Question

我有一个我想尝试使用的结构，如枚举：

public struct SQLDS_statementTypes
{
    public static string Select = "Select", 
        Update = "Update", Insert = "Insert", Delete = "Delete";
}

但它抛出一个错误：“运算符'=='不能应用于此语句中'SQLDS_statementTypes'和'string'”类型的操作数：

if (statement == SQLDS_statementTypes.Update)

有没有解决这个问题？

Answer 1

为什么不使用常规枚举？ http://msdn.microsoft.com/en-us/library/sbbt4032.aspx

Answer 2

有人正在寻找一些看起来或多或少你正在寻找的东西（我不能找到链接）并且我当时写了这个。您可能希望将类名更改为更符合您的需要。我希望添加/删除值的配置很简单，如果没有我可以详细说明。

public struct Group
{
    #region Code that is to be configured
    public static readonly Group Alpha = new Group("Group Alpha");
    public static readonly Group Beta = new Group("Group Beta");
    public static readonly Group Invalid = new Group("N/A");


    public static IEnumerable<Group> AllGroups
    {
        get
        {
            yield return Alpha;
            yield return Beta;
            yield return Invalid;
            //...
            //add a yield return for all instances here.
        }
    }

    #endregion
    private string value;

    /// <summary>
    /// default constructor
    /// </summary>
    //private Group()
    //{
    //    //you can make this default value whatever you want.  null is another option I considered, but you 
    //    //shouldn't have this me anything that doesn't exist as one of the options defined at the top of 
    //    //the page.
    //    value = "N/A";
    //}
    /// <summary>
    /// primary constructor
    /// </summary>
    /// <param name="value">The string value that this is a wrapper for</param>
    private Group(string value)
    {
        this.value = value;
    }

    /// <summary>
    /// Compares the Group to another group, or to a string value.
    /// </summary>
    /// <param name="obj"></param>
    /// <returns></returns>
    public override bool Equals(object obj)
    {
        if (obj is Group)
        {
            return this.value.Equals(((Group)obj).value);
        }

        string otherString = obj as string;
        if (otherString != null)
        {
            return this.value.Equals(otherString);
        }

        throw new ArgumentException("obj is neither a Group nor a String");
    }

    public override int GetHashCode()
    {
        return value.GetHashCode();
    }

    /// <summary>
    /// returns the internal string that this is a wrapper for.
    /// </summary>
    /// <param name="group"></param>
    /// <returns></returns>
    public static implicit operator string(Group group)
    {
        return group.value;
    }

    /// <summary>
    /// Parses a string and returns an instance that corresponds to it.
    /// </summary>
    /// <param name="input"></param>
    /// <returns></returns>
    public static Group Parse(string input)
    {
        return AllGroups.Where(item => item.value == input).FirstOrDefault();
    }

    /// <summary>
    /// Syntatic sugar for the Parse method.
    /// </summary>
    /// <param name="other"></param>
    /// <returns></returns>
    public static explicit operator Group(string other)
    {
        return Parse(other);
    }

    public override string ToString()
    {
        return value;
    }
}

Answer 3

你做不到。如果你想进行这样的字符串比较，为什么不在公共成员中使用静态类呢？

static class StatementTypes
{
    public static Select
    {
        get { return "Select"; }
    }
}

然后你可以在比较中使用StatementTypes.Select。

Answer 4

错误是正确的，我认为（来自错误）statement的类型为SQLDS_statementTypes，但SQLDS_statementTypes.Update的类型为string，因此您尝试将结构与a进行比较字符串，默认情况下对C＃没有意义。

制作statement类型的string，如果你真的想要这样做，它会编译，但我不确定为什么你不会只使用常规的enum第一名。

您是否想要获得枚举值的string值？ C＃默认情况下已经这样做了：

public enum Coordinates
{
    Cartesian,
    Polar
}

...

// x will contain the string "Cartesian"
var x = Coordinates.Cartesian.ToString();

在C＃中，如何像enum一样使用struct？

4 个答案: