使用Linq

Question

我正在尝试使用Linq获取更一般的实体集合中的所有Point对象。请参阅以下代码中的注释。似乎.Cast（）和.OfType（）似乎没有做我需要的。代码是否是最佳选择？

// IHost has an Entities collection that contains different types of entities that implement IEntity, and one of specific types may be a Point object.
    public System.Linq.ParallelQuery<Point> GetPoints(IHost entityHost)
    {
        // Is this the best way to get a collection of Points from the Entities, using Linq?
        // I believe Entities.OfType<Point> does not work because the type of item in Entities is IEntity
        // I believe Entities.Cast<Point> does not work because there will be exceptions due to non-Point objects in the collection
        return entityHost.Entities.Where(o => o is Point).Cast<Point>();
    }

Answer 1

OfType结合了这两项操作：

 return entityHost.Entities.OfType<Point>()

  

我认为Entities.OfType<Point>不起作用，因为Entities中的项目类型为IEntity

不，那是声明的类型Entities。 OfType查看每个项目的实际类型，如果＆＃34;是＆＃34;则将其添加到结果中。一个Point。 ＆＃34;是＆＃34;＆＃34;我的意思是＆＃34;可以演绎到＆＃34; - 字面意思using the is operator：

static IEnumerable<TResult> OfTypeIterator<TResult>(IEnumerable source)      
{
    foreach (object obj in source) {
        if (obj is TResult) yield return (TResult)obj;
    }
}