從IEnumerable獲取泛型GetOnlyKeys的C＃擴展方法<KeyValuePair <int, string>>

Question

我有一個IEnumberable>，我只想要Keys的列表，但是轉換爲所需的類型（即可能是short而不是int）。這用於一個自定義通用多選控件綁定到，但數據庫需要potientially'短'來保存。

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; 
    } 

任何意見如何使我的通用擴展方法的工作？
謝謝！

Answer 1

你想只獲得轉換爲短的密鑰？

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

如果你想要去的任何類型的，那麼你會做這樣的事情：

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)! 
}