[英]How to make nested foreach loop method generic
我想获取所有(唯一)Apple(或Oranges)对象的列表:
var theBigFruitsList = new List<Fruits>{
new Fruits(){
Apples = new List<Apple>{
new Apple { Id = 1 },
new Apple { Id = 2 }
}
},
Oranges = new List<Orange>{
new Orange { Id = 4 },
new Orange { Id = 5 }
}
},
FruitBoolean = False,
FruitCount = 4,
},
new Fruits(){
Apples = new List<Apple>{
new Apple { Id = 3 },
new Apple { Id = 1 },
}
},
Oranges = new List<Orange>{
new Orange { Id = 6 },
}
}
FruitBoolean = False,
FruitCount = 3,
}
}
我为它写了这个方法:
public static List<Apple> GetApplesFromBigFruitsList(List<Fruits> theBigFruitsList )
{
var dc = new Dictionary<long, Apple>();
foreach (var fruits in theBigFruitsList)
{
foreach (var apple in fruits.Apples)
{
if (!dc.ContainsKey(apple.Id))
dc.Add(apple.Id, apple);
}
}
return dc.Values.ToList();
}
但是,除了苹果和橙子之外,object 中还有许多其他类型的“水果”,我有超过 10 次这种方法,其中苹果这个词只是被橙子取代了。让它通用是有意义的。
我写了这个 function 但它给出了一个错误,因为 Fruits class 没有实现枚举器。 请帮忙!
public static List<T> FilterFruits<T>(T typeToGet, List<Fruits> theBigFruitsList)
{
List<T> fruitResult = new List<T>();
var fruitType = typeToGet.GetType();
foreach (var fruits in theBigFruitsList)
{
foreach (var fruit in fruits) //errors, intention is to loop over all properties in the Fruits entity to find one specific type
if (fruit.GetType() == fruitType) //check if type is Apple
{
fruitResult.AddRange(fruits); //add the Apples to a list
}
}
return fruitResult;
}
课程:
public class Fruits{
public List<Apple> Apples { get; set; }
public List<Orange> Oranges { get; set; }
public List<Pineapple> Pineapples { get; set; }
public List<Mango> Mangos { get; set; }
public bool FruitBoolean { get; set; }
public long FruitCount { get; set; }
}
public class Apple{
public long Id { get; set; }
}
public class Orange{
public long Id { get; set; }
}
public class Pineapple{
public long Id { get; set; }
}
public class Mango{
public long Id { get; set; }
}
所需的方法结果:
var Apples = List<Apple>{
new Apple { Id = 1 },
new Apple { Id = 2 },
new Apple { Id = 3 }
}
将每种水果存储在自己的单独列表中是……很奇怪。 我建议您将它们组合在一个列表中。 如果您无法更改设计,则可以在运行时将它们组合起来,如下所示:
IEnumerable<object> GetAllFruits(Fruits bigFruitlist)
{
return ((IEnumerable<object>)bigFruitlist.Apples)
.Concat((IEnumerable<object>)bigFruitlist.Oranges)
.Concat((IEnumerable<object>)bigFruitlist.Mangoes)
.Concat((IEnumerable<object>)bigFruitlist.Pineapples);
}
当然,如果你所有的水果都有一个共同的接口会更好——那么你就不需要IEnumerable<object>
——但如果你也不能做出改变,这仍然可以工作。
获得组合列表后,rest 很容易:
List<T> FilterFruits<T>(Fruits bigFruitlist)
{
return GetAllFruits(bigFruitList).OfType<T>().ToList();
}
如果出于某种原因您想避免枚举所有列表(即列表很大并且性能是一个问题),您也可以使用列表数组来做到这一点。
object[] GetAllFruitLists(Fruits bigFruitlist)
{
return new object[]
{
bigFruitlist.Apples,
bigFruitlist.Oranges,
bigFruitlist.Mangoes,
bigFruitlist.Pineapples
};
}
List<T> FilterFruits<T>(Fruits bigFruitlist)
{
return GetAllFruitLists(bigFruitList).OfType<List<T>>();
}
要在运行时询问对象的类型,请使用反射。 像这样:
public static List<T> FilterFruits<T>(List<Fruits> fruitsList) where T : IFruit
{
List<T> fruitResult = new List<T>();
var fruitType = typeof(T);
foreach (var fruits in fruitsList)
{
foreach (var fp in typeof(Fruits).GetProperties())
{
if (fp.PropertyType == typeof(List<T>)) //check if type is Apple
{
fruitResult.AddRange((List<T>)(object)fp.GetValue(fruits)); //add the Apples to a list
}
}
}
return fruitResult;
}
要在没有反射的情况下执行此操作(在某些情况下可能太慢),您可以执行以下操作:
public static List<T> GetDistinct<T>( IEnumerable<Fruits> fruitsList) where T : IFruit
{
var ft = typeof(T);
Func<Fruits, List<T>> picker;
if (ft == typeof(Apple))
{
picker = (fruits) => (List<T>)(object)fruits.Apples;
}
else if (ft == typeof(Mango))
{
picker = (fruits) => (List<T>)(object)fruits.Mangos;
}
else
{
throw new NotImplementedException($"Fruit Type {ft.Name} not supported");
}
var rv = new Dictionary<long, T>();
foreach (var t in fruitsList.SelectMany(picker))
{
if (!rv.ContainsKey(t.Id))
{
rv.Add(t.Id, t);
}
}
return rv.Values.ToList();
}
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