将0.0强制转换为两倍有什么问题？ [英] What's wrong with casting 0.0 to double?

问题描述

当我尝试将0.0转换为double时，我有 InvalidCastException ，为什么会这样？代替（float）value 很好。

I have InvalidCastException when I try to cast 0.0 to double, why is that so? It's fine when I do (float)value instead.

推荐答案

通常，当您输入值时键入对象（称为 boxing ），您需要将其 unbox 完全匹配 值类型。您不能将其转换为其他类型。这就是这里发生的情况。

In general, when you put a value type into an object (called boxing) you need to unbox it to the exact same value type. You cannot do a conversion to another type instead. This is what happens here.

如果您真的要转换对象，请先 将其拆箱。假设您的原始值是 float ，然后再将其装在对象中：

If you really want to convert the object, you first need to unbox it. Say your original value was a float before you boxed it in an object:

double d = (double) (float) value;

或使用其他人建议的方法，该方法使用转换。这样做的好处是不必知道原始类型。

Or use the method proposed by others, which uses Convert. This has the advantage that the original type doesn’t have to be known.

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