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FieldInfo.IsInitOnly Property

Gets a value indicating whether the field can only be set in the body of the constructor.

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

public bool IsInitOnly { get; }

Property Value

Type: System.Boolean
true if the field has the InitOnly attribute set; otherwise, false.

If the returned value is true, the field can only be initialized, and is read-only thereafter.

To get the IsInitOnly property, first get the class Type. From the Type, get the FieldInfo. From the FieldInfo, get the IsInitOnly property. To access a non-public field, combine BindingFlags.NonPublic with either or both of BindingFlags.Static and BindingFlags.Instance in the GetField method.

The IsInitOnly property is set when the FieldAttributes.InitOnly attribute is set.

In the following example, two fields are created. The second field is read-only, having no set accessor, and IsInitOnly is set to true.


using System;
using System.Reflection;

 //Make two fields, one public and one read-only. 
public class Myfielda
{
    public string field = "A - public modifiable field";
}
public class Myfieldb
{
    public readonly string field = "B - readonly field";
}

public class Myfieldinfo
{
    public static int Main()
    {
        Console.WriteLine("\nReflection.FieldInfo");
        Myfielda Myfielda = new Myfielda();
        Myfieldb Myfieldb = new Myfieldb();

        //Get the Type and FieldInfo.
        Type MyTypea = typeof(Myfielda);
        FieldInfo Myfieldinfoa = MyTypea.GetField("field",
            BindingFlags.Public | BindingFlags.Instance);
        Type MyTypeb = typeof(Myfieldb);
        FieldInfo Myfieldinfob = MyTypeb.GetField("field",
            BindingFlags.Public | BindingFlags.Instance);

        //Modify the fields. 
        //Note that Myfieldb is not modified, as it is 
        //read-only (IsInitOnly is True).
        Myfielda.field = "A - modified";
        //Myfieldb.field = "B - modified";

        //For the first field, get and display the name, field, and IsInitOnly state.
        Console.Write("\n{0} - {1}, IsInitOnly = {2} ",
            MyTypea.FullName,
            Myfieldinfoa.GetValue(Myfielda),
            Myfieldinfoa.IsInitOnly);

        //For the second field get and display the name, field, and IsInitOnly state.
        Console.Write("\n{0} - {1}, IsInitOnly = {2} ",
            MyTypeb.FullName,
            Myfieldinfob.GetValue(Myfieldb),
            Myfieldinfob.IsInitOnly);

        return 0;
    }
}

This code produces the following output:

Reflection.FieldInfo

Myfielda - A- modified, IsInitOnly = False

Myfieldb - B readonly field, IsInitOnly = True

.NET Framework

Supported in: 4.6, 4.5, 4, 3.5, 3.0, 2.0, 1.1

.NET Framework Client Profile

Supported in: 4, 3.5 SP1

XNA Framework

Supported in: 3.0, 2.0, 1.0

Portable Class Library

Supported in: Portable Class Library

Supported in: Windows Phone 8.1

Supported in: Windows Phone Silverlight 8.1

Supported in: Windows Phone Silverlight 8
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