从IEnumerable获取泛型GetOnlyKeys的C＃扩展方法<KeyValuePair <int, string>>

Question

我有一个IEnumberable>，我只想要Keys的列表，但是转换为所需的类型（即可能是short而不是int）。这用于一个自定义通用多选控件绑定到，但数据库需要potientially'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; 
    } 

任何意见如何使我的通用扩展方法的工作？
谢谢！

Answer 1

你想只获得转换为短的密钥？

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类型的，那么你会做这样的事情：

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)! 
}