Set value of private field

Question

Why is the following code not working:

class Program {     static void Main ( string[ ] args )     {         SomeClass s = new SomeClass( );          s.GetType( ).GetField( "id" , System.Reflection.BindingFlags.NonPublic ) // sorry reasently updated to GetField from GetProperty...             .SetValue( s , "new value" );     } }   class SomeClass {     object id;      public object Id      {         get         {             return id;         }     }    } 

I am trying to set the value of a private field.

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Here is the exeption I get:

 System.NullReferenceException was unhandled   Message=Object reference not set to an instance of an object.   Source=ConsoleApplication7  StackTrace:         at Program.Main(String[] args) in C:\Users\Antonio\Desktop\ConsoleApplication7\ConsoleApplication7\Program.cs:line 18         at System.AppDomain._nExecuteAssembly(RuntimeAssembly assembly, String[] args)         at System.AppDomain.ExecuteAssembly(String assemblyFile, Evidence assemblySecurity, String[] args)         at Microsoft.VisualStudio.HostingProcess.HostProc.RunUsersAssembly()         at System.Threading.ThreadHelper.ThreadStart_Context(Object state)         at System.Threading.ExecutionContext.Run(ExecutionContext executionContext, ContextCallback callback, Object state, Boolean ignoreSyncCtx)         at System.Threading.ExecutionContext.Run(ExecutionContext executionContext, ContextCallback callback, Object state)         at System.Threading.ThreadHelper.ThreadStart()   InnerException: 

Answer 1

Try this (inspired by Find a private field with Reflection?):

var prop = s.GetType().GetField("id", System.Reflection.BindingFlags.NonPublic     | System.Reflection.BindingFlags.Instance); prop.SetValue(s, "new value"); 

My changes were to use the GetField method - you are accessing a field and not a property, and to or NonPublic with Instance.

Answer 2

Evidently, adding BindingFlags.Instance seems to have solved it:

> class SomeClass   {       object id;        public object Id       {           get           {               return id;           }       }   } > var t = typeof(SomeClass)       ; > t [Submission#1+SomeClass] > t.GetField("id") null > t.GetField("id", System.Reflection.BindingFlags.NonPublic | System.Reflection.BindingFlags.Instance); > t.GetField("id", System.Reflection.BindingFlags.NonPublic | System.Reflection.BindingFlags.Instance) [System.Object id] >