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;
}
}
}