The given key was not present in the dictionary? - json

Question

I having trouble deserializing this JSON.
The JSON looks like this:
{
"ticker": {
"high": 91.489,
"low": 88.3,
"avg": 89.8945,
"vol": 233637.9876,
"vol_cur": 2588.09448,
"last": 90.48,
"buy": 90.55,
"sell": 90.48,
"updated": 1372613806,
"server_time": 1372613807
}
}
And my function is this:
Private Function Btce(ByVal Address As String) As String
Dim rt As String = ""
Dim out As String
Dim wRequest As WebRequest
Dim wResponse As WebResponse
Dim SR As StreamReader
Dim Time As Date
Time = Now()
wRequest = WebRequest.Create(Address)
wResponse = wRequest.GetResponse
SR = New StreamReader(wResponse.GetResponseStream)
rt = SR.ReadToEnd
SR.Close()
Dim js As New System.Web.Script.Serialization.JavaScriptSerializer
Dim testObj = js.Deserialize(rt, New Object().GetType())
Dim high = testObj("High")
Dim low = testObj("Low")
Dim avg = testObj("Average")
Dim vol = testObj("Volume")
Dim last = testObj("Last")
Dim buy = testObj("Buy")
Dim sell = testObj("Sell")
out = "Data from btc-e.com" + Environment.NewLine
out += (Time) + Environment.NewLine
out += "High: " + Environment.NewLine
out += "Low: " + Environment.NewLine
out += "Average: " + Environment.NewLine
out += "Volume: " + Environment.NewLine
out += "Last: " + Environment.NewLine
out += "Buy: " + Environment.NewLine
out += "Sell: "
Return out
End Function
Then I get this in the console:
An unhandled exception of type 'System.Collections.Generic.KeyNotFoundException' occurred in Microsoft.VisualBasic.dll
Additional information: The given key was not present in the dictionary.

Answer 1

One of the problems is that you are looking for "Average" in testObj, but in the JSON it is "avg". And you are also looking for "Volume", not "vol".
In addition, the data returned by the deserialization is not a straight collection, it is a System.Collections.Dictionary(Of String, Object) where there is one entry for each of the representing the ticker objects in the json.
Each ticker object contains a String Key and a Value where Value is a System.Collections.Generic.KeyValuePair, which is case-sensitive. Value contains the collection of data (i.e. "high", 9.4189).
Based on this, your code should look like:
Dim js As New System.Web.Script.Serialization.JavaScriptSerializer
Dim cObjects = js.Deserialize(rt, New Object().GetType())
Dim counter As Integer
Dim out As New System.Text.StringBuilder(1000)
' Use a stringbuilder to capture the output; much more efficient than constant string concat
out.Append("Data from btc-e.com").AppendLine()
For Each testObj In cObjects
Dim high = testObj.Value("high")
Dim low = testObj.Value("low")
Dim avg = testObj.Value("avg")
Dim vol = testObj.Value("vol")
Dim last = testObj.Value("last")
Dim buy = testObj.Value("buy")
Dim sell = testObj.Value("sell")
' Since you will be processing multiple records, show something
' in the output about where you are
counter += 1
out.Append("Element ").Append(counter).AppendLine()
out.Append(DateTime.Now).AppendLine()
out.Append("High: ").Append(high).AppendLine()
out.Append("Low: ").Append(low).AppendLine()
out.Append("Average: ").Append(avg).AppendLine()
out.Append("Volume: ").Append(vol).AppendLine()
out.Append("Last: ").Append(last).AppendLine()
out.Append("Buy: ").Append(buy).AppendLine()
out.Append("Sell: ").Append(sell).AppendLine()
Next
Return out.ToString()

Answer 2

When deserializing to an object graph, you can just use DeserializeObject
The keys you are looking for are not present under the object you've just deserialized, but are in fact keys of the object under "ticker".
The default equality comparer used for dictionaries is probably case sensitive. You might want to construct a new dictionary while explicitly specifying StringComparer.***IgnoreCase, where *** is any of Ordinal, InvariantCulture or CurrentCulture.
For example:
Dim testObj = js.Deserialize(Of Dictionary(Of String, Dictionary(Of String, Single)))(rt)("ticker")
testObj = New Dictionary(Of String, Single)(testObj, StringComparer.InvariantCultureIgnoreCase)
Dim high = testObj("High")