c# String.IsNullOrWhiteSpace(strSearch) 공백문자, Null 확인하기

C#에서 문자열이, 공백문자(White Space)나 Null인지 확인하는 함수

if (String.IsNullOrWhiteSpace(strSearch))

참고로 해당 함수는 .NET 4.0에서 지원.

The correct way in .NET 4.0 is:

if (String.IsNullOrWhiteSpace(strSearch))

The String.IsNullOrWhiteSpace method used above is equivalent to:

if (strSearch == null || strSearch == String.Empty || strSearch.Trim().Length == 0) 
// String.Empty is the same as ""

Reference for IsNullOrWhiteSpace method

http://msdn.microsoft.com/en-us/library/system.string.isnullorwhitespace.aspx

Indicates whether a specified string is Nothing, empty, or consists only of white-space characters.

In earlier versions, you could do something like this:

if (String.IsNullOrEmpty(strSearch) || strSearch.Trim().Length == 0)

The String.IsNullOrEmpty method used above is equivalent to:

if (strSearch == null || strSearch == String.Empty)

Which means you still need to check for your "IsWhiteSpace" case with the .Trim().Length == 0as per the example.

Reference for IsNullOrEmpty method

http://msdn.microsoft.com/en-us/library/system.string.isnullorempty.aspx

Indicates whether the specified string is Nothing or an Empty string.

Explanation:

You need to ensure strSearch (or any variable for that matter) is not null before you dereference it using the dot character (.) - i.e. before you do strSearch.SomeMethod() or strSearch.SomeProperty you need to check that strSearch != null.

In your example you want to make sure your string has a value, which means you want to ensure the string:

• Is not null
• Is not the empty string (String.Empty / "")
• Is not just whitespace

In the cases above, you must put the "Is it null?" case first, so it doesn't go on to check the other cases (and error) when the string is null.

참고: https://stackoverflow.com/questions/8206810/object-reference-not-set-to-an-instance-of-an-object