Question

假设我有一个名为MyThings的集合，它包含类Thing的对象，我有一个名为ShinyThing的类，它是从Thing派生的，所以我做：

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

如何使用派生类的属性过滤集合boxWithMyThings？

Answer 1

想必你只想要ShinyThings？如果是，请使用OfType：

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

Answer 2

只要OfType实施boxWithMyThings，您就可以尝试使用IEnumerable<Thing>方法：

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

如果您想要过滤多种类型（不只是ShinyThings，您可以将Concat与许多类似的来电一起使用：

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转换来将所有Where谓词放在一个大Where子句中，这可能不太可读但效率更高：

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;
     });

如何根据派生类字段过滤基类集合？

2 个答案: