKey("location") Then location = place.Get("location")
   
    If place.ContainsKey("id") Then EventArray(i).EventPlaceID = place.Get("id")
    Log("Place ID: " & EventArray(i).EventPlaceID)
   
    If place.ContainsKey("location") AND location.ContainsKey("latitude") Then EventArray(i).EventLocationlatitude = location.Get("latitude")
    Log("Latitude: " & EventArray(i).EventLocationlatitude)
   
    If place.ContainsKey("location") AND location.ContainsKey("longitude") Then EventArray(i).EventLocationLongitude = location.Get("longitude")
    Log("Longitude: " & EventArray(i).EventLocationLongitude)
End If

Thanks for the help!