是什么铸造并使用＆QUOT之间的差;如＆QUOT;在C＃中？ [英] What is the difference between casting and using "as" in C#?

问题描述

如果是有区别的，就是做以下投的两种方法之间的区别？

在这种情况下，电子是 GridViewRowEventArgs 对象。

 的GridView GV =（GridView控件）e.Row.FindControl（货车）; //第一种方式GridView控件GV2 = e.Row.FindControl（GV）作为GridView控件; //第二种方法
 

解决方案

的区别是：

• 如果一个转换失败，它抛出一个<一个href=\"http://msdn.microsoft.com/en-us/library/system.invalidcastexception.aspx\"><$c$c>InvalidCastException.


• 如果在为运营商失败，它只是返回一个空引用。


• 您不能使用为与非空值类型（例如，你不能这样做 0为int ）。


• 转换操作符也用于拆箱。 （为可用于拆箱到一个空值类型。）


• 转换操作符还可以执行用户定义的转换。

编辑：我的written什么时候，我觉得在其他地方合适的做法是使用哪个运营商。这可能是值得一读...

If there is a difference, what is the difference between the two ways of doing the following cast?

In this case e is a GridViewRowEventArgs object.

GridView gv = (GridView)e.Row.FindControl("gv"); //first way

GridView gv2 = e.Row.FindControl("gv") as GridView; //second way

解决方案

The differences are:

• If a cast fails, it throws an InvalidCastException.
• If the as operator fails, it just returns a null reference.
• You can't use as with non-nullable value types (e.g. you can't do "o as int").
• The cast operator is also used for unboxing. (as can be used to unbox to a nullable value type.)
• The cast operator can also perform user-defined conversions.

EDIT: I've written elsewhere about when I feel it's appropriate to use which operator. That might be worth a read...

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