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  
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