Question

I am new to Windows phone.

I’m storing four values in Dictionary<string, object>. Once I completed when I check the entries it is showing 7 entries where three are null Keys and values.

code:

   Dictionary<string, string> obj = new Dictionary<string, string>();
    private void button1_Click(object sender, RoutedEventArgs e)
    {
        obj.Add("K2", "V2");
        obj.Add("K3", "V3");
        obj.Add("K4", "V4");
        obj.Add("K5", "V5");
    }

Any help?

code where i used up dictionary:

  private void GetLoginCallback(IAsyncResult asynchronousResult)
        {
            try
            {
                Dictionary<string,object> Parameters = new Dictionary<string,object>();

                /**httprequest for making asynchronous call**/
                HttpWebRequest httpRequest = (HttpWebRequest)asynchronousResult.AsyncState;
                /**response from the httprequest**/
                HttpWebResponse httpresponse = (HttpWebResponse)httpRequest.EndGetResponse(asynchronousResult);
                /**Reading the response as stream**/
                Stream streamResponse = httpresponse.GetResponseStream();
                using(StreamReader streamRead = new StreamReader(streamResponse))
                {
                    var response = streamRead.ReadToEnd();
                    //Deployment.Current.Dispatcher.BeginInvoke(new Action(() =>
                    //{
                    if (response != null && httpresponse.StatusCode == HttpStatusCode.OK)
                    {
                        WebHeaderCollection headers = httpresponse.Headers;
                        /**getting Session_ID **/
                        string session_cookie = headers[DisplayMessage.Set_Cookie];
                        string sessionCookie = headers[DisplayMessage.Set_Cookie];
                        string[] values = sessionCookie.Split(DisplayMessage.Split_SemiCollen);
                        string[] jID = values[0].Split(DisplayMessage.Split_EqualTo);
                        jsessionId = jID[1];

                        /**storing Authentication parameters in dictionary**/
                            Parameters.Add("Username", "test4");
                            Parameters.Add("Password", "*****");
                            Parameters.Add("JSessionID", "FGBfdhhfuhuhhbh_Path");
                            Parameters.Add("SessionCookie","FGBfdhhfuhuhhbh_Path;dpk");


                        //}));
                    };
                }
            }
            catch(Exception ex)
            {

            }
        }

Answer 1

If you mean that in the debugger, the dictionary is showing with 4 items that are what you are expecting and 3 items that are empty, that’s because that’s how the data is stored internally. Dictionary is implemented as a hash table. And there are two reasons why it’s a good idea to have empty items in a hash table:

1. With hash tables, there is always the possibility of a collision (two keys that map to the same “bucket”). If you keep a fraction of the hash table empty, there will be only a small amount of collisions, on average (assuming a good hash function for the given items).

2. With collections that grow one item at a time, it’s better to allocate more memory than you need right now, so you don’t have to copy the whole collection every time you add a new item. Other collections behave this way too, for example List<T>.

But you don’t have to actually worry about this, because when you access the dictionary from your code, you won’t see those empty items.