Extension Method的两个小例子（Dictionary_FindKeyByValue && T_Clone）

直接上代码了，以后碰到类似的就直接用了

public static TKey FindKeyByValue<TKey, TValue>(this IDictionary<TKey, TValue> dictionary, TValue value)
        {
            if (dictionary == null)
                throw new ArgumentNullException("dictionary");

            foreach (KeyValuePair<TKey, TValue> pair in dictionary)
                if (value.Equals(pair.Value)) return pair.Key;

            throw new Exception("the value is not found in the dictionary");
        }

   

  public static T Clone<T>(this T source)
        {
            T Cloned = (T)Activator.CreateInstance(source.GetType());

            (from Property in source.GetType().GetProperties()

             where Property.GetGetMethod() != null && Property.GetSetMethod() != null
             select Property).ToList().ForEach(Property =>
             {
                 // Check if the object inherits from ICollection (The ICollection interface is the base interface for classes in the System.Collections namespace
                 if (!Property.PropertyType.GetInterfaces().Contains(typeof(ICollection)))
                 {
                     object PropertyValue = Property.GetGetMethod().Invoke(source, Property.GetGetMethod().GetParameters());

                     if (PropertyValue != null && PropertyValue is DependencyObject) { PropertyValue = PropertyValue.Clone(); }

                     // if PropertyValue is not a value type and is itself a dependency object, it must be "cloned" as well
                     Property.GetSetMethod().Invoke(Cloned, new object[] { PropertyValue });
                 }
                 else if (Property.PropertyType.GetInterfaces().Contains(typeof(ICollection)))
                 {
                     ICollection CollectionValue = (ICollection)Property.GetGetMethod().Invoke(source, new object[] { }); Property.SetValue(Cloned, CollectionValue, null);
                 }

             });
            return Cloned;
        }