將 VBA 選擇案例轉換為 C# (Convert VBA select case to C#)

問題描述

將 VBA 選擇案例轉換為 C# (Convert VBA select case to C#)

Select Case True
 Case Not A.Name Is Nothing
   Set Name = A.Name
 Case Not A.Age Is Nothing
   Set Age = A.Age
 Case Not A.School Is Nothing
   Set School = A.School
End Select

在VB中Select Case True是允許使用的。但對於 C#，它給出了一個錯誤。如何將此 VB 代碼轉換為 C#？

參考解法

方法 1:

There is no direct analog in C# because C# case labels must be constant expressions. Select Case True is an unusual construct that serves as an alternative to if‑else constructs.

I suggest replacing it with the far more common pattern:

if (A.Name != null)
    Name = A.Name;
if (A.Age != null)
    Age = A.Age;
// ... etc

方法 2:

Using switch case in c# is some different. I think this example can be able to useful to you.

using System;
using System.Collections.Generic;
using System.Linq;

public class Example
{
   public static void Main()
   {
      var values = new List<object>();
      for (int ctr = 0; ctr <= 7; ctr++) {
         if (ctr == 2)
            values.Add(DiceLibrary.Roll2());
         else if (ctr == 4)
            values.Add(DiceLibrary.Pass());
         else
            values.Add(DiceLibrary.Roll());
      }

      Console.WriteLine($"The sum of { values.Count } die is { DiceLibrary.DiceSum(values) }");
   }
}

public static class DiceLibrary
{
   // Random number generator to simulate dice rolls.
   static Random rnd = new Random();

   // Roll a single die.
   public static int Roll()
   {
      return rnd.Next(1, 7);
   }

   // Roll two dice.
   public static List<object> Roll2()
   {
      var rolls = new List<object>();
      rolls.Add(Roll());
      rolls.Add(Roll());
      return rolls;
   }

   // Calculate the sum of n dice rolls.
   public static int DiceSum(IEnumerable<object> values)
   {
      var sum = 0;
      foreach (var item in values)
      {
            switch (item)
            {
               // A single zero value.
               case 0:
                  break;
               // A single value.
               case int val:
                  sum += val;
                  break;
               // A non‑empty collection.
               case IEnumerable<object> subList when subList.Any():
                  sum += DiceSum(subList);
                  break;
               // An empty collection.
               case IEnumerable<object> subList:
                  break;
               //  A null reference.
               case null:
                  break;
               // A value that is neither an integer nor a collection.
               default:
                  throw new InvalidOperationException("unknown item type");
            }
      }
      return sum;
   }

   public static object Pass()
   {
      if (rnd.Next(0, 2) == 0)
         return null;
      else
         return new List<object>();
   }
}

You can give more information here about switch case

方法 3:

Your VBA code mimics an If‑Then‑ElseIf ... block, so how about:

if (A.Name != null)
{
    Name = A.Name;
}
else if (A.Age != null)
{
    Age = A.Age;    
}
else if (A.School != null)
{
    School = A.School;
}   

(by Ramesh Perera、Eric J.、Arash Yazdani、Gustav)

參考文件

1. Convert VBA select case to C# (CC BY‑SA 2.5/3.0/4.0)