C# 将对象转换为枚举
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C# Casting with objects to Enums
提问by sweetfa
This question relates to casting of enums within generic methods
这个问题与通用方法中的枚举转换有关
Given an enum
给定一个枚举
public enum Crustaceans
{
Frog = 1,
Toad = 4
}
I can create an instance of my enum simply enough
我可以简单地创建我的枚举实例
short val = 4;
Crustaceans crusty = (Crustaceans) val;
However, if
然而，如果
short val = 4;
object obj = (object) val;
Crustaceans crusty = (Crustaceans)obj;
a runtime exception is thrown attempting to perform the initialisation of crusty.
尝试执行硬皮的初始化时抛出运行时异常。
Can anyone explain why this is happening, and why it is not legal to do such a thing.
谁能解释为什么会发生这种情况，以及为什么这样做是不合法的。
Not that I really wanted to do this, but I cam across an issue when trying to get something similar happening with generics and effectively that is what is happening under the covers. i.e.
并不是说我真的想这样做，但是我在尝试使用泛型实现类似的事情时遇到了一个问题，实际上这就是幕后发生的事情。IE
public T dosomething<T>(short val) where T : new()
{
T result = (T)(object) val;
return result;
}
So what I am attempting to do is have a generic function that works with enums and non-enums (not so critical-but would be nice) that can be set to a short value without throwing an exception and actually initialising the correct enum value.
所以我试图做的是有一个通用函数，它可以与枚举和非枚举一起使用（不是那么重要 - 但会很好），可以设置为一个短值而不抛出异常并实际初始化正确的枚举值。
采纳答案by Tigran
Something like this probablywill help you:
像这样的事情可能会帮助你：
public T dosomething<T>(object o)
{
T enumVal= (T)Enum.Parse(typeof(T), o.ToString());
return enumVal;
}
But this will work onlywith enums, for clear reason of using Enum.Parse(..)
但这仅适用于枚举，因为使用的明确原因Enum.Parse(..)
And use this like, for example:
并使用它，例如：
object o = 4;
dosomething<Crustaceans>(o);
That will return Toadin yourcase.
这将Toad在您的情况下返回。
回答by Tal Segal
There are cases when you can not use Generics (like in a WPF Converter when you get the value as an object).
In this case you can not cast to intbecause the enum type may not be an int.
This is a general way to do it without Generics.
The Example is given inside a WPF Converter, but the code inside is general:
在某些情况下，您不能使用泛型（例如在 WPF 转换器中，当您将值作为 时object）。在这种情况下，您不能强制转换为，int因为枚举类型可能不是int. 这是没有泛型的通用方法。该示例在 WPF 转换器中给出，但里面的代码是通用的：
using System;
using System.Windows;
using System.Windows.Data;
.
.
.
public object ConvertBack(object value, Type targetType, object parameter, System.Globalization.CultureInfo culture)
{
var enumType = value.GetType();
var underlyingType = Enum.GetUnderlyingType(enumType);
var numericValue = System.Convert.ChangeType(value, underlyingType);
return numericValue;
}
回答by Evgeniy Miroshnichenko
By default enum digit values have type = int. In your code you want to cast value that have short type to enum type. For that, you have to set short type to your enum values. This will work:
默认情况下，枚举数字值具有 type = int。在您的代码中，您希望将具有短类型的值转换为枚举类型。为此，您必须将短类型设置为您的枚举值。这将起作用：
public enum Crustaceans : short // <--
{
Frog = 1,
Toad = 4
}
short @short = 1;
object @object = @short;
var @enum = (Crustaceans)@object; // @enum = Crustaceans.Frog
if you don't want to change default enum values type
如果您不想更改默认枚举值类型
public enum Crustaceans
{
Frog = 1,
Toad = 4
}
object @object = Crustaceans.Frog;
var @enum = (Crustaceans)@object; // @enum = Crustaceans.Frog
or
或者
public enum Crustaceans
{
Frog = 1,
Toad = 4
}
int @integer= 1;
var @enum = (Crustaceans)@integer; // @enum = Crustaceans.Frog
回答by hazzik
In case of integral types boxed as objects the correct way to do the conversion is using Enum.ToObjectmethod:
如果整数类型装箱为对象，正确的转换方法是使用Enum.ToObject方法：
public T Convert<T>(object o)
{
T enumVal= (T)Enum.ToObject(typeof(T), o);
return enumVal;
}
