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COM Interop Sample: COM Client and .NET Server

This sample demonstrates the interoperation of a COM Client and a .NET Server that performs mortgage calculations. In this example, the client creates and calls an instance of the managed Loan class, passes four arguments (one of those four being equal to zero) to the instance, and displays the computations. Code examples from this sample appear throughout this section.

COM Client

// ConLoan.cpp : Defines the entry point for the console application.
#include "stdafx.h"
#import "..\LoanLib\LoanLib.tlb" raw_interfaces_only
using namespace LoanLib;

int main(int argc, char* argv[])
{
    HRESULT hr = CoInitialize(NULL);

    ILoanPtr pILoan(__uuidof(Loan));

    if (argc < 5) 
    {
        printf("Usage: ConLoan Balance Rate Term Payment\n");
        printf("    Either Balance, Rate, Term, or Payment must be 0\n");
        return -1;
    }

    double openingBalance = atof(argv[1]);
    double rate = atof(argv[2])/100.0;
    short  term = atoi(argv[3]);
    double payment = atof(argv[4]);

    pILoan->put_OpeningBalance(openingBalance);
    pILoan->put_Rate(rate);
    pILoan->put_Term(term);
    pILoan->put_Payment(payment);

    if (openingBalance == 0.00) 
         pILoan->ComputeOpeningBalance(&openingBalance);
    if (rate == 0.00) pILoan->ComputeRate(&rate);
    if (term == 0) pILoan->ComputeTerm(&term);
    if (payment == 0.00) pILoan->ComputePayment(&payment);

    printf("Balance = %.2f\n", openingBalance);
    printf("Rate    = %.1f%%\n", rate*100);
    printf("Term    = %.2i\n", term);
    printf("Payment = %.2f\n", payment);

    VARIANT_BOOL MorePmts;
    double Balance = 0.0;
    double Principal = 0.0;
    double Interest = 0.0;

    printf("%4s%10s%12s%10s%12s\n", "Nbr", "Payment", "Principal", "Interest", "Balance");
    printf("%4s%10s%12s%10s%12s\n", "---", "-------", "---------", 
"--------", "-------");

    pILoan->GetFirstPmtDistribution(payment, &Balance, &Principal, &Interest, &MorePmts);

    for (short PmtNbr = 1; MorePmts; PmtNbr++) 
    {
        printf("%4i%10.2f%12.2f%10.2f%12.2f\n",
        PmtNbr, payment, Principal, Interest, Balance);
      
        pILoan->GetNextPmtDistribution(payment, &Balance, &Principal, &Interest, &MorePmts); 
    }

    CoUninitialize();
    return 0;
}

.NET Server

Imports System
Imports System.Reflection

<Assembly: AssemblyKeyFile("sample.snk")>
Namespace LoanLib    
    
    Public Interface ILoan        
        Property OpeningBalance() As Double
        Property Rate() As Double       
        Property Payment() As Double       
        Property Term() As Short        
        Property RiskRating() As String
        Function ComputePayment() As Double
        Function ComputeOpeningBalance() As Double
        Function ComputeRate() As Double
        Function ComputeTerm() As Short
        Function GetFirstPmtDistribution(PmtAmt As Double, _
           ByRef Balance As Double, ByRef PrinPortion As Double, _
           ByRef IntPortion As Double) As Boolean
        Function GetNextPmtDistribution(PmtAmt As Double, _
           ByRef Balance As Double, ByRef PrinPortion As Double, _
           ByRef IntPortion As Double) As Boolean
    End Interface    
    
    Public Class Loan
        Implements ILoan
        Private m_openingBalance As Double
        Private m_rate As Double
        Private m_payment As Double
        Private m_term As Short
        Private m_riskRating As String 
        
        Public Property OpeningBalance() As Double _
        Implements ILoan.OpeningBalance
        
            Get
                Return m_openingBalance
            End Get
            Set
                m_openingBalance = value
            End Set
        End Property 
        
        Public Property Rate() As Double _
        Implements ILoan.Rate
        
            Get
                Return m_rate
            End Get
            Set
                m_rate = value
            End Set
        End Property 
        
        Public Property Payment() As Double _
        Implements ILoan.Payment
        
            Get
                Return m_payment
            End Get
            Set
                m_payment = value
            End Set
        End Property 
        
        Public Property Term() As Short _
        Implements ILoan.Term
        
            Get
                Return m_term
            End Get
            Set
                m_term = value
            End Set
        End Property 
        
        Public Property RiskRating() As String _
        Implements ILoan.RiskRating
        
            Get
                Return m_riskRating
            End Get
            Set
                m_riskRating = value
            End Set
        End Property
         
        Public Function ComputePayment() As Double _
        Implements ILoan.ComputePayment
        
            Payment = Util.Round(OpeningBalance *(Rate / _
               (1 - Math.Pow(1 + Rate, - Term))), 2)
            Return Payment
        End Function        
        
        Public Function ComputeOpeningBalance() As Double _
        Implements ILoan.ComputeOpeningBalance
        
            OpeningBalance = Util.Round(Payment /(Rate / _
               (1 - Math.Pow(1 + Rate, - Term))), 2)
            Return OpeningBalance
        End Function        
        
        Public Function ComputeRate() As Double _
        Implements ILoan.ComputeRate
        
            Dim DesiredPayment As Double = Payment
            
            For m_rate = 0.001 To 28.0 - 0.001 Step 0.001
                Payment = Util.Round(OpeningBalance *(Rate / _
                   (1 - Math.Pow(1 + Rate, - Term))), 2)
                
                If Payment >= DesiredPayment Then
                    Exit For
                End If
            Next
            Return Rate
        End Function        
        
        Public Function ComputeTerm() As Short _
        Implements ILoan.ComputeTerm
        
            Dim DesiredPayment As Double = Payment
            
            For m_term = 1 To 479
                Payment = Util.Round(OpeningBalance *(Rate / _
                   (1 - Math.Pow(1 + Rate, - Term))), 2)
                
                If Payment <= DesiredPayment Then
                    Exit For
                End If
            Next
            Return Term
        End Function        
        
        Public Function GetFirstPmtDistribution(PmtAmt As Double, _
        ByRef Balance As Double, ByRef PrinPortion As Double, _
        ByRef IntPortion As Double) As Boolean _
        Implements ILoan.GetFirstPmtDistribution
        
            Balance = OpeningBalance
            Return GetNextPmtDistribution(PmtAmt, Balance, PrinPortion, _
               IntPortion)
        End Function        
        
        Public Function GetNextPmtDistribution(PmtAmt As Double, _
        ByRef Balance As Double, ByRef PrinPortion As Double, _
        ByRef IntPortion As Double) As Boolean _
        Implements ILoan.GetNextPmtDistribution
        
            IntPortion = Util.Round(Balance * Rate, 2)
            PrinPortion = Util.Round(PmtAmt - IntPortion, 2)
            Balance = Util.Round(Balance - PrinPortion, 2)
            
            If Balance <= 0.0 Then
                Return False
            End If 
            Return True
        End Function
    End Class    
    
    Friend Class Util
        
        Public Shared Function Round(value As Double, digits As Short) _
                                      As Double
            Dim factor As Double = Math.Pow(10, digits)
            Return Math.Round((value * factor)) / factor
        End Function
        
    End Class
    
End Namespace
[C#]
using System;
using System.Reflection;

[assembly:AssemblyKeyFile("sample.snk")]
namespace LoanLib {
   
    public interface ILoan {
        double OpeningBalance{get; set;}
        double Rate{get; set;}
        double Payment{get; set;}   
        short  Term{get; set;}
        String RiskRating{get; set;}
      
        double ComputePayment();
        double ComputeOpeningBalance();
        double ComputeRate();
        short ComputeTerm();
        bool GetFirstPmtDistribution(double PmtAmt, ref double Balance,
            out double PrinPortion, out double IntPortion);
        bool GetNextPmtDistribution(double PmtAmt, ref double Balance,
            out double PrinPortion, out double IntPortion);
    }

    public class Loan : ILoan {
        private double openingBalance;
        private double rate;
        private double payment;
        private short  term;
        private String riskRating;      
      
        public double OpeningBalance {
            get { return openingBalance; }
            set { openingBalance = value; }
        }
      
        public double Rate {
            get { return rate; }
            set { rate = value; }
        }
      
        public double Payment {
            get { return payment; }
            set { payment = value; }
        }
         
        public short Term {
            get { return term; }
            set { term = value; }
        }

        public String RiskRating {
            get { return riskRating; }
            set { riskRating = value; }
        }

        public double ComputePayment() {
             Payment = Util.Round(OpeningBalance * (Rate / (1 – 
                        Math.Pow((1 + Rate), -Term))), 2);
             return Payment;
        }

        public double ComputeOpeningBalance() {
            OpeningBalance = Util.Round(Payment / (Rate / (1 - Math.Pow((1 
                              + Rate), -Term))), 2);
             return OpeningBalance;
        }

        public double ComputeRate() {
            double DesiredPayment = Payment;

            for (Rate = 0.001; Rate < 28.0; Rate += 0.001) {
                Payment = Util.Round(OpeningBalance * (Rate / (1 – 
                           Math.Pow((1 + Rate), -Term))), 2);

                if (Payment >= DesiredPayment)
                    break;
            }
            return Rate;   
        }

        public short ComputeTerm() {
            double DesiredPayment = Payment;

            for (Term = 1; Term < 480 ; Term ++) {
                Payment = Util.Round(OpeningBalance * (Rate / (1 – 
                           Math.Pow((1 + Rate), -Term))),2);

                if (Payment <= DesiredPayment)
                    break;
            }

            return Term;   
        }

        public bool GetFirstPmtDistribution(double PmtAmt, ref double 
            Balance, out double PrinPortion, out double IntPortion) {
             Balance = OpeningBalance;
             return GetNextPmtDistribution(PmtAmt, ref Balance, out 
             PrinPortion, out IntPortion); 
        }

        public bool GetNextPmtDistribution(double PmtAmt, ref double 
           Balance, out double PrinPortion, out double IntPortion) {
            IntPortion = Util.Round(Balance * Rate, 2);
            PrinPortion = Util.Round(PmtAmt - IntPortion,2);
            Balance = Util.Round(Balance - PrinPortion,2);

            if (Balance <= 0.0) 
                return false;

            return true;
        }
     }

    internal class Util {
        public static double Round(double value, short digits) {
            double factor = Math.Pow(10, digits);
            return Math.Round(value * factor) / factor;
         }
    }
}

See Also

Exposing .NET Framework Components to COM

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