枚举标志属性C#

时间:2013-08-19 09:57:01

标签: c# enums attributes

我看起来有些相同的主题,但却找不到我想要的东西 我应该使用flag enum flag atribute并检查我的数据是否在此枚举的一个集合中 例如,枚举:

[Flags]
private enum MyEnum {
Apple,
Orange,
Tomato,
Potato
Melon,
Watermelon,

Fruit = Apple | Orange,
Vegetable = Tomato | Potato,
Berry = Melon | Watermelon,
}

在方法中,我应检查输入数据。我该怎么做?

private void Checking(string data){
if(MyEnum.Fruit contains data) MessageBox.Show("Fruit");
if(MyEnum.Vegetable contains data) MessageBox.Show("Vegetables");
if(MyEnum.Berry contains data) MessageBox.Show("Berry");
}

应该是什么而不是“包含数据”?

更新

private void ZZZ(){
Cheching("Apple");
}

4 个答案:

答案 0 :(得分:10)

首先,您需要使用powers-of-2序列手动编号您的值:

[Flags]
private enum MyEnum 
{
  None = 0,   // often useful
  Apple = 1,
  Orange = 2,
  Tomato = 4,
  Potato = 8,
  Melon =  16,
  Watermelon = 32,

  Fruit = Apple | Orange,
  Vegetable = Tomato | Potato,
  Berry = Melon | Watermelon,
}

[Flags]属性不是绝对必要的,它只控制ToString()行为。

要检查字符串是否与您的值匹配,您必须先将其设为枚举:

private void Checking(string data)
{      
    MyEnum v = (MyEnum) Enum.Parse(typeof(MyEnum), data);

    if((MyEnum.Fruit & v) != 0) MessageBox.Show("It's a Fruit"); 
    ...
}

但请注意,Enum和这样的字符串与Parse()之间的交换是有限的。

答案 1 :(得分:2)

除Henk Holterman的解决方案外,您还可以使用扩展方法

[Flags]
private enum MyEnum {
  None = 0, 
  Apple = 1,
  Orange = 2,
  Tomato = 4,
  Potato = 8,
  Melon = 16,
  Watermelon = 32,

  Berry = Melon | Watermelon, 
  Fruit = Apple | Orange,
  Vegetable = Potato | Tomato
}

private static class MyEnumExtensions { 
  public static Boolean IsFruit(this MyEnum value) {
    return (value & MyEnum.Fruit) == MyEnum.Fruit;
  }

  public static Boolean IsVegetable(this MyEnum value) {
    return (value & MyEnum.Vegetable) == MyEnum.Vegetable;
  }

  public static Boolean IsBerry(this MyEnum value) {
    return (value & MyEnum.Berry) == MyEnum.Berry;
  }
}

...

MyEnum data = ...

if (data.IsBerry()) {
  MessageBox.Show("Berry");       
} 

答案 2 :(得分:2)

您还可以使用HasFlag - 类的Enum - 方法。正如Henk指出的那样,需要使用powers-of-2序列的值手动为你的枚举赋值。

[Flags]
private enum MyEnum 
{
    Apple = 1,
    Orange = 2,
    Tomato = 4,
    Potato = 8,
    Melon  16,
    Watermelon = 32,

    Fruit = Apple | Orange,
    Vegetable = Tomato | Potato,
    Berry = Melon | Watermelon,
}

然后,要检查您是否可以使用以下方法,该方法适用于枚举的所有组成部分:

void Cheking(string data)
{
    // Get the enum value of the string passed to the method
    MyEnum myEnumData;
    if (Enum.TryParse<MyEnum>(data, out myEnumData))
    {
        // If the string was a valid enum value iterate over all the value of
        // the underlying enum type
        var values = Enum.GetValues(typeof(MyEnum)).OfType<MyEnum>();
        foreach (var value in values)
        {
            // If the value is not a power of 2 it is a composed one. If it furthermore
            // has the flag passed to the method this is one we searched.
            var isPowerOfTwo = (value != 0) && ((value & (value - 1)) == 0);
            if (!isPowerOfTwo && value.HasFlag(myEnumData))
            {
                MessageBox.Show(value.ToString());
            }
        }
    }
    // In case an invalid value had been passed to the method
    // display an error message.
    else
    {
        MessageBox.Show("Invalid Value");
    }
}

或者使用LINQ以较短的方式编写它:

var results = Enum.GetValues(typeof(MyEnum))
                  .OfType<MyEnum>()
                  .Select(x => new { Value = x, IsPowerOfTwo = (x != 0) && ((x & (x - 1)) == 0) } )
                  .Where(x => !x.IsPowerOfTwo && x.Value.HasFlag(myEnumData))
                  .Select(x => x.Value.ToString());

这将给出包含结果的IEnumerable<string>。如果myEnumData的值为MyEnum.Apple,则结果将仅包含值"Fruit"

答案 3 :(得分:1)

正如@Henk Holterman建议的那样,首先需要为枚举值赋值 所有值应为2的幂(并避免使用0,除了“无”的特殊情况) 看起来应该是这样的:

 MyEnum eVal= (MyEnum ) Enum.Parse( typeof(MyEnum), data, true );
 if((MyEnum.Fruit & eVal) != 0) MessageBox.Show("Fruit");

您可能想要阅读有关bitwise和布尔代数的更多信息。