COM Interop 示例：.NET 客户端和 COM 服务器
更新：2007 年 11 月
本示例将说明 .NET 客户端（为访问 COM 服务器而生成）如何创建 COM coclass 的实例并调用类成员来执行抵押贷款计算。
在本示例中，客户端将创建并调用 Loan coclass 的一个实例，将四个参数（其中一个等于零）传递给该实例，并显示计算结果。此处将用整节的篇幅来显示该示例中的各个代码片断。
.NET 客户端
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 服务器
// 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;
}