IsAssignableFrom、IsInstanceOfType 和 is 关键字，有什么区别? [英] IsAssignableFrom, IsInstanceOfType and the is keyword, what is the difference?

问题描述

我有一个安全转换对象的扩展方法，如下所示:

I have an extension method to safe casting objects, that looks like this:

public static T SafeCastAs<T>(this object obj) {
    if (obj == null)
        return default(T);

    // which one I should use?

    // 1. IsAssignableFrom
    if (typeof(T).IsAssignableFrom(obj.GetType()))
        return (T)obj;

    // 2. IsInstanceOfType
    if (typeof(T).IsInstanceOfType(obj))
        return (T) obj;

    // 3. is operator
    if (obj is T)
        return (T) obj;

    return default(T);
}

如您所见，我有 3 个选择，那么我应该使用哪一个?IsAssignableFrom、IsInstanceOfType 和 is 运算符实际上有什么区别?

As you can see, I have 3 choice, so which one I should to use? Actually what is the difference between IsAssignableFrom, IsInstanceOfType, and is operator?

推荐答案

你可以使用任何你拥有的信息.

You use whatever you have the information for.

如果您有要检查的实例和静态类型，请使用 is.

If you have an instance and a static type you want to check against, use is.

如果您没有静态类型，您只有一个 Type 对象，但您有一个要检查的实例，请使用 IsInstanceOfType.

If you don't have the static type, you just have a Type object, but you have an instance you want to check, use IsInstanceOfType.

如果您没有实例，而只想检查 Type 的理论实例与另一个 Type 的理论实例之间的兼容性，请使用 IsAssignableFrom.

If you don't have an instance and you just want to check the compatibility between a theoretical instance of a Type and another Type, use IsAssignableFrom.

但实际上似乎您只是在重新实施 as 运算符(除了你的也适用于不可为空的值类型，这通常不是一个很大的限制).

But really is seems like you are just re-implementing the as operator (except that yours would also work for non-nullable value types, which is usually not a big limitation).

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