泛型集合为何为null?

[leon51]

从一个泛型集合products 中找出所有供应商为“CC”，强转为另一泛型集合productSizes ，下面的代码productSizes 为何为空？是否不能这么写？

List<Product> products = new List<Product>();
list.Add(new Product {id= 1, Name = "A" ,Heigh=10, Width = 10, Length = 20, Suplier = "AA"});
list.Add(new Product {id= 2, Name = "A" ,Heigh=10, Width = 7, Length = 21, Suplier = "BB"});
list.Add(new Product {id= 3, Name = "A" ,Heigh=10, Width = 6, Length = 22, Suplier = "CC"});
list.Add(new Product {id= 4, Name = "A" ,Heigh=10, Width = 9, Length = 19, Suplier = "CC"});
//...

List<ProductSize> productSizes = list
	.Select(p=>p.Suplier, p.Heigh, p.Width, p.Length)
	.Where(p=>p.Suplier == "CC") as List<ProductSize>;

[leon51]

奇怪了，我去掉Where后productSizes仍为null

[楠小南]

两者是什么关系？可以转不，可以转就用cast

List<ProductSize> productSizes = list .Where(p=>p.Suplier == "CC").Cast<ProductSize>().Tolist();

[threenewbee]

List<ProductSize>类型不能从IEnumerable<Product>得到，你得Select(x => new ProductSize() ...)

[by_封爱]

跟where没关系 是转换的问题. 你select出来的对象不能转换为ProductSize 匿名也不行.. 得使用类对象...

List<ProductSize> productSizes = list
    .Select(p=>new ProductSize (){Suplier=p.Suplier, Heigh=p.Heigh, Width=p.Width, Length=p.Length})
    .Where(p=>p.Suplier == "CC").ToList();

[阿蒙Armon]

#4楼正解，as无法转换所以为null