COM Interop 範例：.NET 用戶端與 COM 伺服器

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此範例示範建置來存取 COM 伺服器的 .NET 用戶端如何建立 COM coclass 的執行個體，以及呼叫類別成員來執行貸款計算。

在此範例中，用戶端會建立和呼叫 Loan coclass 執行個體，並將四個引數 (這四個的其中一個等於零) 傳遞給執行個體，然後顯示運算。 這個範例的程式碼片段會出現在本節中。

.NET 用戶端

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 伺服器

// 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;  
}

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