c# - Casting and interface inheritance -

each item has interface, iitem. this, there interface known idrawableitem inherits item.

the code below, trying draw drawable item, cannot collection class stores accepts iitem. can add inherits iitem class, using other methods can achieved casting.

foreach (var item in items) {     item.draw();               // casting go here. } 

i know how cast, as etc... acceptable? best practice?

just wondering if there other ways handle such scenarios.

use enumerable.oftype extract elements of items implement idrawableitem:

foreach(var item in items.oftype<idrawableitem>()) {     item.draw(); } 

to address question nanook asked in comments above code translated code equivalent following:

foreach(var item in items) {      if(item idrawableitem) {         ((idrawable)item).draw();      } } 

of course, there iterator behind scenes looks this:

public static ienumerable<t> oftype<t>(this ienumerable<tsource> source) {     if(source == null) {         throw new argumentnullexception("source");     }     foreach(tsource item in source) {         if(item t) {             yield return (t)item;         }     } } 

so, shows iterate through items once. of course, there no requirement oftype implemented above sensible thing do.