类型检查:typeof、GetType 或 is? [英] Type Checking: typeof, GetType, or is?

问题描述

我见过很多人使用以下代码:

Type t = typeof(obj1);如果 (t == typeof(int))//这里有一些代码

但我知道你也可以这样做:

if (obj1.GetType() == typeof(int))//这里有一些代码

或者这个:

if (obj1 is int)//这里有一些代码

就我个人而言，我觉得最后一个是最干净的，但是有什么我遗漏的地方吗?哪个最好用，还是个人喜好?

解决方案

都不同.

• typeof 采用类型名称(您在编译时指定).
• GetType 获取实例的运行时类型.
如果实例在继承树中，
• is 返回 true.

示例

class Animal { }狗类:动物{}void PrintTypes(Animal a) {Console.WriteLine(a.GetType() == typeof(Animal));//错误的Console.WriteLine(a 是动物);//真的Console.WriteLine(a.GetType() == typeof(Dog));//真的Console.WriteLine(a 是狗);//真的}狗点 = new Dog();PrintTypes(现货)；

<小时><块引用>

typeof(T) 怎么样?编译时也解决了吗?

是的.T 始终是表达式的类型.请记住，泛型方法基本上是具有适当类型的一大堆方法.示例:

string Foo(T 参数) { return typeof(T).Name;}动物可能_a_dog = new Dog();绝对狗_a_dog = new Dog();Foo(可能是_a_dog)；//这会调用 Foo并返回动物"Foo<Animal>(probably_a_dog);//这和上面的完全一样Foo<Dog>(可能是_a_dog);//！！！这不会编译.该参数需要一个 Dog，您不能传入一个 Animal.Foo(绝对_a_dog)；//这会调用 Foo并返回狗"Foo<Dog>(绝对_a_dog);//这和上面的完全一样.Foo<Animal>(绝对_a_dog);//这会调用 Foo并返回动物".Foo((动物)绝对_a_狗);//和上面一样，返回Animal"

I've seen many people use the following code:

Type t = typeof(obj1);
if (t == typeof(int))
    // Some code here

But I know you could also do this:

if (obj1.GetType() == typeof(int))
    // Some code here

Or this:

if (obj1 is int)
    // Some code here

Personally, I feel the last one is the cleanest, but is there something I'm missing? Which one is the best to use, or is it personal preference?

解决方案

All are different.

• typeof takes a type name (which you specify at compile time).
• GetType gets the runtime type of an instance.
• is returns true if an instance is in the inheritance tree.

Example

class Animal { } 
class Dog : Animal { }

void PrintTypes(Animal a) { 
    Console.WriteLine(a.GetType() == typeof(Animal)); // false 
    Console.WriteLine(a is Animal);                   // true 
    Console.WriteLine(a.GetType() == typeof(Dog));    // true
    Console.WriteLine(a is Dog);                      // true 
}

Dog spot = new Dog(); 
PrintTypes(spot);

---

What about typeof(T)? Is it also resolved at compile time?

Yes. T is always what the type of the expression is. Remember, a generic method is basically a whole bunch of methods with the appropriate type. Example:

string Foo<T>(T parameter) { return typeof(T).Name; }

Animal probably_a_dog = new Dog();
Dog    definitely_a_dog = new Dog();

Foo(probably_a_dog); // this calls Foo<Animal> and returns "Animal"
Foo<Animal>(probably_a_dog); // this is exactly the same as above
Foo<Dog>(probably_a_dog); // !!! This will not compile. The parameter expects a Dog, you cannot pass in an Animal.

Foo(definitely_a_dog); // this calls Foo<Dog> and returns "Dog"
Foo<Dog>(definitely_a_dog); // this is exactly the same as above.
Foo<Animal>(definitely_a_dog); // this calls Foo<Animal> and returns "Animal". 
Foo((Animal)definitely_a_dog); // this does the same as above, returns "Animal"

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