Unable to deserialize a JSON array with Json.Net - json

Question

I have a JSON like this:
[
{
"areas": [
{
"area": "New York",
"isDay": true,
"temp": "14"
},
{
"area": "Washington DC",
"isDay": true,
"temp": "30"
},
{
"area": "Los Angles",
"isDay": false,
"temp": "54"
},
{
"area": "San Diego",
"isDay": true,
"temp": "59"
}
],
"status": true,
"code": 200,
"created_at": "2019/06/18 22:26:34.475",
"request_time": "2019/06/18 22:25:28.306"
}
]
I'm trying to get the value of the the area value on the first/second/third object under the Areas array.
I've tried this code to get the value of the first area of the array, which in this case is "New York".
'Note that 'rawJSON' is a string variable that contains the JSON.
Dim jResults As JObject = JObject.Parse(rawJSON)
Dim naming As String = jResults("areas")("name")
However when I run this, I get and exception:
Newtonsoft.Json.JsonReaderException: 'Error reading JObject from JsonReader. Current JsonReader item is not an object: StartArray. Path '', line 1, position 1.'
I am trying to write a function that imports all 'areas' in each array with their identifier of area (such as New York/Washington DC) into a ListBox (so the ListBox will contain, in order: New York, Washington DC, Los Angles).
How can I do this?

Answer 1

There are a couple of problems here:
Your JSON begins and ends with square brackets, so that means it is an array, not a single object. Since it is an array you need to use JArray.Parse() to parse it instead of JObject.Parse().
Inside your array, there is a single object which contains a property areas along with a few other properties like status and code. The value of the areas property is also an array, as denoted by square brackets. So your code needs to account for both of those arrays by adding the indexes. If you want the first item, that would be index zero.
There is no property called name anywhere in the JSON you posted. Instead, the names of the cities are each in a property called area.
Putting it all together, if you want to get the name New York from this JSON, you would do it like this:
Dim jResults As JArray = JArray.Parse(rawJSON)
Dim name As String = jResults(0)("areas")(0)("area")
Demo: https://dotnetfiddle.net/eAfEsx
If you're trying to get multiple names, then you would need a loop. You could do something like this:
Dim names As New List(Of String)()
For Each area As JObject In jResults(0)("areas")
Dim name As String = area("area")
names.Add(name)
Next
Demo: https://dotnetfiddle.net/BtSa6O

Answer 2

As you can see from the JSON structure you have posted, the JSON starts with a square bracket. That's the start of an array, the StartArray: when the JsonReader starts reading the JSON, the first TokenType is a JsonToken.StartArray (what the error is telling you).
Then there's an Object, defined by the braces: { }.
So you have an Array or List of Objects.
The first property of this object (areas) is of Type Array (or List).
It defines a collection of Objects.
Other properties, (status, code, etc.) have a single value.
[
{
"areas": [ { ... }, { ... } ]
"other": "other value"
}
]
You can parse the outer Array with JArray. The first element in the array (and the only one you're showing here), is the outer array. The first property of the first element in the outer array is the areas Array.
So you could write:
Dim areasArray = JArray.Parse(rawJson)(0)("areas")
Dim firstAreaValue = areasArray(0)("area").ToString()
The value of firstAreaValue is then "New York".
This is can be tiresome and prone to errors. You can generate a class Model from the JSON and use this model to deserialize the JSON to .Net classes, making it easier to handle, use as Source of Data, modify, serialize back etc.
Your JSON is an Array of Objects, so let's build the Root Object as a .Net class:
Note that I've set the Type of the CreatedAt and RequestTime properties to DateTime (Date): the string format of the DateTime, "2019/06/18 22:26:34.475", can be deserialized correctly.
DateTimeOffset is probably better. Your choice.
Public Class AreasRoot
<JsonProperty("areas")>
Public Property Areas As List(Of AreaObject)
<JsonProperty("status")>
Public Property Status As Boolean
<JsonProperty("code")>
Public Property Code As Long
<JsonProperty("created_at")>
Public Property CreatedAt As DateTime
<JsonProperty("request_time")>
Public Property RequestTime As DateTime
End Class
The Areas property is an Array or List of another type of object that contains 3 properties:
Public Class AreaObject
<JsonProperty("area")>
Public Property AreaArea As String
<JsonProperty("isDay")>
Public Property IsDay As Boolean
<JsonProperty("temp")>
Public Property Temp As Long
End Class
To deserialize using this Model, call JsonConvert.DeserializeObject(Of Type)(json).
The Type is, as mentioned, an Array or List(Of RootObject):
Dim areasArray = JsonConvert.DeserializeObject(Of List(Of AreasRoot))(rawJson).First()
Now New York is:
Dim firstArea = areasArray.Areas.First().Area
' Or
Dim firstArea = areasArray.Areas(0).Area
You can list all the Area names with:
For Each areaObj In areasArray.Areas
Console.WriteLine(areaObj.Area)
Next