This documentation is archived and is not being maintained.

FieldInfo.SetValue Method (Object, Object)

Sets the value of the field supported by the given object.

Namespace:  System.Reflection
Assembly:  mscorlib (in mscorlib.dll)

public void SetValue(
	Object obj,
	Object value


Type: System.Object
The object whose field value will be set.
Type: System.Object
The value to assign to the field.


_FieldInfo.SetValue(Object, Object)


The caller does not have permission to access this field.


The obj parameter is null and the field is an instance field.


The field does not exist on the object.


The value parameter cannot be converted and stored in the field.

This method will assign value to the field reflected by this instance on object obj. If the field is static, obj will be ignored. For non-static fields, obj should be an instance of a class that inherits or declares the field. The new value is passed as an Object. For example, if the field's type is Boolean, an instance of Object with the appropriate Boolean value is passed. Before setting the value, SetValue checks to see if the user has access permission. This final method is a convenience method for calling the following SetValue method.


Fully trusted code has the permissions that are needed to access and invoke private constructors, methods, fields, and properties using reflection.


Starting with the .NET Framework version 2.0 Service Pack 1, this method can be used to access non-public members if the caller has been granted ReflectionPermission with the ReflectionPermissionFlag.RestrictedMemberAccess flag and if the grant set of the non-public members is restricted to the caller’s grant set, or a subset thereof. (See Security Considerations for Reflection.)

To use this functionality, your application should target the .NET Framework version 3.5 or later.

The following example sets the value of a field, gets and displays the value, modifies the field, and displays the result.

using System;
using System.Reflection;
using System.Globalization;

public class Example
    private string myString;
    public Example()
        myString = "Old value";

    public string StringProperty
            return myString;

public class FieldInfo_SetValue
    public static void Main()
        Example myObject = new Example();
        Type myType = typeof(Example);
        FieldInfo myFieldInfo = myType.GetField("myString", 
            BindingFlags.NonPublic | BindingFlags.Instance); 

        // Display the string before applying SetValue to the field.
        Console.WriteLine( "\nThe field value of myString is \"{0}\".", 
        // Display the SetValue signature used to set the value of a field.
        Console.WriteLine( "Applying SetValue(Object, Object)."); 

        // Change the field value using the SetValue method. 
        myFieldInfo.SetValue(myObject, "New value"); 
        // Display the string after applying SetValue to the field.
        Console.WriteLine( "The field value of mystring is \"{0}\".", 

/* This code example produces the following output:

The field value of myString is "Old value".
Applying SetValue(Object, Object).
The field value of mystring is "New value".

.NET Framework

Supported in: 4, 3.5, 3.0, 2.0, 1.1, 1.0

.NET Framework Client Profile

Supported in: 4, 3.5 SP1

Portable Class Library

Supported in: Portable Class Library

Windows 7, Windows Vista SP1 or later, Windows XP SP3, Windows XP SP2 x64 Edition, Windows Server 2008 (Server Core not supported), Windows Server 2008 R2 (Server Core supported with SP1 or later), Windows Server 2003 SP2

The .NET Framework does not support all versions of every platform. For a list of the supported versions, see .NET Framework System Requirements.