实施通用扩展

Question

I have this method that extends IList<> for special ordering I need to implement. It takes an IList of IDisplayOrderable and an integer forRandom , and returns an ordered list but randomizing the items that have the DisplayOrder equals to the forRandom parameter.

public static IList<IDisplayOrderable> ReorderList(this IList<IDisplayOrderable> lstMain, int forRandom)
{
    List<IDisplayOrderable> result = new List<IDisplayOrderable>();
    Random rnd = new Random();
    result.AddRange(lstMain.Where(x => x.DisplayOrder.GetValueOrDefault(int.MaxValue) < forRandom).OrderBy(x => x.DisplayOrder.GetValueOrDefault(int.MaxValue)));
    result.AddRange(lstMain.Where(x => x.DisplayOrder.GetValueOrDefault(int.MaxValue) == forRandom).Shuffle(rnd));
    result.AddRange(lstMain.Where(x => x.DisplayOrder.GetValueOrDefault(int.MaxValue) > forRandom).OrderBy(x => x.DisplayOrder.GetValueOrDefault(int.MaxValue)));
    return result;
}

The IDisplayOrderable is a simple interface that expose the DisplayOrder for ordering different types.

public interface IDisplayOrderable
{
    Nullable<int> DisplayOrder { get; set; }
}

I want to achieve the same functionality but for a generic list that I wish to explicit set the 'OrderBy' property, something like: MyList.ReorderList(x=>x.DisplayOrder, 1000) but also MyOtherList.ReorderList(x=>x.OtherDisplayOrder, 1000) . I read some about reflection to do this but haven't managed to get something working. Any help or direction would be appreciated

Answer 1

Change ReorderList method so that it accepts a delegate returning the value of your desired property:

public static IList<T> ReorderList(this IList<T> lstMain,Func<T,int?> getter, int forRandom)
{
    List<T> result = new List<T>();
    Random rnd = new Random();
    result.AddRange(lstMain.Where(x => getter(x).GetValueOrDefault(int.MaxValue) < forRandom).OrderBy(x => getter(x).GetValueOrDefault(int.MaxValue)));
    result.AddRange(lstMain.Where(x => x.getter(x).GetValueOrDefault(int.MaxValue) == forRandom).Shuffle(rnd));
    result.AddRange(lstMain.Where(x => getter(x).GetValueOrDefault(int.MaxValue) > forRandom).OrderBy(x => xgetter(x).GetValueOrDefault(int.MaxValue)));
    return result;
}

and call it like:

MyOtherList.ReorderList(x=>x.OtherDisplayOrder, 1000)