C# "as" keyword with objects of various types

How to correctly rewrite this code to be foolproof versus various types of input parameter? C开发者_高级运维urrently this code fails if, for instance, input parameter is a valid instance of DateTime. I've just figured that out - it was wrongly returning false for todays date.

    public override bool IsValid(object value)
    {
        string field = value as string;

        if (String.IsNullOrEmpty(field))
            return false;

        return true;
    }

Would be nice to know if this is possible without having multiple if statements (for every possible value type and even for some reference types, like the string).

EDIT: oh, of course, the requirement is for the object to not be null or whitespace (therefore it has to be castable or parsable to string, I guess).

Your use of as seems atypical and unnecessarily obscure. Given that you goal is to return false if the object is null or empty, use this code instead:

public override bool IsValid(object value)
{
    if (value == null || string.IsNullOrEmpty(value.ToString()))
        return false;

    return true;
}

If you are using .NET 4 and want to check for whitespace also and not just empty strings, the new string.IsNullOrWhiteSpace() would be worth looking at instead of string.IsNullOrEmpty().

why not using value.ToString()? [After null check]

public override bool IsValid(object value)
{
    if(value==null)
       return false;
    string field = value.Tostring();

    if (String.IsNullOrEmpty(field))
        return false;

    return true;
}

Any object can be converted to string, as it has a ToString method. Check if the reference is null, then turn it into a string and check the length:

public override bool IsValid(object value) {
  return value != null && value.ToString().Length > 0;
}