COM Interop Sample: .NET Client and COM Server
This sample demonstrates how a .NET client, built to access a COM server, creates an instance of a COM coclass and calls class members to perform mortgage calculations.
In this example, the client creates and calls an instance of the Loan coclass, passes four arguments (one of those four being equal to zero) to the instance, and displays the computations. Code fragments from this sample appear throughout this section.
.NET Client
Imports System
Imports Microsoft.VisualBasic
Imports LoanLib
Public Class LoanApp
Public Shared Sub Main()
Dim Args As String()
Args = System.Environment.GetCommandLineArgs()
Dim ln As New Loan()
If Args.Length < 5 Then
Console.WriteLine("Usage: ConLoan Balance Rate Term Payment")
Console.WriteLine(" Either Balance, Rate, Term, or Payment " _
& "must be 0")
Exit Sub
End If
ln.OpeningBalance = Convert.ToDouble(Args(1))
ln.Rate = Convert.ToDouble(Args(2)) / 100.0
ln.Term = Convert.ToInt16(Args(3))
ln.Payment = Convert.ToDouble(Args(4))
If ln.OpeningBalance = 0.0 Then
ln.ComputeOpeningBalance()
End If
If ln.Rate = 0.0 Then
ln.ComputeRate()
End If
If ln.Term = 0 Then
ln.ComputeTerm()
End If
If ln.Payment = 0.0 Then
ln.ComputePayment()
End If
Console.WriteLine("Balance = {0,10:0.00}", ln.OpeningBalance)
Console.WriteLine("Rate = {0,10:0.0%}", ln.Rate)
Console.WriteLine("Term = {0,10:0.00}", ln.Term)
Console.WriteLine("Payment = {0,10:0.00}" & ControlChars.Cr, _
ln.Payment)
Dim MorePmts As Boolean
Dim Balance As Double = 0.0
Dim Principal As Double = 0.0
Dim Interest As Double = 0.0
Console.WriteLine("{0,4}{1,10}{2,12}{3,10}{4,12}", _
"Nbr", "Payment", "Principal", "Interest", "Balance")
Console.WriteLine("{0,4}{1,10}{2,12}{3,10}{4,12}", _
"---", "-------", "---------", "--------", "-------")
MorePmts = ln.GetFirstPmtDistribution(ln.Payment, Balance, _
Principal, Interest)
Dim PmtNbr As Short
While MorePmts
Console.WriteLine("{0,4}{1,10:0.00}{2,12:0.00}{3,10:0.00}" _
& "{4,12:0.00}", PmtNbr, ln.Payment, Principal, Interest,
Balance)
MorePmts = ln.GetNextPmtDistribution(ln.Payment, Balance, _
Principal, Interest)
PmtNbr += CShort(1)
End While
End Sub
End Class
using System;
using LoanLib;
public class LoanApp {
public static void Main(String[] Args) {
Loan ln = new Loan();
if (Args.Length < 4)
{
Console.WriteLine("Usage: ConLoan Balance Rate Term Payment");
Console.WriteLine(" Either Balance, Rate, Term, or Payment
must be 0");
return;
}
ln.OpeningBalance = Convert.ToDouble(Args[0]);
ln.Rate = Convert.ToDouble(Args[1])/100.0;
ln.Term = Convert.ToInt16(Args[2]);
ln.Payment = Convert.ToDouble(Args[3]);
if (ln.OpeningBalance == 0.00) ln.ComputeOpeningBalance();
if (ln.Rate == 0.00) ln.ComputeRate();
if (ln.Term == 0) ln.ComputeTerm();
if (ln.Payment == 0.00) ln.ComputePayment();
Console.WriteLine("Balance = {0,10:0.00}", ln.OpeningBalance);
Console.WriteLine("Rate = {0,10:0.0%}", ln.Rate);
Console.WriteLine("Term = {0,10:0.00}", ln.Term);
Console.WriteLine("Payment = {0,10:0.00}\n", ln.Payment);
bool MorePmts;
double Balance = 0.0;
double Principal = 0.0;
double Interest = 0.0;
Console.WriteLine("{0,4}{1,10}{2,12}{3,10}{4,12}", "Nbr", "Payment",
"Principal", "Interest", "Balance");
Console.WriteLine("{0,4}{1,10}{2,12}{3,10}{4,12}", "---", "-------",
"---------", "--------", "-------");
MorePmts = ln.GetFirstPmtDistribution(ln.Payment, out Balance,
out Principal, out Interest);
for (short PmtNbr = 1; MorePmts; PmtNbr++) {
Console.WriteLine("{0,4}{1,10:0.00}{2,12:0.00}{3,10:0.00}
{4,12:0.00}", PmtNbr, ln.Payment, Principal, Interest,
Balance);
MorePmts = ln.GetNextPmtDistribution(ln.Payment, ref Balance,
out Principal, out Interest);
}
}
}
COM Server
// Loan.cpp : Implementation of CLoan
#include "stdafx.h"
#include "math.h"
#include "LoanLib.h"
#include "Loan.h"
static double Round(double value, short digits);
STDMETHODIMP CLoan::get_OpeningBalance(double *pVal)
{
*pVal = OpeningBalance;
return S_OK;
}
STDMETHODIMP CLoan::put_OpeningBalance(double newVal)
{
OpeningBalance = newVal;
return S_OK;
}
STDMETHODIMP CLoan::get_Rate(double *pVal)
{
*pVal = Rate;
return S_OK;
}
STDMETHODIMP CLoan::put_Rate(double newVal)
{
Rate = newVal;
return S_OK;
}
STDMETHODIMP CLoan::get_Payment(double *pVal)
{
*pVal = Payment;
return S_OK;
}
STDMETHODIMP CLoan::put_Payment(double newVal)
{
Payment = newVal;
return S_OK;
}
STDMETHODIMP CLoan::get_Term(short *pVal)
{
*pVal = Term;
return S_OK;
}
STDMETHODIMP CLoan::put_Term(short newVal)
{
Term = newVal;
return S_OK;
}
STDMETHODIMP CLoan::ComputePayment(double *pVal)
{
Payment = Round(OpeningBalance * (Rate /
(1 - pow((1 + Rate), -Term))),2);
*pVal = Payment;
return S_OK;
}
STDMETHODIMP CLoan::ComputeOpeningBalance(double *pVal)
{
OpeningBalance = Round(Payment / (Rate /
(1 - pow((1 + Rate), -Term))),2);
*pVal = OpeningBalance ;
return S_OK;
}
STDMETHODIMP CLoan::ComputeRate(double *pVal)
{
double DesiredPayment = Payment;
for (Rate = 0.001; Rate < 28.0; Rate += 0.001)
{
Payment = Round(OpeningBalance * (Rate /
(1 - pow((1 + Rate), -Term))),2);
if (Payment >= DesiredPayment)
break;
}
*pVal = Rate;
return S_OK;
}
STDMETHODIMP CLoan::ComputeTerm(short *pVal)
{
double DesiredPayment = Payment;
for (Term = 1; Term < 480 ; Term ++)
{
Payment = Round(OpeningBalance * (Rate /
(1 - pow((1 + Rate), -Term))),2);
if (Payment <= DesiredPayment)
break;
}
*pVal = Term;
return S_OK;
}
STDMETHODIMP CLoan::GetFirstPmtDistribution(double PmtAmt, double *Balance, double *PrinPortion, double *IntPortion, VARIANT_BOOL *pVal)
{
*Balance = OpeningBalance;
GetNextPmtDistribution(PmtAmt, Balance, PrinPortion, IntPortion,
pVal);
return S_OK;
}
STDMETHODIMP CLoan::GetNextPmtDistribution(double PmtAmt, double *Balance, double *PrinPortion, double *IntPortion, VARIANT_BOOL *pVal)
{
*IntPortion = Round(*Balance * Rate, 2);
*PrinPortion = Round(PmtAmt - *IntPortion, 2);
*Balance = Round(*Balance - *PrinPortion, 2);
if (*Balance <= 0.0)
*pVal = FALSE;
else
*pVal = TRUE;
return S_OK;
}
STDMETHODIMP CLoan::get_RiskRating(BSTR *pVal)
{
*pVal = (BSTR)RiskRating;
return S_OK;
}
STDMETHODIMP CLoan::put_RiskRating(BSTR newVal)
{
RiskRating = newVal;
return S_OK;
}
static double Round(double value, short digits)
{
double factor = pow(10, digits);
return floor(value * factor + 0.5)/factor;
}