Question

My Code goes like this:

    using (StreamReader streamReader1 = new StreamReader(response.GetResponseStream()))
    {
        string resultString = streamReader1.ReadToEnd();
        var ser = new DataContractJsonSerializer(typeof(RootObject));

        var stream = new MemoryStream(Encoding.Unicode.GetBytes(resultString));
        DataContractJsonSerializer jsonSerializer = new DataContractJsonSerializer(typeof(RootObject));
        RootObject myBook = (RootObject)jsonSerializer.ReadObject(stream);

        Deployment.Current.Dispatcher.BeginInvoke(() => Shops.ItemsSource = myBook.SearchResponse.Spell.Results); }

  public class Query
    {
        public string SearchTerms { get; set; }
    }


    public class Result
    {   [DataMember(IsRequired=false)]
        public string Value { get; set; }
    }

    public class Spell
    {
        [DataMember(IsRequired = false)]
        public int Total { get; set; }
        [DataMember(IsRequired = false)]
        public List<Result> Results { get; set; }
    }

    public class SearchResponse
    {
        public bool IsRequired { get; set; }
        public string Version { get; set; }
        public Query Query { get; set; }
        public Spell Spell { get; set; }
    }

    public class RootObject
    {
        public SearchResponse SearchResponse { get; set; }
    }

IF JSON DATA EXISTS

  {"SearchResponse":{"Version":"2.0","Query":{"SearchTerms":"mispell"},"Spell":{"Total":1,"Results":[{"Value":"misspell"}]}}}

IF JSON DATA DOES NOT EXIST

  {"SearchResponse":{"Version":"2.0","Query":{"SearchTerms":"mispel"}}}

The thing is, if Bing doesn’t detect a wrong word, it crashes and gives me an error like NullReferenceException. I have tried to do an IF statement looking at the stream for if it’s value is blank but doesn’t seem to work.

Any ideas?

Answer 1

If you receive a JSON answer without the Spell part, the Spell property in SearchResponse will be null. If it’s null, you may not dereference it like this:

myBook.SearchResponse.Spell.Results

(This hasn’t anything to do with JSON. It’s how C# works.)

So instead of:

Shops.ItemsSource = myBook.SearchResponse.Spell.Results

you probably want to write:

if (myBook.SearchResponse.Spell = null)
    Shops.ItemsSource = myBook.SearchResponse.Spell.Results;
else
    Shops.ItemsSource = new List<Result>();

For your next question: It would be very helpful if your questions would show the exact error message including the stack trace (or at least the exact line where it occurred).