Question

I am writing some class and it wont compile without “using System.Linq”. But i don’t understand why its needed. What i am writing has nothing to do with Linq. How can i find out where a namespace is used?
And the very badly written piece of code (I am trying to figure out what i want it to do):

using System;
using System.Collections;
using System.Collections.Generic;
//using System.Linq;
using System.Text;

namespace DateFilename
{
  public class FailedFieldsList
  {
    private static List<FailedFields> ErrorList = new List<FailedFields>();
    public void AddErrorList(FailedFields errs)
    {
        ErrorList.Add(errs);
    }
    public void addSingleFailedField(string vField, string vMessage) 
    {
        //FailedFields
    }
    public List<FailedFields> GetErrorList()
    {
        return ErrorList;
    }
    public class FailedFields
    {
        public List<FailedField> ListOfFailedFieldsInOneRecord = new List<FailedField>();
        public class FailedField
        {
            public string fieldName;
            public string message;
            public FailedField(string vField, string vMessage)
            {
                this.fieldName = vField;
                this.message = vMessage;
            }
            public override string ToString()
            {
                return fieldName + ", " + message;
            }
        }
        public void addFailedField(FailedField f)
        {
            ListOfFailedFieldsInOneRecord.Add(f);
        }
        public int getFailedFieldsCount()
        {
            return ListOfFailedFieldsInOneRecord.Count();
        }
    }

  }
}

Error message produced when i dont include the linq namespace:
Error 4 Non-invocable member 'System.Collections.Generic.List<DateFilename.FailedFieldsList.FailedFields.FailedField>.Count' cannot be used like a method. D:\Slabo\My Documents\Visual Studio 2008\Projects\DateFilename\DateFilename\FailedFieldsList.cs 47 54 DateFilename

Thanks

Answer 1

The problem is in the last method:

public int getFailedFieldsCount() {
    return ListOfFailedFieldsInOneRecord.Count();
}

The method Count() is not a member of a List(T). The property Count, however, is. If you replace Count() by Count, this will compile without the need for using System.Linq.

By including System.Linq, you enable the extension method Count(), which, confusingly enough, does exactly the same thing.

See List(T) Members on msdn for a breakdown of what’s part of a List(T).