FieldInfo.IsInitOnly Property

Definition

Namespace:

System.Reflection

Assembly:

System.Runtime.dll

Source:

FieldInfo.cs

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

public:
 property bool IsInitOnly { bool get(); };

public bool IsInitOnly { get; }

member this.IsInitOnly : bool

Public ReadOnly Property IsInitOnly As Boolean

Property Value

Boolean

true if the field has the InitOnly attribute set; otherwise, false.

Examples

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 namespace System;
using namespace System::Reflection;

//Make two fields, one public and one read-only.
public ref class Myfielda
{
public:
   String^ field;
   Myfielda()
      : field( "A - public field" )
   {}


   property String^ Field 
   {
      String^ get()
      {
         return field;
      }

      void set( String^ value )
      {
         if ( field != value )
         {
            field = value;
         }
      }

   }

};

public ref class Myfieldb
{
private:
   String^ const field;

public:
   Myfieldb()
      : field( "B - readonly field" )
   {}


   property String^ Field 
   {
      String^ get()
      {
         return field;
      }

   }

};

int main()
{
   Console::WriteLine( "\nReflection.FieldInfo" );
   Myfielda^ myfielda = gcnew Myfielda;
   Myfieldb^ myfieldb = gcnew Myfieldb;
   
   //Get the Type and FieldInfo.
   Type^ MyTypea = Type::GetType( "Myfielda" );
   FieldInfo^ Myfieldinfoa = MyTypea->GetField( "field", static_cast<BindingFlags>(BindingFlags::Public | BindingFlags::Instance) );
   Type^ MyTypeb = Type::GetType( "Myfieldb" );
   FieldInfo^ Myfieldinfob = MyTypeb->GetField( "field", static_cast<BindingFlags>(BindingFlags::NonPublic | 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;
}

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;
    }
}

Imports System.Reflection

'Make two fields, one public and one read-only.
Public Class Myfielda
    Public field As String = "A - public modifiable field"
End Class

Public Class Myfieldb
    Public ReadOnly field As String = "B - readonly field"
End Class

Public Class Myfieldinfo
    Public Shared Function Main() As Integer
        Console.WriteLine("Reflection.FieldInfo")
        Console.WriteLine()
        Dim Myfielda As New Myfielda()
        Dim Myfieldb As New Myfieldb()

        'Get the Type and FieldInfo.
        Dim MyTypea As Type = GetType(Myfielda)
        Dim Myfieldinfoa As FieldInfo = MyTypea.GetField("field", _
            BindingFlags.Public Or BindingFlags.Instance)
        Dim MyTypeb As Type = GetType(Myfieldb)
        Dim Myfieldinfob As FieldInfo = MyTypeb.GetField("field", _
            BindingFlags.Public Or BindingFlags.Instance)

        'Modify the fields.
        'Note that Myfieldb is not modified, as it is
        'read-only (IsInitOnly is True).
        Myfielda.field = "A - modified"
        'For the first field, get and display the name, field, and IsInitOnly state.
        Console.WriteLine("{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.WriteLine("{0} - {1}, IsInitOnly = {2} ", MyTypeb.FullName, _
            Myfieldinfob.GetValue(Myfieldb), Myfieldinfob.IsInitOnly)

        Return 0
    End Function 'Main
End Class

This code produces the following output:

Reflection.FieldInfo

Myfielda - A- modified, IsInitOnly = False

Myfieldb - B readonly field, IsInitOnly = True

Remarks

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.

See also

• FieldAttributes
• GetField(String, BindingFlags)
• Type