如何检查变量的类型是否与存储在变量中的类型匹配 [英] How to check if variable's type matches Type stored in a variable
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问题描述
User u = new User();
Type t = typeof(User);
u is User -> returns true
u is t -> compilation error
如何以这种方式测试某个变量是否属于某种类型?
How do I test if some variable is of some type in this way?
推荐答案
其他答案都包含重大遗漏.
The other answers all contain significant omissions.
is
运算符不检查操作数的运行时类型是否完全是给定的类型;相反,它会检查运行时类型是否与给定类型兼容:
The is
operator does not check if the runtime type of the operand is exactly the given type; rather, it checks to see if the runtime type is compatible with the given type:
class Animal {}
class Tiger : Animal {}
...
object x = new Tiger();
bool b1 = x is Tiger; // true
bool b2 = x is Animal; // true also! Every tiger is an animal.
但是检查类型identity,反射检查identity,而不是兼容性
But checking for type identity with reflection checks for identity, not for compatibility
bool b5 = x.GetType() == typeof(Tiger); // true
bool b6 = x.GetType() == typeof(Animal); // false! even though x is an animal
or with the type variable
bool b7 = t == typeof(Tiger); // true
bool b8 = t == typeof(Animal); // false! even though x is an
如果这不是您想要的,那么您可能想要 IsAssignableFrom:
If that's not what you want, then you probably want IsAssignableFrom:
bool b9 = typeof(Tiger).IsAssignableFrom(x.GetType()); // true
bool b10 = typeof(Animal).IsAssignableFrom(x.GetType()); // true! A variable of type Animal may be assigned a Tiger.
or with the type variable
bool b11 = t.IsAssignableFrom(x.GetType()); // true
bool b12 = t.IsAssignableFrom(x.GetType()); // true! A
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