barcode printing vb.net Part IV in C#

Creator PDF417 in C# Part IV

When calling any of these methods, the Binder-derived object is used to perform type conversions on the supplied method parameters, such as converting an Int32 argument to an Int64, so that the already selected method can be called . As for the BindingFlags parameter, the only flag that can be passed here is BindingFlags.SuppressChangeType . However, binders are free to ignore this flag . Fortunately, the DefaultBinder class heeds this flag . When DefaultBinder sees this flag, it won t convert any arguments . If you use this flag and the arguments passed don t match the arguments expected by the method, an ArgumentException will be thrown . Usually when you use the BindingFlags.ExactBinding flag to bind to a member, you ll specify the BindingFlags.SuppressChangeType flag to invoke the member . If you don t use these two flags in tandem, it s unlikely that invoking the member will be successful unless the arguments you pass happen to be exactly what the method expects . By the way, if you call MemberInfo s InvokeMethod to bind and invoke a member, you ll probably want to specify both or neither of the two binding flags . The following sample application demonstrates the various ways to use reflection to access a type s members . The SomeType class represents a type that has various members: a private field (m_someField), a public constructor (SomeType) that takes an Int32 argument passed by reference, a public method (ToString), a public property (SomeProp), and a public event (SomeEvent) . Having defined the SomeType type, I offer three different methods that use reflection to access SomeType s members . Each method uses reflection in a different way to accomplish the same thing:

The UseInvokeMemberToBindAndInvokeTheMember method demonstrates how to use Type s InvokeMember to both bind and invoke a member . The BindToMemberThenInvokeTheMember method demonstrates how to bind to a member and invoke it later . This technique yields faster-performing code if you intend to invoke the same member on different objects multiple times . The BindToMemberCreateDelegateToMemberThenInvokeTheMember method demonstrates how to bind to an object or member, and then it creates a delegate that refers to that object or member . Calling through the delegate is very fast, and this technique yields even faster performance if you intend to invoke the same member on the same object multiple times . The UseDynamicToBindAndInvokeTheMember method demonstrates how to use C# dynamic primitive type (discussed at the end of 5, Primitive, Reference, and Value Types ) to simplify the syntax for accessing members . In addition, this technique can give reasonably good performance if you intend to invoke the same member on different objects that are all of the same type because the binding will happen once per type and be cached so that it can be invoked multiple times quickly . You can also use this technique to invoke a member on objects of different types .

using System; using System.Reflection; using Microsoft.CSharp.RuntimeBinder;

// This class is used to demonstrate reflection // It has a field, constructor, method, property, and an event internal sealed class SomeType { private Int32 m_someField; public SomeType(ref Int32 x) { x *= 2; } public override String ToString() { return m_someField.ToString(); } public Int32 SomeProp { get { return m_someField; } set { if (value < 1) throw new ArgumentOutOfRangeException("value"); m_someField = value; } public event EventHandler SomeEvent; private void NoCompilerWarnings() { SomeEvent.ToString();} } public static class Program { private const BindingFlags c_bf = BindingFlags.DeclaredOnly | BindingFlags.Public | BindingFlags.NonPublic | BindingFlags.Instance; public static void Main() { Type t = typeof(SomeType); UseInvokeMemberToBindAndInvokeTheMember(t); Console.WriteLine(); BindToMemberThenInvokeTheMember(t); Console.WriteLine(); BindToMemberCreateDelegateToMemberThenInvokeTheMember(t); Console.WriteLine(); UseDynamicToBindAndInvokeTheMember(t); Console.WriteLine(); }

private static void UseInvokeMemberToBindAndInvokeTheMember(Type t) { Console.WriteLine("UseInvokeMemberToBindAndInvokeTheMember"); // Construct an instance of the Type Object[] args = new Object[] { 12 }; // Constructor arguments Console.WriteLine("x before constructor called: " + args[0]); Object obj = t.InvokeMember(null, c_bf | BindingFlags.CreateInstance, null, null, args); Console.WriteLine("Type: " + obj.GetType().ToString()); Console.WriteLine("x after constructor returns: " + args[0]);