来自 IEnumerable> 的通用 GetOnlyKeys 的 C# 扩展方法

Question

我有一个 IEnumberable>我只想要键列表，但转换为所需的类型（即可能是短类型而不是整数）。这用于绑定到的自定义通用多选控件，但数据库可能需要“短”来保存。

public static IEnumerable<T> GetKeysOnly<T>(this IEnumerable<KeyValuePair<int, string>> values)
    {
        Dictionary<int, string> valuesDictionary = values.ToDictionary(i => i.Key, i => i.Value);

        List<int> keyList = new List<int>(valuesDictionary.Keys);

        // Returns 0 records cuz nothing matches
        //List<T> results = keyList.OfType<T>().ToList(); 

        // Throws exception cuz unable to cast any items
        //List<T> results = keyList.Cast<T>().ToList(); 

        // Doesn't compile - can't convert int to T here: (T)i
        //List<T> results = keyList.ConvertAll<T>(delegate(int i) { return (T)i; }); 

        throw new NotImplementedException();
    }

    public static IEnumerable<short> GetKeysOnly(this IEnumerable<KeyValuePair<int, string>> values)
    {
        Dictionary<int, string> valuesDictionary = values.ToDictionary(i => i.Key, i => i.Value);
        List<int> keyList = new List<int>(valuesDictionary.Keys);

        // Works but not flexable and requires extension method for each type
        List<short> results = keyList.ConvertAll(i => (short)i);
        return results;
    }

关于如何使我的通用扩展方法起作用有什么建议吗？
谢谢！

Answer 1

您只想将按键转换为短键吗？

var myList = valuesDictionary.Select(x => (short)x.Key).ToList();
// A Dictionary can be enumerated like a List<KeyValuePair<TKey, TValue>>

如果你想进入任何类型，那么你会这样做：

public static IEnumerable<T> ConvertKeysTo<T>(this IEnumerable<KeyValuePair<int, string>> source)
{
     return source.Select(x => (T)Convert.ChangeType(x.Key, typeof(T)));
     // Will throw an exception if x.Key cannot be converted to typeof(T)!
}