c# - 如何根据派生类字段过滤基类集合？

Question

假设我有一个名为的集合MyThings，其中包含该类的对象，Thing并且我有一个名为的类ShinyThing，它是从 派生的Thing，所以我这样做：

MyThings boxWithMyThings = new MyThings();
ShinyThing Diamond = new ShinyThing(){ facets =  10; weight = 500 };
boxWithMyThings.Add(Diamond);

如何boxWithMyThings使用派生类的属性过滤集合？

Answer 1

大概你只想要ShinyThings？如果是这样，请使用OfType：

// I'm assuming MyThings implements IEnumerable<MyThing>
var heavyShinyThings = boxWithMyThings.OfType<ShinyThing>()
                                      .Where(x => x.weight > 100);

Answer 2

您可以尝试使用该OfType方法，只要boxWithMyThings实现IEnumerable<Thing>：

var filtered = boxWithMyThings.OfType<ShingThing>().Where(st => st.facets == 10);

如果要过滤多种类型（不仅ShinyThings可以Concat与许多类似的调用一起使用：

IEnumerable<Thing> shinyEnough = boxWithMyThings.OfType<ShingThing>().Where(st => st.shininess >= 10);
IEnumerable<Thing> dirtyEnough = boxWithMyThings.OfType<DirtyThing>().Where(dt => dt.dirtiness >= 10);
var veryDirtyAndVeryCleanObjects = shinyEnough.Concat(dirtyEnough); 

当然，您可以通过检查类型和强制转换，将Where这里的所有谓词放入一个大Where子句中，这样可读性可能会降低，但效率会更高：

boxWithMyThings.Where(t =>  
     { 
         if (t is ShinyThing) 
                return (t as ShinyThing).shininess >= 10;
         else if (t is DirtyThing) 
                return (t as DirtyThing).dirtiness >= 10; 
         else return false;
     });