FieldInfo.SetValue Method (Object, Object)

July 28, 2014

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

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

public void SetValue(
	Object obj,
	Object value
)

Parameters

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

ExceptionCondition
FieldAccessException

The field is not accessible.

TargetException

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

ArgumentException

The field does not exist on the object.

-or-

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

MethodAccessException

The member is invoked late-bound through mechanisms such as Type.InvokeMember.

In Windows Phone apps, only accessible fields can be set using reflection.

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 nonstatic 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 is of type Boolean, the new value must be boxed as an instance of Object.

Version Notes

Windows Phone

 SetValue throws an ArgumentNullException exception instead of a TargetException exception when obj is null.

If you call the SetValue method on a field that is defined as both public and constant, a MemberAccessException exception is thrown instead of a FieldAccessException exception.

The following example gets the value of each field of the Example class, modifies the value by appending a string to it, and sets the new value. It then retrieves the new value and displays the result. If a field value cannot be retrieved because of the field's access level, the exception is caught and a message is displayed. The internal fields (Friend fields in Visual Basic) are accessible in this example because the Example and Test classes are in the same assembly.


using System;
using System.Reflection;

public class Test
{
    public static string SA = "A public shared field.";
    internal static string SB = "A friend shared field.";
    protected static string SC = "A protected shared field.";
    private static string SD = "A private shared field.";

    public string A = "A public instance field.";
    internal string B = "A friend instance field.";
    protected string C = "A protected instance field.";
    private string D = "A private instance field.";
}

public class Example
{
    public static void Demo(System.Windows.Controls.TextBlock outputBlock)
    {
        // Create an instance of Test, and get a Type object.
        Test myInstance = new Test();
        Type t = typeof(Test);

        // Get the shared fields of Test, and change their values. This does not 
        // require an instance of Test, so Nothing is passed to SetValue.
        FieldInfo[] sharedFields = t.GetFields(BindingFlags.Public | BindingFlags.NonPublic | 
                                               BindingFlags.Static);
        foreach( FieldInfo f in sharedFields )
        {
            try
            {
                // Append a marker to the old value.
                string newValue = f.GetValue(null) + " -modified-";

                f.SetValue(null, newValue);

                outputBlock.Text += String.Format("The value of Shared field {0} is: {1}\n", 
                                                  f.Name, 
                                                  f.GetValue(null));
            }
            catch
            {
                outputBlock.Text += 
                   String.Format("The value of Shared field {0} is not accessible.\n", f.Name);
            }
        }

        // Get the instance fields of Test, and change their values for the instance 
        // created earlier.
        FieldInfo[] instanceFields = t.GetFields(BindingFlags.Public | BindingFlags.NonPublic | 
                                                 BindingFlags.Instance);
        foreach( FieldInfo f in instanceFields )
        {
            try
            {
                // Append a marker to the old value.
                string newValue = f.GetValue(myInstance) + " -modified-";

                f.SetValue(myInstance, newValue);

                outputBlock.Text += String.Format("The value of instance field {0} is: {1}\n", 
                                                  f.Name, 
                                                  f.GetValue(myInstance));
            }
            catch
            {
                outputBlock.Text += 
                   String.Format("The value of instance field {0} is not accessible.\n", f.Name);
            }
        }
    }
}

/* This example produces the following output:

The value of Shared field SA is: A public shared field. -modified-
The value of Shared field SB is: A friend shared field. -modified-
The value of Shared field SC is not accessible.
The value of Shared field SD is not accessible.
The value of instance field A is: A public instance field. -modified-
The value of instance field B is: A friend instance field. -modified-
The value of instance field C is not accessible.
The value of instance field D is not accessible.
 */


Windows Phone OS

Supported in: 8.1, 8.0, 7.1, 7.0

Windows Phone

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