Parsing Json using Vb.net Json.NET - json

Question

Hey all I am getting the following error at random spots in my code:
Object reference not set to an instance of an object.
I know why I am getting it. It does not find the correct property that I have it looking for and therefore it gives the error. Some may have that property and some, as this error shows, may not.
What can I do in order to check first to make sure it has that property? Currently I just have a Try/catch method in place so it can keep going if it does find something that's not there.
For Each Row In json("data")
Try
thePostID = DirectCast(Row("id").ToString(), String)
thePostType = DirectCast(Row("type").ToString(), String)
thePosterID = DirectCast(Row("from")("id").ToString(), String)
thePosterName = DirectCast(Row("from")("name").ToString(), String)
Catch ex As NullReferenceException
msgbox("Did not find that particular property!")
End Try
Next
update
{
"data": [
{
"id": "102zzz533zz_10z52zz9zzzz94z3",
"from": {
"id": "102zzzzz95zzz7",
"name": "Jim zzzzz"
},
"likes": {
"data": [
{
"id": "85zzzzz35zzzz0",
"name": "Anna zzzzz"
},
{
"id": "10zzzz93z31zzzzz",
"name": "Vanessa zzzz zzzz"
},
{
"id": "1zzz44zzz48731z6",
"name": "Leta zzzzzz"
}
],
"paging": {
"cursors": {
"after": "MTAyMdfasdfwrtMTkyNg=",
"before": "ODUasdfasrU5Mwerw"
}
}
}
etc...
This JSON above follows in the same data path as all the others.
Using #Andrews code below:
thePostLikes = NullSafeSelect(Row, "likes.data.id")
If thePostLikes <> "NA" Then
For Each Row2 In json("likes")("data")
thePostLikesID += NullSafeSelect(Row2, "id") & ","
thePostLikesName += NullSafeSelect(Row2, "name") & ","
Next
End If
The value of thePostLikes is always Nothing

Answer 1

There may be a more graceful way to do this that's built in to JSON.NET, but here's a helper function that will just return Nothing if the path you supply doesn't exist:
Function NullSafeSelect(ByVal obj As JToken, ByVal path As String) As String
Dim result As String = Nothing
Dim value As JToken = obj.SelectToken(path, False)
if (value IsNot Nothing)
result = value.ToString()
End If
Return value
End Function
You would call it from your loop like this:
For Each row in json("data")
Dim thePostID As String = NullSafeSelect(row, "id")
Dim thePostType As String = NullSafeSelect(row, "type")
Dim thePosterId As String = NullSafeSelect(row, "from.id")
' ... etc
Next
Note that you do not need the DirectCast because the return type of the function is already String.