unable to add choices to SPFieldChoice programatically

Question

I am not able to add a new choice value to a SPFieldChoice column of a list. Here is my code

        using (SPWeb myWeb = SPContext.Current.Web)
        {
            myWeb.AllowUnsafeUpdates = true;
            SPList myList = myWeb.Lists["DemoList"]; //Gets a list named "MyList"

            //Gets the field named "ChoiceField". Since ChoiceField is an SPFieldChoice I can cast it as
            // such. SPFieldChoice also inherits SPField.
            SPFieldChoice dropDown = (SPFieldChoice)myList.Fields["My Choice"];

            //Add some values
            dropDown.Choices.Add(txtNewChoice.Text);

            dropDown.Update(); //Need to update the column for the changes to take affect

            myList.Update();

            myWeb.Update();
            myWeb.AllowUnsafeUpdates = false;

            foreach (var item in dropDown.Choices)
            {
                result.Text += item.ToString();
            }
        }

Please let me know if I missed any point. NOTE I am using a sandboxed solution to deploy the web part

Answer 1

This thread might be a little stale but this could help someone else. Here is what I'm doing:

public static SPFieldChoice Create_Choice(SPFieldCollection spFieldCollection, string staticName, string displayName, string description, string[] choices, bool allowFillInChoices, bool required)
{
  //Declarations
  SPFieldChoice spFieldChoice;
  string fieldSchema;
  string choiceElements = string.Empty;
  int choiceIndexOfStart;
  int choiceIndexOfEnd;

  //Create field.
  if (spFieldCollection.TryGetFieldByStaticName(staticName) == null)
  { spFieldCollection.Add(spFieldCollection.CreateNewField(SPFieldType.Choice.ToString(), staticName));        
  }
  spFieldChoice = (SPFieldChoice)spFieldCollection.TryGetFieldByStaticName(staticName);
  spFieldChoice.Title = displayName;
  spFieldChoice.StaticName = staticName;
  spFieldChoice.Description = description;
  spFieldChoice.Required = required;
  spFieldChoice.FillInChoice = allowFillInChoices;
  spFieldChoice.Update();

  //Add choices. 
  //--------------
  //Note: There is a bug in the SP object model when adding choices through a Sandbox solution. The logical way of
  //adding choices does not work. Below is a workaround which adds choices through the SchemaXml directly. The Update() method
  //is not called after making these changes.
  //See the following for more information: http://sharepoint.stackexchange.com/questions/29519/add-choice-to-spfieldchoice-from-an-eventreceiver-in-sandboxed
  //--------------

  //Build choice xml element.
  foreach (string choice in choices)
  { choiceElements += "<CHOICE>" + choice + "</CHOICE>";
  }

  //Update field schema.
  fieldSchema = spFieldChoice.SchemaXml;
  choiceIndexOfStart = fieldSchema.IndexOf("<CHOICES>");
  if (choiceIndexOfStart >= 0)
  { choiceIndexOfEnd = fieldSchema.IndexOf("</CHOICES>");
    fieldSchema = fieldSchema.Remove(choiceIndexOfStart, choiceIndexOfEnd - choiceIndexOfStart); 
    fieldSchema = fieldSchema.Replace("</CHOICES>", "<CHOICES>" + choiceElements + "</CHOICES>"); 
  }
  else
  { fieldSchema = fieldSchema.Replace("<CHOICES/>", "<CHOICES>" + choiceElements + "</CHOICES>"); 
  }

  spFieldChoice.SchemaXml = fieldSchema;

  return spFieldChoice;
}

Answer 2

the following post: http://mastervanou.wordpress.com/2009/05/14/return-values-of-an-spfieldchoice-object/ described how you should programmatically add choices.