FieldBuilder Class
Summary
Represents a field in a TypeBuilder. The FieldBuilder class allows you to define the name, attributes, and type of the field. It is used in conjunction with the TypeBuilder class to dynamically create types at runtime.
Syntax
public sealed class FieldBuilder : FieldInfo
Constructors
-
FieldBuilder()Protected constructor. Instances are created by the TypeBuilder.DefineField method.
Methods
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SetConstant(object value)Sets the constant value of the field.Parameters:
value: The constant value of the field. -
SetCustomAttribute(CustomAttributeBuilder customBuilder)Applies a custom attribute to this field.Parameters:
customBuilder: An instance ofCustomAttributeBuilderthat represents the custom attribute to be applied. -
SetOffset(int offset)Sets the field's offset within the type.Parameters:
offset: The offset of the field within the type. -
GetFieldAccessors(MethodBuilder setAccessor, MethodBuilder getAccessor)Returns the method builders for the getter and setter of the field.Parameters:
setAccessor: AMethodBuilderrepresenting the setter of the field.getAccessor: AMethodBuilderrepresenting the getter of the field.
Properties
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FieldTypeGets the type of the field.Return Value:
Type- The type of the field. -
NameGets the name of the field.Return Value:
string- The name of the field. -
DeclaringTypeGets the type that declares this field.Return Value:
Type- The declaring type. -
IsLiteralGets a value indicating whether the field is a literal.Return Value:
bool-trueif the field is a literal; otherwise,false. -
IsInitOnlyGets a value indicating whether the field is read-only.Return Value:
bool-trueif the field is read-only; otherwise,false. -
AttributesGets the field's attributes.Return Value:
FieldAttributes- The field's attributes.
Remarks
The FieldBuilder class is part of the System.Reflection.Emit namespace, which provides types that allow you to create an assembly in a subdirectory of the current directory, a new assembly in memory, or a stream in memory.
Fields are defined on a TypeBuilder object using the TypeBuilder.DefineField method. This method returns a FieldBuilder instance.
You can then use the methods of FieldBuilder to set its constant value, custom attributes, and offset.
Example
// Example demonstrating the use of FieldBuilder
using System;
using System.Reflection;
using System.Reflection.Emit;
public class DynamicTypeGenerator
{
public static Type CreateDynamicTypeWithField()
{
AssemblyName assemblyName = new AssemblyName("MyDynamicAssembly");
AssemblyBuilder assemblyBuilder = AppDomain.CurrentDomain.DefineDynamicAssembly(assemblyName, AssemblyBuilderAccess.RunAndSave);
ModuleBuilder moduleBuilder = assemblyBuilder.DefineDynamicModule("MyDynamicModule");
TypeBuilder typeBuilder = moduleBuilder.DefineType("MyDynamicClass");
// Define a string field named 'Message'
FieldBuilder fieldBuilder = typeBuilder.DefineField("Message", typeof(string), FieldAttributes.Public);
// Set a constant value for the field
fieldBuilder.SetConstant("Hello from dynamic field!");
// Define a constructor
MethodBuilder constructorBuilder = typeBuilder.DefineConstructor(MethodAttributes.Public, CallingConventions.Standard, Type.EmptyTypes);
ILGenerator constructorIL = constructorBuilder.GetILGenerator();
constructorIL.Emit(OpCodes.Ldarg_0);
constructorIL.Emit(OpCodes.Call, typeof(object).GetConstructor(Type.EmptyTypes));
constructorIL.Emit(OpCodes.Ret);
return typeBuilder.CreateType();
}
public static void Main(string[] args)
{
Type dynamicType = CreateDynamicTypeWithField();
object instance = Activator.CreateInstance(dynamicType);
FieldInfo messageField = dynamicType.GetField("Message");
if (messageField != null)
{
object value = messageField.GetValue(instance);
Console.WriteLine($"Field 'Message' value: {value}");
}
}
}