C＃中的大小寫/轉換語句

Question

我想知道是否有一種方法可以聲明很多case語句而不必全部編寫。 例如，我的代碼：

            switch (Weight)
            {
                case 0 to 2;
                    ShippingCost = "3.69";

                case 3 to 4;
                    ShippingCost = "4.86";

                case 5 to 6;
                    ShippingCost = "5.63";

                case 7 to 8;
                    ShippingCost = "5.98";

                case 9 to 10;
                    ShippingCost = "6.28";

                case 11 to 30;
                    ShippingCost = "15.72";

            }

我開始將VB轉換為C＃，並意識到要擁有多個case語句，必須聲明它們。 如您所見，我有11到30，並且不想擁有所有這些行。

Answer 1

您不能像在VB中那樣在C＃中使用比較。 但是，您可以使用掉落情況，例如：

case 0:
case 1:
case 2:
  ShippingCost = "3.69";
  break;

case 3:
case 4:
  ShippingCost = "4.86";
  break;

請注意，非空情況需要throw ， return或break語句。 另請注意，您只能在空箱情況下失敗。

編輯：

為完整性起見，正如其他人指出的那樣，在這種情況下使用一系列if語句可能更明智，例如：

if(Weight<=2) {
  ShippingCost = "3.69";
}
else if(Weight <= 4) {
  ShippingCost = "4.86";
}
... etc

Answer 2

在C＃中有直接等效項，但是，您可以使用穿透（fall-through），因此不必重復執行：

switch (Weight)
{
    case 0:
    case 1:
    case 2:
       ShippingCost = "3.69";
       break;
       ...

在這種情況下，如果語句可能更適合您：

if(Weight >= 0 && Weight <= 2){
    ShippingCost = "3.69";
} else if(Weight >= 3 && Weight <= 4){
    ShippingCost = "4.86";
}
...

Answer 3

像這樣嘗試：此解決方案無需在else if語句中寫&&

if(Weight >= 11 && Weight <= 30)
{
   ShippingCost = "15.72";
}
else if(Weight >= 9)
{
   ShippingCost = "6.28";
}
else if(Weight >= 7)
{
   ShippingCost = "5.98";
}
else if(Weight >= 5)
{
   ShippingCost = "5.63";
}
else if(Weight >= 3)
{
   ShippingCost = "4.86";
}
else if(Weight >= 0)
{
   ShippingCost = "3.69";
}

Answer 4

您也可以將其編寫為Linq one襯紙：

var ShippingCost = (new[] { new { w = 2, p = "3,69" }, 
                            new { w = 4, p = "4.86" }, 
                            new { w = 6, p = "5.63" }, 
                            new { w = 8, p = "5.98" }, 
                            new { w = 10, p = "6.28" }, 
                            new { w = 30, p = "15.72" }})
             .First(x => Weight <= x.w).p;

正如其他人已經指出的那樣，您希望確保重量超過30的物品的運輸也得到正確處理。

Answer 5

如何使用這種方法

private static double GetShippingCost(double weight)
{
    if (weight > 30) throw new ArgumentException("Weight over allowed maximum", "weight");

    if (weight <= 2) return 3.69;
    if (weight <= 4) return 4.86;
    if (weight <= 6) return 5.63;
    if (weight <= 8) return 5.98;
    if (weight <= 10) return 6.28;
    if (weight <= 30) return 15.72;

}

Answer 6

使用case的替代方法是編寫某種類來進行映射，例如：

public sealed class CostsPerWeight
{
    class CostPerWeight
    {
        public int Low;
        public int High;
        public double Cost;
    }

    readonly List<CostPerWeight> costs = new List<CostPerWeight>();

    public CostsPerWeight Add(int low, int high, double result)
    {
        // Error handling omitted for brevity. 
        // Real code should check that low < high and that ranges do not overlap.

        costs.Add(new CostPerWeight { Low = low, High = high, Cost = result } );
        return this;
    }

    public double Cost(int weight)
    {
        // This throws if the weight isn't in the list.
        // If that's not what you want, you'd have to add extra error handling here.
        return costs.First(x => x.Low <= weight && weight <= x.High).Cost;
    }
}

您將這樣使用（在此示例中，我使用雙精度代替字符串代替了字符串，但是您可以使用所需的任何類型）：

var costs = new CostsPerWeight()
    .Add( 0,  2,  3.69)
    .Add( 3,  4,  4.86)
    .Add( 5,  6,  5.63)
    .Add( 7,  8,  5.98)
    .Add( 9, 10,  6.28)
    .Add(11, 30, 15.72);

double shippingCost = costs.Cost(weight);

如果VB中有很多這樣的switch語句，那么值得考慮使用這種方法。

（使用此代碼而不是Linq單行代碼的好處是，它更易於記錄和進行單元測試。您還可以創建CostsPerWeight類實例並將其傳遞給CostsPerWeight -對於解耦代碼，依賴性注入和單元測試非常有用。 ）

在我看來，基於權重查找成本的概念正在被要求封裝在類中，而不是零碎地嵌入到代碼的各個部分中。

這是CostsPerWeight擴展示例，具有更多錯誤處理：

public class CostsPerWeight
{
    class CostPerWeight
    {
        public int Low;
        public int High;
        public double Cost;
    }

    readonly List<CostPerWeight> costs = new List<CostPerWeight>();

    double min = double.MaxValue;
    double max = double.MinValue;
    double costForMin;

    public CostsPerWeight Add(int low, int high, double cost)
    {
        if (low > high)
            throw new ArgumentException(nameof(low) + " must be less than " + nameof(high));

        if (cost < 0)
            throw new ArgumentOutOfRangeException(nameof(cost), "cost must be greater than zero");

        costs.Add(new CostPerWeight { Low = low, High = high, Cost = cost } );

        if (low < min)
        {
            min = low;
            costForMin = cost;
        }

        if (high > max)
            max = high;

        return this;
    }

    public double Cost(int weight)
    {
        if (weight < min)
            return costForMin;

        if (weight > max)
            throw new InvalidOperationException($"Weight {weight} is out of range: Must be <= {max}");

        return costs.First(x => x.Low <= weight && weight <= x.High).Cost;
    }
}

Answer 7

最清晰的方法是將數據放入對象中。

  private struct ShippingCost
  {
      public int MinWeight;
      public int MaxWeight;
      public decimal Cost;

      public ShippingCost(int min, int max, decimal cost)
      {
         MinWeight = min;
         MaxWeight = max;
         Cost = cost;
      }
  }

  private List<ShippingCost> Costs = new List<ShippingCost>
  {
      new ShippingCost(0, 2, 3.69m),
      new ShippingCost(3, 4, 4.86m),
      new ShippingCost(5, 6, 5.63m),
      new ShippingCost(7, 8, 5.98m),
      new ShippingCost(9, 10, 6.28m),
      new ShippingCost(11, 30, 15.72m),
  };

  // Choose shipping cost
  public decimal CalcShippingCost(int weight)
  {
      foreach (ShippingCost sc in Costs)
      {
          if (weight >= sc.MinWeight && weight <= sc.MaxWeight)
              return sc.Cost;
      }

      return 0.00m;     // default cost
  }

Answer 8

您無法在C＃中做到這一點。 如果您的體重最大值是30，最好的選擇是使用默認情況。

否則，如果您不想要類似

case 11:
case 12:
case 13:
....
case 28:
case 29:
case 30:

“老式” if / else if將是最易讀的解決方案

Answer 9

我建議將數據存儲在容器中並遍歷該容器。 您可以創建自己的類或使用諸如Tuple的.net類：

var shippingCostsByWeight = new List<Tuple<int, int, string>>
{
    new Tuple<int, int, string>(0, 2, "3.69"),
    new Tuple<int, int, string>(3, 4, "4.86"),
    new Tuple<int, int, string>(5, 6, "5.63"),
    new Tuple<int, int, string>(7, 8, "5.98"),
    new Tuple<int, int, string>(9, 10, "6.28"),
    new Tuple<int, int, string>(11, 30, "15.72"),
};

ShippingCost = shippingCostsByWeight
                .First(tuple => weight >= tuple.Item1 && weight <= tuple.Item2).Item3;

Answer 10

您可以使用以下情況切換語句：

case 0:
case 1:
case 2:
  shippingCost = "3.69";
  break;

... and so on

這將導致0將shippingCost設置為3.69以及1和2。:)
那就是我的解決方案