Object reference not set to an instance of an object

Question

I keep getting this error when I run the program      Object reference not set to an instance of an object     Description  An unhandled exception occurred during the execution of the current web request     Please review the stack trace for more information about the error and where it originated in the code     Exception Details  System NullReferenceException  Object reference not set to an instance of an object    Source Error   Line with error   Line 156         if  strSearch          strSearch Trim   Length    0    What is the correct way it should be written

User · Answer

strSearch in this case is probably null  not simply empty    Try using   String IsNullOrEmpty strSearch    if you are just trying to determine if the string doesn t have any contents

User · Answer

I want to extend MattMitchell s answer by saying you can create an extension method for this functionality   public static IsEmptyOrWhitespace this string value        return String IsEmptyOrWhitespace value       This makes it possible to call   string strValue  if  strValue IsEmptyOrWhitespace            do stuff   To me this is a lot cleaner than calling the static String function  while still being NullReference safe

User · Answer

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    0 as 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

User · Answer

All versions of  Net   if  String IsNullOrEmpty strSearch     strSearch Trim   Length    0     Net 4 0 or later   if  String IsNullOrWhitespace strSearch

User · Answer

I know this was posted about a year ago  but this is for users for future reference   I came across similar issue  In my case  i will try to be brief  please do let me know if you would like more detail   i was trying to check if a string was empty or not  string is the subject of an email   It always returned the same error message no matter what i did  I knew i was doing it right but it still kept throwing the same error message  Then it dawned in me that  i was checking if the subject  string  of an email  instance object   what if the email instance  was already a null at the first place  How could i check for a subject of an email  if the email is already a null  i checked if the the email was empty  it worked fine    while checking for the subject string  i used IsNullorWhiteSpace    IsNullOrEmpty   methods   if  email    null              break        else               your code here

[c#] Object reference not set to an instance of an object.

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