Artículo
11/18/2011

FieldBuilder Class

Microsoft Silverlight will reach end of support after October 2021. Learn more.

Defines and represents a field. This class cannot be inherited.

Inheritance Hierarchy

System.Object
  System.Reflection.MemberInfo
    System.Reflection.FieldInfo
      System.Reflection.Emit.FieldBuilder

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

Syntax

'Declaration
<ComVisibleAttribute(True)> _
<ClassInterfaceAttribute(ClassInterfaceType.None)> _
Public NotInheritable Class FieldBuilder _
    Inherits FieldInfo

[ComVisibleAttribute(true)]
[ClassInterfaceAttribute(ClassInterfaceType.None)]
public sealed class FieldBuilder : FieldInfo

The FieldBuilder type exposes the following members.

Properties

	Name	Description
	Attributes	Gets the attributes of this field. (Overrides FieldInfo.Attributes.)
	DeclaringType	Gets a reference to the Type object for the type that declares this field. (Overrides MemberInfo.DeclaringType.)
	FieldHandle	Gets the internal metadata handle for this field. (Overrides FieldInfo.FieldHandle.)
	FieldType	Gets the Type object that represents the type of this field. (Overrides FieldInfo.FieldType.)
	IsAssembly	Gets a value that indicates whether the potential visibility of this field is described by FieldAttributes.Assembly; that is, the field is visible at most to other types in the same assembly, and is not visible to derived types outside the assembly. (Inherited from FieldInfo.)
	IsFamily	Gets a value that indicates whether the visibility of this field is described by FieldAttributes.Family; that is, the field is visible only within its class and derived classes. (Inherited from FieldInfo.)
	IsFamilyAndAssembly	Gets a value that indicates whether the visibility of this field is described by FieldAttributes.FamANDAssem; that is, the field can be accessed from derived classes, but only if they are in the same assembly. (Inherited from FieldInfo.)
	IsFamilyOrAssembly	Gets a value that indicates whether the potential visibility of this field is described by FieldAttributes.FamORAssem; that is, the field can be accessed by derived classes wherever they are, and by classes in the same assembly. (Inherited from FieldInfo.)
	IsInitOnly	Gets a value that indicates whether the field can be set only in the body of the constructor. (Inherited from FieldInfo.)
	IsLiteral	Gets a value that indicates whether the value is written at compile time and cannot be changed. (Inherited from FieldInfo.)
	IsNotSerialized	Gets a value that indicates whether this field has the NotSerialized attribute. (Inherited from FieldInfo.)
	IsPinvokeImpl	Gets a value that indicates whether the corresponding PinvokeImpl attribute is set in FieldAttributes. (Inherited from FieldInfo.)
	IsPrivate	Gets a value that indicates whether the field is private. (Inherited from FieldInfo.)
	IsPublic	Gets a value that indicates whether the field is public. (Inherited from FieldInfo.)
	IsSpecialName	Gets a value that indicates whether the field has a name that has special significance. (Inherited from FieldInfo.)
	IsStatic	Gets a value that indicates whether the field is static (Shared in Visual Basic). (Inherited from FieldInfo.)
	MemberType	Gets a value that indicates that this member is a field. (Inherited from FieldInfo.)
	MetadataToken	Gets a value that identifies a metadata element. (Inherited from MemberInfo.)
	Module	Gets the module in which the type that contains this field is being defined. (Overrides MemberInfo.Module.)
	Name	Gets the name of this field. (Overrides MemberInfo.Name.)
	ReflectedType	Gets the reference to the Type object from which this object was obtained. (Overrides MemberInfo.ReflectedType.)

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Methods

	Name	Description
	Equals(Object)	Determines whether the specified Object is equal to the current Object. (Inherited from Object.)
	Finalize	Allows an object to try to free resources and perform other cleanup operations before the Object is reclaimed by garbage collection. (Inherited from Object.)
	GetCustomAttributes(Boolean)	Returns all the custom attributes defined for this field. (Overrides MemberInfo.GetCustomAttributes(Boolean).)
	GetCustomAttributes(Type, Boolean)	Returns all the custom attributes defined for this field identified by the given type. (Overrides MemberInfo.GetCustomAttributes(Type, Boolean).)
	GetHashCode	Serves as a hash function for a particular type. (Inherited from Object.)
	GetRawConstantValue	Returns a literal value associated with the field by a compiler. (Inherited from FieldInfo.)
	GetToken	Returns the token representing this field.
	GetType	Gets the Type of the current instance. (Inherited from Object.)
	GetValue	Retrieves the value of the field supported by the given object. (Overrides FieldInfo.GetValue(Object).)
	IsDefined	Gets a value that indicates whether an attribute having the specified type is defined on a field. (Overrides MemberInfo.IsDefined(Type, Boolean).)
	MemberwiseClone	Creates a shallow copy of the current Object. (Inherited from Object.)
	SetConstant	Sets the default value of this field.
	SetCustomAttribute	Sets a custom attribute using a custom attribute builder.
	SetValue(Object, Object)	Sets the value of the field that is supported by the given object. (Inherited from FieldInfo.)
	SetValue(Object, Object, BindingFlags, Binder, CultureInfo)	Sets the value of the field supported by the given object. (Overrides FieldInfo.SetValue(Object, Object, BindingFlags, Binder, CultureInfo).)
	ToString	Returns a string that represents the current object. (Inherited from Object.)

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Remarks

Get an instance of FieldBuilder by calling the TypeBuilder.DefineField method.

Note:
The SetValue method is currently not supported. As a workaround, retrieve the FieldInfo by reflecting on the finished type and call SetValue to set the value of the field.

Examples

The following code sample illustrates the use of FieldBuilder.

Note:
To run this example, see Building Examples That Use a Demo Method and a TextBlock Control.

Imports System.Reflection
Imports System.Reflection.Emit

Public Class Example
   Public Shared Sub Demo(ByVal outputBlock As System.Windows.Controls.TextBlock)

      ' Create an assembly.
      Dim myAssemblyName As New AssemblyName()
      myAssemblyName.Name = "DynamicAssembly"
      Dim myAssembly As AssemblyBuilder = _
         AppDomain.CurrentDomain.DefineDynamicAssembly(myAssemblyName, _
                                                AssemblyBuilderAccess.Run)
      ' Create a dynamic module in Dynamic Assembly.
      Dim myModuleBuilder As ModuleBuilder = myAssembly.DefineDynamicModule("MyModule")
      ' Define a public class named "MyClass" in the assembly.
      Dim myTypeBuilder As TypeBuilder = myModuleBuilder.DefineType("MyClass", _
                                          TypeAttributes.Public)

      ' Define a private String field named "MyField" in the type.
      Dim myFieldBuilder As FieldBuilder = myTypeBuilder.DefineField("MyField", _
                  GetType(String), FieldAttributes.Private Or FieldAttributes.Static)

      ' Create the constructor.
      Dim constructorArgs As Type() = {GetType(String)}
      Dim constructor As ConstructorBuilder = _
                  myTypeBuilder.DefineConstructor(MethodAttributes.Public, _
                           CallingConventions.Standard, constructorArgs)
      Dim constructorIL As ILGenerator = constructor.GetILGenerator()
      constructorIL.Emit(OpCodes.Ldarg_0)
      Dim superConstructor As ConstructorInfo = GetType(Object).GetConstructor(New Type() {})
      constructorIL.Emit(OpCodes.Call, superConstructor)
      constructorIL.Emit(OpCodes.Ldarg_0)
      constructorIL.Emit(OpCodes.Ldarg_1)
      constructorIL.Emit(OpCodes.Stfld, myFieldBuilder)
      constructorIL.Emit(OpCodes.Ret)

      ' Create the MyMethod method.
      Dim myMethodBuilder As MethodBuilder = myTypeBuilder.DefineMethod("MyMethod", _
                        MethodAttributes.Public, GetType(String), Nothing)
      Dim methodIL As ILGenerator = myMethodBuilder.GetILGenerator()
      methodIL.Emit(OpCodes.Ldarg_0)
      methodIL.Emit(OpCodes.Ldfld, myFieldBuilder)
      methodIL.Emit(OpCodes.Ret)
      outputBlock.Text &= "Name: " & myFieldBuilder.Name & vbCrLf
      outputBlock.Text &= "DeclaringType: " & myFieldBuilder.DeclaringType.ToString() & vbCrLf
      outputBlock.Text &= "Type: " & myFieldBuilder.FieldType.ToString() & vbCrLf
      outputBlock.Text &= "Token: " & myFieldBuilder.GetToken().Token.ToString() & vbCrLf

      Dim myType As Type = myTypeBuilder.CreateType()
      ' Create an instance of the "HelloWorld" class.
      Dim helloWorld As Object = Activator.CreateInstance(myType, New Object() {"HelloWorld"})
      ' Invoke the "MyMethod" method of the "MyClass" class.
      Dim myObject As Object = myType.InvokeMember("MyMethod", _
                     BindingFlags.InvokeMethod, Nothing, helloWorld, Nothing)
      outputBlock.Text &= "MyClass.MyMethod returned: """ & myObject & """" & vbCrLf

   End Sub 
End Class

using System;
using System.Reflection;
using System.Reflection.Emit;

public class Example
{
   public static void Demo(System.Windows.Controls.TextBlock outputBlock)
   {
      // Create an assembly.
      AssemblyName myAssemblyName = new AssemblyName();
      myAssemblyName.Name = "DynamicAssembly";
      AssemblyBuilder myAssembly =
         AppDomain.CurrentDomain.DefineDynamicAssembly(myAssemblyName, 
               AssemblyBuilderAccess.Run);
      // Create a dynamic module in Dynamic Assembly.
      ModuleBuilder myModuleBuilder = myAssembly.DefineDynamicModule("MyModule");
      // Define a public class named "MyClass" in the assembly.
      TypeBuilder myTypeBuilder = myModuleBuilder.DefineType("MyClass", TypeAttributes.Public);

      // Define a private String field named "MyField" in the type.
      FieldBuilder myFieldBuilder = myTypeBuilder.DefineField("MyField",
          typeof(string), FieldAttributes.Private | FieldAttributes.Static);
      // Create the constructor.
      Type[] constructorArgs = { typeof(String) };
      ConstructorBuilder constructor = myTypeBuilder.DefineConstructor(
         MethodAttributes.Public, CallingConventions.Standard, constructorArgs);
      ILGenerator constructorIL = constructor.GetILGenerator();
      constructorIL.Emit(OpCodes.Ldarg_0);
      ConstructorInfo superConstructor = typeof(Object).GetConstructor(new Type[0]);
      constructorIL.Emit(OpCodes.Call, superConstructor);
      constructorIL.Emit(OpCodes.Ldarg_0);
      constructorIL.Emit(OpCodes.Ldarg_1);
      constructorIL.Emit(OpCodes.Stfld, myFieldBuilder);
      constructorIL.Emit(OpCodes.Ret);

      // Create the MyMethod method.
      MethodBuilder myMethodBuilder = myTypeBuilder.DefineMethod("MyMethod",
                           MethodAttributes.Public, typeof(String), null);
      ILGenerator methodIL = myMethodBuilder.GetILGenerator();
      methodIL.Emit(OpCodes.Ldarg_0);
      methodIL.Emit(OpCodes.Ldfld, myFieldBuilder);
      methodIL.Emit(OpCodes.Ret);
      outputBlock.Text += "Name: " + myFieldBuilder.Name + "\n";
      outputBlock.Text += "DeclaringType: " + myFieldBuilder.DeclaringType + "\n";
      outputBlock.Text += "Type: " + myFieldBuilder.FieldType + "\n";
      outputBlock.Text += "Token: " + myFieldBuilder.GetToken().Token + "\n";

      Type myType = myTypeBuilder.CreateType();
      // Create an instance of the "HelloWorld" class.
      Object helloWorld = Activator.CreateInstance(myType, new Object[] { "HelloWorld" });
      // Invoke the "MyMethod" method of the "MyClass" class.
      Object myObject = myType.InvokeMember("MyMethod",
                        BindingFlags.InvokeMethod, null, helloWorld, null);
      outputBlock.Text += "MyClass.MyMethod returned: \"" + myObject + "\"" + "\n";
   }
}

Version Information

Silverlight

Supported in: 5, 4, 3

Platforms

For a list of the operating systems and browsers that are supported by Silverlight, see Supported Operating Systems and Browsers.

Thread Safety

Any public static (Shared in Visual Basic) members of this type are thread safe. Any instance members are not guaranteed to be thread safe.

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