What does Object reference not set to an instance of an object mean

Question

I am receiving this error and I m not sure what it means      Object reference not set to an instance of an object

User · Answer

Not to be blunt but it means exactly what it says  One of your object references is NULL  You ll see this when you try and access the property or method of a NULL d object

User · Answer

If I have the class   public class MyClass      public void MyMethod                  and I then do   MyClass myClass   null  myClass MyMethod      The second line throws this exception becuase I m calling a method on a reference type object that is null  I e  has not been  instantiated by calling myClass   new MyClass

User · Answer

Another easy way to get this    Person myPet   GetPersonFromDatabase        check for myPet    null    AND for myPet PetType    null  if   myPet PetType     cat     lt --- fall down go boom

User · Answer

what does this error mean  Object reference not set to an instance of an object    exactly what it says  you are trying to use a null object as if it was a properly referenced object

User · Answer

Most of the time  when you try to assing value into object  and if the value is null  then this kind of exception occur  Please check this link   for the sake of self learning  you can put some check condition  like  if  myObj   null  Console Write  myObj is NULL

User · Answer

Variables in  NET are either reference types or value types  Value types are primitives such as integers and booleans  or structures  and can be identified because they inherit from System ValueType   Boolean variables  when declared  have a default value   bool mybool    mybool    false   Reference types  when declared  do not have a default value   class ExampleClass      ExampleClass exampleClass       null   If you try to access a member of a class instance using a null reference then you get a System NullReferenceException  Which is the same as Object reference not set to an instance of an object   The following code is a simple way of reproducing this   static void Main string   args        var exampleClass   new ExampleClass        var returnedClass   exampleClass ExampleMethod        returnedClass AnotherExampleMethod      NullReferenceException here     class ExampleClass       public ReturnedClass ExampleMethod                 return null           class ReturnedClass       public void AnotherExampleMethod                   This is a very common error and can occur because of all kinds of reasons  The root cause really depends on the specific scenario that you ve encountered   If you are using an API or invoking methods that may return null then it s important to handle this gracefully  The main method above can be modified in such a way that the NullReferenceException should never be seen by a user   static void Main string   args        var exampleClass   new ExampleClass        var returnedClass   exampleClass ExampleMethod         if  returnedClass    null                  throw a meaningful exception or give some useful feedback to the user          return             returnedClass AnotherExampleMethod        All of the above really just hints of  NET Type Fundamentals  for further information I d recommend either picking up CLR via C  or reading this MSDN article by the same author - Jeffrey Richter  Also check out  much more complex  example of when you can encounter a NullReferenceException   Some teams using Resharper make use of JetBrains attributes to annotate code to highlight where nulls are  not  expected

User · Answer

It means you did something like this   Class myObject   GetObjectFromFunction      And without doing   if myObject  null   you go ahead do myObject Method

User · Answer

In a nutshell it means   You are trying to access an object without instantiating it   You might need to use the  new  keyword to instantiate it first i e create an instance of it   For eg   public class MyClass      public int Id  get  set      MyClass myClass   myClass Id   0   lt ----------- An error will be thrown here   because myClass is null here      You will have to use   myClass   new MyClass    myClass Id   0    Hope I made it clear

[.net] What does "Object reference not set to an instance of an object" mean?

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