How add items to a list in foreach loop using c#

Question

I am using following snippet to some items to a list of strings. But it is throwing an exception.

List<string> guids = null;
QueryExpression qExp = new QueryExpression
{
    EntityName = "account",
    ColumnSet = col1,
    Criteria = new FilterExpression
    {
        Conditions = { 
            new ConditionExpression("statecode",ConditionOperator.Equal,0)
        }
    }
};
sp.CallerId = g1;
EntityCollection ec1 = sp.RetrieveMultiple(qExp);
foreach (Entity item in ec1.Entities)
{
   guids.Add(Convert.ToString(item.Attributes["accountid"]));
}

Exception: Object reference not set to an instance of an object

Possible duplicate of [What is a NullReferenceException and how do I fix it?](http://stackoverflow.com/questions/4660142/what-is-a-nullreferenceexception-and-how-do-i-fix-it) — Ron Beyer, Dec 10 '15 at 14:46

score 2 · Answer 1 · answered Dec 10 '15 at 14:41

2

Change List<string> guids = null; to List<string> guids = new List<string>(); and all will be well.

You must initialise the list before you can start writing to it. You are setting it to null, thus the exception.

answered Dec 10 '15 at 14:41

David Arno

40,354
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score 2 · Accepted Answer · answered Dec 10 '15 at 15:03

2

Why not use LINQ:

List<string> guids = ec1.Entities
   .Select(entity => Convert.ToString(entity.Attributes["accountid"]))
   .ToList();

answered Dec 10 '15 at 15:03

Magnus

1,022
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Can be done even shorter: `List guids = ec1.Entities.Select(e => e.Id.ToString()).ToList();` – Henk van Boeijen Dec 10 '15 at 22:33
Yes, they are. "accountid" is the primary key field of entity account. The entity rows returned by RetrieveMultiple always contain the primary key, which is held by the Id property. – Henk van Boeijen Dec 11 '15 at 17:38
That's probably why I don't work with Dynamics CRM... B-) – Magnus Dec 14 '15 at 13:53
It's actually a fine piece of software. Microsoft did a good job here. There are always things to improve, but that also applies to my own work. – Henk van Boeijen Dec 14 '15 at 14:36

score 1 · Answer 3 · answered Dec 10 '15 at 14:41

1

You cannot use List<string> guids = null;

Try to do List<string> guids = new List<string>();

answered Dec 10 '15 at 14:41

CBreeze

2,629
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How add items to a list in foreach loop using c#

3 Answers3

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