使用System.Reflection檢索const字符串字段的列表

Question

我已經創建了一個類類（顯示其中的一個類），並帶有我想實例化的const字符串。

public static class HTDB_Cols
{
    public sealed class Assistant
    {
        public const string EntryID  = "entryID",
                CustName  = "custName",
                SerialNum  = "serialNum",
                UserName  = "userName",
                Password  = "password",
                EndDate  = "end_date",
                CustID  = "custID",
                TmpCheck  = "tmpCheck",
                Isfamily  = "isfamily",
                Isserver  = "isserver";
    }
}               

public static class DB
{    
    public static void insert(string TableName)
    {
        ColumnsCollection = typeof(HTDB_Cols).GetNestedTypes().Where(f => f.DeclaringType.Name.ToLower().Equals(TableName.ToLower()));
    } 
}

上面的代碼顯示了我的嘗試，但是即使經過大量的試驗和錯誤，我仍然無法理解它。

我想擁有所有列的列表作為const集合數組或列表。

Answer 1

var dict = typeof(HTDB_Cols).GetNestedTypes()
            .First(t=>String.Compare(t.Name,TableName,true)==0)
            .GetFields()
            .ToDictionary(f => f.Name, f => f.GetValue(null));

取得清單

var list = typeof(HTDB_Cols).GetNestedTypes()
            .First(t => String.Compare(t.Name, TableName, true) == 0)
            .GetFields()
            .Select(f => f.GetValue(null) as string)
            .ToList();

Answer 2

看起來您需要的是一個enum ：

enum Assistant
{
    EntryID,
    CustName,
    SerialNum,
    UserName,
    Password,
    EndDate,
    CustID,
    TmpCheck,
    Isfamily,
    Isserver
};

然后，您可以通過執行以下操作將所有這些名稱獲取為字符串：

string[] allNames = Enum.GetNames(typeof(Assistant));

只要您可以接受讓變量名成為您關心的實際值，這就是有效的選擇。 我注意到它們在您的示例中並不完全相同，但主要只是大小寫。 如果您可以使用變量名稱作為值，或者將變量名稱更改為所需的值，那么這可能是您的最佳選擇。

現在，如果讓變量名與其代表的值不同真的很重要，或者如果您需要代表非法標識符的值（例如，其中一個值帶有空格，那是不好的，並且它們不能永遠不要以數字開頭，否則它們可能太長而不能成為方便的名稱）。 如果真是這樣，那么您真正想要的是一個由字符串支持的枚舉，而不是整數或其他數字類型。 在C＃中，這並不是嚴格可行的，但是由於在我實際編寫以下類之前就​​已經提出了，這是我創建自己的字符串支持的枚舉的最佳嘗試。 如果您確實需要與它們表示的字符串值不同的變量名，那么這應該對您有用。

所有重要的內容都位於頂部， Equals之后的大多數內容都只是語法糖。

public struct StringEnum
{
    #region Code that is to be configured
    //For each value to be publicly exposed add a new field.
    public static readonly StringEnum Alpha = new StringEnum("Alpha Value");
    public static readonly StringEnum Beta = new StringEnum("Beta Value");
    public static readonly StringEnum Invalid = new StringEnum("Invalid");


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

            //TODO refactor to use reflection so it doesn't need to be manually updated.
        }
    }

    #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 
    //    //(if this is a class an not a struct), but you 
    //    //shouldn't have this be anything that doesn't exist as one of the options defined at the top of 
    //    //the page.
    //    value = "Invalid";
    //}
    /// <summary>
    /// primary constructor
    /// </summary>
    /// <param name="value">The string value that this is a wrapper for</param>
    private StringEnum(string value)
    {
        this.value = value;
    }

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

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

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

    /// <summary>
    /// Strongly typed equals method.
    /// </summary>
    /// <param name="other">Another StringEnum to compare this object to.</param>
    /// <returns>True if the objects are equal.</returns>
    public bool Equals(StringEnum other)
    {
        return value == other.value;
    }

    /// <summary>
    /// Equals method typed to a string.
    /// </summary>
    /// <param name="other">A string to compare this object to.  
    /// There must be a Group associated with that string.</param>
    /// <returns>True if 'other' represents the same Group as 'this'.</returns>
    public bool Equals(string other)
    {
        return value == other;
    }

    /// <summary>
    /// Overridden equals operator, for convenience.
    /// </summary>
    /// <param name="first"></param>
    /// <param name="second"></param>
    /// <returns>True if the objects are equal.</returns>
    public static bool operator ==(StringEnum first, StringEnum second)
    {
        return object.Equals(first, second);
    }

    public static bool operator !=(StringEnum first, StringEnum second)
    {
        return !object.Equals(first, second);
    }

    /// <summary>
    /// Properly overrides GetHashCode so that it returns the hash of the wrapped string.
    /// </summary>
    /// <returns></returns>
    public override int GetHashCode()
    {
        return value.GetHashCode();
    }

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

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

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

    /// <summary>
    /// A string representation of this object.
    /// </summary>
    /// <returns></returns>
    public override string ToString()
    {
        return value;
    }
}