General list <T> as IEnumerable <object>

Question

I am trying to make a List in IEnumerable, so I can verify that different lists are not null or empty:

Suppose myList is a List <T>. Then in the caller code I wanted:

       Validator.VerifyNotNullOrEmpty(myList as IEnumerable<object>,
                                     @"myList",
                                     @"ClassName.MethodName");

The validation code will be:

     public static void VerifyNotNullOrEmpty(IEnumerable<object> theIEnumerable,
                                        string theIEnumerableName,
                                        string theVerifyingPosition)
    {
        string errMsg = theVerifyingPosition + " " + theIEnumerableName;
        if (theIEnumerable == null)
        {
            errMsg +=  @" is null";
            Debug.Assert(false);
            throw new ApplicationException(errMsg);

        }
        else if (theIEnumerable.Count() == 0)
        {
            errMsg +=  @" is empty";
            Debug.Assert(false);
            throw new ApplicationException(errMsg);

        }
    }

However, this does not work. It compiles, but theIEnumerable is null! Why?

Answer 1

IEnumerable<object> IEnumerable<T>, List<T>. . 2575363 , ( Java, ). # 4.0, , .

, , , x as T, ((T)x), . 2139798. InvalidCastException . ( , (.. IEnumerable<object> List<T>), .)

, , IEnumerable<T> IEnumerable<object> .

 public static void VerifyNotNullOrEmpty<T>(IEnumerable<T> theIEnumerable,
                                            string theIEnumerableName,
                                            string theVerifyingPosition) { ... }

Answer 2

List IEnumerable, , , , :

 public static void VerifyNotNullOrEmpty<T>(this IEnumerable<T> theIEnumerable,
                                    string theIEnumerableName,
                                    string theVerifyingPosition)
{
    string errMsg = theVerifyingPosition + " " + theIEnumerableName;
    if (theIEnumerable == null)
    {
        errMsg +=  @" is null";
        Debug.Assert(false);
        throw new ApplicationException(errMsg);

    }
    else if (theIEnumerable.Count() == 0)
    {
        errMsg +=  @" is empty";
        Debug.Assert(false);
        throw new ApplicationException(errMsg);

    }
}

:

var myList = new List<string>
{
    "Test1",
    "Test2"
};

myList.VerifyNotNullOrEmpty("myList", "My position");

:

 public static void VerifyNotNullOrEmpty<T>(this IEnumerable<T> items,
                                    string name,
                                    string verifyingPosition)
{
    if (items== null)
    {
        Debug.Assert(false);
        throw new NullReferenceException(string.Format("{0} {1} is null.", verifyingPosition, name));
    }
    else if ( !items.Any() )
    {
        Debug.Assert(false);
        // you probably want to use a better (custom?) exception than this - EmptyEnumerableException or similar?
        throw new ApplicationException(string.Format("{0} {1} is empty.", verifyingPosition, name));

    }
}

Answer 3

, 3.0:

IEnumerable<object> :

var myEnumerable = myList.Cast<object>();

EDIT: , IEnumerable, :

public static void VerifyNotNullOrEmpty(IEnumerable theIEnumerable,
                                        string theIEnumerableName,
                                        string theVerifyingPosition)

, foreach theIEnumerable.Cast<object>().Count()

, IEnumerable<object>