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COM Interop-exempel: .NET-klient och COM-server

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Det här exemplet visar hur en .NET-klient, som skapats för att komma åt en COM-server, skapar en instans av en COM-samklass och anropar klassmedlemmar för att utföra hypoteksberäkningar.

I det här exemplet skapar och anropar klienten en instans av lånekoklassen, skickar fyra argument (en av dessa fyra är lika med noll) till instansen och visar beräkningen. Kodfragment från det här exemplet visas i hela det här avsnittet.

.NET-klient

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;  
}

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