C# 0 The Complete Reference

PART I

C h a p t e r   1 7 :  

R u n t i m e   T y p e   I D ,   R e f l e c t i o n ,   a n d   A t t r i b u t e s  

469

PART IPART I

   Boolean IsBetween(Int32 i)

   Void Set(Int32 a, Int32 b)

   Void Set(Double a, Double b)

   Void Show()

As you can see, only those methods explicitly defined by 

MyClass

 are displayed.

Calling Methods Using Reflection

Once you know what methods a type supports, you can call one or more of them. To do 

this, you will use the 

Invoke( )

 method that is contained in 

MethodInfo

. One of its forms 

is shown here:

object Invoke(object 

ob

, object[ ] 

args

)

Here, 

ob

 is a reference to the object on which the method is invoked. For 

static

 methods, pass 

null

 to 

ob.

 Any arguments that need to be passed to the method are specified in the array 

args.

 If no arguments are needed, 

args

 must be 

null

. Also, 

args

 must contain exactly the same 

number of elements as there are arguments. Therefore, if two arguments are needed, then 

args

 must be two elements long. It can’t, for example, be three or four elements long. The 

value returned by the invoked method is returned by 

Invoke( )

.

To call a method, simply call 

Invoke( )

 on an instance of 

MethodInfo

 that was obtained 

by calling 

GetMethods( )

. The following program demonstrates the procedure:

// Invoke methods using reflection.

using System;

using System.Reflection;

class MyClass {

  int x;

  int y;

  public MyClass(int i, int j) {

    x = i;

    y = j;

  }

  public int Sum() {

    return x+y;

  }

  public bool IsBetween(int i) {

    if((x < i) && (i < y)) return true;

    else return false;

  }

  public void Set(int a, int b) {

    Console.Write("Inside Set(int, int). ");

    x = a;

www.freepdf-books.com

---

470

 

P a r t   I :  

T h e   C #   L a n g u a g e

    y = b;

    Show();

  }

  // Overload set.

  public void Set(double a, double b) {

    Console.Write("Inside Set(double, double). ");

    x = (int) a;

    y = (int) b;

    Show();

  }

  public void Show() {

    Console.WriteLine("Values are x: {0}, y: {1}", x, y);

  }

}

class InvokeMethDemo {

  static void Main() {

    Type t = typeof(MyClass);

    MyClass reflectOb = new MyClass(10, 20);

    int val;

    Console.WriteLine("Invoking methods in " + t.Name);

    Console.WriteLine();

    MethodInfo[] mi = t.GetMethods();

    // Invoke each method.

    foreach(MethodInfo m in mi) {

      // Get the parameters.

      ParameterInfo[] pi = m.GetParameters();

      if(m.Name.CompareTo("Set")==0 &&

         pi[0].ParameterType == typeof(int)) {

        object[] args = new object[2];

        args[0] = 9;

        args[1] = 18;

        m.Invoke(reflectOb, args);

      }

      else if(m.Name.CompareTo("Set")==0 &&

              pi[0].ParameterType == typeof(double)) {

        object[] args = new object[2];

        args[0] = 1.12;

        args[1] = 23.4;

        m.Invoke(reflectOb, args);

      }

      else if(m.Name.CompareTo("Sum")==0) {

        val = (int) m.Invoke(reflectOb, null);

        Console.WriteLine("sum is " + val);

      }

      else if(m.Name.CompareTo("IsBetween")==0) {

        object[] args = new object[1];

        args[0] = 14;

        if((bool) m.Invoke(reflectOb, args))

www.freepdf-books.com

---