如何基於派生類字段過濾基類集合？

Question

假設我有一個名為MyThings的集合，其中包含Thing類的對象，而我有一個名為ShinyThing的類，該類派生自Thing ，所以我這樣做：

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

如何使用派生類的屬性過濾集合boxWithMyThings ？

Answer 1

想必您只想要ShinyThings？ 如果是這樣，請使用OfType ：

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

Answer 2

你可以嘗試使用OfType方法，只要boxWithMyThings實現IEnumerable<Thing> ：

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

如果要過濾多種類型（不僅是ShinyThings還可以將Concat與許多類似的調用一起使用：

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); 

當然，您可以通過檢查類型和類型轉換將此處的所有Where謂詞放到一個大的Where子句中，這可能不那么可讀，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;
     });